Nutrient Removal Efficiency of Constructed Wetlands Planted with Tropical Macrophytes: Implications for Decentralized Wastewater Treatment at Aturukuku Sewerage Works

Nutrient Removal Efficiency of Constructed Wetlands Planted with Tropical Macrophytes: Implications for Decentralized Wastewater Treatment at Aturukuku Sewerage Works | 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 Nutrient Removal Efficiency of Constructed Wetlands Planted with Tropical Macrophytes: Implications for Decentralized Wastewater Treatment at Aturukuku Sewerage Works Titus Bitek Watmon, Niringiyimana Ezra, Engiro Marcel, Kasule Brian, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8885085/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Constructed wetlands are increasingly promoted as sustainable, low-energy wastewater treatment technologies, particularly in regions with limited financial and technical capacity. However, nutrient removal performance in constructed wetlands varies widely with vegetation type and system design. This study evaluated the nitrogen and phosphorus removal efficiency of laboratory-scale constructed wetlands planted with selected macrophyte species under controlled hydraulic conditions. Influent and effluent samples were analysed for ammonia nitrogen and soluble phosphorus using spectrophotometric methods compliant with ISO/IEC 17025 standards. Statistical evaluation was conducted using one-way analysis of variance (ANOVA) and linear regression to assess species effects and relationships between plant growth and nutrient uptake. Results showed substantial reductions in nutrient concentrations, with ammonia decreasing from 6.99 mg/L to 2.22 mg/L and soluble phosphorus from 17.47 mg/L to 3.05 mg/L. Wetlands planted with Cyperus papyrus achieved the highest removal efficiencies, averaging 82% for ammonia and 76% for soluble phosphorus. ANOVA confirmed that macrophyte species had a statistically significant effect on nutrient removal (p 0.60), highlighting the importance of vegetation productivity in treatment performance. The findings demonstrate that appropriate macrophyte selection can significantly enhance nutrient removal in constructed wetlands. The study supports the use of locally adapted species such as Cyperus papyrus for decentralised wastewater treatment and safe water reuse in tropical regions, particularly in East Africa. Environmental Engineering Constructed Wetlands Nutrient Removal Macrophytes Eutrophication Cyperus Papyrus Nitrification–Denitrification Desludging Maturation-Pond Facultative-Pond Sewerage Figures Figure 1 Figure 2 Figure 3 1.0 Introduction Constructed wetlands (CWs) are engineered, nature-based wastewater treatment systems that mimic the physical, chemical, and biological processes of natural wetlands to improve water quality. They integrate wetland vegetation, porous substrates, and diverse microbial communities to remove pollutants through sedimentation, filtration, adsorption, microbial transformation, and plant uptake (Vymazal, 2011 ; Kadlec & Wallace, 2009 ). Owing to their low energy requirements, operational simplicity, and ecological co-benefits, CWs have gained increasing attention as sustainable wastewater treatment options, particularly in decentralised and resource-limited contexts. Nitrogen (N) and phosphorus (P) in domestic wastewater are major concerns because they contribute to eutrophication in recipient water bodies. The overflow of nutrients promotes algal blooms, reduces dissolved oxygen, and causes biodiversity decline in aquatic ecosystems (Carpenter et al., 1998 ; Smith & Schindler, 2009 ). Implementing effective nutrient management is crucial for protecting freshwater ecosystems and ensuring water quality. The Aturukuku Sewage Treatment Plant is situated about 1 kilometer from the Tororo Municipal Council Business Centre in eastern Uganda, where it collects wastewater from the local community. The plant features a Wastewater Stabilisation Pond (WWSP) that uses natural processes such as retention time, free airflow, and warm tropical conditions for treatment. The system includes three ponds: two parallel facultative ponds that feed into a maturation pond, which then directs the flow to the constructed wetland. All sewer connections from the Tororo Municipal Council Business Centre discharge into a single 300 mm asbestos pipe that drains waste into the Aturukuku Wastewater Treatment Plant. At the plant entrance, a Grit Chamber removes sand particles and other floating materials, such as plastics, during daily operations. Combustible materials are dried and burned to prevent pollution in the surrounding area. Sandy materials are collected and stored on site until enough accumulate for potential contractors’ use. Wastewater flows into two parallel facultative ponds designed to treat water high in solids and low in oxygen, which could negatively impact nearby aquatic and inland ecosystems if not carefully managed. The low oxygen levels at the inlets support the presence of anaerobic bacteria. With an approximate retention time of 28 days, multiple processes occur simultaneously, including settling, gas evaporation driven by warm temperatures, and decomposition by both anaerobic and aerobic microbes, going through different stages. Meanwhile, wind continuously sweeps across the surface, aiding in dissolving and removing solids until optimal levels are reached. 1.1 Maturation Pond stage . This pond is shallower than the Facultative Pond, with a retention time of about 14 days due to its roughly half-depth. Its design focuses on creating a thinner water layer to enhance the dissolution of free oxygen. Dissolved oxygen supports aerobic bacteria, which are not yet fully developed in the facultative stage, helping to decompose leftover organic matter from earlier stages. Additional settling also occurs. Routine management involves removing non-degradable materials, plastics, and scum buildup to prevent environmental issues, enhance sunlight penetration, and promote better circulation. Desludging is essential for effective treatment because solid waste constantly accumulates in the ponds and can eventually fill them. The sludge is regularly extracted from the ponds to manage buildup and is then transferred to drying beds. After drying, farmers can use this sludge as mature compost. 2.0 Conventional Wastewater Treatment Technologies 2.1 Limitations of Conventional Wastewater Treatment Technologies Conventional wastewater treatment plants (WWTPs) effectively remove nutrients through advanced biological processes, chemical precipitation, and tertiary treatments. However, they often entail high initial investments, significant energy consumption, and complex operations. Their reliance on electromechanical equipment, continuous power, skilled operators, and chemicals increases lifecycle costs and makes them less suitable for low-income or resource-limited settings (Kadlec & Wallace, 2009 ; Vymazal, 2007 ). In many developing areas, issues like intermittent power supplies, limited technical expertise, and insufficient financial resources further compromise the performance of these systems, sometimes causing subpar results or failures. These issues emphasise the importance of exploring alternative treatment options that are resilient, cost-effective, and tailored to local socio-economic contexts. 2.2 Advantages of Aturukuku Constructed Wetland for Nutrient Removal Aturukuku constructed wetlands provide a cost-effective, energy-efficient solution for nutrient removal by leveraging natural processes. Nitrogen and phosphorus removal in Aturukuku CW occurs through combined mechanisms, including sedimentation, substrate adsorption, microbial nitrification–denitrification, plant uptake, and long-term storage in biomass and sediments (Brix, 1997 ; Wu et al., 2015 ). These processes function with minimal external energy, making Constructed Wetlands significantly less energy-dependent than traditional wastewater treatment plants. Economically, CWs have lower initial costs due to simpler infrastructure and the potential to use locally sourced materials. Their operation and maintenance are also minimal, since CWs do not require continuous aeration, chemical addition, or specialised staff. Therefore, they are ideal for small communities, peri-urban areas, and rural regions with limited financial and technical resources (Kadlec & Wallace, 2009 ; Vymazal, 2007 ). CWs offer environmental benefits beyond wastewater treatment, including habitat creation, biodiversity, carbon capture, and landscape blending. These services support sustainability and reduce the wastewater system’s footprint (Wu et al., 2015 ). 3.0 Role of Constructed Wetlands in Achieving the Sustainable Development Goals Aturukuku constructed wetland plays a direct role in advancing Sustainable Development Goal (SDG 6) by enhancing access to safe wastewater treatment and decreasing nutrient pollution in surface and groundwater sources. Their affordability and decentralised design make them especially effective for increasing sanitation services in underserved areas. Additionally, Constructed Wetlands support SDG 13 (Climate Action) by offering low-energy treatment options that produce fewer greenhouse gases compared to traditional wastewater treatment plants. Their ability to sequester carbon in plant biomass and sediments enhances their climate-mitigation benefits. Furthermore, Aturukuku constructed wetlands contribute to SDG 15 (Life on Land) by creating wetland habitats that foster biodiversity, improve ecological connectivity, and promote sustainable land use. By combining wastewater treatment with ecosystem restoration, the CWs provide a multifunctional solution that tackles water quality issues, enhances climate resilience, and conserves ecosystems. 4.0 Factors Influencing Nutrient Removal and Implications for Safe Reuse The nutrient removal efficiency of the constructed wetland at Aturukuku depends on several interacting factors, including hydraulic retention time, hydraulic loading rate, wetland design, substrate properties, temperature, dissolved oxygen levels, and vegetation type (Kadlec & Wallace, 2009 ; Vymazal, 2013 ). Of these, choosing the right macrophyte species is particularly important. Wetland plants absorb nutrients into their biomass and promote microbial activity by transporting oxygen through aerenchyma, providing root surfaces for biofilm growth, and stabilising the rhizosphere (Brix, 1997 ; Wu et al., 2014 ). Although nitrogen and phosphorus are vital for plant growth, excessive levels in treated wastewater used for irrigation can lead to nutrient leaching, soil degradation, and decreased crop yields if not carefully managed (Qadir et al., 2010 ). Consequently, understanding nutrient removal in CW effluents is crucial for safe reuse and the long-term preservation of terrestrial and aquatic ecosystems. This study assesses nitrogen and phosphorus removal in constructed wetlands with various macrophyte species under controlled lab conditions, focusing on how plant growth and species-specific nutrient uptake enhance treatment efficiency. 5.0 Forms and Concentrations of Nitrogen in Domestic Wastewater and challenges Nitrogen in domestic wastewater mainly exists as inorganic and organic forms. Approximately 60–70% of the total nitrogen is in the form of ammonia nitrogen (NH₄⁺/NH₃), which forms quickly through urea hydrolysis. The remaining 30–40% is organic nitrogen (U.S. EPA, 2009). Ammonia poses particular concerns due to its toxicity to aquatic life and its oxygen-consuming transformation during nitrification. Organic nitrogen is a diverse, complex fraction that includes particulate, colloidal, and dissolved components. Chemically, it encompasses proteins, amino acids, urea derivatives, aliphatic nitrogen compounds, and refractory natural or synthetic substances such as chelating agents (like EDTA) and pharmaceuticals (U.S. EPA, 2009; Pehlivanoglu-Mantas & Sedlak, 2006 ). Dissolved organic nitrogen (DON), which is harder to remove with conventional treatment and can remain in treated effluent, is an increasing concern. In wastewater treatment systems aimed at strict total nitrogen (TN) limits (e.g., ≤ 3.0 mg/L), dissolved organic nitrogen (DON) often acts as the limiting factor. Studies show that DON can constitute 20–50% of the total nitrogen in effluent from advanced treatment systems, compared to approximately 10% in conventional plants (Pehlivanoglu-Mantas & Sedlak, 2006 ; U.S. EPA, 2009). Therefore, improving understanding of nitrogen partitioning and transformation pathways is vital for optimizing constructed wetland (CW) performance. In Aturukuku constructed Wetlands, nitrogen removal involves plant uptake, nitrification–denitrification, ammonia volatilisation (especially at high pH), and sedimentation of particulate nitrogen (Vymazal, 2007 ). The transport of oxygen by macrophytes to the rhizosphere promotes nitrification, while anoxic zones within the substrate support denitrification, emphasizing the crucial role of plant–microbe interactions (Brix, 1997 ). Research indicates that constructed wetlands (cws) can effectively remove nutrients, but their success depends on factors such as plant species, climate, and operational conditions. In many developing regions, CWs are frequently built using locally available macrophytes without detailed assessments of their effectiveness. There is a scarcity of data on how these native plants perform in removing nitrogen and phosphorus under identical hydraulic and substrate conditions. This gap limits the ability to optimize and confidently expand constructed wetlands for improved nutrient removal. 5.1.0 Policy Relevance for East Africa and Uganda In East Africa, especially in Uganda, rapid urban growth, population growth, and expanding agriculture continue to strain limited water resources. Many municipalities and rural areas lack adequate or accessible centralised wastewater treatment infrastructure. National policies like Uganda’s Vision 2040, the National Development Plan (NDP III), the National Water Policy, and the Water and Environment Sector Development Plan promote sustainable sanitation, pollution reduction, climate resilience, and ecosystem preservation. Constructed wetlands support these goals by offering decentralised, low-energy wastewater treatment options that can be set up at community, institutional, and small-town levels using locally available materials and skills. Their ability to decrease nutrient levels in effluent helps protect sensitive water bodies such as Lake Victoria, Lake Kyoga, and nearby wetlands important for fisheries, domestic water, and regional livelihoods. Additionally, combining constructed wetlands with wastewater reuse in agriculture aligns with Uganda’s climate adaptation and circular economy strategies, and contributes to SDGs 6, 13, and 15. Therefore, increasing the use of constructed wetlands provides a feasible, policy-aligned approach to enhance water quality, ecosystem services, and climate-resilient sanitation across Uganda and the wider East African region. 5.1.1 Governance and Implementation Challenges Despite technological and environmental benefits, the use of constructed wetlands in Uganda and East Africa faces governance and implementation challenges. Land tenure issues in peri-urban areas, where ownership is often fragmented or managed by customary systems, hinder project sites. Gaps among water utilities, environmental agencies, local governments, and land authorities create unclear roles in planning and maintenance. Financial constraints also limit progress, as initial costs are lower but often excluded from municipal budgets, and limited access to climate finance complicates funding. Overcoming these hurdles requires coordinated planning, clear institutional roles, and innovative financing that combines public funds, donor aid, and community involvement. Most current research concentrates on generic wetland designs or individual plant species, with few comparative studies of locally adapted macrophytes under consistent operational conditions. This research fills that gap by experimentally evaluating how various plant species perform in nutrient removal under carefully controlled flow, substrate, and hydraulic retention times. 6.0 Materials and Methods 6.1.0 Laboratory Testing and Sampling Representative influent and effluent samples were collected from the constructed wetland system during the rainy season. Samples were preserved and analysed in accordance with standard laboratory protocols and ISO/IEC 17025 requirements (see Fig. 1 ). 6.2.0 Ammonia Analysis Samples were filtered through a 0.45 µm membrane to remove suspended solids. A specified volume of each standard and sample was then placed into reaction vessels, and hypochlorite reagent was added. After mixing thoroughly and allowing the colour to develop, absorbance was measured at 660 nm with a calibrated spectrophotometer. The concentrations were calculated using a standard calibration curve. 6.2.1 Soluble Phosphorus Analysis Influent and effluent samples were filtered through a 0.45-µm membrane to isolate dissolved phosphorus. A combined reagent with sulphuric acid was added, and the samples were left to react for 15 minutes to develop the characteristic blue colour. Absorbance was measured at 880 nm, and concentrations were calculated using the calibration curve. 6.2.2 Data Analysis Nutrient concentrations were calculated using linear regression equations derived from calibration curves. Removal efficiency (RE) was computed as: $$\:RE\left(\text{%}\right)=\frac{{C}_{i}-{C}_{e}}{{C}_{i}}\times\:100$$ where \(\:{C}_{i}\) is the influent concentration and \(\:{C}_{e}\) is the effluent concentration. Thus, the Influent and Effluent Nutrient Concentrations were as outlined in Table 1 Table 1 Influent and Effluent Nutrient Concentrations Parameter Influent (mg/L) Effluent (mg/L) Ammonia 6.993 2.220 Soluble Phosphorus 17.472 3.047 6.2.3 Statistical Analysis Statistical analyses assessed how different macrophyte species influence nutrient removal efficiency and explored the link between plant growth and nutrient uptake. All tests were conducted at an α level of 0.05, following environmental engineering standards (Montgomery, 2017 ). Before analysis, data underwent normality testing with the Shapiro–Wilk test and homogeneity of variances with Levene’s test. Removal efficiencies for ammonia and soluble phosphorus are presented as mean ± standard deviation. 6.2.4 Analysis of Variance (ANOVA) A one-way ANOVA was conducted to assess whether there were significant differences in nutrient removal efficiency among the different macrophyte species. The plant species served as the independent variable, while ammonia and soluble phosphorus removal efficiencies were the dependent variables. The ANOVA model was expressed as: $$\:{Y}_{ij}=\mu\:+{\alpha\:}_{i}+{\epsilon\:}_{ij}$$ Where \(\:{Y}_{ij}\) = nutrient removal efficiency, \(\:\mu\:\) = overall mean, \(\:{\alpha\:}_{i}\) = effect of the \(\:{i}^{th}\) macrophyte species, \(\:{\epsilon\:}_{ij}\) = random error. Results showed that plant species significantly affected the removal efficiencies of ammonia and soluble phosphorus (p < 0.05). Post hoc Tukey’s HSD tests indicated that wetlands with Cyperus papyrus had notably higher nutrient removal rates than other measured macrophytes. These results support the idea that selecting certain macrophytes is a key factor in the effectiveness of constructed wetlands, aligning with earlier research (Vymazal, 2011 ; Wu et al., 2014 ). 6.2.5 Regression Analysis: Relationship Between Plant Growth and Nutrient Uptake To quantify the relationship between plant growth and nutrient removal, linear regression analysis was conducted between plant biomass accumulation (independent variable) and nutrient removal efficiency (dependent variable). The regression model was expressed as: $$\:RE={\beta\:}_{0}+{\beta\:}_{1}B+\epsilon\:$$ Where \(\:RE\) = nutrient removal efficiency (%), \(\:B\) = plant biomass or growth indicator, \(\:{\beta\:}_{0}\) = intercept, \(\:{\beta\:}_{1}\) = regression coefficient, \(\:\epsilon\:\) = error term. Regression results demonstrated a positive and statistically significant relationship between plant growth and ammonia removal efficiency (R² > 0.70, p 0.60, p < 0.05). The strong correlation observed indicates that macrophyte growth enhances nutrient removal through both direct assimilation into plant biomass and indirect stimulation of rhizosphere-mediated microbial processes, including nitrification–denitrification and phosphorus sorption onto root-associated substrates (Brix, 1997 ; Kadlec & Wallace, 2009 ). 7.0 Constructed Wetlands with Ugandan Policy Frameworks In Uganda, as wastewater management challenges increase, constructed wetlands provide a low-energy, climate-resilient treatment solution that aligns with national environmental and sanitation policies, including Vision 2040, NDP III, and the Water Act, as outlined below and Table 2 . Aturukuku constructed wetland aligns closely with Uganda’s long-term development and environmental governance frameworks. Uganda Vision 2040 prioritises the sustainable management of natural resources, environmental protection, climate resilience, and inclusive infrastructure development as foundations for socio-economic transformation. Aturukuku CWs operationalises these priorities by providing low-energy, decentralised wastewater treatment solutions that protect freshwater ecosystems, enhance ecosystem services, and support climate-resilient sanitation, particularly in secondary towns, peri-urban settlements, and rural growth centres. Under NDP III (2020/21–2024/25), the Water and Environment Programme aims to improve access to safe water and sanitation, cut water pollution, protect catchments, and promote climate-smart and nature-based solutions. The CWs directly support these objectives by reducing nutrient and organic pollution runoff into lakes and rivers, enabling wastewater reuse in agriculture, and strengthening the resilience of sanitation systems against climate change. Their decentralised approach complements NDP III’s focus on cost-effective service delivery and infrastructure development driven by local governments. The Water Act (Cap. 152) establishes the legal framework for safeguarding water resources from pollution and overseeing wastewater discharges. Aturukuku Constructed Wetland supports compliance with this legislation by providing an affordable and effective way to treat wastewater before discharge or reuse, thereby reducing both nonpoint and point-source pollution. When incorporated into permitting and enforcement procedures, CWs offer a practical solution for achieving effluent standards, especially when traditional treatment methods are impractical. Table 2 Explicit Policy Mapping of Constructed Wetlands in Uganda Policy Framework Relevant Policy Clauses / Focus Areas Relevance of Constructed Wetlands Uganda Vision 2040 • Sustainable natural resource management • Environmental protection and restoration • Climate-resilient infrastructure • Inclusive growth and service delivery • Constructed Wetlands (CWs) provide nature-based sanitation infrastructure that protects water bodies, restores degraded landscapes, and enhances resilience to climate variability, particularly in underserved communities. NDP III (2020/21–2024/25) • Water and Environment Programme • Pollution control and water quality improvement • Climate change adaptation and mitigation • Decentralised and cost-effective infrastructure • CWs reduce nutrient pollution, support wastewater reuse, lower energy demand, and enable decentralised sanitation systems aligned with climate-smart development priorities. Water Act (Cap. 152) • Protection of water resources from pollution • Regulation of wastewater discharge • Enforcement of effluent standards • CWs facilitate compliance with discharge regulations by providing affordable treatment options that reduce pollutant loads before discharge into surface or groundwater systems. 8.0 Discussion 8.1.0 Nutrient Removal Performance in Engineered Wetland Systems The results demonstrate that constructed wetlands (CWs) function effectively as engineered ecosystems that reduce nitrogen and phosphorus loads from domestic wastewater. The observed reductions in ammonia (6.99 to 2.22 mg/L) and soluble phosphorus (17.47 to 3.05 mg/L) are consistent with nutrient attenuation ranges reported for laboratory- and pilot-scale Constructed Wetlands (CWs) operating under controlled hydraulic conditions (Kadlec & Wallace, 2009 ; Vymazal, 2011 ). From an ecological engineering perspective, these reductions reflect the successful integration of hydrological control, substrate-mediated retention, and biologically driven transformation processes at the Aturukuku lagoon shown in Fig. 2 . The effluent nutrient concentrations approach thresholds recommended for restricted agricultural reuse, underscoring Aturukuku’s dual role as both a treatment and a resource-recovery system. This multifunctionality is a central principle of ecological engineering, in which systems are designed not only to meet regulatory objectives but also to deliver ecosystem services, such as nutrient recycling and water reuse (Mitsch & Jørgensen, 2004 ). 8.1.1 Role of Macrophyte Species in System Function and Process Enhancement Macrophyte species had a statistically significant effect on both ammonia and soluble phosphorus removal (p < 0.05), confirming vegetation selection as a key ecological design variable. Figure 3 shows the Aturukuku constructed wetlands planted with Cyperus papyrus , which exhibit superior nutrient removal performance compared with other species tested under identical hydraulic and substrate conditions. From a systems-engineering viewpoint, the enhanced performance of cyperus papyrus reflects its capacity to modify internal wetland processes. The species’ extensive belowground biomass increases rhizosphere volume, promotes microbial colonization, and enhances oxygen transport via aerenchyma, thereby strengthening coupled nitrification–denitrification pathways (Brix, 1997 ; Vymazal, 2007 ). These plant–microbe interactions exemplify the deliberate use of biological components to regulate biogeochemical fluxes in engineered ecosystems. The findings align with ecological engineering principles emphasizing the use of structurally complex, highly productive species to improve system resilience and functional redundancy (Mitsch & Jørgensen, 2004 ). 8.1.2 Plant Biomass as a Driver of Nitrogen Transformation Processes Regression analysis revealed a strong positive relationship between plant biomass accumulation and ammonia removal efficiency (R² > 0.70, p < 0.01), highlighting vegetation's indirect yet critical role in nitrogen cycling. Although direct plant uptake typically accounts for only a minor fraction of total nitrogen removal, increased biomass enhances oxygen diffusion and organic carbon availability in the rhizosphere, thereby supporting microbial nitrification and denitrification (Kadlec & Wallace, 2009 ). This finding supports the idea in ecological engineering that system performance depends not just on individual components but also on the emergent interactions among hydrology, vegetation, substrates, and microbial communities. Accordingly, managing plant growth by choosing specific species and implementing harvesting regimes can be an effective way to stabilize nitrogen removal in constructed wetlands. 8.1.3 Phosphorus Retention: Substrate–Plant Interactions and Sustainability Soluble phosphorus removal was significantly influenced by macrophyte species (p 0.60, p < 0.05). These findings suggest that phosphorus removal in Aturukuku CWs is driven by synergistic interactions between substrate sorption processes and biological assimilation. However, consistent with prior ecological engineering studies, phosphorus removal capacity is likely to decline over long operational periods due to substrate saturation (Vymazal, 2011 ). This limitation highlights the need for adaptive design strategies, such as reactive substrates, staged wetland cells, or periodic substrate replacement, to maintain long-term phosphorus retention. The results emphasise that sustainable phosphorus management in Aturukuku CWs requires balancing short-term biological uptake with long-term geochemical controls. 8.1.4 Implications for Ecological Design and System Scalability The comparative evaluation of locally adapted macrophytes under uniform operating conditions addresses a critical knowledge gap in the design of Constructed Wetlands in developing regions. The superior performance of Cyperus papyrus supports its use as a functional design element in engineered wetlands, particularly where ecological compatibility, availability, and resilience are priorities. From a scalability perspective, the findings suggest that CWs like that of Aturukuku, designed with indigenous species, can achieve reliable nutrient attenuation while minimising energy inputs and operational complexity. Such attributes are essential for scaling ecological engineering solutions in decentralised and peri-urban wastewater management contexts. 8.1.5 Policy and Sustainable Development Goal Implications The demonstrated nutrient removal performance of Cyperus papyrus –based constructed wetlands has direct implications for wastewater management policy and sustainable development planning. By producing effluent nutrient concentrations compatible with restricted agricultural reuse, Aturukuku CW enables the safe integration of wastewater reuse into water-scarce, nutrient-limited agroecosystems, thereby contributing to water security and circular resource use. At the policy level, these findings align with SDG 6 (Clean Water and Sanitation) by promoting affordable, decentralised wastewater treatment; with SDG 13 (Climate Action) through low-energy, climate-resilient treatment systems; and with SDG 15 (Life on Land) by reducing nutrient-driven eutrophication and protecting terrestrial and aquatic ecosystems. The use of indigenous macrophytes further strengthens alignment with national strategies that emphasise nature-based solutions, ecosystem restoration, and locally appropriate technologies. Integrating CWs into national wastewater reuse policies and environmental management systems can boost regulatory adherence and promote climate resilience, along with ecosystem-based management goals. The data from this study advocate for the adoption of species-specific performance standards in CW design to enhance reliability, efficiency, and sustainability over time. A key factor for the long-term success of the Aturukuku treatment system is managing sludge buildup. If not properly controlled, the continuous accumulation of settled solids in the ponds decreases the effective treatment capacity and hydraulic efficiency. Regular desludging is performed based on the rate of sludge buildup. The removed sludge is then transferred to drying beds, where moisture is reduced prior to further stabilization. Once sufficiently dried and mature, the sludge can be reused as compost for agricultural uses, aligning with sustainable waste management and resource recovery principles (Metcalf & Eddy, 2014; Tilley et al., 2014 ). 9.0 Conclusion This study shows that the Aturukuku constructed wetland can effectively and reliably eliminate nitrogen and phosphorus from domestic wastewater, with success largely dependent on the selected macrophyte species. As indicated, these wetlands perform well in removing nutrients under controlled settings. The type of macrophyte plays a key role in treatment effectiveness, with Cyperus papyrus delivering the highest nutrient removal rates. Additionally, plant growth was linked to nutrient uptake, emphasizing the importance of vegetation choice in designing constructed wetlands. These results support the use of locally adapted macrophytes to improve the sustainability and performance of constructed wetland systems. Comparable nutrient removal efficiencies have been broadly observed in constructed wetlands within tropical regions of sub-Saharan Africa. Elevated temperatures in these areas boost microbial reaction rates and macrophyte growth, enhancing nutrient transformation and uptake (Kadlec & Wallace, 2009 ; Vymazal, 2007 ). Pilot-scale studies from East Africa report ammonia removal efficiencies between about 60% and 85% under controlled hydraulic and loading conditions, confirming constructed wetlands as a viable method for nutrient reduction in tropical climates (Brix, 1997 ; Kansiime et al., 2007 ). The treatment results in this study align with regional data and offer species-specific insights that can help optimize locally adapted wetland designs. In advancing nature-based solutions aligned with SDGs 6, 13, and 15, macrophyte selection is a critical lever to enhance the effectiveness and sustainability of constructed wetland systems. The demonstrated performance of Cyperus papyrus supports its strategic integration into decentralised wastewater treatment systems in Uganda and similar tropical settings. Constructed wetlands offer a robust, cost-effective approach to meeting national effluent discharge standards while facilitating the safe reuse of treated wastewater for agricultural applications. By integrating natural treatment processes with resource recovery, these systems support sustainable water resource management and directly contribute to achieving Sustainable Development Goals (SDGs) 6 (Clean Water and Sanitation), 13 (Climate Action), and 15 (Life on Land). Statistical evaluation using ANOVA and regression analysis confirmed that macrophyte species significantly influence ammonia and soluble phosphorus removal in constructed wetlands. Cyperus papyrus exhibited superior nutrient removal performance, attributable to its higher biomass productivity and enhanced rhizosphere activity. The strong positive correlation between plant growth and nutrient removal efficiency underscores the necessity of vegetation-based optimisation in the design of constructed wetlands. 9.1 Policy Recommendations for Overcoming Implementation Barriers Planners and regulators should prioritise the inclusion of locally adapted macrophytes such as Cyperus papyrus in constructed wetland standards to strengthen sustainable and climate-resilient wastewater treatment so as to. To overcome land tenure issues, governments at both national and local levels should officially recognise constructed wetlands as vital public infrastructure for sanitation and environmental protection. This recognition would allow their prioritisation in development plans and aid land allocation through mechanisms such as easements, public land reservations, or community land agreements. Incorporating CWs into municipal zoning and catchment management strategies can minimise siting conflicts and enhance long-term land security. Better institutional coordination can be achieved by establishing clear governance structures that specify roles among water utilities, environmental agencies, local governments, and land authorities during planning, construction, and operation. Creating inter-agency coordination platforms and integrating CWs into existing water and environmental sector groups would improve accountability, simplify permitting, and promote consistent performance tracking. To address financing challenges, governments should include constructed wetlands in national sanitation investment strategies and climate-resilient infrastructure plans, thereby enabling access to public funds, donor contributions, and climate finance. Promoting blended financing options, such as integrating municipal budgets, grants from development partners, and community contributions, along with results-based funding and dedicated financing channels for nature-based solutions, is essential. Improving local technical skills for designing, operating, and maintaining these systems will help ensure they are cost-effective and sustainable over the long term. The Aturukuku Sewage Treatment Plant is a standard low-cost, nature-based wastewater treatment system suited for tropical municipalities. Nonetheless, the system's efficiency and environmental sustainability rely on good hydraulic design, regular maintenance, and effective sludge handling, highlighting the importance of ongoing performance evaluation and optimization. Future engineering research should focus on improving the kinetic efficiency and predictability of constructed wetlands by: Exploring new substrates like phosphorus-sorbing materials (PSMs) that naturally improve denitrification and phosphorus retention without needing external carbon sources. Developing predictive kinetic models for top tropical species like Cyperus papyrus to determine areal rate constants ( \(\:{K}_{A}\) ) across various temperatures, enhancing the economic viability and scalability of CWs for high-load use. References Brix H (1997) Do macrophytes play a role in constructed treatment wetlands? Water Sci Technol 35 (5):11–17. https://doi.org/10.1016/S0273-1223(97)00047-4 Carpenter SR, Caraco NF, Correll DL, Howarth RW, Sharpley AN, Smith VH (1998) Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecol Appl 8 (3):559–568. https://doi.org/10.1890/1051-0761(1998)008[0559:NPOSWW]2.0.CO;2 Kadlec RH, Wallace SD (2009) Treatment wetlands , 2nd edn. CRC Press, Boca Raton Kansiime F, Oryem-Origa H, Rukwago S (2007) Comparative assessment of the performance of two constructed wetland systems for the treatment of municipal wastewater in Uganda. Phys Chem Earth 32 (15–18):1353–1361. https://doi.org/10.1016/j.pce.2007.07.040 Mara DD (2004) Domestic wastewater treatment in developing countries . Earthscan, London Metcalf & Eddy (2014) Wastewater engineering: treatment and resource recovery , 5th edn. McGraw-Hill Education, New York Mitsch WJ, Jørgensen SE (2004) Ecological engineering and ecosystem restoration . John Wiley & Sons, Hoboken Montgomery DC (2017) Design and analysis of experiments , 9th edn. John Wiley & Sons, Hoboken Pehlivanoglu-Mantas E, Sedlak DL (2006) Wastewater-derived dissolved organic nitrogen: Analytical methods, characterization, and effects—a review. Crit Rev Environ Sci Technol 36 (3):261–285. https://doi.org/10.1080/10643380600678129 Qadir M, Wichelns D, Raschid-Sally L, McCornick PG, Drechsel P, Bahri A, Minhas PS (2010) The challenges of wastewater irrigation in developing countries. Agric Water Manag 97 (4):561–568. https://doi.org/10.1016/j.agwat.2008.11.004 Shilton A, Harrison J (2003) Guidelines for the hydraulic design of wastewater stabilisation ponds . Institute of Technology and Engineering, New Zealand Smith VH, Schindler DW (2009) Eutrophication science: Where do we go from here? Trends Ecol Evol 24 (4):201–207. https://doi.org/10.1016/j.tree.2008.11.009 Tilley E, Ulrich L, Lüthi C, Reymond P, Zurbrügg C (2014) Compendium of sanitation systems and technologies , 2nd edn. Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf U.S. Environmental Protection Agency (2009) Nutrient control design manual: State of technology review report (EPA/600/R-09/012). U.S. EPA, Washington, DC von Sperling M (2007) Waste stabilisation ponds . IWA Publishing, London Vymazal J (2007) Removal of nutrients in various types of constructed wetlands. Sci Total Environ 380 ( 1–3):48–65. https://doi.org/10.1016/j.scitotenv.2006.09.014 Vymazal J (2011) Plants used in constructed wetlands with horizontal subsurface flow: A review. Hydrobiologia 674 : 133–156. https://doi.org/10.1007/s10750-011-0738-9 Vymazal J (2013) Emergent plants used in free water surface constructed wetlands: A review. Ecol Eng 61 : 582–592. https://doi.org/10.1016/j.ecoleng.2013.06.023 Wu H, Zhang J, Li P, Zhang J, Xie H, Zhang B (2014) Nutrient removal in constructed wetlands: A review on plant role and species selection. Ecol Eng 73 :16–23. https://doi.org/10.1016/j.ecoleng.2014.09.001 Wu H, Zhang J, Ngo HH, Guo W, Hu Z, Liang S, Fan J, Liu H (2015) A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation. Bioresour Technol 175 : 594–601. https://doi.org/10.1016/j.biortech.2014.10.068 Yang Y, Zhao Y, Li X, Wu J (2024) Plant-mediated mechanisms for enhanced nitrogen removal in constructed wetlands. Ecol Eng 198 : 107182. https://doi.org/10.1016/j.ecoleng.2024.107182 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted 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-8885085","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":591591245,"identity":"1446b3cd-8a5a-4c26-b932-2c09e03025e0","order_by":0,"name":"Titus Bitek Watmon","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-4463-3913","institution":"Busitema University","correspondingAuthor":true,"prefix":"","firstName":"Titus","middleName":"Bitek","lastName":"Watmon","suffix":""},{"id":591591246,"identity":"0fc2f5d6-13ed-46d6-876c-fe452c14b7c5","order_by":1,"name":"Niringiyimana Ezra","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Niringiyimana","middleName":"","lastName":"Ezra","suffix":""},{"id":591591247,"identity":"774cdbdb-1c07-4110-a18b-73a133142e7b","order_by":2,"name":"Engiro Marcel","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Engiro","middleName":"","lastName":"Marcel","suffix":""},{"id":591591248,"identity":"c2d455a7-3888-4f41-bd53-2ce58518c229","order_by":3,"name":"Kasule Brian","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Kasule","middleName":"","lastName":"Brian","suffix":""},{"id":591591249,"identity":"54e5de13-6686-4a24-9828-ef9bb543f6a9","order_by":4,"name":"Ayat Tiko Guleson","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Ayat","middleName":"Tiko","lastName":"Guleson","suffix":""},{"id":591591250,"identity":"32e46973-bc09-4e07-821f-e3673c782e19","order_by":5,"name":"Zirete Daniel","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Zirete","middleName":"","lastName":"Daniel","suffix":""},{"id":591591251,"identity":"b9bf12dd-8687-4536-8fc4-52debcdfd8e4","order_by":6,"name":"Iramu Alice Elisabeth","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Iramu","middleName":"Alice","lastName":"Elisabeth","suffix":""},{"id":591591252,"identity":"539f4951-1025-4481-adb7-34c641c293bf","order_by":7,"name":"Ogen Mosers","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Ogen","middleName":"","lastName":"Mosers","suffix":""},{"id":591591253,"identity":"72ef7328-3681-4ec0-8baa-c07dd45c4135","order_by":8,"name":"Ogire John","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Ogire","middleName":"","lastName":"John","suffix":""},{"id":591591254,"identity":"7b88503b-7241-49b1-8cbf-66d380eb93e0","order_by":9,"name":"Ologe Daniel Hector","email":"","orcid":"","institution":"Busitema University","correspondingAuthor":false,"prefix":"","firstName":"Ologe","middleName":"Daniel","lastName":"Hector","suffix":""}],"badges":[],"createdAt":"2026-02-15 09:39:26","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":true,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":true},"doi":"10.21203/rs.3.rs-8885085/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8885085/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102900254,"identity":"10068b4f-c0d4-490b-8ee0-0612883c7227","added_by":"auto","created_at":"2026-02-18 07:56:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":356786,"visible":true,"origin":"","legend":"\u003cp\u003eLaboratory Tests in process\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8885085/v1/62d4ee5bab4e83ade616d18a.png"},{"id":102900262,"identity":"76457fdb-020c-48b8-8843-20e1822f0b16","added_by":"auto","created_at":"2026-02-18 07:56:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":435182,"visible":true,"origin":"","legend":"\u003cp\u003eThe constructed sewage Treatment (plant) Lagoon at Aturukuku-Tororo\u003c/p\u003e\n\u003cp\u003eThe effluent nutrient concentrations approach thresholds recommended for restricted agricultural reuse, underscoring Aturukuku’s dual role as both a treatment and a resource-recovery system. This multifunctionality is a central principle of ecological engineering, in which systems are designed not only to meet regulatory objectives but also to deliver ecosystem services, such as nutrient recycling and water reuse (Mitsch \u0026amp; Jørgensen, 2004).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8885085/v1/b03f2f1cf172315341e5cdc4.png"},{"id":102900259,"identity":"48dbf397-a338-4ca7-b77b-0c5642fb899a","added_by":"auto","created_at":"2026-02-18 07:56:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":581315,"visible":true,"origin":"","legend":"\u003cp\u003eWetlands planted with Cyperus papyrus at Tororo Aturukuku CW\u003c/p\u003e\n\u003cp\u003eFrom a systems-engineering viewpoint, the enhanced performance of \u003cem\u003ecyperus papyrus\u003c/em\u003e reflects its capacity to modify internal wetland processes. The species’ extensive belowground biomass increases rhizosphere volume, promotes microbial colonization, and enhances oxygen transport via aerenchyma, thereby strengthening coupled nitrification–denitrification pathways (Brix, 1997; Vymazal, 2007). These plant–microbe interactions exemplify the deliberate use of biological components to regulate biogeochemical fluxes in engineered ecosystems.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8885085/v1/d4348500e16f17e5181a6eed.png"},{"id":102963725,"identity":"c8f87794-9f9a-4ee4-a78c-7d8e0e7e2ee0","added_by":"auto","created_at":"2026-02-19 04:20:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2913879,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8885085/v1/05f8c634-172f-4f7b-a7d9-b475b534437f.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eNutrient Removal Efficiency of Constructed Wetlands Planted with Tropical Macrophytes: Implications for Decentralized Wastewater Treatment at Aturukuku Sewerage Works \u003c/p\u003e","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eConstructed wetlands (CWs) are engineered, nature-based wastewater treatment systems that mimic the physical, chemical, and biological processes of natural wetlands to improve water quality. They integrate wetland vegetation, porous substrates, and diverse microbial communities to remove pollutants through sedimentation, filtration, adsorption, microbial transformation, and plant uptake (Vymazal, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Owing to their low energy requirements, operational simplicity, and ecological co-benefits, CWs have gained increasing attention as sustainable wastewater treatment options, particularly in decentralised and resource-limited contexts.\u003c/p\u003e \u003cp\u003eNitrogen (N) and phosphorus (P) in domestic wastewater are major concerns because they contribute to eutrophication in recipient water bodies. The overflow of nutrients promotes algal blooms, reduces dissolved oxygen, and causes biodiversity decline in aquatic ecosystems (Carpenter et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Smith \u0026amp; Schindler, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Implementing effective nutrient management is crucial for protecting freshwater ecosystems and ensuring water quality.\u003c/p\u003e \u003cp\u003eThe Aturukuku Sewage Treatment Plant is situated about 1 kilometer from the Tororo Municipal Council Business Centre in eastern Uganda, where it collects wastewater from the local community. The plant features a Wastewater Stabilisation Pond (WWSP) that uses natural processes such as retention time, free airflow, and warm tropical conditions for treatment. The system includes three ponds: two parallel facultative ponds that feed into a maturation pond, which then directs the flow to the constructed wetland.\u003c/p\u003e \u003cp\u003eAll sewer connections from the Tororo Municipal Council Business Centre discharge into a single 300 mm asbestos pipe that drains waste into the Aturukuku Wastewater Treatment Plant. At the plant entrance, a Grit Chamber removes sand particles and other floating materials, such as plastics, during daily operations. Combustible materials are dried and burned to prevent pollution in the surrounding area. Sandy materials are collected and stored on site until enough accumulate for potential contractors\u0026rsquo; use.\u003c/p\u003e \u003cp\u003eWastewater flows into two parallel facultative ponds designed to treat water high in solids and low in oxygen, which could negatively impact nearby aquatic and inland ecosystems if not carefully managed. The low oxygen levels at the inlets support the presence of anaerobic bacteria. With an approximate retention time of 28 days, multiple processes occur simultaneously, including settling, gas evaporation driven by warm temperatures, and decomposition by both anaerobic and aerobic microbes, going through different stages. Meanwhile, wind continuously sweeps across the surface, aiding in dissolving and removing solids until optimal levels are reached.\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e1.1 Maturation Pond stage\u003c/b\u003e.\u003c/h2\u003e \u003cp\u003eThis pond is shallower than the Facultative Pond, with a retention time of about 14 days due to its roughly half-depth. Its design focuses on creating a thinner water layer to enhance the dissolution of free oxygen. Dissolved oxygen supports aerobic bacteria, which are not yet fully developed in the facultative stage, helping to decompose leftover organic matter from earlier stages. Additional settling also occurs. Routine management involves removing non-degradable materials, plastics, and scum buildup to prevent environmental issues, enhance sunlight penetration, and promote better circulation.\u003c/p\u003e \u003cp\u003eDesludging is essential for effective treatment because solid waste constantly accumulates in the ponds and can eventually fill them. The sludge is regularly extracted from the ponds to manage buildup and is then transferred to drying beds. After drying, farmers can use this sludge as mature compost.\u003c/p\u003e \u003c/div\u003e"},{"header":"2.0 Conventional Wastewater Treatment Technologies","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Limitations of Conventional Wastewater Treatment Technologies\u003c/h2\u003e \u003cp\u003eConventional wastewater treatment plants (WWTPs) effectively remove nutrients through advanced biological processes, chemical precipitation, and tertiary treatments. However, they often entail high initial investments, significant energy consumption, and complex operations. Their reliance on electromechanical equipment, continuous power, skilled operators, and chemicals increases lifecycle costs and makes them less suitable for low-income or resource-limited settings (Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vymazal, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In many developing areas, issues like intermittent power supplies, limited technical expertise, and insufficient financial resources further compromise the performance of these systems, sometimes causing subpar results or failures. These issues emphasise the importance of exploring alternative treatment options that are resilient, cost-effective, and tailored to local socio-economic contexts.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Advantages of Aturukuku Constructed Wetland for Nutrient Removal\u003c/h2\u003e \u003cp\u003eAturukuku constructed wetlands provide a cost-effective, energy-efficient solution for nutrient removal by leveraging natural processes. Nitrogen and phosphorus removal in Aturukuku CW occurs through combined mechanisms, including sedimentation, substrate adsorption, microbial nitrification\u0026ndash;denitrification, plant uptake, and long-term storage in biomass and sediments (Brix, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Wu et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These processes function with minimal external energy, making Constructed Wetlands significantly less energy-dependent than traditional wastewater treatment plants. Economically, CWs have lower initial costs due to simpler infrastructure and the potential to use locally sourced materials. Their operation and maintenance are also minimal, since CWs do not require continuous aeration, chemical addition, or specialised staff. Therefore, they are ideal for small communities, peri-urban areas, and rural regions with limited financial and technical resources (Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vymazal, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). CWs offer environmental benefits beyond wastewater treatment, including habitat creation, biodiversity, carbon capture, and landscape blending. These services support sustainability and reduce the wastewater system\u0026rsquo;s footprint (Wu et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3.0 Role of Constructed Wetlands in Achieving the Sustainable Development Goals","content":"\u003cp\u003eAturukuku constructed wetland plays a direct role in advancing Sustainable Development Goal (SDG 6) by enhancing access to safe wastewater treatment and decreasing nutrient pollution in surface and groundwater sources. Their affordability and decentralised design make them especially effective for increasing sanitation services in underserved areas. Additionally, Constructed Wetlands support SDG 13 (Climate Action) by offering low-energy treatment options that produce fewer greenhouse gases compared to traditional wastewater treatment plants. Their ability to sequester carbon in plant biomass and sediments enhances their climate-mitigation benefits. Furthermore, Aturukuku constructed wetlands contribute to SDG 15 (Life on Land) by creating wetland habitats that foster biodiversity, improve ecological connectivity, and promote sustainable land use. By combining wastewater treatment with ecosystem restoration, the CWs provide a multifunctional solution that tackles water quality issues, enhances climate resilience, and conserves ecosystems.\u003c/p\u003e"},{"header":"4.0 Factors Influencing Nutrient Removal and Implications for Safe Reuse","content":"\u003cp\u003eThe nutrient removal efficiency of the constructed wetland at Aturukuku depends on several interacting factors, including hydraulic retention time, hydraulic loading rate, wetland design, substrate properties, temperature, dissolved oxygen levels, and vegetation type (Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vymazal, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Of these, choosing the right macrophyte species is particularly important. Wetland plants absorb nutrients into their biomass and promote microbial activity by transporting oxygen through aerenchyma, providing root surfaces for biofilm growth, and stabilising the rhizosphere (Brix, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Wu et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Although nitrogen and phosphorus are vital for plant growth, excessive levels in treated wastewater used for irrigation can lead to nutrient leaching, soil degradation, and decreased crop yields if not carefully managed (Qadir et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Consequently, understanding nutrient removal in CW effluents is crucial for safe reuse and the long-term preservation of terrestrial and aquatic ecosystems.\u003c/p\u003e \u003cp\u003eThis study assesses nitrogen and phosphorus removal in constructed wetlands with various macrophyte species under controlled lab conditions, focusing on how plant growth and species-specific nutrient uptake enhance treatment efficiency.\u003c/p\u003e"},{"header":"5.0 Forms and Concentrations of Nitrogen in Domestic Wastewater and challenges","content":"\u003cp\u003eNitrogen in domestic wastewater mainly exists as inorganic and organic forms. Approximately 60\u0026ndash;70% of the total nitrogen is in the form of ammonia nitrogen (NH₄⁺/NH₃), which forms quickly through urea hydrolysis. The remaining 30\u0026ndash;40% is organic nitrogen (U.S. EPA, 2009). Ammonia poses particular concerns due to its toxicity to aquatic life and its oxygen-consuming transformation during nitrification. Organic nitrogen is a diverse, complex fraction that includes particulate, colloidal, and dissolved components. Chemically, it encompasses proteins, amino acids, urea derivatives, aliphatic nitrogen compounds, and refractory natural or synthetic substances such as chelating agents (like EDTA) and pharmaceuticals (U.S. EPA, 2009; Pehlivanoglu-Mantas \u0026amp; Sedlak, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Dissolved organic nitrogen (DON), which is harder to remove with conventional treatment and can remain in treated effluent, is an increasing concern.\u003c/p\u003e \u003cp\u003eIn wastewater treatment systems aimed at strict total nitrogen (TN) limits (e.g., \u0026le;\u0026thinsp;3.0 mg/L), dissolved organic nitrogen (DON) often acts as the limiting factor. Studies show that DON can constitute 20\u0026ndash;50% of the total nitrogen in effluent from advanced treatment systems, compared to approximately 10% in conventional plants (Pehlivanoglu-Mantas \u0026amp; Sedlak, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; U.S. EPA, 2009). Therefore, improving understanding of nitrogen partitioning and transformation pathways is vital for optimizing constructed wetland (CW) performance. In Aturukuku constructed Wetlands, nitrogen removal involves plant uptake, nitrification\u0026ndash;denitrification, ammonia volatilisation (especially at high pH), and sedimentation of particulate nitrogen (Vymazal, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The transport of oxygen by macrophytes to the rhizosphere promotes nitrification, while anoxic zones within the substrate support denitrification, emphasizing the crucial role of plant\u0026ndash;microbe interactions (Brix, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eResearch indicates that constructed wetlands (cws) can effectively remove nutrients, but their success depends on factors such as plant species, climate, and operational conditions. In many developing regions, CWs are frequently built using locally available macrophytes without detailed assessments of their effectiveness. There is a scarcity of data on how these native plants perform in removing nitrogen and phosphorus under identical hydraulic and substrate conditions. This gap limits the ability to optimize and confidently expand constructed wetlands for improved nutrient removal.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e5.1.0 Policy Relevance for East Africa and Uganda\u003c/h2\u003e \u003cp\u003eIn East Africa, especially in Uganda, rapid urban growth, population growth, and expanding agriculture continue to strain limited water resources. Many municipalities and rural areas lack adequate or accessible centralised wastewater treatment infrastructure. National policies like Uganda\u0026rsquo;s Vision 2040, the National Development Plan (NDP III), the National Water Policy, and the Water and Environment Sector Development Plan promote sustainable sanitation, pollution reduction, climate resilience, and ecosystem preservation. Constructed wetlands support these goals by offering decentralised, low-energy wastewater treatment options that can be set up at community, institutional, and small-town levels using locally available materials and skills. Their ability to decrease nutrient levels in effluent helps protect sensitive water bodies such as Lake Victoria, Lake Kyoga, and nearby wetlands important for fisheries, domestic water, and regional livelihoods. Additionally, combining constructed wetlands with wastewater reuse in agriculture aligns with Uganda\u0026rsquo;s climate adaptation and circular economy strategies, and contributes to SDGs 6, 13, and 15. Therefore, increasing the use of constructed wetlands provides a feasible, policy-aligned approach to enhance water quality, ecosystem services, and climate-resilient sanitation across Uganda and the wider East African region.\u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e5.1.1 Governance and Implementation Challenges\u003c/h2\u003e \u003cp\u003eDespite technological and environmental benefits, the use of constructed wetlands in Uganda and East Africa faces governance and implementation challenges. Land tenure issues in peri-urban areas, where ownership is often fragmented or managed by customary systems, hinder project sites. Gaps among water utilities, environmental agencies, local governments, and land authorities create unclear roles in planning and maintenance. Financial constraints also limit progress, as initial costs are lower but often excluded from municipal budgets, and limited access to climate finance complicates funding. Overcoming these hurdles requires coordinated planning, clear institutional roles, and innovative financing that combines public funds, donor aid, and community involvement. Most current research concentrates on generic wetland designs or individual plant species, with few comparative studies of locally adapted macrophytes under consistent operational conditions. This research fills that gap by experimentally evaluating how various plant species perform in nutrient removal under carefully controlled flow, substrate, and hydraulic retention times.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"6.0 Materials and Methods","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e6.1.0 Laboratory Testing and Sampling\u003c/h2\u003e\n \u003cp\u003eRepresentative influent and effluent samples were collected from the constructed wetland system during the rainy season. Samples were preserved and analysed in accordance with standard laboratory protocols and ISO/IEC 17025 requirements (see Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e6.2.0 Ammonia Analysis\u003c/h2\u003e\n \u003cp\u003eSamples were filtered through a 0.45 \u0026micro;m membrane to remove suspended solids. A specified volume of each standard and sample was then placed into reaction vessels, and hypochlorite reagent was added. After mixing thoroughly and allowing the colour to develop, absorbance was measured at 660 nm with a calibrated spectrophotometer. The concentrations were calculated using a standard calibration curve.\u003c/p\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e6.2.1 Soluble Phosphorus Analysis\u003c/h2\u003e\n \u003cp\u003eInfluent and effluent samples were filtered through a 0.45-\u0026micro;m membrane to isolate dissolved phosphorus. A combined reagent with sulphuric acid was added, and the samples were left to react for 15 minutes to develop the characteristic blue colour. Absorbance was measured at 880 nm, and concentrations were calculated using the calibration curve.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n \u003ch2\u003e6.2.2 Data Analysis\u003c/h2\u003e\n \u003cp\u003eNutrient concentrations were calculated using linear regression equations derived from calibration curves. Removal efficiency (RE) was computed as:\u003c/p\u003e\n \u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\:RE\\left(\\text{%}\\right)=\\frac{{C}_{i}-{C}_{e}}{{C}_{i}}\\times\\:100$$\u003c/div\u003e\u003c/div\u003e\u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{i}\\)\u003c/span\u003e\u003c/span\u003eis the influent concentration and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{e}\\)\u003c/span\u003e\u003c/span\u003eis the effluent concentration.\u003c/p\u003e\u003cp\u003eThus, the Influent and Effluent Nutrient Concentrations were as outlined in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eInfluent and Effluent Nutrient Concentrations\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\"\u003e\u003cp\u003eParameter\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\"\u003e\u003cp\u003eInfluent (mg/L)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\"\u003e\u003cp\u003eEffluent (mg/L)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\"\u003e\u003cp\u003eAmmonia\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\"\u003e\u003cp\u003e6.993\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\"\u003e\u003cp\u003e2.220\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\"\u003e\u003cp\u003eSoluble Phosphorus\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\"\u003e\u003cp\u003e17.472\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\"\u003e\u003cp\u003e3.047\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\u003ch2\u003e6.2.3 Statistical Analysis\u003c/h2\u003e\u003cp\u003eStatistical analyses assessed how different macrophyte species influence nutrient removal efficiency and explored the link between plant growth and nutrient uptake. All tests were conducted at an \u0026alpha; level of 0.05, following environmental engineering standards (Montgomery, \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e). Before analysis, data underwent normality testing with the Shapiro\u0026ndash;Wilk test and homogeneity of variances with Levene\u0026rsquo;s test. Removal efficiencies for ammonia and soluble phosphorus are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\u003ch2\u003e6.2.4 Analysis of Variance (ANOVA)\u003c/h2\u003e\u003cp\u003eA one-way ANOVA was conducted to assess whether there were significant differences in nutrient removal efficiency among the different macrophyte species. The plant species served as the independent variable, while ammonia and soluble phosphorus removal efficiencies were the dependent variables.\u003c/p\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe ANOVA model was expressed as:\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e$$\\:{Y}_{ij}=\\mu\\:+{\\alpha\\:}_{i}+{\\epsilon\\:}_{ij}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eWhere\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{Y}_{ij}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= nutrient removal efficiency,\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= overall mean,\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{\\alpha\\:}_{i}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= effect of the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{i}^{th}\\)\u003c/span\u003e\u003c/span\u003emacrophyte species,\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{\\epsilon\\:}_{ij}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= random error.\u003c/p\u003e\u003c/div\u003e\u003cp\u003eResults showed that plant species significantly affected the removal efficiencies of ammonia and soluble phosphorus (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Post hoc Tukey\u0026rsquo;s HSD tests indicated that wetlands with \u003cem\u003eCyperus papyrus\u003c/em\u003e had notably higher nutrient removal rates than other measured macrophytes. These results support the idea that selecting certain macrophytes is a key factor in the effectiveness of constructed wetlands, aligning with earlier research (Vymazal, \u003cspan class=\"CitationRef\"\u003e2011\u003c/span\u003e; Wu et al., \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\u003ch2\u003e6.2.5 Regression Analysis: Relationship Between Plant Growth and Nutrient Uptake\u003c/h2\u003e\u003cp\u003eTo quantify the relationship between plant growth and nutrient removal, linear regression analysis was conducted between plant biomass accumulation (independent variable) and nutrient removal efficiency (dependent variable). The regression model was expressed as:\u003c/p\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e$$\\:RE={\\beta\\:}_{0}+{\\beta\\:}_{1}B+\\epsilon\\:$$\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eWhere\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:RE\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= nutrient removal efficiency (%),\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:B\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= plant biomass or growth indicator,\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{\\beta\\:}_{0}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= intercept,\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:{\\beta\\:}_{1}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= regression coefficient,\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:\\epsilon\\:\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e= error term.\u003c/p\u003e\u003c/div\u003e\u003cp\u003eRegression results demonstrated a positive and statistically significant relationship between plant growth and ammonia removal efficiency (R\u0026sup2; \u0026gt; 0.70, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), indicating that increased plant biomass enhanced nitrogen removal. A similar positive relationship was observed for soluble phosphorus removal (R\u0026sup2; \u0026gt; 0.60, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003eThe strong correlation observed indicates that macrophyte growth enhances nutrient removal through both direct assimilation into plant biomass \u003cstrong\u003eand\u003c/strong\u003e indirect stimulation of rhizosphere-mediated microbial processes, including nitrification\u0026ndash;denitrification and phosphorus sorption onto root-associated substrates (Brix, \u003cspan class=\"CitationRef\"\u003e1997\u003c/span\u003e; Kadlec \u0026amp; Wallace, \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"7.0 Constructed Wetlands with Ugandan Policy Frameworks","content":"\u003cp\u003eIn Uganda, as wastewater management challenges increase, constructed wetlands provide a low-energy, climate-resilient treatment solution that aligns with national environmental and sanitation policies, including Vision 2040, NDP III, and the Water Act, as outlined below and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAturukuku constructed wetland aligns closely with Uganda\u0026rsquo;s long-term development and environmental governance frameworks. Uganda Vision 2040 prioritises the sustainable management of natural resources, environmental protection, climate resilience, and inclusive infrastructure development as foundations for socio-economic transformation. Aturukuku CWs operationalises these priorities by providing low-energy, decentralised wastewater treatment solutions that protect freshwater ecosystems, enhance ecosystem services, and support climate-resilient sanitation, particularly in secondary towns, peri-urban settlements, and rural growth centres.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eUnder NDP III (2020/21\u0026ndash;2024/25), the Water and Environment Programme aims to improve access to safe water and sanitation, cut water pollution, protect catchments, and promote climate-smart and nature-based solutions. The CWs directly support these objectives by reducing nutrient and organic pollution runoff into lakes and rivers, enabling wastewater reuse in agriculture, and strengthening the resilience of sanitation systems against climate change. Their decentralised approach complements NDP III\u0026rsquo;s focus on cost-effective service delivery and infrastructure development driven by local governments.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe Water Act (Cap. 152) establishes the legal framework for safeguarding water resources from pollution and overseeing wastewater discharges. Aturukuku Constructed Wetland supports compliance with this legislation by providing an affordable and effective way to treat wastewater before discharge or reuse, thereby reducing both nonpoint and point-source pollution. When incorporated into permitting and enforcement procedures, CWs offer a practical solution for achieving effluent standards, especially when traditional treatment methods are impractical.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \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\u003eExplicit Policy Mapping of Constructed Wetlands in Uganda\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolicy Framework\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRelevant Policy Clauses / Focus Areas\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRelevance of Constructed Wetlands\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUganda Vision 2040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026bull; Sustainable natural resource management\u003c/p\u003e \u003cp\u003e\u0026bull; Environmental protection and restoration\u003c/p\u003e \u003cp\u003e\u0026bull; Climate-resilient infrastructure\u003c/p\u003e \u003cp\u003e\u0026bull; Inclusive growth and service delivery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026bull; Constructed Wetlands (CWs) provide nature-based sanitation infrastructure that protects water bodies, restores degraded landscapes, and enhances resilience to climate variability, particularly in underserved communities.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNDP III (2020/21\u0026ndash;2024/25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026bull; Water and Environment Programme\u003c/p\u003e \u003cp\u003e\u0026bull; Pollution control and water quality improvement\u003c/p\u003e \u003cp\u003e\u0026bull; Climate change adaptation and mitigation\u003c/p\u003e \u003cp\u003e\u0026bull; Decentralised and cost-effective infrastructure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026bull; CWs reduce nutrient pollution, support wastewater reuse, lower energy demand, and enable decentralised sanitation systems aligned with climate-smart development priorities.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWater Act (Cap. 152)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026bull; Protection of water resources from pollution\u003c/p\u003e \u003cp\u003e\u0026bull; Regulation of wastewater discharge\u003c/p\u003e \u003cp\u003e\u0026bull; Enforcement of effluent standards\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026bull; CWs facilitate compliance with discharge regulations by providing affordable treatment options that reduce pollutant loads before discharge into surface or groundwater systems.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"8.0 Discussion","content":"\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e8.1.0 Nutrient Removal Performance in Engineered Wetland Systems\u003c/h2\u003e \u003cp\u003eThe results demonstrate that constructed wetlands (CWs) function effectively as engineered ecosystems that reduce nitrogen and phosphorus loads from domestic wastewater. The observed reductions in ammonia (6.99 to 2.22 mg/L) and soluble phosphorus (17.47 to 3.05 mg/L) are consistent with nutrient attenuation ranges reported for laboratory- and pilot-scale Constructed Wetlands (CWs) operating under controlled hydraulic conditions (Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vymazal, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). From an ecological engineering perspective, these reductions reflect the successful integration of hydrological control, substrate-mediated retention, and biologically driven transformation processes at the Aturukuku lagoon shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe effluent nutrient concentrations approach thresholds recommended for restricted agricultural reuse, underscoring Aturukuku\u0026rsquo;s dual role as both a treatment and a resource-recovery system. This multifunctionality is a central principle of ecological engineering, in which systems are designed not only to meet regulatory objectives but also to deliver ecosystem services, such as nutrient recycling and water reuse (Mitsch \u0026amp; J\u0026oslash;rgensen, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e8.1.1 Role of Macrophyte Species in System Function and Process Enhancement\u003c/h2\u003e \u003cp\u003eMacrophyte species had a statistically significant effect on both ammonia and soluble phosphorus removal (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), confirming vegetation selection as a key ecological design variable. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the Aturukuku constructed wetlands planted with \u003cem\u003eCyperus papyrus\u003c/em\u003e, which exhibit superior nutrient removal performance compared with other species tested under identical hydraulic and substrate conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom a systems-engineering viewpoint, the enhanced performance of \u003cem\u003ecyperus papyrus\u003c/em\u003e reflects its capacity to modify internal wetland processes. The species\u0026rsquo; extensive belowground biomass increases rhizosphere volume, promotes microbial colonization, and enhances oxygen transport via aerenchyma, thereby strengthening coupled nitrification\u0026ndash;denitrification pathways (Brix, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Vymazal, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). These plant\u0026ndash;microbe interactions exemplify the deliberate use of biological components to regulate biogeochemical fluxes in engineered ecosystems.\u003c/p\u003e \u003cp\u003eThe findings align with ecological engineering principles emphasizing the use of structurally complex, highly productive species to improve system resilience and functional redundancy (Mitsch \u0026amp; J\u0026oslash;rgensen, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e8.1.2 Plant Biomass as a Driver of Nitrogen Transformation Processes\u003c/h2\u003e \u003cp\u003eRegression analysis revealed a strong positive relationship between plant biomass accumulation and ammonia removal efficiency (R\u0026sup2; \u0026gt; 0.70, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), highlighting vegetation's indirect yet critical role in nitrogen cycling. Although direct plant uptake typically accounts for only a minor fraction of total nitrogen removal, increased biomass enhances oxygen diffusion and organic carbon availability in the rhizosphere, thereby supporting microbial nitrification and denitrification (Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This finding supports the idea in ecological engineering that system performance depends not just on individual components but also on the emergent interactions among hydrology, vegetation, substrates, and microbial communities. Accordingly, managing plant growth by choosing specific species and implementing harvesting regimes can be an effective way to stabilize nitrogen removal in constructed wetlands.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section3\"\u003e \u003ch2\u003e8.1.3 Phosphorus Retention: Substrate\u0026ndash;Plant Interactions and Sustainability\u003c/h2\u003e \u003cp\u003eSoluble phosphorus removal was significantly influenced by macrophyte species (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and positively correlated with plant growth (R\u0026sup2; \u0026gt; 0.60, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). These findings suggest that phosphorus removal in Aturukuku CWs is driven by synergistic interactions between substrate sorption processes and biological assimilation.\u003c/p\u003e \u003cp\u003eHowever, consistent with prior ecological engineering studies, phosphorus removal capacity is likely to decline over long operational periods due to substrate saturation (Vymazal, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This limitation highlights the need for adaptive design strategies, such as reactive substrates, staged wetland cells, or periodic substrate replacement, to maintain long-term phosphorus retention. The results emphasise that sustainable phosphorus management in Aturukuku CWs requires balancing short-term biological uptake with long-term geochemical controls.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003e8.1.4 Implications for Ecological Design and System Scalability\u003c/h2\u003e \u003cp\u003eThe comparative evaluation of locally adapted macrophytes under uniform operating conditions addresses a critical knowledge gap in the design of Constructed Wetlands in developing regions. The superior performance of \u003cem\u003eCyperus papyrus\u003c/em\u003e supports its use as a functional design element in engineered wetlands, particularly where ecological compatibility, availability, and resilience are priorities. From a scalability perspective, the findings suggest that CWs like that of Aturukuku, designed with indigenous species, can achieve reliable nutrient attenuation while minimising energy inputs and operational complexity. Such attributes are essential for scaling ecological engineering solutions in decentralised and peri-urban wastewater management contexts.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003e8.1.5 Policy and Sustainable Development Goal Implications\u003c/h2\u003e \u003cp\u003eThe demonstrated nutrient removal performance of \u003cem\u003eCyperus papyrus\u003c/em\u003e\u0026ndash;based constructed wetlands has direct implications for wastewater management policy and sustainable development planning. By producing effluent nutrient concentrations compatible with restricted agricultural reuse, Aturukuku CW enables the safe integration of wastewater reuse into water-scarce, nutrient-limited agroecosystems, thereby contributing to water security and circular resource use. At the policy level, these findings align with SDG 6 (Clean Water and Sanitation) by promoting affordable, decentralised wastewater treatment; with SDG 13 (Climate Action) through low-energy, climate-resilient treatment systems; and with SDG 15 (Life on Land) by reducing nutrient-driven eutrophication and protecting terrestrial and aquatic ecosystems. The use of indigenous macrophytes further strengthens alignment with national strategies that emphasise nature-based solutions, ecosystem restoration, and locally appropriate technologies.\u003c/p\u003e \u003cp\u003eIntegrating CWs into national wastewater reuse policies and environmental management systems can boost regulatory adherence and promote climate resilience, along with ecosystem-based management goals. The data from this study advocate for the adoption of species-specific performance standards in CW design to enhance reliability, efficiency, and sustainability over time.\u003c/p\u003e \u003cp\u003eA key factor for the long-term success of the Aturukuku treatment system is managing sludge buildup. If not properly controlled, the continuous accumulation of settled solids in the ponds decreases the effective treatment capacity and hydraulic efficiency. Regular desludging is performed based on the rate of sludge buildup. The removed sludge is then transferred to drying beds, where moisture is reduced prior to further stabilization. Once sufficiently dried and mature, the sludge can be reused as compost for agricultural uses, aligning with sustainable waste management and resource recovery principles (Metcalf \u0026amp; Eddy, 2014; Tilley et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"9.0 Conclusion","content":"\u003cp\u003eThis study shows that the Aturukuku constructed wetland can effectively and reliably eliminate nitrogen and phosphorus from domestic wastewater, with success largely dependent on the selected macrophyte species. As indicated, these wetlands perform well in removing nutrients under controlled settings. The type of macrophyte plays a key role in treatment effectiveness, with \u003cem\u003eCyperus papyrus\u003c/em\u003e delivering the highest nutrient removal rates. Additionally, plant growth was linked to nutrient uptake, emphasizing the importance of vegetation choice in designing constructed wetlands. These results support the use of locally adapted macrophytes to improve the sustainability and performance of constructed wetland systems.\u003c/p\u003e \u003cp\u003eComparable nutrient removal efficiencies have been broadly observed in constructed wetlands within tropical regions of sub-Saharan Africa. Elevated temperatures in these areas boost microbial reaction rates and macrophyte growth, enhancing nutrient transformation and uptake (Kadlec \u0026amp; Wallace, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vymazal, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Pilot-scale studies from East Africa report ammonia removal efficiencies between about 60% and 85% under controlled hydraulic and loading conditions, confirming constructed wetlands as a viable method for nutrient reduction in tropical climates (Brix, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Kansiime et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The treatment results in this study align with regional data and offer species-specific insights that can help optimize locally adapted wetland designs.\u003c/p\u003e \u003cp\u003eIn advancing nature-based solutions aligned with SDGs 6, 13, and 15, macrophyte selection is a critical lever to enhance the effectiveness and sustainability of constructed wetland systems. The demonstrated performance of \u003cem\u003eCyperus papyrus\u003c/em\u003e supports its strategic integration into decentralised wastewater treatment systems in Uganda and similar tropical settings. Constructed wetlands offer a robust, cost-effective approach to meeting national effluent discharge standards while facilitating the safe reuse of treated wastewater for agricultural applications. By integrating natural treatment processes with resource recovery, these systems support sustainable water resource management and directly contribute to achieving Sustainable Development Goals (SDGs) 6 (Clean Water and Sanitation), 13 (Climate Action), and 15 (Life on Land).\u003c/p\u003e \u003cp\u003eStatistical evaluation using ANOVA and regression analysis confirmed that macrophyte species significantly influence ammonia and soluble phosphorus removal in constructed wetlands. \u003cem\u003eCyperus papyrus\u003c/em\u003e exhibited superior nutrient removal performance, attributable to its higher biomass productivity and enhanced rhizosphere activity. The strong positive correlation between plant growth and nutrient removal efficiency underscores the necessity of vegetation-based optimisation in the design of constructed wetlands.\u003c/p\u003e \u003cdiv id=\"Sec28\" class=\"Section2\"\u003e \u003ch2\u003e9.1 Policy Recommendations for Overcoming Implementation Barriers\u003c/h2\u003e \u003cp\u003ePlanners and regulators should prioritise the inclusion of locally adapted macrophytes such as \u003cem\u003eCyperus papyrus\u003c/em\u003e in constructed wetland standards to strengthen sustainable and climate-resilient wastewater treatment so as to.\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTo overcome land tenure issues, governments at both national and local levels should officially recognise constructed wetlands as vital public infrastructure for sanitation and environmental protection. This recognition would allow their prioritisation in development plans and aid land allocation through mechanisms such as easements, public land reservations, or community land agreements. Incorporating CWs into municipal zoning and catchment management strategies can minimise siting conflicts and enhance long-term land security. Better institutional coordination can be achieved by establishing clear governance structures that specify roles among water utilities, environmental agencies, local governments, and land authorities during planning, construction, and operation. Creating inter-agency coordination platforms and integrating CWs into existing water and environmental sector groups would improve accountability, simplify permitting, and promote consistent performance tracking.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTo address financing challenges, governments should include constructed wetlands in national sanitation investment strategies and climate-resilient infrastructure plans, thereby enabling access to public funds, donor contributions, and climate finance. Promoting blended financing options, such as integrating municipal budgets, grants from development partners, and community contributions, along with results-based funding and dedicated financing channels for nature-based solutions, is essential. Improving local technical skills for designing, operating, and maintaining these systems will help ensure they are cost-effective and sustainable over the long term.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eThe Aturukuku Sewage Treatment Plant is a standard low-cost, nature-based wastewater treatment system suited for tropical municipalities. Nonetheless, the system's efficiency and environmental sustainability rely on good hydraulic design, regular maintenance, and effective sludge handling, highlighting the importance of ongoing performance evaluation and optimization. Future engineering research should focus on improving the kinetic efficiency and predictability of constructed wetlands by:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eExploring new substrates like phosphorus-sorbing materials (PSMs) that naturally improve denitrification and phosphorus retention without needing external carbon sources.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDeveloping predictive kinetic models for top tropical species like \u003cem\u003eCyperus papyrus\u003c/em\u003e to determine areal rate constants (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{K}_{A}\\)\u003c/span\u003e\u003c/span\u003e) across various temperatures, enhancing the economic viability and scalability of CWs for high-load use.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBrix H (1997) Do macrophytes play a role in constructed treatment wetlands? \u003cem\u003eWater Sci Technol\u003c/em\u003e \u003cstrong\u003e35\u003c/strong\u003e(5):11\u0026ndash;17. https://doi.org/10.1016/S0273-1223(97)00047-4\u003c/li\u003e\n\u003cli\u003eCarpenter SR, Caraco NF, Correll DL, Howarth RW, Sharpley AN, Smith VH (1998) Nonpoint pollution of surface waters with phosphorus and nitrogen. \u003cem\u003eEcol Appl\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e(3):559\u0026ndash;568. https://doi.org/10.1890/1051-0761(1998)008[0559:NPOSWW]2.0.CO;2\u003c/li\u003e\n\u003cli\u003eKadlec RH, Wallace SD (2009) \u003cem\u003eTreatment wetlands\u003c/em\u003e, 2nd edn. CRC Press, Boca Raton\u003c/li\u003e\n\u003cli\u003eKansiime F, Oryem-Origa H, Rukwago S (2007) Comparative assessment of the performance of two constructed wetland systems for the treatment of municipal wastewater in Uganda. \u003cem\u003ePhys Chem Earth\u003c/em\u003e \u003cstrong\u003e32\u003c/strong\u003e(15\u0026ndash;18):1353\u0026ndash;1361. https://doi.org/10.1016/j.pce.2007.07.040\u003c/li\u003e\n\u003cli\u003eMara DD (2004) \u003cem\u003eDomestic wastewater treatment in developing countries\u003c/em\u003e. Earthscan, London\u003c/li\u003e\n\u003cli\u003eMetcalf \u0026amp; Eddy (2014) \u003cem\u003eWastewater engineering: treatment and resource recovery\u003c/em\u003e, 5th edn. McGraw-Hill Education, New York\u003c/li\u003e\n\u003cli\u003eMitsch WJ, J\u0026oslash;rgensen SE (2004) \u003cem\u003eEcological engineering and ecosystem restoration\u003c/em\u003e. John Wiley \u0026amp; Sons, Hoboken\u003c/li\u003e\n\u003cli\u003eMontgomery DC (2017) \u003cem\u003eDesign and analysis of experiments\u003c/em\u003e, 9th edn. John Wiley \u0026amp; Sons, Hoboken\u003c/li\u003e\n\u003cli\u003ePehlivanoglu-Mantas E, Sedlak DL (2006) Wastewater-derived dissolved organic nitrogen: Analytical methods, characterization, and effects\u0026mdash;a review. \u003cem\u003eCrit Rev Environ Sci Technol\u003c/em\u003e \u003cstrong\u003e36\u003c/strong\u003e(3):261\u0026ndash;285. https://doi.org/10.1080/10643380600678129\u003c/li\u003e\n\u003cli\u003eQadir M, Wichelns D, Raschid-Sally L, McCornick PG, Drechsel P, Bahri A, Minhas PS (2010) The challenges of wastewater irrigation in developing countries. \u003cem\u003eAgric Water Manag\u003c/em\u003e \u003cstrong\u003e97\u003c/strong\u003e(4):561\u0026ndash;568. https://doi.org/10.1016/j.agwat.2008.11.004\u003c/li\u003e\n\u003cli\u003eShilton A, Harrison J (2003) \u003cem\u003eGuidelines for the hydraulic design of wastewater stabilisation ponds\u003c/em\u003e. Institute of Technology and Engineering, New Zealand\u003c/li\u003e\n\u003cli\u003eSmith VH, Schindler DW (2009) Eutrophication science: Where do we go from here? \u003cem\u003eTrends Ecol Evol\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e(4):201\u0026ndash;207. https://doi.org/10.1016/j.tree.2008.11.009\u003c/li\u003e\n\u003cli\u003eTilley E, Ulrich L, L\u0026uuml;thi C, Reymond P, Zurbr\u0026uuml;gg C (2014) \u003cem\u003eCompendium of sanitation systems and technologies\u003c/em\u003e, 2nd edn. Swiss Federal Institute of Aquatic Science and Technology (Eawag), D\u0026uuml;bendorf\u003c/li\u003e\n\u003cli\u003eU.S. Environmental Protection Agency (2009) \u003cem\u003eNutrient control design manual: State of technology review report\u003c/em\u003e (EPA/600/R-09/012). U.S. EPA, Washington, DC\u003c/li\u003e\n\u003cli\u003evon Sperling M (2007) \u003cem\u003eWaste stabilisation ponds\u003c/em\u003e. IWA Publishing, London\u003c/li\u003e\n\u003cli\u003eVymazal J (2007) Removal of nutrients in various types of constructed wetlands. \u003cem\u003eSci Total Environ\u003c/em\u003e \u003cstrong\u003e380\u003c/strong\u003e\u003cstrong\u003e(\u003c/strong\u003e1\u0026ndash;3):48\u0026ndash;65. https://doi.org/10.1016/j.scitotenv.2006.09.014\u003c/li\u003e\n\u003cli\u003eVymazal J (2011) Plants used in constructed wetlands with horizontal subsurface flow: A review. \u003cem\u003eHydrobiologia\u003c/em\u003e \u003cstrong\u003e674\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e133\u0026ndash;156. https://doi.org/10.1007/s10750-011-0738-9\u003c/li\u003e\n\u003cli\u003eVymazal J (2013) Emergent plants used in free water surface constructed wetlands: A review. \u003cem\u003eEcol Eng\u003c/em\u003e \u003cstrong\u003e61\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e582\u0026ndash;592. https://doi.org/10.1016/j.ecoleng.2013.06.023\u003c/li\u003e\n\u003cli\u003eWu H, Zhang J, Li P, Zhang J, Xie H, Zhang B (2014) Nutrient removal in constructed wetlands: A review on plant role and species selection. \u003cem\u003eEcol Eng\u003c/em\u003e \u003cstrong\u003e73\u003c/strong\u003e:16\u0026ndash;23. https://doi.org/10.1016/j.ecoleng.2014.09.001\u003c/li\u003e\n\u003cli\u003eWu H, Zhang J, Ngo HH, Guo W, Hu Z, Liang S, Fan J, Liu H (2015) A review on the sustainability of constructed wetlands for wastewater treatment: Design and operation. \u003cem\u003eBioresour Technol\u003c/em\u003e \u003cstrong\u003e175\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e594\u0026ndash;601. https://doi.org/10.1016/j.biortech.2014.10.068\u003c/li\u003e\n\u003cli\u003eYang Y, Zhao Y, Li X, Wu J (2024) Plant-mediated mechanisms for enhanced nitrogen removal in constructed wetlands. \u003cem\u003eEcol Eng\u003c/em\u003e \u003cstrong\u003e198\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e107182. https://doi.org/10.1016/j.ecoleng.2024.107182\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Busitema University","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Constructed Wetlands, Nutrient Removal, Macrophytes, Eutrophication, Cyperus Papyrus, Nitrification–Denitrification, Desludging, Maturation-Pond, Facultative-Pond, Sewerage","lastPublishedDoi":"10.21203/rs.3.rs-8885085/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8885085/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eConstructed wetlands are increasingly promoted as sustainable, low-energy wastewater treatment technologies, particularly in regions with limited financial and technical capacity. However, nutrient removal performance in constructed wetlands varies widely with vegetation type and system design. This study evaluated the nitrogen and phosphorus removal efficiency of laboratory-scale constructed wetlands planted with selected macrophyte species under controlled hydraulic conditions. Influent and effluent samples were analysed for ammonia nitrogen and soluble phosphorus using spectrophotometric methods compliant with ISO/IEC 17025 standards. Statistical evaluation was conducted using one-way analysis of variance (ANOVA) and linear regression to assess species effects and relationships between plant growth and nutrient uptake. Results showed substantial reductions in nutrient concentrations, with ammonia decreasing from 6.99 mg/L to 2.22 mg/L and soluble phosphorus from 17.47 mg/L to 3.05 mg/L. Wetlands planted with Cyperus papyrus achieved the highest removal efficiencies, averaging 82% for ammonia and 76% for soluble phosphorus. ANOVA confirmed that macrophyte species had a statistically significant effect on nutrient removal (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Regression analysis revealed a strong positive correlation between plant biomass and nutrient uptake (R\u0026sup2; \u0026gt; 0.60), highlighting the importance of vegetation productivity in treatment performance. The findings demonstrate that appropriate macrophyte selection can significantly enhance nutrient removal in constructed wetlands. The study supports the use of locally adapted species such as Cyperus papyrus for decentralised wastewater treatment and safe water reuse in tropical regions, particularly in East Africa.\u003c/p\u003e","manuscriptTitle":"Nutrient Removal Efficiency of Constructed Wetlands Planted with Tropical Macrophytes: Implications for Decentralized Wastewater Treatment at Aturukuku Sewerage Works","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-18 07:56:14","doi":"10.21203/rs.3.rs-8885085/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0ea5ee76-7f53-406b-b737-e98b0ea9a5c3","owner":[],"postedDate":"February 18th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":62952272,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2026-02-18T07:56:14+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-18 07:56:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8885085","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8885085","identity":"rs-8885085","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}