Performance Modeling of Decentralized Wastewater Treatment in Rural Azerbaijan: Environmental Impacts and Sustainable Solutions from Shamakhi-Gobustan Region

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Pasha, Orkhan Mikayil, Isa Gasimov, Elkhan Aliyev This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6983156/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 Access to safe sanitation remains a persistent global challenge, particularly in rural and semi-urban areas where centralized wastewater infrastructure is lacking. This study assesses the environmental impacts of uncontrolled domestic wastewater discharge and proposes a sustainable decentralized treatment model for the Shamakhi-Gobustan region in Azerbaijan. Field investigations revealed elevated levels of biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrates, and coliform bacteria in groundwater, exceeding WHO standards. To strengthen analytical rigor, a mass balance-based performance modeling framework was employed to quantify pollutant removal efficiencies across treatment stages. A pilot system – comprising a sedimentation tank, anaerobic baffled reactor, constructed wetlands, and solar-powered pumps—was implemented in Padar village. The system achieved average reductions of 85% in BOD and 70% in COD, with significant improvements in nitrate removal and microbial safety. Model predictions closely aligned with observed results, confirming the reliability and scalability of the approach. The proposed model demonstrates strong potential for replication in similarly water-scarce, infrastructure-limited regions. This work contributes to global efforts toward Sustainable Development Goals (SDGs) 6 (Clean Water and Sanitation) and 11 (Sustainable Cities and Communities). Future research is recommended to assess long-term performance, enhance system design, and explore cost-effective innovations using modeling tools. Environmental Engineering Ecological Modeling Environmental Policy decentralized wastewater treatment performance modeling constructed wetlands anaerobic baffled reactor rural wastewater SDG 6 SDG 11 water safety Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Access to safe and sustainable sanitation remains a critical challenge for many rural and semi-urban communities around the world. According to the WHO and UNICEF Joint Monitoring Programme, over 1.7 billion people still lack access to safely managed sanitation services, with the vast majority residing in rural and peri-urban areas [1, 2]. The absence of appropriate wastewater treatment infrastructure results in extensive environmental degradation, groundwater pollution, and elevated public health risks [3, 4]. Figure 1 illustrates the global disparities in sanitation service levels, emphasizing the urgent need for decentralized and context-specific solutions, particularly in low- and middle-income countries. Traditional centralized wastewater treatment systems require substantial capital investment and high operational expenditures, making them impractical for rural areas characterized by dispersed populations and limited financial capacity [6, 7]. Consequently, decentralized wastewater treatment systems (DEWATS) have emerged as a viable and sustainable alternative that can be tailored to local geographic, climatic, and socio-economic conditions [8, 9]. In recent years, the integration of performance modeling into DEWATS planning has gained prominence, enabling quantitative assessment of pollutant removal efficiencies and providing critical insights for system optimization and scalability [9, 10]. The Shamakhi-Gobustan region of Azerbaijan exemplifies a context where centralized wastewater infrastructure is virtually nonexistent. Small rural villages typically depend on rudimentary methods, such as septic pits or uncontrolled discharge into nearby lands and waterways [6, 12]. The region’s shallow groundwater table – ranging from 2 to 8 meters – heightens the risk of contamination from untreated wastewater infiltration [4, 29]. According to recent assessments by the Azerbaijan State Water Resources Agency (ADWRA) and the Ministry of Ecology and Natural Resources, approximately 65% of rural settlements lack any formal wastewater management system [28, 32]. This study aims to evaluate the environmental impacts of unregulated domestic wastewater discharge in the Shamakhi-Gobustan region and to assess the viability and performance of decentralized wastewater treatment solutions. A hybrid treatment system was piloted in three representative villages – Padar and Jangi (Gobustan District), and Chukhuryurd (Shamakhi District) – combining sedimentation, anaerobic baffled reactors, constructed wetlands, and solar-powered pumping technologies. The findings contribute to the broader understanding of sustainable sanitation practices for water-scarce and infrastructure-limited settings. Moreover, the study aligns with global sustainability goals, particularly SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities) [5, 9, 21, 32]. 2. Literature Review Access to safely managed sanitation remains a pressing global and regional concern [ 1 ]. According to estimates by UN-Water and the World Health Organization, more than two billion people globally still lack access to safely managed drinking water and sanitation services [ 2 ]. This gap is particularly severe in low-income and rural areas, where infrastructure development has been either delayed or remains insufficient [ 3 ]. In Azerbaijan, the challenge is especially pronounced in the rural areas of the Shamakhi and Gobustan districts, where the absence of centralized wastewater systems contributes to significant environmental degradation and public health risks [ 6 , 12 ]. Decentralized wastewater treatment systems (DEWATS) have gained increasing recognition as sustainable alternatives to centralized approaches [ 11 ]. These systems offer advantages such as lower capital and operational costs, minimal energy demands, and the flexibility to adapt to a range of climatic and geographical conditions [ 5 , 7 , 8 , 18 ]. DEWATS are particularly well-suited to rural and peri-urban areas, where population densities and funding limitations make centralized sewer networks impractical [ 6 , 8 , 17 ]. Within decentralized systems, various pre-treatment approaches – such as bioflocculation – have been investigated for improving energy efficiency and facilitating downstream treatment, especially in managing greywater in rural contexts [ 14 ]. Additionally, membrane-based technologies such as nanofiltration (NF) and reverse osmosis (RO) have been tested for enhanced nutrient removal, though their application is often constrained by high energy and maintenance costs [ 15 ]. Constructed wetlands, a commonly used DEWATS component, have shown pollutant removal efficiencies of up to 90% for biochemical oxygen demand (BOD), alongside significant reductions in nutrient and pathogen concentrations [ 19 , 26 , 33 , 35 ]. Similarly, floating treatment wetlands (FTWs) – an adaptation of conventional constructed wetlands – have demonstrated promising performance while maintaining simplicity and low operational requirements [ 13 ]. Anaerobic baffled reactors (ABRs) offer BOD and chemical oxygen demand (COD) removal efficiencies of 60–75%, and may also support biogas recovery, adding value to decentralized sanitation solutions [ 22 , 26 ]. Hybrid treatment configurations combining ABRs and constructed wetlands have been successfully piloted in India, Turkey, and Latin America, demonstrating technical viability, adaptability, and potential for scalability [ 8 , 24 , 25 ]. Figure 2 presents a comparative summary of the BOD and COD removal performance across several decentralized treatment technologies. In addition to performance, other critical criteria such as maintenance complexity and cost levels play key roles in technology selection. Table 1 summarizes these aspects for four commonly applied decentralized wastewater treatment technologies: constructed wetlands, anaerobic baffled reactors, membrane bioreactors, and septic systems. Table 1 Performance Comparison of Selected Decentralized Wastewater Treatment Technologies Summary of typical pollutant removal efficiencies, maintenance requirements, and cost levels. Data compiled from global pilot studies and literature sources Technology BOD Removal (%) COD Removal (%) Maintenance Cost Level Constructed Wetlands 90 80 Low Low Anaerobic Baffled Reactor 75 70 Moderate Moderate Membrane Bioreactor 95 90 High High Septic System 65 60 Low Low In Azerbaijan, preliminary pilot studies led by the Azerbaijan State Water Resources Agency (ADWRA) and the Ministry of Ecology and Natural Resources suggest that decentralized models can significantly improve sanitation outcomes in rural regions like Shamakhi-Gobustan [ 4 , 32 ]. The region's semi-arid climate, shallow groundwater levels, and inadequate infrastructure present an ideal testbed for decentralized systems [ 29 , 31 ]. Moreover, additional factors such as seasonal rainfall variability, low stream flows, and aquifer vulnerability due to unregulated wastewater discharge further underscore the urgency of implementing such systems [ 12 , 36 ]. This literature review highlights the necessity of piloting and evaluating decentralized treatment models tailored to Azerbaijan’s rural realities. The findings also reinforce the global imperative to achieve Sustainable Development Goals – specifically SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities) [ 2 , 21 ]. 3. Methodology 3.1 Study Area and Site Selection The Shamakhi-Gobustan region in central Azerbaijan was selected as the pilot site due to its semi-arid climate, shallow groundwater levels, limited centralized infrastructure, and increasing vulnerability to environmental degradation. Three rural settlements were included in the study: Padar and Jangi villages (Gobustan district) and Chukhuryurd village (Shamakhi district). Site selection was based on several criteria, including settlement size, proximity to surface water bodies, existing wastewater management practices, and observed contamination risks. Technical site access and field implementation support were facilitated through collaboration with “ Aqualink” LLC , which operates water treatment activities in the Shamakhi-Gobustan region. 3.2 Field Sampling and Monitoring Comprehensive field sampling was conducted at five monitoring points within each village to evaluate the quality of surface water, groundwater, and untreated domestic wastewater. Seasonal sampling was performed over a 12-month period, encompassing both dry and wet conditions. Key pollution indicators included biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate, total coliform bacteria, and Escherichia coli , following the protocols outlined in APHA Standard Methods [7]. 3.3 System Design and Treatment Process A pilot hybrid decentralized wastewater treatment system was constructed in Padar village. The treatment system comprised the following main components: A primary sedimentation tank for the removal of suspended solids [6]; An anaerobic baffled reactor (ABR) to reduce the organic load and facilitate initial anaerobic treatment [16]; A horizontal subsurface flow constructed wetland , planted with native macrophytes for nutrient uptake and pathogen removal [11]; A solar-powered pumping and monitoring unit , designed to optimize hydraulic loading while ensuring energy efficiency [17]. The system layout was designed to ensure modularity and low maintenance needs while maintaining high treatment efficiency. Technical assistance and operational oversight were provided by the Azerbaijan State Water Resources Agency (ADWRA) and the Ministry of Ecology and Natural Resources. A schematic illustration of the treatment train and flow direction is provided in Figure 3 . 3.4 Modeling Approach To enhance the analytical rigor of the study, a mass balance-based performance model was developed to simulate pollutant removal efficiencies across each treatment stage [10]. The model assumes steady-state flow conditions and consistent biological activity, reflecting field-operational parameters commonly observed in decentralized systems [9]. The pollutant removal efficiency RRR for each parameter was calculated using the following equation: Model inputs were derived from the field monitoring data collected throughout the 12-month sampling period, including seasonal variations. The simulation covered key pollutants such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate, and total coliform bacteria. The modeling results were validated by comparing simulated effluent concentrations against measured field data, thereby enabling scenario-based analysis and evaluation of system scalability under different environmental and design conditions [20, 21]. 3.5 Model Results The model-based pollutant removal efficiencies derived from field-monitored influent and effluent concentrations are summarized in Table 2. The simulation results represent average performance over a 12-month monitoring period, incorporating seasonal variations in flow and pollutant loads. Table 2. Model-Based Removal Efficiencies of the Pilot Decentralized Wastewater Treatment System Pollutant Influent Concentration C in (mg/L) Effluent Concentration C out (mg/L) Removal Efficiency (%) Biochemical Oxygen Demand (BOD) 22 3.3 85% Chemical Oxygen Demand (COD) 58 18 70% Nitrate (NO₃⁻) 65 32.5 50% Total Coliform Bacteria (MPN/100 mL) >100,000 95% The model outcomes closely aligned with observed field monitoring data, confirming the system’s treatment stability and operational robustness under variable rural conditions. The consistency between modeled and observed removal rates validates the applicability of mass balance modeling for decentralized systems in resource-constrained regions [21, 22]. Furthermore, the modeling framework allows for future scenario analysis, including adjustments in system scale, hydraulic loading, and influent pollutant concentrations – thus offering a valuable tool for optimizing design and forecasting long-term performance in similar rural settings. 3.6 Limitations and Uncertainty Considerations While the performance modeling conducted in this study provides valuable insights into system efficiency and scalability, several limitations and sources of uncertainty must be acknowledged: Short monitoring duration: The 12-month field monitoring period may not fully capture interannual variability or extreme weather events, which could influence system performance under longer-term climatic fluctuations. Assumptions of steady-state conditions: The mass balance model assumes steady hydraulic loading and stable biological activity. In practice, flow rates and influent pollutant concentrations can fluctuate daily or seasonally, introducing deviations from model predictions. Simplified removal coefficients: The pollutant removal coefficients used in the model were derived from averaged field data and literature values. These may not reflect localized biological and geochemical processes, especially in systems affected by temperature extremes or operational disruptions. Limited replication: The pilot system was implemented in a single village (Padar), and though results are promising, further validation across multiple rural settings is needed to generalize findings across different topographies, settlement sizes, and socio-economic contexts. Lack of real-time sensor data: The system did not incorporate automated monitoring technologies such as remote sensors or real-time analytics, which could enhance performance evaluation accuracy and facilitate proactive maintenance. Despite these limitations, the strong alignment between modeled and observed results supports the use of mass balance modeling as a practical tool for evaluating decentralized wastewater treatment in rural regions. Future studies should aim to incorporate dynamic models, sensitivity analyses, and real-time data integration to improve predictive accuracy and resilience planning. 4. Results Baseline field investigations confirmed that untreated domestic wastewater discharges from households in Padar, Jangi, and Chukhuryurd villages were contributing to significant surface and shallow groundwater contamination. Measured concentrations of biochemical oxygen demand (BOD) ranged from 18 to 25 mg/L, while chemical oxygen demand (COD) levels reached 45–70 mg/L. Total coliform and Escherichia coli counts exceeded WHO safe thresholds by factors of 50 to 100, and nitrate concentrations were as high as 65 mg/L, surpassing safe drinking water limits [ 3 , 7 , 29 ]. The pilot decentralized wastewater treatment system implemented in Padar village demonstrated substantial reductions in pollutant concentrations. Monitoring over 12 months showed average BOD removal of 85%, COD reductions of around 70%, and nitrate removal of 50%. Moreover, coliform and E. coli levels were reduced by more than 95%, bringing the treated effluent within WHO environmental discharge standards [ 8 , 24 ]. Model-based results were in close agreement with the empirical monitoring data, validating the robustness of the mass balance framework. Simulated removal efficiencies also indicated 85% BOD reduction, 70% COD reduction, 50% nitrate removal, and over 95% pathogen elimination [ 9 , 10 , 24 ]. This alignment confirmed the model’s reliability in replicating real-world treatment performance under variable rural operating conditions. A comparative analysis between the treated effluent from Padar and the untreated wastewater samples from Jangi and Chukhuryurd further highlighted the advantages of the hybrid decentralized system in reducing pollution loads. Importantly, no significant seasonal variation in treatment performance was observed throughout the pilot period, reflecting high system stability and resilience [ 4 , 31 ]. Comparison of key water quality parameters (BOD, COD, Nitrate, Coliform bacteria) between treated wastewater from Padar village and untreated domestic wastewater from Jangi and Chukhuryurd villages in the Shamakhi-Gobustan region of Azerbaijan 5. Discussion The results of this study clearly demonstrate that decentralized wastewater treatment systems offer a viable and sustainable solution for rural and semi-urban areas, particularly in water-scarce regions such as Shamakhi-Gobustan. The pilot system implemented at Padar village achieved substantial reductions in key pollution parameters: BOD by 85%, COD by 70%, nitrate concentrations by 50%, and coliform bacteria by more than 95%. These findings are comparable to – or even surpass – results from similar pilot initiatives conducted in rural Turkey, India, and Latin America, where constructed wetlands and anaerobic baffled reactors achieved BOD reductions of 75–80% (Varma et al., 2022; Nansubuga et al., 2016; Leal et al., 2010) [ 14 , 17 , 37 ]. The integration of a mass balance-based performance model provided robust quantitative verification of treatment efficiency, validating the stability and predictability of the hybrid system under local environmental conditions. This modeling approach allowed the estimation of pollutant removal efficiencies with strong agreement to empirical data, thereby enhancing the system's scalability assessment [ 9 , 10 ]. Moreover, modeling enables scenario-based evaluations, which can assist policymakers in optimizing design parameters for future decentralized installations. The hybrid system – combining sedimentation tanks, anaerobic baffled reactors, and constructed wetlands – proved both highly effective and energy-efficient. The incorporation of solar-powered pumping further reduced the system’s carbon footprint and enhanced its applicability in rural areas with limited access to grid electricity. One of the system’s key advantages is its scalability and modularity. The Padar pilot demonstrated that the design could be readily adapted for implementation in Jangi and Chukhuryurd villages with minimal modifications. This supports the feasibility of DEWATS as a flexible sanitation solution for settlements ranging in size from a few hundred to several thousand inhabitants [ 13 , 18 , 34 ]. These results contribute directly to achieving SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities), offering a low-cost, community-driven, and environmentally sustainable sanitation model. Given the increasing impacts of climate variability and water scarcity, decentralized systems offer notable resilience compared to centralized wastewater networks, which are often vulnerable to infrastructure failures and high maintenance demands. Despite the promising results, this study acknowledges several limitations. The monitoring period was limited to 12 months, and long-term evaluation is required to assess system durability under varying seasonal and environmental conditions. Additional pilot replications in other regions of Azerbaijan and neighboring countries are recommended to validate scalability and transferability. Future research should also investigate the integration of smart sensors, remote monitoring technologies, and advanced treatment modules to further optimize performance, minimize operational costs, and establish next-generation smart decentralized sanitation systems for rural and peri-urban settings [ 10 , 18 , 20 ]. 6. Conclusion This study has demonstrated the technical feasibility and environmental effectiveness of decentralized wastewater treatment systems as a viable alternative for rural and semi-urban communities in Azerbaijan. The pilot project, implemented in Padar village and supported by comparative data from Jangi and Chukhuryurd villages, confirmed that hybrid systems – combining sedimentation tanks, anaerobic baffled reactors, constructed wetlands, and solar-powered components – can achieve high pollutant removal rates with minimal energy input and low maintenance demands. Empirical results revealed reductions of 85% in BOD, 70% in COD, and 50% in nitrate concentrations, while coliform bacteria levels were reduced by over 95%, bringing effluent values within WHO discharge standards. The application of mass balance performance modeling further validated these findings, demonstrating strong agreement between field observations and modeled outcomes. This modeling framework also offers valuable insights for optimizing future decentralized system designs and evaluating scalability across diverse rural contexts. The scalability and adaptability of DEWATS present a significant opportunity to address the sanitation gap affecting an estimated 65% of rural communities in Azerbaijan, where centralized wastewater infrastructure remains limited. Adoption of such decentralized systems can substantially contribute to the achievement of SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities), by providing communities with affordable, locally managed, and environmentally sustainable sanitation solutions. Nonetheless, this research acknowledges several limitations. The monitoring period was confined to 12 months, and long-term studies are needed to assess the system's resilience under seasonal and environmental variability. Future research should prioritize expanding pilot studies to other regions within Azerbaijan and neighboring countries to validate scalability and contextual adaptability. Furthermore, the integration of smart sensors, advanced monitoring systems, and modular process controls could further enhance performance efficiency and support the development of next-generation smart decentralized sanitation frameworks for rural development. 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Reviews Environ Sci Bio/Technology 15:465–478. https://doi.org/10.1007/s11157-016-9400-3 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-6983156","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":476861873,"identity":"10ba2b03-68bd-44f6-9059-cee037e744f8","order_by":0,"name":"Natig H. Pasha","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYHACNijJfAAqkECcFgk2BrYEqGpitTAw8BgQp8Wc/fizBz932NXxsed8/Pjzx2EGfvYcA4Yff3BrsezJMTfsPZMswcbzdrOERMJhBsmeNwaMPTy4tRgcyGGT4G1jlmCTyN0gYQDUYnADaAuPBB4t558/k/zbVg/UkvP4RwJQiz1QC+MfAzxabiSYSfO2HQZpYZM4ALJFIseAmQdPEFjOeGMmLdt2XLKN55mZZUNaOo/EmWcFh2UO4NZizp/+TPJtWzW/fHvy45s/bKzl+NuTNz58gyfEkNwMcQs4qPDYgUXLKBgFo2AUjAIMAAAOm0u7tCvgjQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-5666-6835","institution":"Azerbaijan Technical University","correspondingAuthor":true,"prefix":"","firstName":"Natig","middleName":"H.","lastName":"Pasha","suffix":""},{"id":476861874,"identity":"b4015c82-f7b0-4a2c-bdae-1cc409fea7b7","order_by":1,"name":"Orkhan Mikayil","email":"","orcid":"https://orcid.org/0009-0000-9536-2407","institution":"Aqualink LLC","correspondingAuthor":false,"prefix":"","firstName":"Orkhan","middleName":"","lastName":"Mikayil","suffix":""},{"id":476861875,"identity":"8f98069a-491a-413b-8d72-cfeda6e69cde","order_by":2,"name":"Isa Gasimov","email":"","orcid":"https://orcid.org/0009-0008-5760-5314","institution":"Baku Engineering University","correspondingAuthor":false,"prefix":"","firstName":"Isa","middleName":"","lastName":"Gasimov","suffix":""},{"id":476889669,"identity":"ad307242-a33d-4454-9545-23529970fa0d","order_by":3,"name":"Elkhan Aliyev","email":"","orcid":"https://orcid.org/0009-0004-4756-5524","institution":"Odlar Yurdu University","correspondingAuthor":false,"prefix":"","firstName":"Elkhan","middleName":"","lastName":"Aliyev","suffix":""}],"badges":[],"createdAt":"2025-06-26 11:41:56","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6983156/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6983156/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85548835,"identity":"3a2d76b2-590f-44d7-bc91-5cb0c7b196ea","added_by":"auto","created_at":"2025-06-27 09:19:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":67503,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGlobal Sanitation Service Levels (WHO/UNICEF JMP, 2023)\u003c/strong\u003e\u003cbr\u003e\n\u003cem\u003eDistribution of the global population according to sanitation service levels based on the WHO/UNICEF Joint Monitoring Programme 2023 report. Categories include safely managed, basic, limited, unimproved, and open defecation services\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6983156/v1/36aed4234171cc24c82cc4d6.png"},{"id":85548834,"identity":"bd5f67fb-15c7-4fa5-91a4-8cf0d99a0d61","added_by":"auto","created_at":"2025-06-27 09:19:35","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":62501,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of Wastewater Treatment Technologies\u003c/strong\u003e\u003cbr\u003e\n\u003cem\u003ePerformance comparison of four decentralized wastewater treatment technologies in terms of BOD and COD removal efficiencies. Data adapted from global DEWATS pilot studies and literature sources\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6983156/v1/0b50fae8744aabaaeed19897.png"},{"id":85548836,"identity":"7e150910-3bf3-4c66-80e1-440c1e763e8b","added_by":"auto","created_at":"2025-06-27 09:19:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":34262,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProposed Decentralized Wastewater Treatment System (Pilot Site).\u003c/strong\u003e\u003cbr\u003e\n\u003cem\u003eSchematic representation of the hybrid decentralized wastewater treatment system implemented at Padar village, Azerbaijan. The system integrates household wastewater inflow, sedimentation tank, anaerobic baffled reactor (ABR), horizontal subsurface flow constructed wetlands, and a solar-powered pumping and monitoring unit\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6983156/v1/18deff0c148f0b0c22183757.png"},{"id":85548841,"identity":"f631a39a-fb45-4001-8a81-a8e56acabb22","added_by":"auto","created_at":"2025-06-27 09:19:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":59121,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eWater Quality Comparison Across Pilot Villages\u003cbr\u003e\n\u003c/strong\u003eComparison of key water quality parameters (BOD, COD, Nitrate, Coliform bacteria) between treated wastewater from Padar village and untreated domestic wastewater from Jangi and Chukhuryurd villages in the Shamakhi-Gobustan region of Azerbaijan\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6983156/v1/35f33e16ad8b14ba13773a27.png"},{"id":85550919,"identity":"da9e30d0-137c-4908-bf15-08cd0ba150d8","added_by":"auto","created_at":"2025-06-27 09:43:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1060545,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6983156/v1/6c03e930-bb91-488a-92e8-e78408b743c1.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003ePerformance Modeling of Decentralized Wastewater Treatment in Rural Azerbaijan: Environmental Impacts and Sustainable Solutions from Shamakhi-Gobustan Region\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAccess to safe and sustainable sanitation remains a critical challenge for many rural and semi-urban communities around the world. According to the WHO and UNICEF Joint Monitoring Programme, over 1.7 billion people still lack access to safely managed sanitation services, with the vast majority residing in rural and peri-urban areas [1, 2]. The absence of appropriate wastewater treatment infrastructure results in extensive environmental degradation, groundwater pollution, and elevated public health risks [3, 4].\u003c/p\u003e\n\u003cp\u003eFigure 1 illustrates the global disparities in sanitation service levels, emphasizing the urgent need for decentralized and context-specific solutions, particularly in low- and middle-income countries.\u003c/p\u003e\n\u003cp\u003eTraditional centralized wastewater treatment systems require substantial capital investment and high operational expenditures, making them impractical for rural areas characterized by dispersed populations and limited financial capacity [6, 7]. Consequently, decentralized wastewater treatment systems (DEWATS) have emerged as a viable and sustainable alternative that can be tailored to local geographic, climatic, and socio-economic conditions [8, 9]. In recent years, the integration of performance modeling into DEWATS planning has gained prominence, enabling quantitative assessment of pollutant removal efficiencies and providing critical insights for system optimization and scalability [9, 10].\u003c/p\u003e\n\u003cp\u003eThe Shamakhi-Gobustan region of Azerbaijan exemplifies a context where centralized wastewater infrastructure is virtually nonexistent. Small rural villages typically depend on rudimentary methods, such as septic pits or uncontrolled discharge into nearby lands and waterways [6, 12]. The region\u0026rsquo;s shallow groundwater table \u0026ndash; ranging from 2 to 8 meters \u0026ndash; heightens the risk of contamination from untreated wastewater infiltration [4, 29].\u003c/p\u003e\n\u003cp\u003eAccording to recent assessments by the Azerbaijan State Water Resources Agency (ADWRA) and the Ministry of Ecology and Natural Resources, approximately 65% of rural settlements lack any formal wastewater management system [28, 32]. This study aims to evaluate the environmental impacts of unregulated domestic wastewater discharge in the Shamakhi-Gobustan region and to assess the viability and performance of decentralized wastewater treatment solutions. A hybrid treatment system was piloted in three representative villages \u0026ndash; Padar and Jangi (Gobustan District), and Chukhuryurd (Shamakhi District) \u0026ndash; combining sedimentation, anaerobic baffled reactors, constructed wetlands, and solar-powered pumping technologies.\u003c/p\u003e\n\u003cp\u003eThe findings contribute to the broader understanding of sustainable sanitation practices for water-scarce and infrastructure-limited settings. Moreover, the study aligns with global sustainability goals, particularly SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities) [5, 9, 21, 32].\u003c/p\u003e"},{"header":"2. Literature Review","content":"\u003cp\u003eAccess to safely managed sanitation remains a pressing global and regional concern [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e]. According to estimates by UN-Water and the World Health Organization, more than two billion people globally still lack access to safely managed drinking water and sanitation services [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e]. This gap is particularly severe in low-income and rural areas, where infrastructure development has been either delayed or remains insufficient [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e]. In Azerbaijan, the challenge is especially pronounced in the rural areas of the Shamakhi and Gobustan districts, where the absence of centralized wastewater systems contributes to significant environmental degradation and public health risks [\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eDecentralized wastewater treatment systems (DEWATS) have gained increasing recognition as sustainable alternatives to centralized approaches [\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e]. These systems offer advantages such as lower capital and operational costs, minimal energy demands, and the flexibility to adapt to a range of climatic and geographical conditions [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. DEWATS are particularly well-suited to rural and peri-urban areas, where population densities and funding limitations make centralized sewer networks impractical [\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eWithin decentralized systems, various pre-treatment approaches \u0026ndash; such as bioflocculation \u0026ndash; have been investigated for improving energy efficiency and facilitating downstream treatment, especially in managing greywater in rural contexts [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. Additionally, membrane-based technologies such as nanofiltration (NF) and reverse osmosis (RO) have been tested for enhanced nutrient removal, though their application is often constrained by high energy and maintenance costs [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eConstructed wetlands, a commonly used DEWATS component, have shown pollutant removal efficiencies of up to 90% for biochemical oxygen demand (BOD), alongside significant reductions in nutrient and pathogen concentrations [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. Similarly, floating treatment wetlands (FTWs) \u0026ndash; an adaptation of conventional constructed wetlands \u0026ndash; have demonstrated promising performance while maintaining simplicity and low operational requirements [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Anaerobic baffled reactors (ABRs) offer BOD and chemical oxygen demand (COD) removal efficiencies of 60\u0026ndash;75%, and may also support biogas recovery, adding value to decentralized sanitation solutions [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eHybrid treatment configurations combining ABRs and constructed wetlands have been successfully piloted in India, Turkey, and Latin America, demonstrating technical viability, adaptability, and potential for scalability [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e presents a comparative summary of the BOD and COD removal performance across several decentralized treatment technologies.\u003c/p\u003e\n\u003cp\u003eIn addition to performance, other critical criteria such as maintenance complexity and cost levels play key roles in technology selection. Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes these aspects for four commonly applied decentralized wastewater treatment technologies: constructed wetlands, anaerobic baffled reactors, membrane bioreactors, and septic systems.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003e\u003cstrong\u003ePerformance Comparison of Selected Decentralized Wastewater Treatment Technologies\u003c/strong\u003e \u003cem\u003eSummary of typical pollutant removal efficiencies, maintenance requirements, and cost levels. Data compiled from global pilot studies and literature sources\u003c/em\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTechnology\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBOD Removal (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCOD Removal (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMaintenance\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCost Level\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eConstructed Wetlands\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAnaerobic Baffled Reactor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eModerate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eModerate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMembrane Bioreactor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHigh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHigh\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSeptic System\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eIn Azerbaijan, preliminary pilot studies led by the Azerbaijan State Water Resources Agency (ADWRA) and the Ministry of Ecology and Natural Resources suggest that decentralized models can significantly improve sanitation outcomes in rural regions like Shamakhi-Gobustan [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. The region\u0026apos;s semi-arid climate, shallow groundwater levels, and inadequate infrastructure present an ideal testbed for decentralized systems [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. Moreover, additional factors such as seasonal rainfall variability, low stream flows, and aquifer vulnerability due to unregulated wastewater discharge further underscore the urgency of implementing such systems [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThis literature review highlights the necessity of piloting and evaluating decentralized treatment models tailored to Azerbaijan\u0026rsquo;s rural realities. The findings also reinforce the global imperative to achieve Sustainable Development Goals \u0026ndash; specifically SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities) [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e"},{"header":"3. Methodology","content":"\u003ch3\u003e3.1 Study Area and Site Selection\u003c/h3\u003e\n\u003cp\u003eThe Shamakhi-Gobustan region in central Azerbaijan was selected as the pilot site due to its semi-arid climate, shallow groundwater levels, limited centralized infrastructure, and increasing vulnerability to environmental degradation. Three rural settlements were included in the study: Padar and Jangi villages (Gobustan district) and Chukhuryurd village (Shamakhi district). Site selection was based on several criteria, including settlement size, proximity to surface water bodies, existing wastewater management practices, and observed contamination risks. Technical site access and field implementation support were facilitated through collaboration with \u0026ldquo;\u003cstrong\u003eAqualink\u0026rdquo; LLC\u003c/strong\u003e, which operates water treatment activities in the Shamakhi-Gobustan region.\u003c/p\u003e\n\u003ch3\u003e3.2 Field Sampling and Monitoring\u003c/h3\u003e\n\u003cp\u003eComprehensive field sampling was conducted at five monitoring points within each village to evaluate the quality of surface water, groundwater, and untreated domestic wastewater. Seasonal sampling was performed over a 12-month period, encompassing both dry and wet conditions. Key pollution indicators included biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate, total coliform bacteria, and \u003cem\u003eEscherichia coli\u003c/em\u003e, following the protocols outlined in APHA Standard Methods [7].\u003c/p\u003e\n\u003ch3\u003e3.3 System Design and Treatment Process\u003c/h3\u003e\n\u003cp\u003eA pilot hybrid decentralized wastewater treatment system was constructed in Padar village. The treatment system comprised the following main components:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eA \u003cstrong\u003eprimary sedimentation tank\u003c/strong\u003e for the removal of suspended solids [6];\u003c/li\u003e\n \u003cli\u003eAn \u003cstrong\u003eanaerobic baffled reactor (ABR)\u003c/strong\u003e to reduce the organic load and facilitate initial anaerobic treatment [16];\u003c/li\u003e\n \u003cli\u003eA \u003cstrong\u003ehorizontal subsurface flow constructed wetland\u003c/strong\u003e, planted with native macrophytes for nutrient uptake and pathogen removal [11];\u003c/li\u003e\n \u003cli\u003eA \u003cstrong\u003esolar-powered pumping and monitoring unit\u003c/strong\u003e, designed to optimize hydraulic loading while ensuring energy efficiency [17].\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eThe system layout was designed to ensure modularity and low maintenance needs while maintaining high treatment efficiency. Technical assistance and operational oversight were provided by the Azerbaijan State Water Resources Agency (ADWRA) and the Ministry of Ecology and Natural Resources.\u003c/p\u003e\n\u003cp\u003eA schematic illustration of the treatment train and flow direction is provided in \u003cstrong\u003eFigure 3\u003c/strong\u003e.\u003c/p\u003e\n\u003ch3\u003e3.4 Modeling Approach\u003c/h3\u003e\n\u003cp\u003eTo enhance the analytical rigor of the study, a mass balance-based performance model was developed to simulate pollutant removal efficiencies across each treatment stage [10]. The model assumes steady-state flow conditions and consistent biological activity, reflecting field-operational parameters commonly observed in decentralized systems [9].\u003c/p\u003e\n\u003cp\u003eThe pollutant removal efficiency RRR for each parameter was calculated using the following equation:\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\" width=\"616\" height=\"228\"\u003e\u003c/p\u003e\n\u003cp\u003eModel inputs were derived from the field monitoring data collected throughout the 12-month sampling period, including seasonal variations. The simulation covered key pollutants such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate, and total coliform bacteria.\u003c/p\u003e\n\u003cp\u003eThe modeling results were validated by comparing simulated effluent concentrations against measured field data, thereby enabling scenario-based analysis and evaluation of system scalability under different environmental and design conditions [20, 21].\u003c/p\u003e\n\u003ch3\u003e3.5 Model Results\u003c/h3\u003e\n\u003cp\u003eThe model-based pollutant removal efficiencies derived from field-monitored influent and effluent concentrations are summarized in Table 2. The simulation results represent average performance over a 12-month monitoring period, incorporating seasonal variations in flow and pollutant loads.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2. Model-Based Removal Efficiencies of the Pilot Decentralized Wastewater Treatment System\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"642\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePollutant\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInfluent\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eConcentration\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eC\u003csub\u003ein\u003c/sub\u003e\u003c/em\u003e (mg/L)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEffluent\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eConcentration\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eC\u003csub\u003eout\u003c/sub\u003e\u003c/em\u003e (mg/L)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRemoval Efficiency\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003eBiochemical Oxygen Demand (BOD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e3.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e85%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003eChemical Oxygen Demand (COD)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e70%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003eNitrate (NO₃⁻)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e32.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e50%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003eTotal Coliform Bacteria (MPN/100 mL)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u0026gt;100,000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u0026lt;5,000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25%;\"\u003e\n \u003cp\u003e\u0026gt;95%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe model outcomes closely aligned with observed field monitoring data, confirming the system\u0026rsquo;s treatment stability and operational robustness under variable rural conditions. The consistency between modeled and observed removal rates validates the applicability of mass balance modeling for decentralized systems in resource-constrained regions [21, 22].\u003c/p\u003e\n\u003cp\u003eFurthermore, the modeling framework allows for future scenario analysis, including adjustments in system scale, hydraulic loading, and influent pollutant concentrations \u0026ndash; thus offering a valuable tool for optimizing design and forecasting long-term performance in similar rural settings.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.6 Limitations and Uncertainty Considerations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWhile the performance modeling conducted in this study provides valuable insights into system efficiency and scalability, several limitations and sources of uncertainty must be acknowledged:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eShort monitoring duration:\u003c/strong\u003e The 12-month field monitoring period may not fully capture interannual variability or extreme weather events, which could influence system performance under longer-term climatic fluctuations.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eAssumptions of steady-state conditions:\u003c/strong\u003e The mass balance model assumes steady hydraulic loading and stable biological activity. In practice, flow rates and influent pollutant concentrations can fluctuate daily or seasonally, introducing deviations from model predictions.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eSimplified removal coefficients:\u003c/strong\u003e The pollutant removal coefficients used in the model were derived from averaged field data and literature values. These may not reflect localized biological and geochemical processes, especially in systems affected by temperature extremes or operational disruptions.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eLimited replication:\u003c/strong\u003e The pilot system was implemented in a single village (Padar), and though results are promising, further validation across multiple rural settings is needed to generalize findings across different topographies, settlement sizes, and socio-economic contexts.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eLack of real-time sensor data:\u003c/strong\u003e The system did not incorporate automated monitoring technologies such as remote sensors or real-time analytics, which could enhance performance evaluation accuracy and facilitate proactive maintenance.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eDespite these limitations, the strong alignment between modeled and observed results supports the use of mass balance modeling as a practical tool for evaluating decentralized wastewater treatment in rural regions. Future studies should aim to incorporate dynamic models, sensitivity analyses, and real-time data integration to improve predictive accuracy and resilience planning.\u003c/p\u003e"},{"header":"4. Results","content":"\u003cp\u003eBaseline field investigations confirmed that untreated domestic wastewater discharges from households in Padar, Jangi, and Chukhuryurd villages were contributing to significant surface and shallow groundwater contamination. Measured concentrations of biochemical oxygen demand (BOD) ranged from 18 to 25 mg/L, while chemical oxygen demand (COD) levels reached 45\u0026ndash;70 mg/L. Total coliform and \u003cem\u003eEscherichia coli\u003c/em\u003e counts exceeded WHO safe thresholds by factors of 50 to 100, and nitrate concentrations were as high as 65 mg/L, surpassing safe drinking water limits [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe pilot decentralized wastewater treatment system implemented in Padar village demonstrated substantial reductions in pollutant concentrations. Monitoring over 12 months showed average BOD removal of 85%, COD reductions of around 70%, and nitrate removal of 50%. Moreover, coliform and \u003cem\u003eE. coli\u003c/em\u003e levels were reduced by more than 95%, bringing the treated effluent within WHO environmental discharge standards [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eModel-based results were in close agreement with the empirical monitoring data, validating the robustness of the mass balance framework. Simulated removal efficiencies also indicated 85% BOD reduction, 70% COD reduction, 50% nitrate removal, and over 95% pathogen elimination [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. This alignment confirmed the model\u0026rsquo;s reliability in replicating real-world treatment performance under variable rural operating conditions.\u003c/p\u003e \u003cp\u003eA comparative analysis between the treated effluent from Padar and the untreated wastewater samples from Jangi and Chukhuryurd further highlighted the advantages of the hybrid decentralized system in reducing pollution loads. Importantly, no significant seasonal variation in treatment performance was observed throughout the pilot period, reflecting high system stability and resilience [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eComparison of key water quality parameters (BOD, COD, Nitrate, Coliform bacteria) between treated wastewater from Padar village and untreated domestic wastewater from Jangi and Chukhuryurd villages in the Shamakhi-Gobustan region of Azerbaijan\u003c/p\u003e"},{"header":"5. Discussion","content":"\u003cp\u003eThe results of this study clearly demonstrate that decentralized wastewater treatment systems offer a viable and sustainable solution for rural and semi-urban areas, particularly in water-scarce regions such as Shamakhi-Gobustan. The pilot system implemented at Padar village achieved substantial reductions in key pollution parameters: BOD by 85%, COD by 70%, nitrate concentrations by 50%, and coliform bacteria by more than 95%. These findings are comparable to \u0026ndash; or even surpass \u0026ndash; results from similar pilot initiatives conducted in rural Turkey, India, and Latin America, where constructed wetlands and anaerobic baffled reactors achieved BOD reductions of 75\u0026ndash;80% (Varma et al., 2022; Nansubuga et al., 2016; Leal et al., 2010) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe integration of a mass balance-based performance model provided robust quantitative verification of treatment efficiency, validating the stability and predictability of the hybrid system under local environmental conditions. This modeling approach allowed the estimation of pollutant removal efficiencies with strong agreement to empirical data, thereby enhancing the system's scalability assessment [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, modeling enables scenario-based evaluations, which can assist policymakers in optimizing design parameters for future decentralized installations.\u003c/p\u003e \u003cp\u003eThe hybrid system \u0026ndash; combining sedimentation tanks, anaerobic baffled reactors, and constructed wetlands \u0026ndash; proved both highly effective and energy-efficient. The incorporation of solar-powered pumping further reduced the system\u0026rsquo;s carbon footprint and enhanced its applicability in rural areas with limited access to grid electricity. One of the system\u0026rsquo;s key advantages is its scalability and modularity. The Padar pilot demonstrated that the design could be readily adapted for implementation in Jangi and Chukhuryurd villages with minimal modifications. This supports the feasibility of DEWATS as a flexible sanitation solution for settlements ranging in size from a few hundred to several thousand inhabitants [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThese results contribute directly to achieving SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities), offering a low-cost, community-driven, and environmentally sustainable sanitation model. Given the increasing impacts of climate variability and water scarcity, decentralized systems offer notable resilience compared to centralized wastewater networks, which are often vulnerable to infrastructure failures and high maintenance demands.\u003c/p\u003e \u003cp\u003eDespite the promising results, this study acknowledges several limitations. The monitoring period was limited to 12 months, and long-term evaluation is required to assess system durability under varying seasonal and environmental conditions. Additional pilot replications in other regions of Azerbaijan and neighboring countries are recommended to validate scalability and transferability. Future research should also investigate the integration of smart sensors, remote monitoring technologies, and advanced treatment modules to further optimize performance, minimize operational costs, and establish next-generation smart decentralized sanitation systems for rural and peri-urban settings [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e"},{"header":"6. Conclusion","content":"\u003cp\u003eThis study has demonstrated the technical feasibility and environmental effectiveness of decentralized wastewater treatment systems as a viable alternative for rural and semi-urban communities in Azerbaijan. The pilot project, implemented in Padar village and supported by comparative data from Jangi and Chukhuryurd villages, confirmed that hybrid systems \u0026ndash; combining sedimentation tanks, anaerobic baffled reactors, constructed wetlands, and solar-powered components \u0026ndash; can achieve high pollutant removal rates with minimal energy input and low maintenance demands.\u003c/p\u003e \u003cp\u003eEmpirical results revealed reductions of 85% in BOD, 70% in COD, and 50% in nitrate concentrations, while coliform bacteria levels were reduced by over 95%, bringing effluent values within WHO discharge standards. The application of mass balance performance modeling further validated these findings, demonstrating strong agreement between field observations and modeled outcomes. This modeling framework also offers valuable insights for optimizing future decentralized system designs and evaluating scalability across diverse rural contexts.\u003c/p\u003e \u003cp\u003eThe scalability and adaptability of DEWATS present a significant opportunity to address the sanitation gap affecting an estimated 65% of rural communities in Azerbaijan, where centralized wastewater infrastructure remains limited. Adoption of such decentralized systems can substantially contribute to the achievement of SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities), by providing communities with affordable, locally managed, and environmentally sustainable sanitation solutions.\u003c/p\u003e \u003cp\u003eNonetheless, this research acknowledges several limitations. The monitoring period was confined to 12 months, and long-term studies are needed to assess the system's resilience under seasonal and environmental variability. Future research should prioritize expanding pilot studies to other regions within Azerbaijan and neighboring countries to validate scalability and contextual adaptability. Furthermore, the integration of smart sensors, advanced monitoring systems, and modular process controls could further enhance performance efficiency and support the development of next-generation smart decentralized sanitation frameworks for rural development.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors gratefully acknowledge the support provided by \u003cb\u003eAqualink LLC\u003c/b\u003e, particularly for facilitating site access, technical input during the pilot system installation, and field coordination in Padar village. The collaboration enabled effective integration of research and implementation, contributing to the reliability of monitoring results and real-world relevance of the proposed model.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWHO/UNICEF Joint Water Supply, \u0026amp; Sanitation Monitoring Programme (2015) Progress on sanitation and drinking water: 2015 update and MDG assessment. World Health Organization. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.who.int/publications/i/item/9789241509145\u003c/span\u003e\u003cspan address=\"https://www.who.int/publications/i/item/9789241509145\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWHO and UNICEF (2023) Progress on household drinking water, sanitation and hygiene 2000\u0026ndash;2022. 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(2018). Performance of integrated ecological treatment system for decentralized rural wastewater and significance of plant harvest management. Ecological Engineering, 124, 69\u0026ndash;76. https://doi.org/10.1016/j.ecoleng.2018.09.005\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVan Ornelas Y, Parks J, Tran T, Abrell L, Reynolds KA, Beamer PI (2019) Seasonal variation of water quality in unregulated domestic wells. Int J Environ Res Public Health 16(9):1569. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/ijerph16091569\u003c/span\u003e\u003cspan address=\"10.3390/ijerph16091569\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNansubuga I, Banadda N, Verstraete W, Rabaey K (2016) A review of sustainable sanitation systems in Africa. Reviews Environ Sci Bio/Technology 15:465\u0026ndash;478. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11157-016-9400-3\u003c/span\u003e\u003cspan address=\"10.1007/s11157-016-9400-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","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":"decentralized wastewater treatment, performance modeling, constructed wetlands, anaerobic baffled reactor, rural wastewater, SDG 6, SDG 11, water safety","lastPublishedDoi":"10.21203/rs.3.rs-6983156/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6983156/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAccess to safe sanitation remains a persistent global challenge, particularly in rural and semi-urban areas where centralized wastewater infrastructure is lacking. This study assesses the environmental impacts of uncontrolled domestic wastewater discharge and proposes a sustainable decentralized treatment model for the Shamakhi-Gobustan region in Azerbaijan. Field investigations revealed elevated levels of biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrates, and coliform bacteria in groundwater, exceeding WHO standards. To strengthen analytical rigor, a mass balance-based performance modeling framework was employed to quantify pollutant removal efficiencies across treatment stages. A pilot system \u0026ndash; comprising a sedimentation tank, anaerobic baffled reactor, constructed wetlands, and solar-powered pumps\u0026mdash;was implemented in Padar village. The system achieved average reductions of 85% in BOD and 70% in COD, with significant improvements in nitrate removal and microbial safety. Model predictions closely aligned with observed results, confirming the reliability and scalability of the approach. The proposed model demonstrates strong potential for replication in similarly water-scarce, infrastructure-limited regions. This work contributes to global efforts toward Sustainable Development Goals (SDGs) 6 (Clean Water and Sanitation) and 11 (Sustainable Cities and Communities). Future research is recommended to assess long-term performance, enhance system design, and explore cost-effective innovations using modeling tools.\u003c/p\u003e","manuscriptTitle":"Performance Modeling of Decentralized Wastewater Treatment in Rural Azerbaijan: Environmental Impacts and Sustainable Solutions from Shamakhi-Gobustan Region","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-27 09:19:30","doi":"10.21203/rs.3.rs-6983156/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":"5a436f02-cbf7-4797-865d-a888d2119e49","owner":[],"postedDate":"June 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":50641366,"name":"Environmental Engineering"},{"id":50641367,"name":"Ecological Modeling"},{"id":50641368,"name":"Environmental Policy"}],"tags":[],"updatedAt":"2025-06-27T09:19:30+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-27 09:19:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6983156","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6983156","identity":"rs-6983156","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}