Decentralized Wastewater Treatment Systems Research Articles

Testing Fairness Principles for Public Environmental Infrastructure Decisions

Public infrastructure decisions affect many stakeholders with various benefits and costs. For public decisions, it is crucial that decision-making processes and outcomes are fair. Fairness concepts have rarely been explored in public infrastructure planning. We close this gap for a global issue of growing importance: replacing sewer-based, centralized by decentralized wastewater systems. We empirically study fairness principles in this policy-relevant context, and identify possible influencing factors in a representative online survey of 472 Swiss German residents. In a transition phase, innovative, decentralized pilot wastewater systems are installed in households. We designed two vignettes for this context to test the adhesion to principles of distributive justice—equality, equity, and need—at individual and community levels. A third vignette tests procedural justice with increasing fulfilment of fair process criteria. The results confirm our hypotheses: equity is perceived as fairer than equality at individual and collective levels. Contrary to expectations and literature, need is perceived as even fairer than equity. Procedural justice results confirm literature, e.g., the majority (92%) of respondents deems a policy fair that includes them in decision-making. Only few demographic and explanatory factors are significantly correlated with respondents’ fairness perceptions. Although unexpected, this is positive, implying that introducing decentralized wastewater technology can be designed for the entire population independent of characteristics of individuals. Generally, our results confirm literature: fairness perceptions depend on the circumstances. Hence, they should be elicited in the exact application context to be able to enter negotiation processes and provide concrete advice to decision makers.

Urban water resource management: experience from the revival of Rajokri lake in Delhi

<abstract> <p>Water bodies are critical in maintaining and sustaining ecosystems. However, urban water bodies are often ignored during development projects, and comprehensive plans for their revival and rejuvenation are not seen as priorities. This paper describes the rejuvenation project for a dry water body at Rajokri, Delhi, India. A "scientific wetland with active biodigester" (SWAB) system was developed to treat domestic wastewater, which was then used to fill the lake. The SWAB effectively removed about 89% removal of oil and grease, 86% biological oxygen demand (BOD), 85% chemical oxygen demand (COD) and 86% of total suspended solids (TSS) when the respective inlet concentrations were 18 ± 1.14 mg/L, 124 ± 2.9 mg/L, 480 ± 11.9 mg/L and 116 ± 1.82 from the raw wastewater. The SWAB system provides completely natural treatment with zero electrical consumption. The revival of the water body using a decentralized wastewater treatment system has immensely helped in management of urban wastewater, ground water recharge and enhanced ecosystem and biodiversity values. The project demonstrates the integration of socio-cultural, societal, ecological, ecosystem and technological aspects for the revival of the lake.</p> </abstract>

Assessment of water reuse potential of wastewater treatment systems used in Mumbai, India

Ever growing population of Mumbai has put additional pressure on existing infrastructure in terms of huge demand for portable water as well as treatment of city’s waste water. Study aimed at review of city’s wastewater in order to understand the reality of treatment quality of wastewater, it’s reusability in terms of offsetting growing water demands of domestic, industrial and agricultural fields in and around the city. Literature review and case study method was used in order to get primary as well as secondary data for achieving data regarding overall functioning and water balance of the city. Because of lot of irregularities, current wastewater management systems are asking for paradigm shift from current centralized wastewater treatment systems to decentralized wastewater treatment systems. Conventional treatment systems treat wastewater as a ‘waste’ yet there is some reuse potential. Concept of collecting water and wastewater separately for better treatment, increased reuse potential, savings upon energy and better nutrient recovery can be used in order to move towards more ecologically and economically sound waste water management systems. To demonstrate this idea documentary and discourse analysis is used. The paper starts by providing general overview about water scarcity and security in India and then proceeds to provide comparative analysis between centralized and decentralized treatment systems used in the city in order to identify it’s water reuse potential. Second, legislative and policy framework used in the city for wastewater treatment and management which is then followed by outline of the current situation and reflections on system dynamics in City. Third, the paper ends with a discussion on practical implications, policy options and conclusion. The presented study gives conceptual model based on Net Zero concept which can be helpful in making of sustainable future cities.

Improving the performance of activated sludge process with integrated algal biofilm for domestic wastewater treatment: System behavior during the start-up phase

This study aims to enhance nutrient removal in an existing activated sludge process based decentralized wastewater treatment system by introducing illumination and algal biofilms in the aeration chamber. The aeration tank (AT) has been modified with the addition of blue light-emitting diode (LED) lights and silicon carbide foam filters as supporting media for algal biofilm growth. The light intensity (varied between 100 and 200 W/180 m3) had shown a strong correlation with the chlorophyll concentration in the mixed liquor. The nitrogen removal has increased from 48 ± 9% to 63 ± 6% and P removal from 37 ± 12% to 70 ± 12% in the modified aeration tank using 200 W LEDs with 12:12 light: dark cycle. Decreasing the light period to 8-h had decreased the carbon and nutrient removal to 32 ± 11% and 45 ± 10% respectively. The influent C/N showed a strong association with carbon and nutrient removal.

"Who Cares?": The Acceptance of Decentralized Wastewater Systems in Regions without Water Problems.

There is a growing interest in decentralized wastewater treatment systems, especially in regions with water scarcity problems or water management issues. This study aims to determine whether the perceived advantages and disadvantages (leading to acceptance) of decentralized wastewater plants in such regions are the same in regions where the population is not aware of these water issues. Firstly, this study systematically reviews previous findings on public perceptions of the acceptance of decentralized wastewater treatment systems. Then, the study details the results of a focus group study to determine whether the elements identified in the literature are also relevant in a region where people are unaware of water problems. The results show that a lack of awareness of water issues seems to be a critical factor influencing acceptance. Reframing the usefulness of these systems by focusing on other aspects, such as environmental sustainability, is key.

Phosphorus removal in a pilot scale free water surface constructed wetland: hydraulic retention time, seasonality and standing stock evaluation

Constructed wetlands (CWs) are decentralized wastewater treatment systems considered to be green and low cost. They have the potential to effectively remove pollutants and recycle nutrients with plant composting. However, they need large areas to implement them due to the usual high Hydraulic Retention Times (HRT), reaching up to 50 days. The main objective of the present study was to evaluate the influence of HRT (HRT = 3, 7, and 10 days), and seasonality on Total Phosphorus (TP) removal, and standing stock in a pilot scale free water surface CW (FWS CW). Unplanted and planted (Eichhornia crassipes) tanks were evaluated in wet and dry seasons. The FWS CW was set up as a complementary treatment to a secondary level wastewater treatment plant. The system was monitored weekly for ten months, totalizing 29 replicate samplings (n = 58). Planted tanks were harvested every week to keep free space for plant reproduction (∼40%). The mean removal efficiency of TP ranged between 82% and 95% without a significant difference between HRT (pvalue > 0.05). However, when the effects of the sedimentation of the unplanted tanks were disregarded, the lowest HRT (3 days) tank presented the highest standing stock of TP. The wet season presented a significant difference in TP removal results (pvalue < 0.05), associated with higher macrophyte growth rate due to more intense solar irradiation and incorporation of TP by E. crassipes. The results point out advances in P removal and recycling by a low-cost ecological engineering system.

‘Solar septic tank’: evaluation of innovative decentralized treatment of blackwater in developing countries

Abstract An innovative decentralized wastewater treatment system, namely the ‘Solar Septic Tank (SST)’, was constructed and tested at the household scale in a community in central Thailand. This study aimed to investigate the long-term performance of the SST in treating blackwater subject to year-round variation. Results of the 3-year continuous operation and monitoring showed significant improvement in the SST effluent quality with the potential to minimize environmental problems and public health risks. The SST achieved significantly higher total chemical oxygen demand, soluble chemical oxygen demand, total biochemical oxygen demand (TBOD), soluble biochemical oxygen demand, total kjeldahl nitrogen, total solid and total volatile solid removal efficiencies than a conventional septic tank (CST). The average TBOD concentration of the SST effluent was 150 ± 75 mg/L, meeting the Thai discharge standard (less than 200 mg/L of TBOD), while the average TBOD concentration of the CST was 240 ± 140 mg/L, higher than the Thai discharge standard. The Escherichia coli inactivation in the SST was 1–2 log reduction more than that in the CST. The removal efficiencies of TBOD and pathogens exhibited positive correlation with the ratios of the SST temperature.

Integration of Mathematical Median Ranked Set Sample and Decision Making AHP Tools to Enhance Decentralized Wastewater Treatment System

Environmental issues, including wastewater treatment plant sitting, usually have various aspects of criteria and involve many stakeholders from various backgrounds and levels. It is characterized as multi-criteria decision-making problem that requires extensive environmental, financial, social, operational and technical evaluations. Furthermore, the various background of involved stakeholders and conflict of interests among them complicate the decision-making process. The Median Ranked Set sample (MRSS) and Analytic Hierarchy Process (AHP) were integrated in this research to improve the decision-making process. MRSS was used to enhance the weighting process, to minimize inconsistency, uncertainty as well as conflict of interest during the stakeholder’s preferences determination, while AHP was used to determine the final priorities of the evaluation criteria. The stakeholders were divided into four groups in which four experts are in each to form 4-by-4 matrix. The results show that the environmental criteria got the highest importance followed by social and economic criteria, respectively. Furthermore, the most important criteria are outflow emissions (importance weight = 0.27) followed by public acceptance (importance weight = 0.22). Furthermore, the best decentralized option for wastewater treatment in rural area is based on cluster level and by using the activated sludge as a wastewater treatment technology with suitability index equals to 4.26 and 4.22, respectively. While, the modified septic tank is best treatment option (with suitability index = 3.85) for wastewater treatment on household level. The introduced integrated model may offer a promising tool to improve the decision-making process and will help the environmental planners in term of uncertainty reduction and subjectivity of human judgments.

Environmental analysis of servicing centralised and decentralised wastewater treatment for population living in neighbourhoods

The planning and construction of large-scale wastewater infrastructure, such as sewerage networks and wastewater treatment plants, is undertaken by the public sector or by publicly regulated monopolies. Only on smaller scales can infrastructure be managed by private companies or through local collective initiatives. Within this framework of water cycle management, there is an increasing movement of the population towards cities where economic activity is concentrated. This scenario is particularly pronounced in certain regions of the world and makes it necessary to rethink whether decentralised treatment offers a way of ensuring the servicing of wastewater treatment in new urban developments, alleviating pressure on facilities that are at the limit of their capacity.In this study four systems were evaluated: two centralised and two decentralised configurations, from an environmental and economic perspective, posing as working hypothesis how different wastewater treatment schemes influence the carbon footprint of the population living in a neighbourhood. The analysis of the results identifies that the decentralised systems present a reduction in the carbon footprint of residents of around 20–23 % depending on the technology considered. In addition, reclaimed water can meet the water quality requirements for irrigation of the green areas in the neighbourhood. Although decentralised systems have higher construction costs, they can be amortised due to lower energy consumption, so the payback time is estimated to be 8–9 years, lower than that of centralised systems. Considering the problems associated with changing and replacing existing networks, decentralised wastewater treatment systems is especially recommended for new dwelling developments, based on its environmental and economic indicators.

Nitrifying and Denitrifying Microbial Communities in Centralized and Decentralized Biological Nitrogen Removing Wastewater Treatment Systems

Biological nitrogen removal (BNR) in centralized and decentralized wastewater treatment systems is assumed to be driven by the same microbial processes and to have communities with a similar composition and structure. There is, however, little information to support these assumptions, which may impact the effectiveness of decentralized systems. We used high-throughput sequencing to compare the structure and composition of the nitrifying and denitrifying bacterial communities of nine onsite wastewater treatment systems (OWTS) and one wastewater treatment plant (WTP) by targeting the genes coding for ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ). The amoA diversity was similar between the WTP and OWTS, but nosZ diversity was generally higher for the WTP. Beta diversity analyses showed the WTP and OWTS promoted distinct amoA and nosZ communities, although there is a core group of N-transforming bacteria common across scales of BNR treatment. Our results suggest that advanced N-removal OWTS have microbial communities that are sufficiently distinct from those of WTP with BNR, which may warrant different management approaches.

Wastewater reclamation and reuse potentials in agriculture: towards environmental sustainability

Water scarcity is the major concern that impacts the global economy and the livelihood of mankind. Climate change, rapid population growth, freshwater pollution, and depletion are among the factors that aggravate the situation. Although not yet exhaustively exploited, reclamation and reuse of wastewater are considered as potential mechanisms to mitigate the challenge. In relation to reclamation, conventional wastewater treatment plants are designed to remove organic matter, total solids, and nutrients but fail to remove the emerging micropollutants. A decentralized wastewater treatment system is another potential and emerging approach for sustainable water reuse at the point of the wastewater generation. However, its application is not exclusively independent of the centralized system; rather the integration of the two systems is recommendable to depend on the local situations. To remove micropollutants, integrating advanced wastewater technologies should be considered as well as advanced analytical instruments for proper monitoring. Although the reuse of reclaimed water in crop irrigation is a well-established practice, it lacks uniformity across the globe. Furthermore, if not properly monitored, the reuse of reclaimed water also has adverse effects on the soil properties and public health. Therefore, the aim of this work is to review the impacts of global freshwater scarcity, water resources management and monitoring practice, state-of-the-art (waste)water treatment technologies and experience of reusing reclaimed water, particularly in agricultural irrigation.

Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants - Part I: Photosynthetic efficiency, leaf gas exchange and tissue mineral content

There is increasing interest and wide recognition of the potential use of human-excreta derived materials (HEDM) as fertilizer to supply essential nutrients needed for crop production. However, most work on HEDM has focussed on yield responses using soils and very little done on soil-less media using hydroponics. Further, physiological responses of plants to different HEDM in a hydroponic production system is currently not well-understood. This study investigated the effect of Decentralized Waste-water Treatment System (DEWATS) effluents and Nitrified Urine Concentrate (NUC) on leaf gas exchange, photosynthetic efficiency and mineral content of hydroponically-grown tomato. The experiment was conducted in a polyethylene tunnel using a complete randomised design comprising of three treatments namely: DEWATS effluent, NUC and commercial hydroponic fertilizer mix (CHFM). Sampling conducted both before and after flowering showed significant differences (P < 0.05) among different nutrient sources for all physiological parameters (leaf gas exchange and chlorophyll fluorescence) and mineral content. Leaf N and P were significantly (P < 0.05) higher in NUC treatment whereas Ca and K were high in the CHFM treatment. The current study demonstrated that HEDM such as NUC and DEWATS effluent could be an effective source of nutrients of agricultural crops in hydroponic systems with results comparable to commercial fertilizer mix.

Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants - Part II: Growth and yield

Disposal of human excreta derived materials (HEDM), particularly domestic wastewater, presents a challenge in areas served with on-site sanitation systems, most particular in informal settlements. The use of HEDM for agricultural food production represents a couple of opportunities such as improved sanitation, household food security as well as the generation of informal income. In this study, tomato seedlings ‘Monica’ cv were grown in a hydroponic system and irrigated with HEDM (effluents from decentralized wastewater treatment system and nitrified urine concentrate). A commercial hydroponic fertilizer mixture was used concurrently as a control treatment. All the treatments were applied to the plants through fertigation using a drip irrigation system. Plant growth (plant height, stem diameter, leaf area index, root:shoot ratio and plant dry matter), physiological (photosynthesis and chlorophyll), yield components (fruit number, fruit mass, harvest index and crop yield), leaf nutrient composition (N, P, K, Mg, Ca, Cu, Mn, Fe, Zn and Na) and microbiological (Aerobic count, coliforms and faecal coliforms) parameters were measured to assess the potential of these HEDMs as nutrient sources for hydroponically produced tomatoes. The results showed that irrigating the tomatoes with HEDM increased harvest index relative to crops irrigated with a commercial hydroponic fertilizer mix. Tomato plants irrigated with a commercial hydroponic fertilizer mix achieved the highest growth and yield, however, irrigation with human excreta based sources improved plant physiological performance and leaf nutrient composition compared to crops irrigated with commercial fertilizer mix. In terms of microbiological analysis, tomatoes harvested from plants treated with HEDM recorded the highest population of bacterial count as compared to the commercial hydroponic fertilizer mix.These results showed that nutrients derived from human excreta can be a good source of nutrients for hydroponically grown tomatoes. Moreover this practice can effectively address the challenges of human waste disposal while at the same time providing the much-needed resources for increased food production through urban agriculture. However, further research on the effect of heavy metals, pathogens on tomato fruit quality is still needed for the adaptation of wastewater as nutrients sources for hydroponically grown tomatoes.

Drying characteristics of faecal sludge from different on-site sanitation facilities

Drying is one of the treatment techniques used for the dual purpose of safe disposal and energy recovery of faecal sludge (FS). Limited data are available regarding the FS drying process. In this paper the drying properties of FS were investigated using samples from ventilated improved pit (VIP) latrines and urine diversion dry toilets (UDDT) and an anaerobic baffle reactor (ABR) from a decentralized wastewater treatment systems. Moisture content, total solids content, volatile solids content, water activity, coupled thermogravimetry & differential thermal analysis (TGA-DTA) and calorific value tests were used to characterize FS drying. Drying kinetics and water activity measured at different moisture content during drying (100 °C) were similar for the samples from different on-site sanitation facilities. Experimental heat of drying results revealed that FS requires two to three times that of the latent heat of vaporization of water for drying. Drying temperature was more significant than the sludge source in determining the final volatile solids content of the dried samples. This was reinforced by the dynamic TGA that showed considerable thermal degradation (2–11% dry solid mass) near 200 °C. Below 200 C, the calorific value of the dried samples exhibited no significant difference. The average calorific values of VIP, UDDT and ABR samples at 100 °C were 14.78, 15.70, 17.26 MJ/kg dry solid, respectively. This suggests that the fuel value of FS from the aforementioned sanitation facilities will not be significantly affected by drying temperature below 200 °C. Based on this study, the most suitable temperature for drying of FS for a solid fuel application was found to be 150 °C.

Photosynthetic efficiency of hydroponically-grown tomato plants to decentralized wastewater treatment systems (DEWATS) effluents and nitrified urine concentrate (NUC) as nutrient sources

There is increasing interest and wide recognition of the potential use of human-excreta derived materials (HEDM) as fertiliser to supply essential nutrients needed for crop production. This has additional benefits as part of a reuse-oriented sustainable sanitation approach in efforts aimed at addressing sanitation challenges in many parts of the developing world. However, most work on HEDMs has focused on yield responses when compared to chemical commercial fertiliser sources using soils. Not much work has considered different systems such as hydroponic production. The physiological responses of plants to different HEDM when used in a hydroponic system is currently not well understood. This study evaluated the effect of decentralized wastewater treatment system (DEWATS) effluents and nitrified urine concentrate (NUC) as nutrient sources on hydroponically grown tomatoes. The study was conducted using 'Monica' determinate tomatoes planted in a polyethylene tunnel located at Newlands-Mashu Research Station, KwaZulu-Natal, South Africa. The experiment was laid out using a complete randomized block design and comprised of three treatments, namely, DEWATS effluent, NUC and commercial hydroponic fertilizer mix (CHFM). Each treatment was replicated three times giving nine experimental units of five plants each planted in a 5 L polyethylene pot. Data was collected on the following physiological variables: leaf area index (LAI), chlorophyll content index (CCI), stomatal conductance (gs), net CO(2) assimilation rate (A), intercellular CO(2) concentration (Ci) and the ratio of intercellular CO(2) and atmospheric CO(2) (Ci/Ca) were evaluated at vegetative stage, three weeks after transplanting. Results showed that tomato plants receiving CHFM had the highest LAI (3.00), followed by NUC (1.85) and DEWATS (1.48). CCI was significantly higher in the NUC treatments (42.58) compared to the CHFM (30.51) and DEWATS effluent (23.60). DEWATS effluent reported high values of A (22.75) followed by CHFM (22.40) and NUC by (14.56). The value of gs was higher in the DEWATS effluent (0.44) compared to the values of 0.110 and 0.021 observed for NUC and CHFM, respectively. Further, Ci was higher using DEWATS effluent compared to NUC and CHFM. The current study demonstrated that the use of HEDM such as NUC and DEWATS effluent as nutrient sources have comparable effects with commercial fertilizer mix with respect to the physiology of hydroponically grown tomatoes.

Ecological Resilience Restoration in the Watershed of the Hancang River

Hancang River is a river on the eastern border of Jinan City. In recent years, with the development of cities, river flow has dropped sharply, river water has been polluted, and the ecological environment of the basin has declined. Improving the water ecological environment and enhancing the resilience of the water ecology of the river basin were set as the research goals, especially coupling of hydrological and ecological processes and the recycling of sewage resources. The “patch-corridor-matrix” theory of landscape ecology, the Least-cost distance model and the Arc Hydro Tools module of the ArcGIS platform were used to describe the river system and basin boundaries, optimize the current water network and the path network of the ecosystem. A novel ecological network and water network were proposed to form the final aquatic ecosystem, which combines the hydrological process with the ecosystem, and three decentralized wastewater treatment systems were designed to reduce the wastewater directly flowing into the river. The ecosystem resilience of the basin will be enhanced.

Study on hybrid biorack constructed wetland

Decentralized Wastewater Treatment Systems (DWTS) based on natural mechanisms of purification are appropriate for Indian conditions. Biorack constructed wetland are recent developments in the domestic wastewater treatment. In the present study the concept of biorack wetland is extended to Hybrid Biorack Constructed Wetland (HBCW) in which bioracks are supplemented by brickbat as support medium for wetland vegetation. Three separate HBCW reactors were developed with Typha angustifolia, Canna indica and dual-species (Typha angustifolia and Canna indica). Batch studies were carried out on these reactors for secondary treatment of domestic wastewater. COD removal was determined for feed wastewater strength of 100 to 200 mg COD/L by these developed reactors. The growth of vegetation was also monitored. Typha angustifolia and Canna indica were found to be an appropriate combination as dual-species. The COD removal by dual-species is 5 to 10% greater than mono-species under similar conditions of feed and support medium. HBCW is efficient to an extent of 65 to 75% for COD removal. This is preliminary study conducted on HBCW. Further studies on pilot/field scale will provide better insight to assess its suitability as an alternative biological treatment.

Development of field-scale composite biorack constructed wetland – startup phase

Constructed Wetlands (CW) with Biorack (BR) technology have been studied extensively in recent years with positive outcomes compared to conventional CWs. A field scale application of the same has been worked upon in the Composite Biorack Constructed Wetland (CBCW) which is a secondary wastewater treatment facility of the Decentralized Wastewater Treatment System (DWTS) at Walchand College of Engineering, Sangli (M.S.), India. The CBCW is a multi-compartment system comprising of compartments with brickbats as supporting medium and BR Compartments (BRC) and has been in operation since May, 2018. The CBCW is vegetated with Typha angustifolia L. and Canna indica macrophytes. Being a unique CW, studies on difficulties aroused during the startup phase need to be addressed so as to arrive at proper troubleshooting techniques for future references. The paper addresses various issues, specifically growth of vegetation and their early wiltage in CBCW, for a period of 150 days. Using alternative modes of plantation, it is concluded that vegetation acclimatization, proper suspension and grip of the bulb and roots of saplings in racks, fluctuating inflow of wastewater are few reasons influencing development of vegetation. An improvement by about 12% is obtained in COD removal in the latter period of study implying establishing of vegetation in CBCW.

Batch UV Disinfection for Small Flow Onsite Wastewater Treatment

HighlightsThe onsite batch UV disinfection system has potential to replace traditional flow-through system.Advantages of UV batch UV system include lamp life savings and controlled dosage by controlling re-circulation time.Higher re-circulation flow rate within batch UV system does not improve disinfection performance.Batch UV system saves energy compared to flow-through system when daily circulation time can be designed for less than 2.5 hours.Abstract. Many small flow and residential wastewater generators are not connected to centralized treatment facilities. Decentralized wastewater treatment systems require effluent disinfection to minimize the public health hazard associated with onsite reuse of the water. The objective of this study was to investigate the performance of an onsite batch UV disinfection system for reuse of wastewater. The field tests were performed with residential wastewater that was treated by septic tank and peat filtration before UV disinfection. E. coli counts were reduced by 1.4 log after 2.5 h contact time. Circulation flow rates did not affect the disinfection efficacy. UV batch disinfection, with hours of operation, has potential to significantly inactivate pathogens but needs site-specific optimization for daily onsite wastewater treatment. Keywords: Clostridium perfringens, Coliphages, Escherichia coli, Onsite wastewater, UV disinfection, Wastewater reuse.

Genome-Centered Metagenomics Analysis Reveals the Microbial Interactions of a Syntrophic Consortium during Methane Generation in a Decentralized Wastewater Treatment System

The application of anaerobic digestors to decentralized wastewater treatment systems (DWTS) has gained momentum worldwide due to their ease of operation, high efficiency, and ability to recycle wastewater. However, the microbial mechanisms responsible for the high efficiency and ability of DWTS to recycle wastewater are still unclear. In this study, the microbial community structure and function of two different anaerobic bioreactors (a primary sludge digestor, PSD, and anaerobic membrane bioreactor, AnMBR) of a DWTS located in Germany was investigated using 16S rRNA gene amplicon and metagenomic sequencing, respectively. The results showed that the microbial community structure was remarkably different in PSD and AnMBR. Methanobacteriaceae and Syntrophaceae were identified as the families that significantly differed in abundance between these two bioreactors. We also used genome-centered metagenomics to predict the microbial interactions and methane-generating pathway, which yielded 21 near-complete assembled genomes (MAGs) (average completeness of 93.0% and contamination of 2.9%). These MAGs together represented the majority of the microbial community. MAGs affiliated with methanogenic archaea, including Methanobacterium sp., Methanomicrobiales archaea, Methanomassiliicoccales archaea, and Methanosaeta concilii, were recruited, along with other syntrophic bacterial MAGs associated with anaerobic digestion. Key genes encoding enzymes involved in specific carbohydrate-active and methanogenic pathways in MAGs were identified to illustrate the microbial functions and interactions that occur during anaerobic digestion in the wastewater treatment. From the MAG information, it was predicted that bacteria affiliated with Bacteroidetes, Prolixibacteraceae, and Synergistaceae were the key bacteria involved in anaerobic digestion. In the methane production step, Methanobacterium sp. performed hydrogenotrophic methanogenesis, which reduced carbon dioxide to methane with hydrogen as the primary electron donor. Taken together, our findings provide a clear understanding of the methane-generating pathways and highlight the syntrophic interactions that occur during anaerobic digestion in DWTS.