Faecal sludge accumulation and characterization in informal settlements of Kampala: insights for facilities design

Faecal sludge accumulation and characterization in informal settlements of Kampala: insights for facilities design | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Faecal sludge accumulation and characterization in informal settlements of Kampala: insights for facilities design Charles B. Niwagaba, Abubakar Batte, Davis Majara, Alex Y. Katukiza, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5981958/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 May, 2025 Read the published version in Discover Sustainability → Version 1 posted 11 You are reading this latest preprint version Abstract The design and management of onsite sanitation containments for faecal sludge (FS) in informal settlements presents significant public health and environmental challenges, exacerbated by limited data on sludge accumulation and quality. This study aimed to determine properties and accumulation rate of FS in pit latrines and septic tanks to improve sanitation design and management strategies. Fieldwork was conducted in 22 onsite containments (11 pit latrines and 11 septic tanks) in Kawempe Division, Kampala. The in-situ FS volume was measured using a Volaser device, while laboratory analyses determined key physico-chemical parameters, including total solids (TS), volatile solids (VS), and chemical oxygen demand (COD). The findings revealed median FS accumulation rates of 214 L/cap.year for pit latrines and 348 L/cap.year for septic tanks, with significant variability across different containment types. Correlation analysis showed a strong relationship between TS and VS (R² = 0.93), while TS and COD exhibited a moderate correlation (R² = 0.47). These insights suggest that TS can be a cost-effective proxy for VS estimation, reducing laboratory analysis costs in resource-limited settings. This study provides data for optimizing faecal sludge management (FSM), supporting the design of more efficient sanitation systems in high-density urban settlements. The findings contribute to improved sludge containment planning, desludging frequency estimation, and the selection of appropriate treatment technologies in similar contexts. Faecal sludge accumulation rates pit latrines septic tanks Volaser Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. INTRODUCTION Faecal sludge (FS) comprises human faeces and urine, as well as anal cleaning and any other non-faecal materials discharged and accumulating in onsite sanitation containments (OSCs) such as pit latrines and septic tanks. The management of FS, which accumulates in these sanitation containments presents a significant global challenge due to its potential risks to public health and the environment. This challenge is exacerbated by the rapid expansion in population, particularly in low- and middle-income countries, where a corresponding provision of sanitation services has not kept pace [ 1 – 3 ]. Global reliance on these technologies is projected to escalate from 2.7 billion to 4.9 billion users by 2030 [ 4 , 5 ]. In spite of the increasing number of users of OSC, generating large quantities of FS, their management has lacked the necessary focus it requires in the last two decades to ensure protection of the environment and public health [ 6 , 7 ]. Faecal sludge management (FSM) encompasses the generation and management of FS in storage containments, collection, transport, treatment, and safe disposal and/or reuse of treated FS solids and the resulting liquid supernatant. The trend of urbanization shows an increasing population using non-standardized OSCs for their sanitation needs [ 4 , 8 , 9 ]. Standardized OSC systems follow established design criteria, with a well-documented components and operational procedures with recognized guidelines and standards for construction, installation, and maintenance to ensure their effectiveness and safety in managing fecal sludge. On the other hand, non-standardized OSC systems lack established design criteria and they vary significantly in design, construction, and operation, deviating from specific standards or best practices in FSM. Unfortunately, many OSCs in low-income countries are non-standardised, and are constructed by masons who know how to build but with little or no competence in their functioning and operation. For instance, in this study, septic tanks used were watertight tanks with only one chamber, cable of keeping untreated sewage separated from soil-water environment [ 10 ]. The high population density in informal settlements and typical flood-prone locations of urban areas necessitates standardized OSCs for FSM [ 11 , 12 ]. The Shit Flow Diagram (SFD) of Kampala indicates that 24% of accumulated FS is safely contained onsite and 46% unsafely managed [ 13 ]. The percentages of FS ending in the various environments as shown in the SFD were based on assumptions and interviews with key informants[ 13 ]. To enhance the accuracy of FS estimates across the sanitation service chain and address inadequate FSM, there is a need to develop ways of characterising FS. An initial crucial step involves determining the quantities and qualities (Q&Q) of FS [ 14 ]. In comparison to wastewater sludge, FS exhibits greater variability in its characteristics based on the region, city, district, household, and source [ 6 , 15 ]. This variability is influenced by a range of factors such as containment technology, retention time, household users' habits and preferences as well as collection practices [ 16 , 17 ]. Therefore, developing FSM solutions cannot be independently based on centralised wastewater treatment since it is homogenized during transport in a sewer and relying on it results into inappropriately designed systems that are prone to failure [ 18 ]. The design and quality of OSCs contribute to variations in the Q&Q of FS within cities and containment types in different locations. Therefore, the choice of containment technology should be based on local conditions such as climate, soil permeability, social demographics, economic status, service levels and affordability [ 19 , 20 ]. The quantity of the excreta (urine and faeces) generated daily also varies significantly, based on factors such as the quantity and type of food consumed, fluids intake, physical activity and climate [ 21 , 22 ]. This highlights the need for collecting accurate faecal sludge accumulation data which are specific to each location and, thus, reliable for the planning, design and implementing appropriate technologies for FS containment and treatment [ 8 , 23 ]. Previous attempts to model FS Q&Q utilized numerical mass balance methods that drew upon data collected from individual pit latrines to predict average accumulation rates for a neighborhood or city [ 8 , 24 ]. The lack of standardized approaches and methodologies in scientific literature impedes comparisons and the application of these models in different situations [ 9 ]. Estimating city-wide FS accumulation rates is complex, often hindered by data scarcity [ 25 ]. The challenge arises from FS storage in in-accessible underground non-standardized containments, with limited records of construction and maintenance. Yet, these containment technologies are at the beginning of the sanitation and FSM service chain [ 26 ]. Another major contributor to this problem is the fact that there are inconsistent results in literature on the relationship between organic properties of FS which are major determinants of its accumulation rate. The organic properties of FS significantly influence its accumulation rate. Higher organic content tends to accelerate decomposition, affecting the volume and density, and as well reducing the overall volume of sludge, thereby resulting into lower accumulation rates over time [ 27 , 28 ]. Microbial activity, driven by organic matter, further alters sludge stability and separation dynamics. Understanding these relationships is crucial for devising efficient management strategies that directly impact the treatment effectiveness and the overall performance of the system [ 28 , 29 ]. The importance of deriving relationships between FS characteristics cannot be over-emphasized. Most low-income countries do not routinely apply analytical techniques for the assessment of all necessary sludge characteristics due to costs involved [ 6 ]. However, if relationships can be found with parameters such as TS, that are resource efficient and cheaper to measure, then that would resolve the challenge of under-resourced laboratories in low-income countries while providing a simple method to indirectly derive other parameters, such as COD, which are pivotal for FS management and treatment. In a study conducted in seven countries, including Kampala, Uganda an empirical relationship for Volatile Solids (VS) and TS of 0.49 ( R 2 = 0.88) was obtained. However, no relationship between COD and TS was established. Earlier, [ 8 ] estimated the sludge accumulation in Kampala City to be 270 L/cap.year for pit latrines and 280 L/cap.year for septic tanks. Studies by Strande [ 8 ] found that COD and TS strongly correlated with R 2 = 0.86. The relationship between VS and TS has been shown by different studies, while that of COD and TS from the different studies are inconsistent. The pH value indicates the acidity or alkalinity of the fecal sludge which provides information about the state of biodegradation and stabilization of the organic matter in FS [ 30 ]. Extreme pH values can impact the treatment processes and the potential for resource recovery from the sludge. EC values are proportional to the concentration of dissolved solids and salts and can be used to predict quality parameters like total solids (TS) and chemical oxygen demand (COD) [ 30 , 31 ]. Consequently, more studies are necessary to improve the understanding of the relationships between FS characteristics and reduce the costs of laboratory analysis in under-resourced settings in low-income countries, while at the same time improving design parameters. This study determined the FS characteristics (Quantities and qualities) in lined pit latrines and septic tanks in informal settlements in Kampala City, Uganda, and derived the correlation between various parameters necessary for developing appropriate FS management solutions. 2 MATERIALS AND METHODS 2.1. Study area This study field-tested a standardized approach for estimating faecal sludge Q&Q in Kawempe division in Kampala city (Fig. 1 ). FIGURE 1 It is the second largest division in Kampala with a population of approximately 400,000 people (UBOS, 2017) and 95% of its residents rely entirely on onsite sanitation (Mukwaya, 2013). The study area included Kalerwe, Makerere Kikoni, Kikumi kikumi, and Kikoni. It was selected because it represents a typical urban poor area with high population density and a mix of non standardised OSCs. 2.2. FS Sampling locations The sampling sites used for the study were purposively selected, where the enrolled onsite containments had to be fully lined pit latrines or septic tanks. In the selected neighborhood close to Makerere University, a total of 22 non standardised containments that included 11 lined pit latrines and 11 septic tanks were identified. This number of lined pit latrines and septic tanks selected in the study area represented these types of containments accessible in the area, where their users accepted the study to be conducted, the rest having either refused or inaccessible or using unlined pit latrines and there were no sewer connections in the area. Prior to interviews and sampling, verbal consent was obtained from the users, and they were free to withdraw at any time if they felt uncomfortable during the interview. A questionnaire developed by [ 8 ] and [ 32 ] was used to collect the demographic, environmental and technical (DET) information from the users but in cases where some information was unknown by the users such as containment age, it was obtained from the owners of each OSC who were contacted by telephone (Supplementary material). The key information collected included the number of users, containment age, desludging interval, containment type, types of wastewaters entering the system and whether solid waste entered the containment. To cater for cases where people leave home either for work or school, population equivalents were derived and utilised. The numbers of the onsite containments that were sampled from the locations shown in Table 1 . Table 1 Locations and number of samples taken per selected neighborhood in Kawempe division Sampling location Septic tanks Lined pit latrines Kalerwe (4) 2 2 Makerere Kavule (2) - 2 Kikumi Kikumi (5) 2 3 Kikoni (11) 7 4 Faecal sludge sampling was carried out according to Koottatep [ 33 ] using the cone sampling technique with a locally fabricated sampler. Faecal sludge sampling for laboratory analysis was done once for each containment, but the measurement of FS volume was done once every week for eight weeks, from March to May 2023 and this is a wet season in Kampala. FS volume was used to determine the accumulation and filling rates. A ratio of 1:3:2 for samples from the top, middle, and bottom layers respectively was strategically designed to account for the vertical stratification of the sludge within the containment. This decision was informed by the understanding that over time, the settling process in a containment system leads to the stratification of sludge components, with heavier and larger particles tending to settle towards the bottom layers, while the less heavy particles and those disturbed during the use stay in the middle and the much lighter particles stay in the top layers. In the 1:3:2 sampling strategy adopted, the largest sample proportion was taken from the middle layer (3 parts), which represents the majority proportion in a containment which is in use, as continuous flushing or dropping in of contents disturbs a part of the settling sludge to be in second layer that is relatively more liquid than the settled sludge. The second largest part was sludge from the bottom layer (2 parts), where the majority of settled and compacted sludge accumulates. Finally, the smallest sample from near the top layer (1 part) was included to represent the uppermost portion, recognizing its lesser density, floating characteristics, and a high likelihood of containing more liquid and less settled material. The above sampling strategy aimed to ensure a good representation of the various layers of FS within the containment, acknowledging the stratification phenomenon and seeking a balanced representation of settled and less settled components for a more accurate analysis of the sludge composition. Representative composite samples, approximately 1L in capacity, were secured in bottles and taken for analysis in the laboratory of the College of Natural Sciences Chemistry at of Makerere University. 2.3. Analytical methods In the laboratory, the samples were stored at 4°C until analysis, based on standard laboratory methods according to APHA-AWWA-WEF [ 34 ] and Velkushanova et al. [ 35 ]. Table 2 briefly outlines the methods used for analyzing the physico-chemical properties of the FS, encompassing pH, TS, VS, COD, and electrical conductivity. Table 2 Summary of methods used to analyze the faecal sludge properties for all the samples Physico-chemical properties Analytical Method Total Solids (TS) Gravimetric method by oven drying at 105°C for 48 hours or until constant weigh of the sample has been reached Volatile Solids (VS) Ignition method by heating at 550°C for 6 hours pH Electrode method using model PHS-3BW of pH meter Electrical Conductivity (EC) Electrode method using Wagtech International conductivity meter Chemical Oxygen Demand (COD) Closed reflux spectrophotometric method on raw unfiltered using model SPECTRO-UV7 of MRC spectrophotometer Table 2 These parameters were chosen, firstly, because they influence the accumulation of FS in onsite containments. Secondly, the parameters are simple to measure, even under conditions mostly prevalent in low-income countries, with the main idea being to derive relationships between them. 2.4. Determination of in-situ FS volume The Volaser ( www.sandec.ch/volaser ), a volume laser device made to assess volumes of accumulated FS and containment volume was utilized in determining the depth from the drop-hole for pit latrines and the inspection cover (manhole) for septic tanks to the surface of the FS in the containment. It comprises of a tripod and rod housing a laser distance sensor, operated via a smartphone app [ 32 ] (Fig. 2 ). FIGURE 2 In the study, the tripod was positioned above the containment's vertical access point during measurements. The laser sensor was descended into the containment to measure the distance from its top to the FS’s surface. Rotating the rod enabled the measurement of distances to containment walls for internal area and shape determination [ 33 ]. A locally constructed 3.66 m (12ft) collapsible metal probe was forced through the contents of the pit until it could no longer move, where it was assumed that it reached the bottom of the containment. The depth of FS in the containment was recorded in the Volaser application on the smartphone. These distances to the containment walls and the depths of the pit contents were recorded in quadruples through a smartphone App that automatically computed the containment area in m 2 and the in-situ FS volume in m 3 . Each measurement process took less than 10 minutes. 2.5. Data Analysis Data analysis was done in Microsoft Excel 2010 and R Studio (R-4.3.1) for windows 11 (2023). Correlations between VS and TS as well as TS and COD were determined in the same manner as [ 8 ] and [ 32 ]. The calculation of the Faecal Sludge Accumulation Rate (FASR) and filling rates [ 32 ] and are represented by equations (i) and (ii). This approach was applied to both pit latrines and septic tanks, as septic tanks lacked outflows. FSAR-V means Faecal Sludge Accumulation Rate in volume units of L/cap.year. \(\:\varvec{F}\varvec{S}\varvec{A}\varvec{R}\:(\varvec{L}/\varvec{c}\varvec{a}.\varvec{y}\varvec{e}\varvec{a}\varvec{r})=\:\frac{\varvec{T}\varvec{o}\varvec{t}\varvec{a}\varvec{l}\:\varvec{v}\varvec{o}\varvec{l}\varvec{u}\varvec{m}\varvec{e}\:\varvec{o}\varvec{f}\:\varvec{F}\varvec{S}\:\varvec{i}\varvec{n}\varvec{s}\varvec{i}\varvec{d}\varvec{e}\:\varvec{c}\varvec{o}\varvec{n}\varvec{t}\varvec{a}\varvec{i}\varvec{n}\varvec{m}\varvec{e}\varvec{n}\varvec{t}\:\varvec{s}\varvec{y}\varvec{s}\varvec{t}\varvec{e}\varvec{m}\:\varvec{m}\varvec{e}\varvec{a}\varvec{s}\varvec{u}\varvec{r}\varvec{e}\varvec{d}\:\varvec{u}\varvec{s}\varvec{i}\varvec{n}\varvec{g}\:\varvec{V}\varvec{o}\varvec{l}\varvec{a}\varvec{s}\varvec{e}\varvec{r}\:\left(\varvec{L}\right)}{\varvec{N}\varvec{u}\varvec{m}\varvec{b}\varvec{e}\varvec{r}\:\varvec{o}\varvec{f}\:\varvec{u}\varvec{s}\varvec{e}\varvec{r}\varvec{s}\:\times\:\:\varvec{T}\varvec{i}\varvec{m}\varvec{e}\:\varvec{s}\varvec{i}\varvec{n}\varvec{c}\varvec{e}\:\varvec{l}\varvec{a}\varvec{s}\varvec{t}\:\varvec{e}\varvec{m}\varvec{p}\varvec{t}\varvec{y}\varvec{i}\varvec{n}\varvec{g}\:\left(\varvec{y}\varvec{e}\varvec{a}\varvec{r}\varvec{s}\right)}\) ……..(i) \(\:\varvec{F}\varvec{i}\varvec{l}\varvec{l}\varvec{i}\varvec{n}\varvec{g}\:\varvec{r}\varvec{a}\varvec{t}\varvec{e}\:(\varvec{L}/\varvec{d}\varvec{a}\varvec{y})=\:\frac{\varvec{C}\varvec{h}\varvec{a}\varvec{n}\varvec{g}\varvec{e}\:\varvec{i}\varvec{n}\:\varvec{f}\varvec{a}\varvec{e}\varvec{c}\varvec{a}\varvec{l}\:\varvec{s}\varvec{l}\varvec{u}\varvec{d}\varvec{g}\varvec{e}\:\varvec{v}\varvec{o}\varvec{l}\varvec{u}\varvec{m}\varvec{e}\:\varvec{w}\varvec{i}\varvec{t}\varvec{h}\varvec{i}\varvec{n}\:\varvec{c}\varvec{o}\varvec{n}\varvec{t}\varvec{a}\varvec{i}\varvec{n}\varvec{m}\varvec{e}\varvec{n}\varvec{t}\:\left(\varvec{L}\right)}{\varvec{M}\varvec{e}\varvec{a}\varvec{s}\varvec{u}\varvec{r}\varvec{e}\varvec{m}\varvec{e}\varvec{n}\varvec{t}\:\varvec{t}\varvec{i}\varvec{m}\varvec{e}\:\varvec{i}\varvec{n}\varvec{t}\varvec{e}\varvec{r}\varvec{v}\varvec{a}\varvec{l}\:\left(\varvec{d}\varvec{a}\varvec{y}\varvec{s}\right)}\) ….(ii) Given the significant variability and uneven distribution of FS quantities and qualities, means and standard deviations were used to describe normally distributed data while the median values and interquartile ranges were respectively used as the measures of central tendency and dispersion for data that were not normally distributed. The normality of the data were assessed using raincloud plots (combination of box plots, density plots and raw data). Outliers were identified and subsequently eliminated to ensure the integrity and accuracy of the data analysis [ 36 ]. Outliers were identified based on the relative absolute deviations, expressed as a percentage, which were computed for laboratory replicates, filling rates, and accumulation rates according to [ 32 ]. The mean of the replicate was subtracted from each individual triplicate, and the result was divided by the triplicate mean, after which, it was multiplied by 100. Subsequently, absolute average deviations were determined for each rate. Data points with a relative deviation exceeding 50% were excluded from the analysis [ 32 ]. To understand the impact of various parameters used in the accumulation rate calculation (i.e., time, users, and sludge volume), the Demographic, Environmental and Technical (DET) data (Supplementary material) were correlated with the accumulation rate undertaken [ 16 , 17 ]. 3 RESULTS AND DISCUSSION 3.1 Quantities of faecal sludge – accumulation and filling rates Employing the FSAR-V method, this study calculated the median faecal sludge accumulation rate as 214 L/cap.year (IQR: 154, 268) for lined pit latrines, with a mean of 228 L/cap.year (Fig. 3 ). In the case of septic tanks, the median accumulation rate stood at 348 L/cap.year (IQR: 214, 372) with a mean of 317 L/cap.year (Fig. 3 ). The rest of the data on sludge accumulation rates for both lined pit latrines and septic tanks are shown in Fig. 3 . The in-situ volumes of accumulated FS in the containments amounted to 4.2 ± 2.0 m 3 for lined pit latrines and 6.7 ± 3.2 m 3 for septic tanks. The median accumulation rates were considered for central tendency because of the high variability and non-normal distribution of the rates since the mean can heavily influence a few extreme values [ 31 ]. FIGURE 3 Comparable accumulation rates were observed in a different Kampala-based study [ 8 ], estimating 270 L/cap.year for lined pit latrines and 280 L/cap.year for septic tanks. Another earlier study in Asia and Africa reported varying average accumulation rates in different containments (pits and septic tanks) with or without outlet pipes (to drains, river or soak pits) from 14 to 41 L/cap.year with an average of 25 L/cap.year [ 37 ]. However, a study in Sircilla, India reported median accumulation rates in septic tanks and pit latrine containments of 53 L/cap.year using a core sampler and 96 L/cap.year using truck volumes that emptied all contents in the containments and using volume gauges when trucks were not full [ 9 ]. The considerable variation in reported sludge accumulation rates emphasizes the challenge of relying on rates borrowed from literature elsewhere [ 33 , 38 ]. Transferring knowledge on FS accumulation rates from one region to another is difficult due to the different impact of factors such as hydrological and climatic conditions as well as economic, social and user habits [ 8 ]. The study observed that the frequency of emptying practices is correlated with the accumulation rate of FS, where higher accumulation rates associated with more frequent emptying practices (Supplementary material). Containments with higher accumulation rates were found to require emptying twice a year, while those with lower rates were emptied only once in three years. Interestingly, containments of similar volume but one accommodating twice the average number of users (such as 5 to 10) exhibited a fifty percent reduction in their emptying frequency. It was found that containment size and number of users influence the emptying frequency of emptying containment technologies as also supported by literature [ 16 , 17 ]. As expected, the emptying frequency was inversely proportional to the size of containment but directly proportional to the number of users. Septic tanks had higher numbers of users and sludge volume compared to lined pit latrines. However, the time that elapsed since the last desludging did not show a significant difference between the two containment types with p-value of 0.03. The use of the number of users to determine the volume of containment can be challenging due to variations in toilet usage patterns throughout the day (e.g., at home, work, and school) and differences in household and workplace practices [ 16 , 17 ]. This is compounded by the lack of records regarding the periods when people are at home or not. To address this issue, population equivalents were used as a means to account for these diverse usage patterns [ 39 ]. Filling rates measure the net increase in the depth of material in the containments, which comprise inflows of FS minus outflows through, for instance exfiltration and evaporation. Therefore, the net filling rate is influenced by the rate at which non-faecal materials, like solid waste, are added along with the excreta [ 40 ]. The median filling rates were 18.3 L/day for lined pit latrines and 15.1 L/day for septic tanks (Table 3 ). The negative filling rates (Table 3 ) could be attributed to a combination of factors, among which may include, exfiltration and evaporation of the liquid contents from the pit over the measurement period. With time, the pores through which the exfiltration takes place are later filled and blocked by the accumulating solids, which further prevents them from reducing the filling rates [ 38 ]. Table 3 Summary statistics filling rates for pit latrines and septic tanks, L/day (Data are reported as median and interquartile range) Parameter Total (n = 22) Pit Latrine (n = 11) Septic Tanks (n = 11) Minimum -14.59 -4.14 -14.59 25th quartile 4.23 5.19 2.17 Median 16.68 18.26 15.05 Mean 33.26 17.26 49.19 75th quartile 33.43 29.31 62.18 Maximum 218.28 33.44 218.28 Table 3 A higher filling rate reflects among others, large numbers of users per day, misuse of the pits, for instance, disposing of solid wastes, use of improper anal cleansing materials (such leaves, maize cobs, stones, mounds of soil etc) and as well as low breakdown of faecal matter [ 16 , 17 ]. Disposal of solid wastes and other improper anal cleansing materials introduces differential organic and inorganic loading rates in containments. Other factors that potentially affect the filling rates of pits and septic tanks include containment type such as a lined pit latrines with no overflow, or a septic tank with an overflow for supernatant; as well as additional input materials such as grey water or kitchen wastes [ 41 ]. Different filling rates suggest varying hydraulic retention times, which influence degradability characteristics and hence quantity and quality of faecal sludge [ 16 , 17 , 41 ]. Pit latrines in the study area had drop-holes and no water was used to flush them. Septic tanks were connected to flush toilets. Consequently, more water was used in septic tanks than pit latrines. Higher degradation rates of organic materials are generally expected in an environment saturated with water, where anaerobic microbes rapidly accumulate, thus allowing for faster breakdown. In unlined pits where less water is in place, the microbial accumulation is low, resulting into less degradation. Consequently, the microbial degradation efficiency increases with the wetness of the containment, while less wetness, which could among others be affected by the leachate loss results into reduced microbial degradation efficiency. All of these affect the sludge accumulation and therefore the frequence of desludging. Unlike filling rates (L/day), accumulation rates (L/cap.day) of FS take into consideration additional factors, such as the number of users that contribute to the build-up of sludge within the containment. Besides, factors other than the numbers of users and their FS generation impact upon the sludge accumulation rate, as explained above. For efficient FS management, it is essential to consider accumulation rates, population size, and the intended design life when determining the capacity of septic tanks and pit latrines. Previous research has demonstrated that containments with higher accumulation rates were frequently emptied [ 8 , 32 , 42 ]. Consequently, the FS accumulation rate can serve as a valuable tool to estimate the intervals for emptying or desludging containment technologies. 3.2 Qualities of faecal sludge In the context of sustainable management practices of FS, it is essential to consider both qualities and quantities (loadings) simultaneously [ 8 ]. The pH and EC measurements were within ranges normally encountered in literature, for instance 6.5-8.0 for pH [ 20 ], and 0.14 and 24.8 mS/cm for EC [ 30 , 43 , 44 ]. The FS quality parameters analyzed in this study against the DET data of sanitation technology type are presented in Fig. 4 . Using the student’s t-tests, the quality parameters analysed for pit latrines and septic tanks did not significantly differ between each other (Data in Supplementary Material). Except for COD, the parameters for lined pit latrines were higher than those for septic tanks, and encountered ranges expected for FS due to high variability. Several authors have attempted to explain the variability of FS. It has been reported in [ 16 , 17 ] that FS is highly variable due to a number of factors, relating to the socio-economic status of the users, design and construction, as geological conditions of the soil strata in which the containments are placed. Anecdotal evidence suggests that to decrease filling rate, users in different parts of the world may apply materials and additives such as old car batteries, kerosene, effective microorganisms, indigenous organisms, salt, sugar, ash, fertilizer, or even dead objects such as cats and dogs. In addition to these practices influencing the characteristics of FS, they do affect the filling and sludge accumulation rates, too, as discussed in the relevant sections ahead. COD concentrations in this study ranged from 1.5 to 113 g/L, which falls within the reported ranges of 0.2 to 612.5 g/L [ 9 , 45 – 47 ]. For initial evaluation, this study considered TS as it is the most commonly used design parameter for designing established FS treatment technologies such as drying beds [ 20 ]. TS (0.5–66.4 g/L for septic tanks and 7.4–51.2 g/L for pit latrines) and COD concentrations of FS in this study cover a wider range than previously reported for lined pits in Kampala (TS 51.4 ± 29.2 g/L; COD 65.5 ± 44.0 g/L) and for the septic tanks (TS 11.9–72.0 g/L; VS 7.1–33.8 g/L; COD 7.8–43 g/L [ 2 ]). The TS and COD reported in [ 2 ] were conducted during the period September to December, which comprises a mix of wet and dry season. For these parameters, our values of COD and TS obtained in the wet season of March to May were comparable to those reported in [ 2 ] in a mix of wet and dry season. FIGURE 4 In the containments studied, linear correlations were observed between the FS concentrations of TS and COD (Fig. 5 ) and TS and VS (Fig. 6 ). For TS and COD illustrated in Fig. 5 , a weak correlation of 0.53 (R 2 = 0.47) was observed. This correlation had no significant variation with other reported values of 0.15 (R 2 = 0.45) [ 32 ] except for 1.2 (R 2 = 0.8) [ 38 ]. Therefore, TS did not predict COD and investment in analysis of COD is required in low-income countries. This is consistent with [ 32 ]. FIGURE 5 A correlation between VS and TS (R 2 = 0.93) with a slope of 0.61 was observed in this study (Fig. 6 ). The equation slope of 0.61 is consistent not far from recent values of VS/TS of 0.52 (R 2 = 0.88) [ 32 ] and 0.59 (R 2 = 0.97) [ 9 ], and other reported values of 0.64 ± 0.12 and 0.50 ± 0.16 [ 2 ]; 0.54 ± 0.20 and 0.56 ± 0.17 [ 30 ]; 0.77 ± 0.01 and 0.80 ± 0.02 [ 43 ]. Consequently, where analyses of VS are not possible, measurements of TS can be fairly relied upon to predict VS, thereby reducing the cost of analysis. FIGURE 6 Previous studies have linked inconsistencies in the low correlations between TS and COD while strong correlations have been encountered between TS and VS to the possibility of high sand/soil content in the FS [ 32 ]. Many routes leading to sanitation containments, streets within living areas and compounds are not paved. Consequently, the walking with bare feet or shows via unpaved ways, streets and compounds could potentially gather a lot of mud during the wet seasons, which could end up in containments. Besides, soil from the walls of unlined or partially lined pits could potentially collapse/fall in with time, increasing the sand content of the FS. The presence of consistent correlations within a city enables the possibility of making projections, taking into account observed variations based on demographic data. These correlations have the potential to streamline future characterization studies by minimizing the number of required laboratory analyses. Furthermore, they contribute to a deeper comprehension of the underlying connections between these quality parameters, thus aiding in the establishment of a more comprehensive understanding [ 38 ]. 3.3 General Discussion The findings of this study offer valuable insights into the characterization and accumulation of faecal sludge (FS) in informal settlements, which hold significant implications for the design and implementation of effective faecal sludge management (FSM) strategies in resource-constrained settings. By improving the understanding of FS accumulation rates and quality, this research directly addresses a critical gap in the estimation of FS design parameters for onsite sanitation containments (OSCs), particularly in densely populated, low-income areas. One of the most crucial outcomes of this study is the determination of localized faecal sludge accumulation rates of 214 L/cap.year for lined pit latrines and 348 L/cap.year for septic tanks. These rates deviate significantly from the default design assumption of 0.5 L/cap.day (equivalent to 182.5 L/cap.year) commonly used in Uganda, including the design of the Lubigi Sewage and FS Treatment Plant (LSFSTP) [ 48 ]. The underestimation in previous designs, as demonstrated by the overloading of the LSFSTP within the first six months of operation, underscores the importance of context-specific data in FSM system design. These findings suggest that the use of generalized FS accumulation rates can result in system failures, reinforcing the need for localized measurements to guide both the sizing of containment technologies and the design capacity of FS treatment plants (FSTPs). The higher FS accumulation rates observed in septic tanks compared to pit latrines (1.6 times higher) have important implications for containment design and desludging schedules. The correlation between higher user numbers and reduced desludging frequency further highlights the need to consider demographic and technical (DET) factors in the planning phase [ 8 ]. Septic tanks, typically connected to flush toilets, exhibited higher degradation rates due to the availability of water, supporting the notion that moisture content facilitates microbial activity and accelerates organic matter breakdown [ 32 ]. In contrast, pit latrines, which received minimal water, showed higher filling rates, suggesting that water-scarce environments inhibit degradation and require more frequent emptying. This differential behavior indicates that a one-size-fits-all approach to containment design and management is insufficient. Instead, tailored strategies based on user habits, containment types, and environmental conditions should be adopted to optimize desludging intervals and reduce operational costs. For instance, higher-capacity containment structures may be necessary in high-density settlements to minimize frequent emptying, which is often costly and logistically challenging. The strong correlation observed between volatile solids (VS) and total solids (TS) (R² = 0.93) suggests that TS can be effectively used as a proxy for VS in FS characterization. This is particularly important in low-income countries where laboratory resources are limited [ 49 ]. As TS is cheaper and easier to measure, its use can significantly reduce the cost and complexity of FS analysis while providing reliable estimates for designing treatment technologies. This approach is supported by similar studies that identified TS as a reliable indicator of other FS quality parameters [ 8 , 32 ]. The weak correlation between TS and chemical oxygen demand (COD) (R² = 0.47) implies that additional investment in COD analysis is necessary to accurately assess treatment requirements and optimize sludge treatment processes. The variability in FS quality parameters, including TS, VS, and COD, highlights the need for flexible treatment technologies that can handle diverse sludge characteristics. For example, drying beds, commonly used in FS treatment, should be designed to accommodate the high variability in TS concentrations observed in this study (ranging from 11.9 to 72 g/L for septic tanks). Treatment technologies must also be resilient to fluctuations in organic loadings to ensure consistent performance [ 50 ]. The results suggest that modular and scalable treatment systems would be ideal for informal settlements where demographic and environmental conditions are highly dynamic. This study’s accumulation rates are higher than those reported in previous studies conducted in regions such as Sircilla, India, where median rates of 53 L/cap.year were observed using core sampling techniques [ 9 ]. The variation in accumulation rates across regions highlights the influence of local factors such as climate, user behavior, and containment design. Studies in Ouagadougou, Burkina Faso [ 50 ] and Senegal [ 28 ] have similarly demonstrated that regional differences in FS characteristics can significantly impact FSM outcomes. A Volaser was deployed in the field to measure the faecal sludge accumulation rates in seven countries in Africa, Asia and the Middle East. From this study the median and mean faecal sludge accumulation rates in pit latrines (n = 84) and septic tanks (n = 12) were 44 and 622 L/cap.yr and 218 and 1,834 L/Cap.yr respectively. The values of the median and mean faecal sludge accumulation rates were very highly variable as expected for faecal sludge from various containments in different regions. By providing localized data for Kampala, this study contributes to the growing body of knowledge advocating for context-specific FSM solutions. 3.4 Implications of the Findings The findings of this study emphasize the importance of integrating localized FS accumulation data into municipal sanitation planning frameworks. Policymakers should consider revising existing guidelines to incorporate updated FS generation rates, particularly for urban informal settlements. The results also present the need for regular monitoring of FS accumulation rates and quality to inform adaptive management strategies [ 28 ]. This is particularly critical in a number of cities such as Kampala, where rapid urbanization and high population densities place significant strain on sanitation infrastructure. User behaviour, including the disposal of non-faecal materials into containment systems, was identified as a major factor influencing FS accumulation and filling rates. Pit latrines in this study area received more solid waste than septic tanks due to their ease of access and absence of piping systems. This practice not only accelerates the filling of pit latrines but also complicates desludging operations and reduces the efficiency of FS treatment processes [ 51 ]. Public education campaigns promoting proper waste disposal practices could help mitigate these challenges and improve the overall effectiveness of FSM systems. 4 CONCLUSIONS This study provides evidence for the need to adopt localized, context-specific approaches to FSM in urban informal settlements. The findings show that the commonly used design assumption of 0.5 L/cap/day (183 L/Cap/year) across the board for both pits and septic tanks significantly underestimates FS accumulation rates in informal settlements, with measured rates reaching 214 L/cap/year for lined pit latrines and 348 L/cap/year for septic tanks. This discrepancy highlights the inadequacy of generalized design standards and the need for more accurate, site-specific data to guide infrastructure planning and ensure operational sustainability. The research demonstrates that simplified analytical methods, such as using total solids (TS) as a proxy for volatile solids (VS), can enhance the cost-efficiency of FSM system design without compromising accuracy. However, the weak correlation between TS and chemical oxygen demand (COD) emphasizes the need for more comprehensive characterization when assessing treatment requirements. Future research should focus on long-term monitoring of FS accumulation and quality, as well as the development of innovative, cost-effective technologies suited for resource-constrained settings. By addressing these recommendations, cities like Kampala can make significant progress in tackling sanitation challenges, supporting public health, and fostering sustainable urban development. This study provides evidence for the need to adopt localized, context-specific approaches to FSM in urban informal settlements. The findings show that the commonly used design assumption of 0.5 L/cap/day (183 L/Cap/year) across the board for both pits and septic tanks significantly underestimates FS accumulation rates in informal settlements, with measured rates reaching 214 L/cap/year for lined pit latrines and 348 L/cap/year for septic tanks. This discrepancy highlights the inadequacy of generalized design standards and the need for more accurate, site-specific data to guide infrastructure planning and ensure operational sustainability. The research demonstrates that simplified analytical methods, such as using total solids (TS) as a proxy for volatile solids (VS), can enhance the cost-efficiency of FSM system design without compromising accuracy. However, the weak correlation between TS and chemical oxygen demand (COD) emphasizes the need for more comprehensive characterization when assessing treatment requirements. Future research should focus on long-term monitoring of FS accumulation and quality, as well as the development of innovative, cost-effective technologies suited for resource-constrained settings. By addressing these recommendations, cities like Kampala can make significant progress in tackling sanitation challenges, supporting public health, and fostering sustainable urban development. Declarations Ethics approval and consent to participate: The participants who responded to the Demographic, Environmental and Technical (DET) questionnaire were asked for permission to participate. They were free to withdraw from the survey at any time. Privacy and anonymity was respected and no responses are attributable to any individual. The samples picked from containments were from the users of the toilet systems, and it's not possible to attribute any quality parameters to a single individual. Consent for publication: There is no conflict of interest in publishing the work in this article. All authors consent to publishing the contents of this paper. Competing interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution CBN, AB, DM and AYK conceptualized the study; AB and DM wrote and implemented the methodology with the support of all the authors; AB, DM, AM, CBN and MM did the laboratory work, performed the investigation and formal analysis, AB and DM wrote the original first draft preparation, which was majorly revised by CBN; CBN, AM, SS, MM, and RP did the review of the writing and editing; CBN and AYK supervised the entire work. All authors reviewed the final manuscript. Acknowledgement The authors convey their thanks to Dr. Joel Robert Kinobe for the guidance offered in regard to the field use of the Volaser; and to the College of Natural Sciences Chemistry Laboratory of Makerere University particularly the senior technician Mr. Godfrey Mugenyi for providing support during laboratory analysis. The authors are also grateful to the Final Year Project coordinators, Eng. Dr. Robinah N. Kulabako and Eng. Dr. Seith Mugume for their administrative support. Special thanks to Nienke Marije Andriessen and Linda Strande who provided valuable feedback during the course of drafting the manuscript. Data availability All the data used in this study are publicly available and can be accessed via the following link: https://drive.google.com/drive/folders/1j9oMocbARUw8r45YIXgtO4UM3Cg7zV_p?usp=sharing . Open and responsible use of these data is encouraged. References Norström A, Mcconville J, Kain J, Urban CIT, Management W, Torg M. PERI-URBAN AREAS IN DEVELOPING COUNTRIES: THE EXAMPLE OF ADENTA, GHANA Urbanisation of Peri-Urban Accra the Greater Accra Region. 2009, 237–245. Semiyaga S, Okure MAE, Niwagaba CB, Nyenje PM, Kansiime F. Enhancing Faecal Sludge Dewaterability and End-Use by Conditioning with Sawdust and Charcoal Dust. Environ Technol 2017 Inpress, 10.1080/09593330.2017.1300191 Narayan AS, Marks SJ, Meierhofer R, Strande L, Tilley E, Zurbrügg C, Lüthi C. Advancements in and Integration of Water, Sanitation, and Solid Waste for Low- And Middle-Income Countries. Annu Rev Environ Resour. 2021;46:193–219. 10.1146/annurev-environ-030620-042304 . Cairns-Smith S, Hill H, Nazarenko E. Urban Sanitation: Why a Portfolio of Solutions Is Needed. Bost Consult Group Boston USA 2014, 1–30. WHO/UNICEF Progress on Drinking Water, Sanitation and Hygiene in Schools. 2022; ISBN 9789280653649. Strauss M, Larmie S, Heinss U. Treatment of Sludges from On-Site Sanitation — Low-Cost Options. Water Sci Technol. 1997;35:129–36. 10.1016/S0273-1223(97)00103-0 . Peal A, Evans B, Blackett I, Hawkins P, Heymans C. Fecal Sludge Management: A Comparative Analysis of 12 Cities. J Water Sanit Hyg Dev. 2014;4. 10.2166/washdev.2014.026 . Strande L, Schoebitz L, Bischoff F, Ddiba D, Okello F, Englund M, Ward BJ, Niwagaba CB. Methods to Reliably Estimate Faecal Sludge Quantities and Qualities for the Design of Treatment Technologies and Management Solutions. J Environ Manage. 2018;223:898–907. 10.1016/j.jenvman.2018.06.100 . Prasad P, Andriessen N, Moorthy A, Das A, Coppens K, Pradeep R, Strande L. Methods for Estimating Quantities and Qualities (Q&q) of Faecal Sludge: Field Evaluation in Sircilla, India. J Water Sanit Hyg Dev. 2021;11:494–504. 10.2166/washdev.2021.269 . Burchart-Korol D, Zawartka P. Environmental Life Cycle Assessment of Septic Tanks in Urban Wastewater System – a Case Study for Poland. Arch Environ Prot. 2019;45:68–77. 10.24425/aep.2019.130243 . Katukiza AY, Ronteltap M, Oleja A, Niwagaba CB, Kansiime F, Lens PNL. Selection of Sustainable Sanitation Technologies for Urban Slums - a Case of Bwaise III in Kampala, Uganda. Sci Total Environ. 2010;409:52–62. Rotowa OO, Ayadi PA. Faecal Sludge Management in the Residential Cores of Akure, Nigeria Faecal Sludge Management in the Residential Cores of Akure, Nigeria. 2020. Schoebitz L, Niwagaba CB, Strande L. SFD Promotion Initiative Kampala Uganda Final Report. Eawag/Sandec 2016. Andriessen N, Strande L. The Volaser: In Situ Measurements of Volumes of Faecal Sludge. Manag Excreta Wastewater Sludge 2020, 1. Strande L, Ronteltap M, Brdjanovic D. Faecal Sludge Management - Systems Approach Implementation and Operation ; IWA Publishing: London, UK, 2014; ISBN 9781780404738. Niwagaba CB, Mbéguéré M, Strande L. Faecal Sludge Quantification, Characterisation and Treatment Objectives. In Faecal Sludge Management - systems approach implementation and operation ; Strande, L., Ronteltap, M., Brdjanovic, D., Eds.; IWA Publishing: London, UK, 2014; pp. 15–42 ISBN 9781780404738. Gold M, Harada H, Therrien J-D, Nishida T, Cunningham M, Semiyaga S, Fujii S, Dorea C, Nguyen V-A, Strande L. Cross-Country Analysis of Faecal Sludge Dewatering. Environ Technol. 2017. 10.1080/09593330.2017.1374472 . Bassan M, Koné D, Mbéguéré M, Holliger C, Strande L. Success and Failure Assessment Methodology for Wastewater and Faecal Sludge Treatment Projects in Low-Income Countries. J Environ Plan Manag. 2015;58:1690–710. 10.1080/09640568.2014.943343 . Kalbermatten J, Julius D, Gunnerson C. Appropriate Sanitation Alternatives A Technical and Economic Appraisal ; 1982; ISBN 0801825784. Strande L, Ronteltap M, Brdjanovic D. Faecal Sludge Management ; 2014; ISBN 9781780404721. Feachem RG, et al. Sanitation and Disease - Health Aspects of Excreta and Waste‐water Management. JAWRA J Am Water Resour Assoc. 1984;20:803–803. 10.1111/j.1752-1688.1984.tb04765.x . Samal K, Moulick S, Mohapatra BG, Samanta S, Sasidharan S, Prakash B, Sarangi S. Design of Faecal Sludge Treatment Plant (FSTP) and Availability of Its Treatment Technologies. Energy Nexus. 2022;7:100091. 10.1016/j.nexus.2022.100091 . Bassan M, Tchonda T, Yiougo L, Zoellig H, Mahamane I, Mbéguéré M. Characterization of Faecal Sludge during Dry and Rainy Seasons in Ouagadougou, Burkina Faso. In Proceedings of the 36th WEDC Internaional Confrenece. Delivering Water, Santation and Hygiene Services in an Uncertain Environment; 2013; pp. 1–7. Ahamada Z, Maureen NN, Nicholas K, Robert K, Abia K, Allan JK. A Critical Analysis of Physiochemical Properties Influencing Pit Latrine Emptying and Feacal Sludge Disposal in Kampala Slums, Uganda. Afr J Environ Sci Technol. 2016;10:316–28. 10.5897/AJEST2016.2163 . Chandana N, Rao BA. Critical Review on Sludge Management from Onsite Sanitation Systems: A Knowledge to Be Revised in the Current Situation. Environ Res 2022, 203 . Parkinson J, Luthi C, Walther D. Sanitation 21-A Planning Framework for Improving City-Wide Sanitation Services. Iwa, 2014. Koottatep T, Surinkul N, Atitaya P. Accumulation Rates of Thickened-Bottom Sludge and Its Characteristics from Water-Based Onsite Sanitation Systems in Thailand. 2014. Ward BJ, Traber J, Gueye A, Diop B, Morgenroth E, Strande L. Evaluation of Conceptual Model and Predictors of Faecal Sludge Dewatering Performance in Senegal and Tanzania. Water Res. 2019;167. 10.1016/j.watres.2019.115101 . Freitas FS, Pika PA, Kasten S, Jorgensen BB, Rassmann J, Rabouille C, Thomas S, Sass H, Pancost RD, Arndt S. New Insights into Large-Scale Trends of Apparent Organic Matter Reactivity in Marine Sediments and Patterns of Benthic Carbon Transformation. Biogeosciences. 2021;18:4651–79. 10.5194/bg-18-4651-2021 . Ward BJ, Andriessen N, Tembo JM, Kabika J, Grau M, Scheidegger A, Morgenroth E, Strande L. Predictive Models Using Cheap and Easy Field Measurements: Can They Fill a Gap in Planning, Monitoring, and Implementing Fecal Sludge Management Solutions? Water Res. 2021;196:116997. 10.1016/j.watres.2021.116997 . Wanda C, Kengne ES, Wafo GVD, Nzouebet WAL, Nbendah P, Ngandjui YAT, Zapfack L, Noumsi IMK. Quantification and Characterisation of Faecal Sludge from On-Site Sanitation Systems Prior the Design of a Treatment Plant in Bangangte, West Region of Cameroon. Environ Challenges. 2021;5:100236. 10.1016/j.envc.2021.100236 . Andriessen N, Appiah-Effah E, Browne SJI, al Jahjah R, Kabika J, Kinobe JR, Korir N, Nishimwe P, Niwagaba CB, Pradeep R, et al. Quantities and Qualities of Fecal Sludge: Experiences from Field Implementation with a Volaser in 7 Countries during a Pandemic. Front Water. 2023;5. 10.3389/frwa.2023.1130081 . Koottatep T, Ferré A, Chapagain S, Fakkaew K, Strande L. Faecal Sludge Sample Collection and Handling. Methods Faecal Sludge Anal 2021, 55–84. APHA-AWWWA-WEF Standards Methods for the Examination of Water and Wastewater. 20th Edition. Am. Public Heal. Assoc. Am. Water Work. Assoc. Water Environ. Fed. Publ. Washingt. D.C., USA. ISBN 0-87553-047-8 2012. Velkushanova K, Strande L. Faecal Sludge Properties and Considerations for Characterisation ; 2021; ISBN 9781780409115. Schmid H, Huber A. Measuring a Small Number of Samples, and the 3v Fallacy: Shedding Light on Confidence and Error Intervals. IEEE Solid-State Circuits Mag. 2014;6:52–8. 10.1109/MSSC.2014.2313714 . Chowdhry S, Koné D. Business Analysis of Fecal Sludge Management: Emptying and Transportation Services in Africa and Asia ; Seattle, USA, 2012. Strande L, Englund M, Andriessen N, Carbajal JP, Scheidegger A. Estimating Quantities and Qualities (Q&Q) of Faecal Sludge at Community to City-Wide Scales. Methods Faecal Sludge Anal 2021, 115–44. O’Brien JW, Thai PK, Eaglesham G, Ort C, Scheidegger A, Carter S, Mueller JF. A Model to Estimate the Population Contributing to the Wastewater Using Samples Collected on Census Day. Environ Sci Technol. 2014;48:517–25. Brouckaert CJ, Foxon KM, Wood K. Modelling the Filling Rate of Pit Latrines. Water SA. 2013;39:555–62. http://dx.doi.org/10.4314/wsa.v39i4.15 . Andriessen N, Englund M, Gold M, Klinger M, Luthi C, Renggli S, Sam S, Strande L, Ward BJ. Faecal Sludge Management: Highlights and Exercises ; Englund, M., Strande, L., Eds.; Eawag: Swiss Federal Institute of Aquatic Science and Technology: Duebendorf, Switzerland, 2019; ISBN 978-3-906484-70-9. Mills F, Blacket I, Tayler K. Assessing On-Site Systems and Sludge Accumulation Rates to Understand Pit Emptying in Indonesia, Sustainable Water and Sanitation Services For All in a Fast Changing World. WEDC Loughbrgh Univ Hanoi vietnam, 2017, 1–6. Appiah-Effah E, Nyarko KB, Gyasi SF, Awuah E. Faecal Sludge Management in Low Income Areas: A Case Study of Three Districts in the Ashanti Region of Ghana. J Water Sanit Hyg Dev. 2014;4:189–99. 10.2166/washdev.2014.126 . Semiyaga S, Okure MaE, Niwagaba CB, Nyenje PM, Kansiime F. Optimisation of Centrifuge Operating Conditions for Dewatering Physically Conditioned Faecal Sludge from Urban Slums. Environ Technol Innov. 2017;8:28–39. 10.1016/j.eti.2017.03.005 . Shivendra BT. Assessment of Usage of Treated Faecal Sludge for Agriculture. Int J Res Eng Technol. 2016;05:269–74. 10.15623/ijret.2016.0506048 . Sharma N, Gupta S, Vyas AD. Estimation of Fuel Potential of Faecal Sludge in a Water Scarce City, a Case Study of Jaipur Urban, India. Water Pract Technol. 2020;15:506–14. 10.2166/wpt.2020.037 . Vijayan V, Mallik M, Chakravarthy SK. Performance Evaluation: How Faecal Sludge Treatment Plants Are Performing. New Delhi: Centre for Science and Environment; 2020. Niwagaba CB, Mbéguéré M, Strande L. Faecal Sludge Quantification, Characterisation and Treatment Objectives. In Faecal Sludge Management: System Approach for Implementation and Operation. London IWA Publ. Available http //www.eawag.ch/forschung/sandec/publikationen/ewm/dl/fsm_book.pdf . Accessed Feb 2016. 2014, 19–43. Strande L, Ronteltap M, Brdjanovic D. The Global Situation. In Faecal Sludge Management: System Approach for Implementation and Operation. London IWA Publ. Available http//www.eawag.ch/forschung/sandec/publikationen/ewm/dl/fsm_book.pdf . Accessed Feb 2016 2014, 1–13. Bassan M, Mbéguéré M, Tchonda T, Zabsonre F, Strande L. Integrated Faecal Sludge Management Scheme for the Cities of Burkina Faso. J Water Sanit Hyg Dev. 2013;3:216–21. 10.2166/washdev.2013.156 . Still D, Foxon K. Tackling the Challenges of Full Pit Latrines. Volume 2: How Fast Do Pit Toilets Fill up ? A Scientific Understanding of Sludge ; South Africa, 2012; Vol. 2; ISBN 9781431202928. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 25 May, 2025 Read the published version in Discover Sustainability → Version 1 posted Editorial decision: Revision requested 07 May, 2025 Editor assigned by journal 06 May, 2025 Reviews received at journal 01 May, 2025 Reviews received at journal 29 Apr, 2025 Reviews received at journal 26 Apr, 2025 Reviewers agreed at journal 26 Apr, 2025 Reviewers agreed at journal 23 Apr, 2025 Reviewers agreed at journal 22 Apr, 2025 Reviewers invited by journal 22 Apr, 2025 Submission checks completed at journal 17 Apr, 2025 First submitted to journal 03 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5981958","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":446525752,"identity":"8fbacd9a-5959-426d-b32a-422d102e8080","order_by":0,"name":"Charles B. Niwagaba","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4UlEQVRIiWNgGAWjYDACCQaGAyDagIEZREvIkKKFLQHE5SFKCwNEC48BiCashX9278HDPDW18ubsZz6/ulFjwcPAfvjoBryW3DmXcJjn2HHDnT2526xzjgEdxpOWdgOfFgOJHIPDOWzHGDccyN1mnMMG1CLBY0aEln/H7Decf/PMOOcfsVpy22oSN9zIYX6c20aEFok7ZwwO/+07kLxzxjMz5tw+CR42Qn7hn91j/HHGtzrb7fzJjz/nfKuT42c/fAyvFig4DCLYwHHERoRyEKgDEcwfiFQ9CkbBKBgFIwwAAD2WTI79fddyAAAAAElFTkSuQmCC","orcid":"","institution":"Design, Art and Technology (CEDAT), Makerere University","correspondingAuthor":true,"prefix":"","firstName":"Charles","middleName":"B.","lastName":"Niwagaba","suffix":""},{"id":446525754,"identity":"9888e74d-d578-42ff-a672-bccc94c32442","order_by":1,"name":"Abubakar Batte","email":"","orcid":"","institution":"Design, Art and Technology (CEDAT), Makerere University","correspondingAuthor":false,"prefix":"","firstName":"Abubakar","middleName":"","lastName":"Batte","suffix":""},{"id":446525755,"identity":"1d165f88-2d0e-4e31-95f1-93ec51e08ba7","order_by":2,"name":"Davis Majara","email":"","orcid":"","institution":"Design, Art and Technology (CEDAT), Makerere University","correspondingAuthor":false,"prefix":"","firstName":"Davis","middleName":"","lastName":"Majara","suffix":""},{"id":446525756,"identity":"4f8251d5-bb8a-4f6c-8260-d4a604e7f733","order_by":3,"name":"Alex Y. Katukiza","email":"","orcid":"","institution":"Design, Art and Technology (CEDAT), Makerere University","correspondingAuthor":false,"prefix":"","firstName":"Alex","middleName":"Y.","lastName":"Katukiza","suffix":""},{"id":446525759,"identity":"6e723ac6-29a8-4b79-a751-2ad86af9976d","order_by":4,"name":"Ambrose Mukisa","email":"","orcid":"","institution":"College of Natural Sciences, Makerere University, Uganda","correspondingAuthor":false,"prefix":"","firstName":"Ambrose","middleName":"","lastName":"Mukisa","suffix":""},{"id":446525760,"identity":"fe1941b9-d93d-4fa7-93bc-20d532653ede","order_by":5,"name":"Swaib Semiyaga","email":"","orcid":"","institution":"Design, Art and Technology (CEDAT), Makerere University","correspondingAuthor":false,"prefix":"","firstName":"Swaib","middleName":"","lastName":"Semiyaga","suffix":""},{"id":446525761,"identity":"ffa3bd28-205a-4639-96e7-6a975f5925f9","order_by":6,"name":"Musa Manga","email":"","orcid":"","institution":"University of North Carolina at Chapel Hill","correspondingAuthor":false,"prefix":"","firstName":"Musa","middleName":"","lastName":"Manga","suffix":""},{"id":446525762,"identity":"fe40acce-2105-4feb-b95d-35d602058522","order_by":7,"name":"Raffaella Pomi","email":"","orcid":"","institution":"University of Roma “La Sapienza”","correspondingAuthor":false,"prefix":"","firstName":"Raffaella","middleName":"","lastName":"Pomi","suffix":""}],"badges":[],"createdAt":"2025-02-07 14:23:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5981958/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5981958/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s43621-025-01326-2","type":"published","date":"2025-05-25T15:58:02+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81171911,"identity":"ea2ac9a6-f80c-4fd5-8f7c-f81554cb8397","added_by":"auto","created_at":"2025-04-23 05:32:44","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":57324,"visible":true,"origin":"","legend":"\u003cp\u003eMap of Kampala Divisions showing the study area in Kawempe Division\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/cbc36f598c9855cede302284.jpg"},{"id":81173003,"identity":"0b1cbe2b-1747-4cdf-a2e9-4d2455814ca2","added_by":"auto","created_at":"2025-04-23 05:40:44","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":31044,"visible":true,"origin":"","legend":"\u003cp\u003eThe Volaser measuring device (Andriessen et al., 2023)\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/2cf76e5b4b04c3dddad1a6c1.jpg"},{"id":81171913,"identity":"98ed0852-3b40-4449-8b8e-a8af59b572e0","added_by":"auto","created_at":"2025-04-23 05:32:44","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":55211,"visible":true,"origin":"","legend":"\u003cp\u003eFaecal sludge accumulation rates (L/Cap.year) in monitored septic tanks and pit latrines. The raincloud plots reveal non-normal distributions, with both septic tanks (n=10) and pit latrines (n=10) exhibiting left skewness (with an outlier observed in pit latrines). Therefore, the data are reported using median values and interquartile ranges: 348 L/Cap.year (IQR: 214, 372) for septic tanks and 214 L/Cap.year (IQR: 154, 268) for pit latrines\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/b2a9ad3c913f9b84dbc493ca.jpg"},{"id":81173005,"identity":"4de2fd13-f946-4f9e-a52f-a1421ce146f4","added_by":"auto","created_at":"2025-04-23 05:40:45","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":116412,"visible":true,"origin":"","legend":"\u003cp\u003eTS concentration, VS, COD, Electrical conductivity, and pH of faecal sludge, based on collected categories of containment categories in the study area. (The raincloud plots show that for pH, the data is normally distributed for both pit latrines and septic tanks. However, for EC, septic tank is right skewed (3.1 IQR: 1.8, 4.7) while the data for pit latrines is left skewed (18.8 IQR:8.4, 24.8). For TS septic tank data is right skewed (19.5 IQR: 4.5, 38.2) while that of pit latrine is normally distributed. For VS, that of septic tanks is right skewed (6.0 IQR:1.7, 12.7) and that of pit latrines is right skewed (9.0 IQR: 6.7, 13.8). For COD, the septic tank is left skewed (59.2 IQR:35.5, 61.6) while that of pit latrines are right skewed (30.3 IQR:21.0, 47.7))\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/c9ae1fed5589e53b7773e29b.jpg"},{"id":81173004,"identity":"9f6c54ce-856a-4a4b-81aa-e2564e9b0f62","added_by":"auto","created_at":"2025-04-23 05:40:45","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":41610,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of COD and TS evaluated in this study\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/88150f6b88d42cc941f8fc7c.jpg"},{"id":81171927,"identity":"a418357b-44d1-4e7f-916c-4a36ef46b119","added_by":"auto","created_at":"2025-04-23 05:32:45","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":40618,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation of VS and TS evaluated in this study\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/257bdf78df59c8e8f8c3b6d1.jpg"},{"id":83460077,"identity":"592a6e6f-9790-437d-a3ad-7120a89c599a","added_by":"auto","created_at":"2025-05-26 16:09:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1106902,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5981958/v1/75436f96-6e6b-4f91-9ab8-a81d94afcd3a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Faecal sludge accumulation and characterization in informal settlements of Kampala: insights for facilities design","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eFaecal sludge (FS) comprises human faeces and urine, as well as anal cleaning and any other non-faecal materials discharged and accumulating in onsite sanitation containments (OSCs) such as pit latrines and septic tanks. The management of FS, which accumulates in these sanitation containments presents a significant global challenge due to its potential risks to public health and the environment. This challenge is exacerbated by the rapid expansion in population, particularly in low- and middle-income countries, where a corresponding provision of sanitation services has not kept pace [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Global reliance on these technologies is projected to escalate from 2.7\u0026nbsp;billion to 4.9\u0026nbsp;billion users by 2030 [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In spite of the increasing number of users of OSC, generating large quantities of FS, their management has lacked the necessary focus it requires in the last two decades to ensure protection of the environment and public health [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Faecal sludge management (FSM) encompasses the generation and management of FS in storage containments, collection, transport, treatment, and safe disposal and/or reuse of treated FS solids and the resulting liquid supernatant.\u003c/p\u003e \u003cp\u003eThe trend of urbanization shows an increasing population using non-standardized OSCs for their sanitation needs [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Standardized OSC systems follow established design criteria, with a well-documented components and operational procedures with recognized guidelines and standards for construction, installation, and maintenance to ensure their effectiveness and safety in managing fecal sludge. On the other hand, non-standardized OSC systems lack established design criteria and they vary significantly in design, construction, and operation, deviating from specific standards or best practices in FSM. Unfortunately, many OSCs in low-income countries are non-standardised, and are constructed by masons who know how to build but with little or no competence in their functioning and operation. For instance, in this study, septic tanks used were watertight tanks with only one chamber, cable of keeping untreated sewage separated from soil-water environment [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe high population density in informal settlements and typical flood-prone locations of urban areas necessitates standardized OSCs for FSM [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The Shit Flow Diagram (SFD) of Kampala indicates that 24% of accumulated FS is safely contained onsite and 46% unsafely managed [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The percentages of FS ending in the various environments as shown in the SFD were based on assumptions and interviews with key informants[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. To enhance the accuracy of FS estimates across the sanitation service chain and address inadequate FSM, there is a need to develop ways of characterising FS. An initial crucial step involves determining the quantities and qualities (Q\u0026amp;Q) of FS [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn comparison to wastewater sludge, FS exhibits greater variability in its characteristics based on the region, city, district, household, and source [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. This variability is influenced by a range of factors such as containment technology, retention time, household users' habits and preferences as well as collection practices [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Therefore, developing FSM solutions cannot be independently based on centralised wastewater treatment since it is homogenized during transport in a sewer and relying on it results into inappropriately designed systems that are prone to failure [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The design and quality of OSCs contribute to variations in the Q\u0026amp;Q of FS within cities and containment types in different locations. Therefore, the choice of containment technology should be based on local conditions such as climate, soil permeability, social demographics, economic status, service levels and affordability [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The quantity of the excreta (urine and faeces) generated daily also varies significantly, based on factors such as the quantity and type of food consumed, fluids intake, physical activity and climate [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This highlights the need for collecting accurate faecal sludge accumulation data which are specific to each location and, thus, reliable for the planning, design and implementing appropriate technologies for FS containment and treatment [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePrevious attempts to model FS Q\u0026amp;Q utilized numerical mass balance methods that drew upon data collected from individual pit latrines to predict average accumulation rates for a neighborhood or city [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The lack of standardized approaches and methodologies in scientific literature impedes comparisons and the application of these models in different situations [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Estimating city-wide FS accumulation rates is complex, often hindered by data scarcity [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The challenge arises from FS storage in in-accessible underground non-standardized containments, with limited records of construction and maintenance. Yet, these containment technologies are at the beginning of the sanitation and FSM service chain [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Another major contributor to this problem is the fact that there are inconsistent results in literature on the relationship between organic properties of FS which are major determinants of its accumulation rate. The organic properties of FS significantly influence its accumulation rate. Higher organic content tends to accelerate decomposition, affecting the volume and density, and as well reducing the overall volume of sludge, thereby resulting into lower accumulation rates over time [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Microbial activity, driven by organic matter, further alters sludge stability and separation dynamics. Understanding these relationships is crucial for devising efficient management strategies that directly impact the treatment effectiveness and the overall performance of the system [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe importance of deriving relationships between FS characteristics cannot be over-emphasized. Most low-income countries do not routinely apply analytical techniques for the assessment of all necessary sludge characteristics due to costs involved [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, if relationships can be found with parameters such as TS, that are resource efficient and cheaper to measure, then that would resolve the challenge of under-resourced laboratories in low-income countries while providing a simple method to indirectly derive other parameters, such as COD, which are pivotal for FS management and treatment. In a study conducted in seven countries, including Kampala, Uganda an empirical relationship for Volatile Solids (VS) and TS of 0.49 (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.88) was obtained. However, no relationship between COD and TS was established. Earlier, [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] estimated the sludge accumulation in Kampala City to be 270 L/cap.year for pit latrines and 280 L/cap.year for septic tanks. Studies by Strande [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] found that COD and TS strongly correlated with R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.86. The relationship between VS and TS has been shown by different studies, while that of COD and TS from the different studies are inconsistent. The pH value indicates the acidity or alkalinity of the fecal sludge which provides information about the state of biodegradation and stabilization of the organic matter in FS [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Extreme pH values can impact the treatment processes and the potential for resource recovery from the sludge. EC values are proportional to the concentration of dissolved solids and salts and can be used to predict quality parameters like total solids (TS) and chemical oxygen demand (COD) [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Consequently, more studies are necessary to improve the understanding of the relationships between FS characteristics and reduce the costs of laboratory analysis in under-resourced settings in low-income countries, while at the same time improving design parameters. This study determined the FS characteristics (Quantities and qualities) in lined pit latrines and septic tanks in informal settlements in Kampala City, Uganda, and derived the correlation between various parameters necessary for developing appropriate FS management solutions.\u003c/p\u003e"},{"header":"2 MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Study area\u003c/h2\u003e \u003cp\u003eThis study field-tested a standardized approach for estimating faecal sludge Q\u0026amp;Q in Kawempe division in Kampala city (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFIGURE \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e \u003cp\u003eIt is the second largest division in Kampala with a population of approximately 400,000 people (UBOS, 2017) and 95% of its residents rely entirely on onsite sanitation (Mukwaya, 2013). The study area included Kalerwe, Makerere Kikoni, Kikumi kikumi, and Kikoni. It was selected because it represents a typical urban poor area with high population density and a mix of non standardised OSCs.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e2.2. FS Sampling locations\u003c/h3\u003e\n\u003cp\u003eThe sampling sites used for the study were purposively selected, where the enrolled onsite containments had to be fully lined pit latrines or septic tanks. In the selected neighborhood close to Makerere University, a total of 22 non standardised containments that included 11 lined pit latrines and 11 septic tanks were identified. This number of lined pit latrines and septic tanks selected in the study area represented these types of containments accessible in the area, where their users accepted the study to be conducted, the rest having either refused or inaccessible or using unlined pit latrines and there were no sewer connections in the area. Prior to interviews and sampling, verbal consent was obtained from the users, and they were free to withdraw at any time if they felt uncomfortable during the interview. A questionnaire developed by [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] was used to collect the demographic, environmental and technical (DET) information from the users but in cases where some information was unknown by the users such as containment age, it was obtained from the owners of each OSC who were contacted by telephone (Supplementary material). The key information collected included the number of users, containment age, desludging interval, containment type, types of wastewaters entering the system and whether solid waste entered the containment. To cater for cases where people leave home either for work or school, population equivalents were derived and utilised. The numbers of the onsite containments that were sampled from the locations shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLocations and number of samples taken per selected neighborhood in Kawempe division\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSampling location\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSeptic tanks\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLined pit latrines\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKalerwe (4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMakerere Kavule (2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKikumi Kikumi (5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKikoni (11)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFaecal sludge sampling was carried out according to Koottatep [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] using the cone sampling technique with a locally fabricated sampler. Faecal sludge sampling for laboratory analysis was done once for each containment, but the measurement of FS volume was done once every week for eight weeks, from March to May 2023 and this is a wet season in Kampala. FS volume was used to determine the accumulation and filling rates. A ratio of 1:3:2 for samples from the top, middle, and bottom layers respectively was strategically designed to account for the vertical stratification of the sludge within the containment. This decision was informed by the understanding that over time, the settling process in a containment system leads to the stratification of sludge components, with heavier and larger particles tending to settle towards the bottom layers, while the less heavy particles and those disturbed during the use stay in the middle and the much lighter particles stay in the top layers.\u003c/p\u003e \u003cp\u003eIn the 1:3:2 sampling strategy adopted, the largest sample proportion was taken from the middle layer (3 parts), which represents the majority proportion in a containment which is in use, as continuous flushing or dropping in of contents disturbs a part of the settling sludge to be in second layer that is relatively more liquid than the settled sludge. The second largest part was sludge from the bottom layer (2 parts), where the majority of settled and compacted sludge accumulates. Finally, the smallest sample from near the top layer (1 part) was included to represent the uppermost portion, recognizing its lesser density, floating characteristics, and a high likelihood of containing more liquid and less settled material.\u003c/p\u003e \u003cp\u003eThe above sampling strategy aimed to ensure a good representation of the various layers of FS within the containment, acknowledging the stratification phenomenon and seeking a balanced representation of settled and less settled components for a more accurate analysis of the sludge composition. Representative composite samples, approximately 1L in capacity, were secured in bottles and taken for analysis in the laboratory of the College of Natural Sciences Chemistry at of Makerere University.\u003c/p\u003e\n\u003ch3\u003e2.3. Analytical methods\u003c/h3\u003e\n\u003cp\u003eIn the laboratory, the samples were stored at 4\u0026deg;C until analysis, based on standard laboratory methods according to APHA-AWWA-WEF [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] and Velkushanova et al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e briefly outlines the methods used for analyzing the physico-chemical properties of the FS, encompassing pH, TS, VS, COD, and electrical conductivity.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of methods used to analyze the faecal sludge properties for all the samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhysico-chemical properties\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAnalytical Method\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Solids (TS)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGravimetric method by oven drying at 105\u0026deg;C for 48 hours or until constant weigh of the sample has been reached\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVolatile Solids (VS)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIgnition method by heating at 550\u0026deg;C for 6 hours\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElectrode method using model PHS-3BW of pH meter\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrical Conductivity (EC)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eElectrode method using Wagtech International conductivity meter\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemical Oxygen Demand (COD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClosed reflux spectrophotometric method on raw unfiltered using model SPECTRO-UV7 of MRC spectrophotometer\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003cp\u003eThese parameters were chosen, firstly, because they influence the accumulation of FS in onsite containments. Secondly, the parameters are simple to measure, even under conditions mostly prevalent in low-income countries, with the main idea being to derive relationships between them.\u003c/p\u003e \u003cp\u003e2.4. \u003cb\u003eDetermination of\u003c/b\u003e \u003cb\u003ein-situ\u003c/b\u003e \u003cb\u003eFS volume\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe Volaser (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ewww.sandec.ch/volaser\u003c/span\u003e\u003cspan address=\"http://www.sandec.ch/volaser\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e), a volume laser device made to assess volumes of accumulated FS and containment volume was utilized in determining the depth from the drop-hole for pit latrines and the inspection cover (manhole) for septic tanks to the surface of the FS in the containment. It comprises of a tripod and rod housing a laser distance sensor, operated via a smartphone app [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFIGURE \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003c/p\u003e \u003cp\u003eIn the study, the tripod was positioned above the containment's vertical access point during measurements. The laser sensor was descended into the containment to measure the distance from its top to the FS\u0026rsquo;s surface. Rotating the rod enabled the measurement of distances to containment walls for internal area and shape determination [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. A locally constructed 3.66 m (12ft) collapsible metal probe was forced through the contents of the pit until it could no longer move, where it was assumed that it reached the bottom of the containment. The depth of FS in the containment was recorded in the Volaser application on the smartphone. These distances to the containment walls and the depths of the pit contents were recorded in quadruples through a smartphone App that automatically computed the containment area in m\u003csup\u003e2\u003c/sup\u003e and the \u003cem\u003ein-situ\u003c/em\u003e FS volume in m\u003csup\u003e3\u003c/sup\u003e. Each measurement process took less than 10 minutes.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Data Analysis\u003c/h2\u003e \u003cp\u003eData analysis was done in Microsoft Excel 2010 and R Studio (R-4.3.1) for windows 11 (2023). Correlations between VS and TS as well as TS and COD were determined in the same manner as [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The calculation of the Faecal Sludge Accumulation Rate (FASR) and filling rates [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] and are represented by equations (i) and (ii). This approach was applied to both pit latrines and septic tanks, as septic tanks lacked outflows. FSAR-V means Faecal Sludge Accumulation Rate in volume units of L/cap.year.\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{F}\\varvec{S}\\varvec{A}\\varvec{R}\\:(\\varvec{L}/\\varvec{c}\\varvec{a}.\\varvec{y}\\varvec{e}\\varvec{a}\\varvec{r})=\\:\\frac{\\varvec{T}\\varvec{o}\\varvec{t}\\varvec{a}\\varvec{l}\\:\\varvec{v}\\varvec{o}\\varvec{l}\\varvec{u}\\varvec{m}\\varvec{e}\\:\\varvec{o}\\varvec{f}\\:\\varvec{F}\\varvec{S}\\:\\varvec{i}\\varvec{n}\\varvec{s}\\varvec{i}\\varvec{d}\\varvec{e}\\:\\varvec{c}\\varvec{o}\\varvec{n}\\varvec{t}\\varvec{a}\\varvec{i}\\varvec{n}\\varvec{m}\\varvec{e}\\varvec{n}\\varvec{t}\\:\\varvec{s}\\varvec{y}\\varvec{s}\\varvec{t}\\varvec{e}\\varvec{m}\\:\\varvec{m}\\varvec{e}\\varvec{a}\\varvec{s}\\varvec{u}\\varvec{r}\\varvec{e}\\varvec{d}\\:\\varvec{u}\\varvec{s}\\varvec{i}\\varvec{n}\\varvec{g}\\:\\varvec{V}\\varvec{o}\\varvec{l}\\varvec{a}\\varvec{s}\\varvec{e}\\varvec{r}\\:\\left(\\varvec{L}\\right)}{\\varvec{N}\\varvec{u}\\varvec{m}\\varvec{b}\\varvec{e}\\varvec{r}\\:\\varvec{o}\\varvec{f}\\:\\varvec{u}\\varvec{s}\\varvec{e}\\varvec{r}\\varvec{s}\\:\\times\\:\\:\\varvec{T}\\varvec{i}\\varvec{m}\\varvec{e}\\:\\varvec{s}\\varvec{i}\\varvec{n}\\varvec{c}\\varvec{e}\\:\\varvec{l}\\varvec{a}\\varvec{s}\\varvec{t}\\:\\varvec{e}\\varvec{m}\\varvec{p}\\varvec{t}\\varvec{y}\\varvec{i}\\varvec{n}\\varvec{g}\\:\\left(\\varvec{y}\\varvec{e}\\varvec{a}\\varvec{r}\\varvec{s}\\right)}\\)\u003c/span\u003e \u003c/span\u003e \u003cb\u003e\u0026hellip;\u0026hellip;..(i)\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{F}\\varvec{i}\\varvec{l}\\varvec{l}\\varvec{i}\\varvec{n}\\varvec{g}\\:\\varvec{r}\\varvec{a}\\varvec{t}\\varvec{e}\\:(\\varvec{L}/\\varvec{d}\\varvec{a}\\varvec{y})=\\:\\frac{\\varvec{C}\\varvec{h}\\varvec{a}\\varvec{n}\\varvec{g}\\varvec{e}\\:\\varvec{i}\\varvec{n}\\:\\varvec{f}\\varvec{a}\\varvec{e}\\varvec{c}\\varvec{a}\\varvec{l}\\:\\varvec{s}\\varvec{l}\\varvec{u}\\varvec{d}\\varvec{g}\\varvec{e}\\:\\varvec{v}\\varvec{o}\\varvec{l}\\varvec{u}\\varvec{m}\\varvec{e}\\:\\varvec{w}\\varvec{i}\\varvec{t}\\varvec{h}\\varvec{i}\\varvec{n}\\:\\varvec{c}\\varvec{o}\\varvec{n}\\varvec{t}\\varvec{a}\\varvec{i}\\varvec{n}\\varvec{m}\\varvec{e}\\varvec{n}\\varvec{t}\\:\\left(\\varvec{L}\\right)}{\\varvec{M}\\varvec{e}\\varvec{a}\\varvec{s}\\varvec{u}\\varvec{r}\\varvec{e}\\varvec{m}\\varvec{e}\\varvec{n}\\varvec{t}\\:\\varvec{t}\\varvec{i}\\varvec{m}\\varvec{e}\\:\\varvec{i}\\varvec{n}\\varvec{t}\\varvec{e}\\varvec{r}\\varvec{v}\\varvec{a}\\varvec{l}\\:\\left(\\varvec{d}\\varvec{a}\\varvec{y}\\varvec{s}\\right)}\\)\u003c/span\u003e \u003c/span\u003e \u003cb\u003e\u0026hellip;.(ii)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eGiven the significant variability and uneven distribution of FS quantities and qualities, means and standard deviations were used to describe normally distributed data while the median values and interquartile ranges were respectively used as the measures of central tendency and dispersion for data that were not normally distributed. The normality of the data were assessed using raincloud plots (combination of box plots, density plots and raw data). Outliers were identified and subsequently eliminated to ensure the integrity and accuracy of the data analysis [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Outliers were identified based on the relative absolute deviations, expressed as a percentage, which were computed for laboratory replicates, filling rates, and accumulation rates according to [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The mean of the replicate was subtracted from each individual triplicate, and the result was divided by the triplicate mean, after which, it was multiplied by 100. Subsequently, absolute average deviations were determined for each rate. Data points with a relative deviation exceeding 50% were excluded from the analysis [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. To understand the impact of various parameters used in the accumulation rate calculation (i.e., time, users, and sludge volume), the Demographic, Environmental and Technical (DET) data (Supplementary material) were correlated with the accumulation rate undertaken [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"3 RESULTS AND DISCUSSION","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Quantities of faecal sludge – accumulation and filling rates\u003c/h2\u003e \u003cp\u003eEmploying the FSAR-V method, this study calculated the median faecal sludge accumulation rate as 214 L/cap.year (IQR: 154, 268) for lined pit latrines, with a mean of 228 L/cap.year (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In the case of septic tanks, the median accumulation rate stood at 348 L/cap.year (IQR: 214, 372) with a mean of 317 L/cap.year (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The rest of the data on sludge accumulation rates for both lined pit latrines and septic tanks are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The \u003cem\u003ein-situ\u003c/em\u003e volumes of accumulated FS in the containments amounted to 4.2 ± 2.0 m\u003csup\u003e3\u003c/sup\u003e for lined pit latrines and 6.7 ± 3.2 m\u003csup\u003e3\u003c/sup\u003e for septic tanks. The median accumulation rates were considered for central tendency because of the high variability and non-normal distribution of the rates since the mean can heavily influence a few extreme values [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFIGURE \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\u003cp\u003eComparable accumulation rates were observed in a different Kampala-based study [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], estimating 270 L/cap.year for lined pit latrines and 280 L/cap.year for septic tanks. Another earlier study in Asia and Africa reported varying average accumulation rates in different containments (pits and septic tanks) with or without outlet pipes (to drains, river or soak pits) from 14 to 41 L/cap.year with an average of 25 L/cap.year [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. However, a study in Sircilla, India reported median accumulation rates in septic tanks and pit latrine containments of 53 L/cap.year using a core sampler and 96 L/cap.year using truck volumes that emptied all contents in the containments and using volume gauges when trucks were not full [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The considerable variation in reported sludge accumulation rates emphasizes the challenge of relying on rates borrowed from literature elsewhere [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Transferring knowledge on FS accumulation rates from one region to another is difficult due to the different impact of factors such as hydrological and climatic conditions as well as economic, social and user habits [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe study observed that the frequency of emptying practices is correlated with the accumulation rate of FS, where higher accumulation rates associated with more frequent emptying practices (Supplementary material). Containments with higher accumulation rates were found to require emptying twice a year, while those with lower rates were emptied only once in three years. Interestingly, containments of similar volume but one accommodating twice the average number of users (such as 5 to 10) exhibited a fifty percent reduction in their emptying frequency. It was found that containment size and number of users influence the emptying frequency of emptying containment technologies as also supported by literature [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. As expected, the emptying frequency was inversely proportional to the size of containment but directly proportional to the number of users.\u003c/p\u003e \u003cp\u003eSeptic tanks had higher numbers of users and sludge volume compared to lined pit latrines. However, the time that elapsed since the last desludging did not show a significant difference between the two containment types with p-value of 0.03. The use of the number of users to determine the volume of containment can be challenging due to variations in toilet usage patterns throughout the day (e.g., at home, work, and school) and differences in household and workplace practices [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. This is compounded by the lack of records regarding the periods when people are at home or not. To address this issue, population equivalents were used as a means to account for these diverse usage patterns [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFilling rates measure the net increase in the depth of material in the containments, which comprise inflows of FS minus outflows through, for instance exfiltration and evaporation. Therefore, the net filling rate is influenced by the rate at which non-faecal materials, like solid waste, are added along with the excreta [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The median filling rates were 18.3 L/day for lined pit latrines and 15.1 L/day for septic tanks (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The negative filling rates (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) could be attributed to a combination of factors, among which may include, exfiltration and evaporation of the liquid contents from the pit over the measurement period. With time, the pores through which the exfiltration takes place are later filled and blocked by the accumulating solids, which further prevents them from reducing the filling rates [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary statistics filling rates for pit latrines and septic tanks, L/day (Data are reported as median and interquartile range)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003cp\u003e(n = 22)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePit Latrine\u003c/p\u003e \u003cp\u003e(n = 11)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSeptic Tanks\u003c/p\u003e \u003cp\u003e(n = 11)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimum\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-14.59\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-4.14\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-14.59\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e25th quartile\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.23\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.19\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.17\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMedian\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16.68\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.26\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e15.05\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e33.26\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.26\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e49.19\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e75th quartile\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e33.43\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.31\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e62.18\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximum\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e218.28\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33.44\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e218.28\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e \u003cp\u003eA higher filling rate reflects among others, large numbers of users per day, misuse of the pits, for instance, disposing of solid wastes, use of improper anal cleansing materials (such leaves, maize cobs, stones, mounds of soil etc) and as well as low breakdown of faecal matter [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Disposal of solid wastes and other improper anal cleansing materials introduces differential organic and inorganic loading rates in containments. Other factors that potentially affect the filling rates of pits and septic tanks include containment type such as a lined pit latrines with no overflow, or a septic tank with an overflow for supernatant; as well as additional input materials such as grey water or kitchen wastes [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Different filling rates suggest varying hydraulic retention times, which influence degradability characteristics and hence quantity and quality of faecal sludge [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Pit latrines in the study area had drop-holes and no water was used to flush them. Septic tanks were connected to flush toilets. Consequently, more water was used in septic tanks than pit latrines. Higher degradation rates of organic materials are generally expected in an environment saturated with water, where anaerobic microbes rapidly accumulate, thus allowing for faster breakdown. In unlined pits where less water is in place, the microbial accumulation is low, resulting into less degradation. Consequently, the microbial degradation efficiency increases with the wetness of the containment, while less wetness, which could among others be affected by the leachate loss results into reduced microbial degradation efficiency. All of these affect the sludge accumulation and therefore the frequence of desludging.\u003c/p\u003e \u003cp\u003eUnlike filling rates (L/day), accumulation rates (L/cap.day) of FS take into consideration additional factors, such as the number of users that contribute to the build-up of sludge within the containment. Besides, factors other than the numbers of users and their FS generation impact upon the sludge accumulation rate, as explained above. For efficient FS management, it is essential to consider accumulation rates, population size, and the intended design life when determining the capacity of septic tanks and pit latrines. Previous research has demonstrated that containments with higher accumulation rates were frequently emptied [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Consequently, the FS accumulation rate can serve as a valuable tool to estimate the intervals for emptying or desludging containment technologies.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e3.2 Qualities of faecal sludge\u003c/h3\u003e\n\u003cp\u003eIn the context of sustainable management practices of FS, it is essential to consider both qualities and quantities (loadings) simultaneously [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The pH and EC measurements were within ranges normally encountered in literature, for instance 6.5-8.0 for pH [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], and 0.14 and 24.8 mS/cm for EC [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The FS quality parameters analyzed in this study against the DET data of sanitation technology type are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUsing the student’s t-tests, the quality parameters analysed for pit latrines and septic tanks did not significantly differ between each other (Data in Supplementary Material). Except for COD, the parameters for lined pit latrines were higher than those for septic tanks, and encountered ranges expected for FS due to high variability. Several authors have attempted to explain the variability of FS. It has been reported in [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] that FS is highly variable due to a number of factors, relating to the socio-economic status of the users, design and construction, as geological conditions of the soil strata in which the containments are placed. Anecdotal evidence suggests that to decrease filling rate, users in different parts of the world may apply materials and additives such as old car batteries, kerosene, effective microorganisms, indigenous organisms, salt, sugar, ash, fertilizer, or even dead objects such as cats and dogs. In addition to these practices influencing the characteristics of FS, they do affect the filling and sludge accumulation rates, too, as discussed in the relevant sections ahead.\u003c/p\u003e \u003cp\u003eCOD concentrations in this study ranged from 1.5 to 113 g/L, which falls within the reported ranges of 0.2 to 612.5 g/L [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e–\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. For initial evaluation, this study considered TS as it is the most commonly used design parameter for designing established FS treatment technologies such as drying beds [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. TS (0.5–66.4 g/L for septic tanks and 7.4–51.2 g/L for pit latrines) and COD concentrations of FS in this study cover a wider range than previously reported for lined pits in Kampala (TS 51.4 ± 29.2 g/L; COD 65.5 ± 44.0 g/L) and for the septic tanks (TS 11.9–72.0 g/L; VS 7.1–33.8 g/L; COD 7.8–43 g/L [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]). The TS and COD reported in [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] were conducted during the period September to December, which comprises a mix of wet and dry season. For these parameters, our values of COD and TS obtained in the wet season of March to May were comparable to those reported in [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] in a mix of wet and dry season.\u003c/p\u003e \u003cp\u003eFIGURE \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003c/p\u003e \u003cp\u003eIn the containments studied, linear correlations were observed between the FS concentrations of TS and COD (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) and TS and VS (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). For TS and COD illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, a weak correlation of 0.53 (R\u003csup\u003e2\u003c/sup\u003e = 0.47) was observed. This correlation had no significant variation with other reported values of 0.15 (R\u003csup\u003e2\u003c/sup\u003e = 0.45) [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] except for 1.2 (R\u003csup\u003e2\u003c/sup\u003e = 0.8) [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Therefore, TS did not predict COD and investment in analysis of COD is required in low-income countries. This is consistent with [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFIGURE \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u003c/p\u003e \u003cp\u003eA correlation between VS and TS (R\u003csup\u003e2\u003c/sup\u003e = 0.93) with a slope of 0.61 was observed in this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The equation slope of 0.61 is consistent not far from recent values of VS/TS of 0.52 (R\u003csup\u003e2\u003c/sup\u003e = 0.88) [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] and 0.59 (R\u003csup\u003e2\u003c/sup\u003e = 0.97) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and other reported values of 0.64 ± 0.12 and 0.50 ± 0.16 [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]; 0.54 ± 0.20 and 0.56 ± 0.17 [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]; 0.77 ± 0.01 and 0.80 ± 0.02 [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Consequently, where analyses of VS are not possible, measurements of TS can be fairly relied upon to predict VS, thereby reducing the cost of analysis.\u003c/p\u003e \u003cp\u003eFIGURE \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u003c/p\u003e \u003cp\u003ePrevious studies have linked inconsistencies in the low correlations between TS and COD while strong correlations have been encountered between TS and VS to the possibility of high sand/soil content in the FS [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Many routes leading to sanitation containments, streets within living areas and compounds are not paved. Consequently, the walking with bare feet or shows via unpaved ways, streets and compounds could potentially gather a lot of mud during the wet seasons, which could end up in containments. Besides, soil from the walls of unlined or partially lined pits could potentially collapse/fall in with time, increasing the sand content of the FS. The presence of consistent correlations within a city enables the possibility of making projections, taking into account observed variations based on demographic data. These correlations have the potential to streamline future characterization studies by minimizing the number of required laboratory analyses. Furthermore, they contribute to a deeper comprehension of the underlying connections between these quality parameters, thus aiding in the establishment of a more comprehensive understanding [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\n\u003ch3\u003e3.3 General Discussion\u003c/h3\u003e\n\u003cp\u003eThe findings of this study offer valuable insights into the characterization and accumulation of faecal sludge (FS) in informal settlements, which hold significant implications for the design and implementation of effective faecal sludge management (FSM) strategies in resource-constrained settings. By improving the understanding of FS accumulation rates and quality, this research directly addresses a critical gap in the estimation of FS design parameters for onsite sanitation containments (OSCs), particularly in densely populated, low-income areas.\u003c/p\u003e \u003cp\u003eOne of the most crucial outcomes of this study is the determination of localized faecal sludge accumulation rates of 214 L/cap.year for lined pit latrines and 348 L/cap.year for septic tanks. These rates deviate significantly from the default design assumption of 0.5 L/cap.day (equivalent to 182.5 L/cap.year) commonly used in Uganda, including the design of the Lubigi Sewage and FS Treatment Plant (LSFSTP) [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. The underestimation in previous designs, as demonstrated by the overloading of the LSFSTP within the first six months of operation, underscores the importance of context-specific data in FSM system design. These findings suggest that the use of generalized FS accumulation rates can result in system failures, reinforcing the need for localized measurements to guide both the sizing of containment technologies and the design capacity of FS treatment plants (FSTPs).\u003c/p\u003e \u003cp\u003eThe higher FS accumulation rates observed in septic tanks compared to pit latrines (1.6 times higher) have important implications for containment design and desludging schedules. The correlation between higher user numbers and reduced desludging frequency further highlights the need to consider demographic and technical (DET) factors in the planning phase [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Septic tanks, typically connected to flush toilets, exhibited higher degradation rates due to the availability of water, supporting the notion that moisture content facilitates microbial activity and accelerates organic matter breakdown [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In contrast, pit latrines, which received minimal water, showed higher filling rates, suggesting that water-scarce environments inhibit degradation and require more frequent emptying.\u003c/p\u003e \u003cp\u003eThis differential behavior indicates that a one-size-fits-all approach to containment design and management is insufficient. Instead, tailored strategies based on user habits, containment types, and environmental conditions should be adopted to optimize desludging intervals and reduce operational costs. For instance, higher-capacity containment structures may be necessary in high-density settlements to minimize frequent emptying, which is often costly and logistically challenging.\u003c/p\u003e \u003cp\u003eThe strong correlation observed between volatile solids (VS) and total solids (TS) (R² = 0.93) suggests that TS can be effectively used as a proxy for VS in FS characterization. This is particularly important in low-income countries where laboratory resources are limited [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. As TS is cheaper and easier to measure, its use can significantly reduce the cost and complexity of FS analysis while providing reliable estimates for designing treatment technologies. This approach is supported by similar studies that identified TS as a reliable indicator of other FS quality parameters [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The weak correlation between TS and chemical oxygen demand (COD) (R² = 0.47) implies that additional investment in COD analysis is necessary to accurately assess treatment requirements and optimize sludge treatment processes.\u003c/p\u003e \u003cp\u003eThe variability in FS quality parameters, including TS, VS, and COD, highlights the need for flexible treatment technologies that can handle diverse sludge characteristics. For example, drying beds, commonly used in FS treatment, should be designed to accommodate the high variability in TS concentrations observed in this study (ranging from 11.9 to 72 g/L for septic tanks). Treatment technologies must also be resilient to fluctuations in organic loadings to ensure consistent performance [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. The results suggest that modular and scalable treatment systems would be ideal for informal settlements where demographic and environmental conditions are highly dynamic.\u003c/p\u003e \u003cp\u003eThis study’s accumulation rates are higher than those reported in previous studies conducted in regions such as Sircilla, India, where median rates of 53 L/cap.year were observed using core sampling techniques [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The variation in accumulation rates across regions highlights the influence of local factors such as climate, user behavior, and containment design. Studies in Ouagadougou, Burkina Faso [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] and Senegal [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] have similarly demonstrated that regional differences in FS characteristics can significantly impact FSM outcomes. A Volaser was deployed in the field to measure the faecal sludge accumulation rates in seven countries in Africa, Asia and the Middle East. From this study the median and mean faecal sludge accumulation rates in pit latrines (n = 84) and septic tanks (n = 12) were 44 and 622 L/cap.yr and 218 and 1,834 L/Cap.yr respectively. The values of the median and mean faecal sludge accumulation rates were very highly variable as expected for faecal sludge from various containments in different regions. By providing localized data for Kampala, this study contributes to the growing body of knowledge advocating for context-specific FSM solutions.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Implications of the Findings\u003c/h2\u003e \u003cp\u003eThe findings of this study emphasize the importance of integrating localized FS accumulation data into municipal sanitation planning frameworks. Policymakers should consider revising existing guidelines to incorporate updated FS generation rates, particularly for urban informal settlements. The results also present the need for regular monitoring of FS accumulation rates and quality to inform adaptive management strategies [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. This is particularly critical in a number of cities such as Kampala, where rapid urbanization and high population densities place significant strain on sanitation infrastructure.\u003c/p\u003e \u003cp\u003eUser behaviour, including the disposal of non-faecal materials into containment systems, was identified as a major factor influencing FS accumulation and filling rates. Pit latrines in this study area received more solid waste than septic tanks due to their ease of access and absence of piping systems. This practice not only accelerates the filling of pit latrines but also complicates desludging operations and reduces the efficiency of FS treatment processes [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Public education campaigns promoting proper waste disposal practices could help mitigate these challenges and improve the overall effectiveness of FSM systems.\u003c/p\u003e \u003c/div\u003e "},{"header":"4 CONCLUSIONS","content":" \u003cp\u003eThis study provides evidence for the need to adopt localized, context-specific approaches to FSM in urban informal settlements.\u003c/p\u003e \u003cp\u003eThe findings show that the commonly used design assumption of 0.5 L/cap/day (183 L/Cap/year) across the board for both pits and septic tanks significantly underestimates FS accumulation rates in informal settlements, with measured rates reaching 214 L/cap/year for lined pit latrines and 348 L/cap/year for septic tanks. This discrepancy highlights the inadequacy of generalized design standards and the need for more accurate, site-specific data to guide infrastructure planning and ensure operational sustainability.\u003c/p\u003e \u003cp\u003eThe research demonstrates that simplified analytical methods, such as using total solids (TS) as a proxy for volatile solids (VS), can enhance the cost-efficiency of FSM system design without compromising accuracy. However, the weak correlation between TS and chemical oxygen demand (COD) emphasizes the need for more comprehensive characterization when assessing treatment requirements.\u003c/p\u003e \u003cp\u003eFuture research should focus on long-term monitoring of FS accumulation and quality, as well as the development of innovative, cost-effective technologies suited for resource-constrained settings. By addressing these recommendations, cities like Kampala can make significant progress in tackling sanitation challenges, supporting public health, and fostering sustainable urban development.\u003c/p\u003e \u003c/div\u003e\u003cp\u003eThis study provides evidence for the need to adopt localized, context-specific approaches to FSM in urban informal settlements.\u003c/p\u003e\u003cp\u003eThe findings show that the commonly used design assumption of 0.5 L/cap/day (183 L/Cap/year) across the board for both pits and septic tanks significantly underestimates FS accumulation rates in informal settlements, with measured rates reaching 214 L/cap/year for lined pit latrines and 348 L/cap/year for septic tanks. This discrepancy highlights the inadequacy of generalized design standards and the need for more accurate, site-specific data to guide infrastructure planning and ensure operational sustainability.\u003c/p\u003e\u003cp\u003eThe research demonstrates that simplified analytical methods, such as using total solids (TS) as a proxy for volatile solids (VS), can enhance the cost-efficiency of FSM system design without compromising accuracy. However, the weak correlation between TS and chemical oxygen demand (COD) emphasizes the need for more comprehensive characterization when assessing treatment requirements.\u003c/p\u003e\u003cp\u003eFuture research should focus on long-term monitoring of FS accumulation and quality, as well as the development of innovative, cost-effective technologies suited for resource-constrained settings. By addressing these recommendations, cities like Kampala can make significant progress in tackling sanitation challenges, supporting public health, and fostering sustainable urban development.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate:\u003c/strong\u003e \u003cp\u003eThe participants who responded to the Demographic, Environmental and Technical (DET) questionnaire were asked for permission to participate. They were free to withdraw from the survey at any time. Privacy and anonymity was respected and no responses are attributable to any individual. The samples picked from containments were from the users of the toilet systems, and it's not possible to attribute any quality parameters to a single individual.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication:\u003c/strong\u003e \u003cp\u003eThere is no conflict of interest in publishing the work in this article. All authors consent to publishing the contents of this paper.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting interests:\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eCBN, AB, DM and AYK conceptualized the study; AB and DM wrote and implemented the methodology with the support of all the authors; AB, DM, AM, CBN and MM did the laboratory work, performed the investigation and formal analysis, AB and DM wrote the original first draft preparation, which was majorly revised by CBN; CBN, AM, SS, MM, and RP did the review of the writing and editing; CBN and AYK supervised the entire work. All authors reviewed the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors convey their thanks to Dr. Joel Robert Kinobe for the guidance offered in regard to the field use of the Volaser; and to the College of Natural Sciences Chemistry Laboratory of Makerere University particularly the senior technician Mr. Godfrey Mugenyi for providing support during laboratory analysis. The authors are also grateful to the Final Year Project coordinators, Eng. Dr. Robinah N. Kulabako and Eng. Dr. Seith Mugume for their administrative support. Special thanks to Nienke Marije Andriessen and Linda Strande who provided valuable feedback during the course of drafting the manuscript.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eAll the data used in this study are publicly available and can be accessed via the following link: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://drive.google.com/drive/folders/1j9oMocbARUw8r45YIXgtO4UM3Cg7zV_p?usp=sharing\u003c/span\u003e\u003cspan address=\"https://drive.google.com/drive/folders/1j9oMocbARUw8r45YIXgtO4UM3Cg7zV_p?usp=sharing\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Open and responsible use of these data is encouraged.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eNorstr\u0026ouml;m A, Mcconville J, Kain J, Urban CIT, Management W, Torg M. PERI-URBAN AREAS IN DEVELOPING COUNTRIES: THE EXAMPLE OF ADENTA, GHANA Urbanisation of Peri-Urban Accra the Greater Accra Region. 2009, 237\u0026ndash;245.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSemiyaga S, Okure MAE, Niwagaba CB, Nyenje PM, Kansiime F. Enhancing Faecal Sludge Dewaterability and End-Use by Conditioning with Sawdust and Charcoal Dust. Environ Technol 2017 Inpress, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/09593330.2017.1300191\u003c/span\u003e\u003cspan address=\"10.1080/09593330.2017.1300191\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNarayan AS, Marks SJ, Meierhofer R, Strande L, Tilley E, Zurbr\u0026uuml;gg C, L\u0026uuml;thi C. Advancements in and Integration of Water, Sanitation, and Solid Waste for Low- And Middle-Income Countries. Annu Rev Environ Resour. 2021;46:193\u0026ndash;219. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1146/annurev-environ-030620-042304\u003c/span\u003e\u003cspan address=\"10.1146/annurev-environ-030620-042304\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCairns-Smith S, Hill H, Nazarenko E. Urban Sanitation: Why a Portfolio of Solutions Is Needed. Bost Consult Group Boston USA 2014, 1\u0026ndash;30.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWHO/UNICEF Progress on Drinking Water, Sanitation and Hygiene in Schools. 2022; ISBN 9789280653649.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrauss M, Larmie S, Heinss U. Treatment of Sludges from On-Site Sanitation \u0026mdash; Low-Cost Options. Water Sci Technol. 1997;35:129\u0026ndash;36. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/S0273-1223(97)00103-0\u003c/span\u003e\u003cspan address=\"10.1016/S0273-1223(97)00103-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeal A, Evans B, Blackett I, Hawkins P, Heymans C. Fecal Sludge Management: A Comparative Analysis of 12 Cities. J Water Sanit Hyg Dev. 2014;4. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2166/washdev.2014.026\u003c/span\u003e\u003cspan address=\"10.2166/washdev.2014.026\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrande L, Schoebitz L, Bischoff F, Ddiba D, Okello F, Englund M, Ward BJ, Niwagaba CB. Methods to Reliably Estimate Faecal Sludge Quantities and Qualities for the Design of Treatment Technologies and Management Solutions. J Environ Manage. 2018;223:898\u0026ndash;907. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jenvman.2018.06.100\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2018.06.100\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrasad P, Andriessen N, Moorthy A, Das A, Coppens K, Pradeep R, Strande L. Methods for Estimating Quantities and Qualities (Q\u0026amp;q) of Faecal Sludge: Field Evaluation in Sircilla, India. J Water Sanit Hyg Dev. 2021;11:494\u0026ndash;504. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2166/washdev.2021.269\u003c/span\u003e\u003cspan address=\"10.2166/washdev.2021.269\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBurchart-Korol D, Zawartka P. Environmental Life Cycle Assessment of Septic Tanks in Urban Wastewater System \u0026ndash; a Case Study for Poland. Arch Environ Prot. 2019;45:68\u0026ndash;77. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.24425/aep.2019.130243\u003c/span\u003e\u003cspan address=\"10.24425/aep.2019.130243\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKatukiza AY, Ronteltap M, Oleja A, Niwagaba CB, Kansiime F, Lens PNL. Selection of Sustainable Sanitation Technologies for Urban Slums - a Case of Bwaise III in Kampala, Uganda. Sci Total Environ. 2010;409:52\u0026ndash;62.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRotowa OO, Ayadi PA. Faecal Sludge Management in the Residential Cores of Akure, Nigeria Faecal Sludge Management in the Residential Cores of Akure, Nigeria. 2020.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchoebitz L, Niwagaba CB, Strande L. SFD Promotion Initiative Kampala Uganda Final Report. \u003cem\u003eEawag/Sandec\u003c/em\u003e 2016.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndriessen N, Strande L. The Volaser: In Situ Measurements of Volumes of Faecal Sludge. Manag Excreta Wastewater Sludge 2020, 1.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrande L, Ronteltap M, Brdjanovic D. \u003cem\u003eFaecal Sludge Management - Systems Approach Implementation and Operation\u003c/em\u003e; IWA Publishing: London, UK, 2014; ISBN 9781780404738.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNiwagaba CB, Mb\u0026eacute;gu\u0026eacute;r\u0026eacute; M, Strande L. Faecal Sludge Quantification, Characterisation and Treatment Objectives. In \u003cem\u003eFaecal Sludge Management - systems approach implementation and operation\u003c/em\u003e; Strande, L., Ronteltap, M., Brdjanovic, D., Eds.; IWA Publishing: London, UK, 2014; pp. 15\u0026ndash;42 ISBN 9781780404738.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGold M, Harada H, Therrien J-D, Nishida T, Cunningham M, Semiyaga S, Fujii S, Dorea C, Nguyen V-A, Strande L. Cross-Country Analysis of Faecal Sludge Dewatering. Environ Technol. 2017. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/09593330.2017.1374472\u003c/span\u003e\u003cspan address=\"10.1080/09593330.2017.1374472\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBassan M, Kon\u0026eacute; D, Mb\u0026eacute;gu\u0026eacute;r\u0026eacute; M, Holliger C, Strande L. Success and Failure Assessment Methodology for Wastewater and Faecal Sludge Treatment Projects in Low-Income Countries. J Environ Plan Manag. 2015;58:1690\u0026ndash;710. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/09640568.2014.943343\u003c/span\u003e\u003cspan address=\"10.1080/09640568.2014.943343\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKalbermatten J, Julius D, Gunnerson C. \u003cem\u003eAppropriate Sanitation Alternatives A Technical and Economic Appraisal\u003c/em\u003e; 1982; ISBN 0801825784.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrande L, Ronteltap M, Brdjanovic D. \u003cem\u003eFaecal Sludge Management\u003c/em\u003e; 2014; ISBN 9781780404721.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFeachem RG, et al. Sanitation and Disease - Health Aspects of Excreta and Waste‐water Management. JAWRA J Am Water Resour Assoc. 1984;20:803\u0026ndash;803. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/j.1752-1688.1984.tb04765.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1752-1688.1984.tb04765.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSamal K, Moulick S, Mohapatra BG, Samanta S, Sasidharan S, Prakash B, Sarangi S. Design of Faecal Sludge Treatment Plant (FSTP) and Availability of Its Treatment Technologies. Energy Nexus. 2022;7:100091. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.nexus.2022.100091\u003c/span\u003e\u003cspan address=\"10.1016/j.nexus.2022.100091\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBassan M, Tchonda T, Yiougo L, Zoellig H, Mahamane I, Mb\u0026eacute;gu\u0026eacute;r\u0026eacute; M. Characterization of Faecal Sludge during Dry and Rainy Seasons in Ouagadougou, Burkina Faso. In Proceedings of the 36th WEDC Internaional Confrenece. Delivering Water, Santation and Hygiene Services in an Uncertain Environment; 2013; pp. 1\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhamada Z, Maureen NN, Nicholas K, Robert K, Abia K, Allan JK. A Critical Analysis of Physiochemical Properties Influencing Pit Latrine Emptying and Feacal Sludge Disposal in Kampala Slums, Uganda. Afr J Environ Sci Technol. 2016;10:316\u0026ndash;28. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.5897/AJEST2016.2163\u003c/span\u003e\u003cspan address=\"10.5897/AJEST2016.2163\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChandana N, Rao BA. Critical Review on Sludge Management from Onsite Sanitation Systems: A Knowledge to Be Revised in the Current Situation. Environ Res 2022, \u003cem\u003e203\u003c/em\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParkinson J, Luthi C, Walther D. Sanitation 21-A Planning Framework for Improving City-Wide Sanitation Services. Iwa, 2014.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoottatep T, Surinkul N, Atitaya P. Accumulation Rates of Thickened-Bottom Sludge and Its Characteristics from Water-Based Onsite Sanitation Systems in Thailand. 2014.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWard BJ, Traber J, Gueye A, Diop B, Morgenroth E, Strande L. Evaluation of Conceptual Model and Predictors of Faecal Sludge Dewatering Performance in Senegal and Tanzania. Water Res. 2019;167. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.watres.2019.115101\u003c/span\u003e\u003cspan address=\"10.1016/j.watres.2019.115101\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFreitas FS, Pika PA, Kasten S, Jorgensen BB, Rassmann J, Rabouille C, Thomas S, Sass H, Pancost RD, Arndt S. New Insights into Large-Scale Trends of Apparent Organic Matter Reactivity in Marine Sediments and Patterns of Benthic Carbon Transformation. Biogeosciences. 2021;18:4651\u0026ndash;79. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.5194/bg-18-4651-2021\u003c/span\u003e\u003cspan address=\"10.5194/bg-18-4651-2021\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWard BJ, Andriessen N, Tembo JM, Kabika J, Grau M, Scheidegger A, Morgenroth E, Strande L. Predictive Models Using Cheap and Easy Field Measurements: Can They Fill a Gap in Planning, Monitoring, and Implementing Fecal Sludge Management Solutions? Water Res. 2021;196:116997. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.watres.2021.116997\u003c/span\u003e\u003cspan address=\"10.1016/j.watres.2021.116997\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWanda C, Kengne ES, Wafo GVD, Nzouebet WAL, Nbendah P, Ngandjui YAT, Zapfack L, Noumsi IMK. Quantification and Characterisation of Faecal Sludge from On-Site Sanitation Systems Prior the Design of a Treatment Plant in Bangangte, West Region of Cameroon. Environ Challenges. 2021;5:100236. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.envc.2021.100236\u003c/span\u003e\u003cspan address=\"10.1016/j.envc.2021.100236\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndriessen N, Appiah-Effah E, Browne SJI, al Jahjah R, Kabika J, Kinobe JR, Korir N, Nishimwe P, Niwagaba CB, Pradeep R, et al. Quantities and Qualities of Fecal Sludge: Experiences from Field Implementation with a Volaser in 7 Countries during a Pandemic. Front Water. 2023;5. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/frwa.2023.1130081\u003c/span\u003e\u003cspan address=\"10.3389/frwa.2023.1130081\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoottatep T, Ferr\u0026eacute; A, Chapagain S, Fakkaew K, Strande L. Faecal Sludge Sample Collection and Handling. Methods Faecal Sludge Anal 2021, 55\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAPHA-AWWWA-WEF Standards Methods for the Examination of Water and Wastewater. 20th Edition. \u003cem\u003eAm. Public Heal. Assoc. Am. Water Work. Assoc. Water Environ. Fed. Publ. Washingt. D.C., USA. ISBN 0-87553-047-8\u003c/em\u003e 2012.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVelkushanova K, Strande L. \u003cem\u003eFaecal Sludge Properties and Considerations for Characterisation\u003c/em\u003e; 2021; ISBN 9781780409115.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchmid H, Huber A. Measuring a Small Number of Samples, and the 3v Fallacy: Shedding Light on Confidence and Error Intervals. IEEE Solid-State Circuits Mag. 2014;6:52\u0026ndash;8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1109/MSSC.2014.2313714\u003c/span\u003e\u003cspan address=\"10.1109/MSSC.2014.2313714\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChowdhry S, Kon\u0026eacute; D. \u003cem\u003eBusiness Analysis of Fecal Sludge Management: Emptying and Transportation Services in Africa and Asia\u003c/em\u003e; Seattle, USA, 2012.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrande L, Englund M, Andriessen N, Carbajal JP, Scheidegger A. Estimating Quantities and Qualities (Q\u0026amp;Q) of Faecal Sludge at Community to City-Wide Scales. Methods Faecal Sludge Anal 2021, 115\u0026ndash;44.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eO\u0026rsquo;Brien JW, Thai PK, Eaglesham G, Ort C, Scheidegger A, Carter S, Mueller JF. A Model to Estimate the Population Contributing to the Wastewater Using Samples Collected on Census Day. Environ Sci Technol. 2014;48:517\u0026ndash;25.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrouckaert CJ, Foxon KM, Wood K. Modelling the Filling Rate of Pit Latrines. Water SA. 2013;39:555\u0026ndash;62. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://dx.doi.org/10.4314/wsa.v39i4.15\u003c/span\u003e\u003cspan address=\"10.4314/wsa.v39i4.15\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndriessen N, Englund M, Gold M, Klinger M, Luthi C, Renggli S, Sam S, Strande L, Ward BJ. \u003cem\u003eFaecal Sludge Management: Highlights and Exercises\u003c/em\u003e; Englund, M., Strande, L., Eds.; Eawag: Swiss Federal Institute of Aquatic Science and Technology: Duebendorf, Switzerland, 2019; ISBN 978-3-906484-70-9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMills F, Blacket I, Tayler K. Assessing On-Site Systems and Sludge Accumulation Rates to Understand Pit Emptying in Indonesia, Sustainable Water and Sanitation Services For All in a Fast Changing World. WEDC Loughbrgh Univ Hanoi vietnam, 2017, 1\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAppiah-Effah E, Nyarko KB, Gyasi SF, Awuah E. Faecal Sludge Management in Low Income Areas: A Case Study of Three Districts in the Ashanti Region of Ghana. J Water Sanit Hyg Dev. 2014;4:189\u0026ndash;99. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2166/washdev.2014.126\u003c/span\u003e\u003cspan address=\"10.2166/washdev.2014.126\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSemiyaga S, Okure MaE, Niwagaba CB, Nyenje PM, Kansiime F. Optimisation of Centrifuge Operating Conditions for Dewatering Physically Conditioned Faecal Sludge from Urban Slums. Environ Technol Innov. 2017;8:28\u0026ndash;39. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.eti.2017.03.005\u003c/span\u003e\u003cspan address=\"10.1016/j.eti.2017.03.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShivendra BT. Assessment of Usage of Treated Faecal Sludge for Agriculture. Int J Res Eng Technol. 2016;05:269\u0026ndash;74. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.15623/ijret.2016.0506048\u003c/span\u003e\u003cspan address=\"10.15623/ijret.2016.0506048\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma N, Gupta S, Vyas AD. Estimation of Fuel Potential of Faecal Sludge in a Water Scarce City, a Case Study of Jaipur Urban, India. Water Pract Technol. 2020;15:506\u0026ndash;14. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2166/wpt.2020.037\u003c/span\u003e\u003cspan address=\"10.2166/wpt.2020.037\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVijayan V, Mallik M, Chakravarthy SK. Performance Evaluation: How Faecal Sludge Treatment Plants Are Performing. New Delhi: Centre for Science and Environment; 2020.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNiwagaba CB, Mb\u0026eacute;gu\u0026eacute;r\u0026eacute; M, Strande L. Faecal Sludge Quantification, Characterisation and Treatment Objectives. In Faecal Sludge Management: System Approach for Implementation and Operation. \u003cem\u003eLondon IWA Publ. Available http\u003c/em\u003e\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e//www.eawag.ch/forschung/sandec/publikationen/ewm/dl/fsm_book.pdf\u003c/span\u003e\u003cspan address=\"http:////www.eawag.ch/forschung/sandec/publikationen/ewm/dl/fsm_book.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. \u003cem\u003eAccessed Feb\u003c/em\u003e 2016. 2014, 19\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStrande L, Ronteltap M, Brdjanovic D. The Global Situation. In Faecal Sludge Management: System Approach for Implementation and Operation. \u003cem\u003eLondon IWA Publ. Available\u003c/em\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp//www.eawag.ch/forschung/sandec/publikationen/ewm/dl/fsm_book.pdf\u003c/span\u003e\u003cspan address=\"http://www.eawag.ch/forschung/sandec/publikationen/ewm/dl/fsm_book.pdf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. \u003cem\u003eAccessed Feb\u003c/em\u003e 2016 2014, 1\u0026ndash;13.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBassan M, Mb\u0026eacute;gu\u0026eacute;r\u0026eacute; M, Tchonda T, Zabsonre F, Strande L. Integrated Faecal Sludge Management Scheme for the Cities of Burkina Faso. J Water Sanit Hyg Dev. 2013;3:216\u0026ndash;21. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2166/washdev.2013.156\u003c/span\u003e\u003cspan address=\"10.2166/washdev.2013.156\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStill D, Foxon K. \u003cem\u003eTackling the Challenges of Full Pit Latrines. Volume 2: How Fast Do Pit Toilets Fill up ? A Scientific Understanding of Sludge\u003c/em\u003e; South Africa, 2012; Vol. 2; ISBN 9781431202928.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-sustainability","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"disu","sideBox":"Learn more about [Discover Sustainability](https://www.springer.com/43621)","snPcode":"","submissionUrl":"","title":"Discover Sustainability","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Faecal sludge, accumulation rates, pit latrines, septic tanks, Volaser","lastPublishedDoi":"10.21203/rs.3.rs-5981958/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5981958/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe design and management of onsite sanitation containments for faecal sludge (FS) in informal settlements presents significant public health and environmental challenges, exacerbated by limited data on sludge accumulation and quality. This study aimed to determine properties and accumulation rate of FS in pit latrines and septic tanks to improve sanitation design and management strategies. Fieldwork was conducted in 22 onsite containments (11 pit latrines and 11 septic tanks) in Kawempe Division, Kampala. The in-situ FS volume was measured using a Volaser device, while laboratory analyses determined key physico-chemical parameters, including total solids (TS), volatile solids (VS), and chemical oxygen demand (COD). The findings revealed median FS accumulation rates of 214 L/cap.year for pit latrines and 348 L/cap.year for septic tanks, with significant variability across different containment types. Correlation analysis showed a strong relationship between TS and VS (R\u0026sup2; = 0.93), while TS and COD exhibited a moderate correlation (R\u0026sup2; = 0.47). These insights suggest that TS can be a cost-effective proxy for VS estimation, reducing laboratory analysis costs in resource-limited settings. This study provides data for optimizing faecal sludge management (FSM), supporting the design of more efficient sanitation systems in high-density urban settlements. The findings contribute to improved sludge containment planning, desludging frequency estimation, and the selection of appropriate treatment technologies in similar contexts.\u003c/p\u003e","manuscriptTitle":"Faecal sludge accumulation and characterization in informal settlements of Kampala: insights for facilities design","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-23 05:32:40","doi":"10.21203/rs.3.rs-5981958/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-07T12:17:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-06T09:01:14+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-01T22:31:01+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-29T07:14:18+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-26T17:41:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"156957189197575262956256972631550551118","date":"2025-04-26T11:30:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"232508826691137112435920867516529031036","date":"2025-04-23T06:59:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"293367840656926536109300085419674786497","date":"2025-04-23T01:33:48+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-22T18:48:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-17T06:11:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Sustainability","date":"2025-04-03T19:36:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-sustainability","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"disu","sideBox":"Learn more about [Discover Sustainability](https://www.springer.com/43621)","snPcode":"","submissionUrl":"","title":"Discover Sustainability","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a77f1d2d-375a-4562-8b12-00dcb6fe3da9","owner":[],"postedDate":"April 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-05-26T16:02:54+00:00","versionOfRecord":{"articleIdentity":"rs-5981958","link":"https://doi.org/10.1007/s43621-025-01326-2","journal":{"identity":"discover-sustainability","isVorOnly":false,"title":"Discover Sustainability"},"publishedOn":"2025-05-25 15:58:02","publishedOnDateReadable":"May 25th, 2025"},"versionCreatedAt":"2025-04-23 05:32:40","video":"","vorDoi":"10.1007/s43621-025-01326-2","vorDoiUrl":"https://doi.org/10.1007/s43621-025-01326-2","workflowStages":[]},"version":"v1","identity":"rs-5981958","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5981958","identity":"rs-5981958","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}