Decentralized Wastewater Treatment Research Articles

In Situ Treatment of Domestic Food Waste and Bioflocculated Sewage Sludge in Decentralized Wastewater Treatment Plant

In Situ Treatment of Domestic Food Waste and Bioflocculated Sewage Sludge in Decentralized Wastewater Treatment Plant

Microplastics in wastewater and sludge from centralized and decentralized wastewater treatment plants: Effects of treatment systems and microplastic characteristics

Domestic wastewater treatment plants (WWTPs) play a vital role in limiting the release of microplastics (MP) into the environment. This study examined MP removal efficiency from five centralized and four decentralized domestic WWTPs in Bangkok, Thailand. MP concentrations in wastewater and sludge were comparable between centralized and decentralized WWTPs, despite these decentralized WWTPs serving smaller populations and having limited treatment capacity. The elimination of MPs ranged from 50 to 96.8% in centralized WWTPs and 14.2–53.6% in decentralized WWTPs. It is noted that the retained MPs concentrations in sludge ranged from 20,000 to 228,100 MP/kg dry weight. The prevalence of synthetic fibers and fragments could be attributed to their pathways from laundry or car tires, and the accidental release of a variety of plastic wastes ended up in investigated domestic WWTPs. Removal of MPs between the centralized and decentralized WWTPs was influenced by several impact factors including initial MP concentrations, longer retention times, MP fragmentation, and variations of MP concentrations in sludge leading to different activated sludge process configurations. Sewage sludge has become a primary location for the accumulation of incoming microplastics in WWTPs. The MPs entering and leaving each unit process were varied due to the unique characteristics of MPs, and their different treatment efficiencies. While the extended hydraulic retention period in decentralized WWTPs decreased the MP removal efficacy, the centralized WWTP with the two-stage activated sludge process achieved the highest MP removal efficiency.

Sorting Out the Latest Advances in Separators and Pilot-Scale Microbial Electrochemical Systems for Wastewater Treatment: Concomitant Development, Practical Application, and Future Perspective.

To date, dozens of pilot-scale microbial fuel cell (MFC) devices have been successfully developed worldwide for treating various types of wastewater. The availability and configurations of separators are determining factors for the economic feasibility, efficiency, sustainability, and operability of these devices. Thus, the concomitant advances between the separators and pilot-scale MFC configurations deserve further clarification. The analysis of separator configurations has shown that their evolution proceeds as follows: from ion-selective to ion-non-selective, from nonpermeable to permeable, and from abiotic to biotic. Meanwhile, their cost is decreasing and their availability is increasing. Notably, the novel MFCs configured with biotic separators are superior to those configured with abiotic separators in terms of wastewater treatment efficiency and capital cost. Herein, a highly comprehensive review of pilot-scale MFCs (>100 L) has been conducted, and we conclude that the intensive stack of the liquid cathode configuration is more advantageous when wastewater treatment is the highest priority. The use of permeable biotic separators ensures hydrodynamic continuity within the MFCs and simplifies reactor configuration and operation. In addition, a systemic comparison is conducted between pilot-scale MFC devices and conventional decentralized wastewater treatment processes. MFCs showed comparable cost, higher efficiency, long-term stability, and significant superiority in carbon emission reduction. The development of separators has greatly contributed to the availability and usability of MFCs, which will play an important role in various wastewater treatment scenarios in the future.

Effluent quality and reuse potential of wastewater treated in constructed wetlands in Southern Brazil

ABSTRACT The main objective of this study was to evaluate the quality and reuse potential of treated effluents by constructed wetlands (CW) systems utilized for decentralized wastewater treatment in urban and rural scenarios in southern Brazil. The assessment, based on Brazilian discharge standards and wastewater reuse guidelines, revealed a close link between treatment efficiency and technological configurations, considering diverse inlet wastewater sources. Most CW treated effluents complied with regulatory standards for disposal, prompting the exploration of reuse scenarios in urban and agricultural settings. However, the study underscores the imperative for rigorous disinfection due to the limited microbiological removal capacity of CW. Overall, the research emphasizes the adaptability and resilience of CW in treating diverse wastewater compositions, highlighting their pivotal role in advancing circular economy principles within sanitation services. Importantly, the findings suggest significant potential for treated wastewater reuse in both urban and agricultural settings. Urban applications, including toilet flushing, floor washing, and garden irrigation, prove feasible for CW systems situated in residential and commercial buildings. Meanwhile, rural CW systems demonstrate suitability for reclaimed water directed toward crop fertigation, tailored to the specific needs and irrigation methods of various crops.

Biological feasibility of discharge a local WTTP sludge to sewer network and centralized WWTP; a case study: Tehran, Iran

Over the recent years, ever-increasing population growth and higher wastewater production has been a challenge for decentralized wastewater treatment plants (WWTPs). In addition, sludge treatment due to high cost for equipment and place make authorities to find a sustainable approach in both of economical and technical perspectives. One of the proposed solutions is transferring the sludge produced from decentralized WWTP to centralized WWTP. However, the appropriate proportional ratio of raw sludge to raw sewage is a challenge, otherwise, it make anaerobic conditions and sewage rotting along the sewer network based on permissible limit of dihydrogen sulfide (H2S) gas (5 ppm). In the present study, seven reactors with different ratios of sludge to raw sewage (0, 15, 20, 25, 50, 75, 100) were used to stimulate the feasibility of transferring Shahrake Gharb WWTP sludge along the wastewater transfer pipe to the centralized sewage treatment south Tehran WWTP plant in Tehran, Iran. The septic situation and H2S emission of different reactors within 7 h (Time to reach the compound in the south treatment plant) was analyzed by gas meter. The results indicated that the optimum ratio of sludge to raw sewage was 15% without H2S production during 7 h. In addition, due to the high volume of sludge produced by the Shahrake Gharb WWTP, the optimal ratio of lime to total solids (TS) in sludge (gr/gr) (0.6) increased the sludge loading rate from 15 to 30% without any H2S emission during the stimulation study period. Therefore, the lime stabilization and transfer of sludge from a decentralized WWTP to a centralized WWTP is a feasible way to manage the sludge and enhance the treatment capacity in local WWTP.

Progress in Multi-Soil-Layering Systems for Wastewater Treatment

The use of decentralized wastewater treatment technologies is a reasonable solution for rural areas. As a decentralized treatment technology, the multi-soil-layering (MSL) system has recently drawn an increasing amount of attention owing to its merits, such as a high hydraulic load rate, small land area occupation, low probability of clogging, low investment, and low operation cost. This review summarizes the progress in MSL systems in the past decade, focusing on the directions of efforts for system optimization, the latest applications of MSL systems to various wastewater treatments, and the integration of MSL with other technologies. The great application potential of MSL systems is illustrated, and future research directions regarding better application of MSL systems are provided.

Responses of Freshwater Invertebrates to Imhoff Tank Sewage Effluents: A Preliminary Study in Four Watercourses with Different Ecological Status (Abruzzo, Central Italy)

In many EU countries, a large proportion of domestic effluents is treated in small, decentralized wastewater treatment plants (WWTPs) which often lack appropriate treatment technologies. The low efficiency of these systems and their incorrect maintenance often contribute to environmental deterioration, with a large quantity of inadequately treated sewage dispersed in the soil or discharged into superficial watercourses. In the Abruzzo region (Central Italy), almost all rivers and streams receive wastewater from Imhoff tanks with only primary treatments. The ecological impacts of these effluents have rarely been investigated. This paper aimed to evaluate the response of freshwater invertebrates to Imhoff effluents in receiving watercourses with different ecological status. Our results showed that wastewater from Imhoff plants negatively affected the structure and composition of freshwater communities, with a reduction in the richness and abundance of more sensitive taxa and an increase in the most tolerant ones. These negative effects were more accentuated during low flow periods and in streams with moderate ecological status. To improve the ecological status of rivers and streams and to limit the diffusion of pathogens and micropollutants in freshwater, a more efficient (secondary treatments, possibly with nature-based solutions) and sustainable (water reuse or sewage sludge recycling) approach to wastewater treatment in decentralized WWTPs is urgently needed.

Microplastics affect membrane biofouling and microbial communities during gravity-driven membrane filtration of primary wastewater

Recently, gravity-driven membrane (GDM) filtration has been adopted as an alternative solution for decentralized wastewater treatment due to easy installation and maintenance, reduced energy and operation cost, and low global warming impact. This study investigated the influence of microplastic size (0.5–0.8 μm and 40–48 μm) and amount (0.1 and 0.2 g/L) on the membrane performance and microbial community in GDM systems for primary municipal wastewater treatment. The results showed that dosing microplastics in the GDM systems led to 9–54% lower permeate flux than that in the control. This was attributed to more cake formation (up to 6.4-fold) with more deposition of extracellular polymeric substances (EPS, up to 1.5-fold) and divalent cations (up to 2.1-fold) in the presence of microplastics, especially with increasing microplastic amount or size. However, the dosed microplastics promoted formation of heterogeneous cake layers with more porous nature, possibly because microplastics created void space in the cake and also tended to bind with divalent cations to reduce EPS-divalent cations interactions. In the biofilm of the GDM systems, the presence of microplastics could lower the number of total species, but it greatly enhanced the abundance of certain dominant prokaryotes (Phenylobacterium haematophilum, Planctomycetota bacterium, and Flavobacteriales bacterium), eukaryotes (Stylonychia lemnae, Halteria grandinella, and Paramicrosporidium saccamoebae), and virus (phylum Nucleocytoviricota), as well as amino acid and lipid metabolic functions. Especially, the small-size microplastics at a higher dosed amount led to more variations of microbial community structure and microbial metabolic functions.

Mechanistic insights into different illumination positions control algae production in anaerobic dynamic membrane filtration (AnDM) during decentralized wastewater treatment

Sunlight illumination has the potential to control the stability and sustainability of dynamic membrane (DM) systems. In this study, an up-flow anaerobic sludge blanket (UASB) reactor was combined with DM under different illumination positions (direct, indirect and no illumination) to treat wastewater. Results indicated that the UASB achieved a COD removal up to 87.05 % with an average methane production of 0.28 L/d. Following treatment by the UASB, it was found that under illumination, the removal of organic substances by DM exhibited poor performance due to algal proliferation. However, the DM systems demonstrated efficient removal of ammonia nitrogen, ranging from 96.21 % to 97.67 % after stabilization. Total phosphorus removal was 45.72 %, and membrane flux remained stable when directly illuminated. Conversely, the DM system subjected to indirect illumination showed unstable membrane flux and severe fouling resistance. These findings offer valuable insights into optimizing illumination positions in DM systems under anaerobic conditions.

The Best Solution for Centralized and Decentralized Wastewater Treatment in the Makkah Region in Saudi Arabia

The research establishes the best solution for centralized and decentralized wastewater treatment in the Makkah region in Saudi Arabia. The research used a thematic coding approach to identify literature materials on the research problem. The literature review indicated that wastewater treatment could be optimized by integrating multiple practices. The proposed solutions include creating awareness and optimizing safety standards, expanding the treatment plants and optimizing them, integrating treatment processes through centralized and decentralized wastewater treatment plants, using simple systems and technologies, expanding existing plants, optimizing performance, adopting cost-efficient strategies, and using the Right Technology, Control, and Integration Systems.

Smartphone-based colorimetric method for decentralized wastewater treatment monitoring by inexperienced users

Rural areas often rely on decentralized wastewater treatment systems, including individual sewage treatment systems (ISTS), for remote houses, farms, and other establishments. For practical and financial reasons, ISTSs are often exempt from routine monitoring of effluent quality. As a result, they cannot guarantee the same level of treatment performance as their large-scale counterparts. A smartphone-based colorimetric monitoring method has been developed and tested to address this issue. This method can be easily adopted by untrained system owners. It uses modified test strips with built-in color reference zones and fiducial markers, which simplifies data acquisition and interpretation, eliminating the need for positioning accessories or controlled lighting. The proposed method ensures reliable results even when using a regular smartphone with default picture quality settings. The method has been tested with test strips measuring five different relevant wastewater quality parameters: pH, phosphates, ammonium, nitrates, and nitrites. For each type of test strip, the software installed on a smartphone provides a correlation for interpolating the measurements. The R2-values ranged from 0.881 to 0.993 for different reagents. The accuracy of this method was verified using lab-grade reference sensors and was found to be sufficient for the intended purpose.

Characterization of Low-Volume Meat Processing Wastewater and Impact of Facility Factors

Low-volume meat processing facilities often rely on decentralized wastewater treatment due to cost constraints and the lack of access to centralized treatment. Improved characterization of these facilities’ wastewater is crucial for meeting local groundwater discharge permits. This study also directly correlates treatment systems and facility characteristics to the results of the characterization. The total nitrogen (TN), biochemical oxygen demand (BOD), and phosphorus (P) reductions ranged from −15% to 83%, 43% to 95%, and −75% to 62%, respectively. Slaughtering and smoking were found to significantly increase nutrient concentrations. The average TN leaving the slaughterhouses and processing-only facilities was 519 mg/L-N and 154 mg/L-N, respectively. The average BOD produced by the slaughterhouses and processors was 3002 mg/L and 1660 mg/L, respectively. Filtration was found to reduce BOD, chemical oxygen demand (COD), and trace metals. Aeration in a treatment lagoon was found to significantly reduce BOD, COD, and N compounds. The results indicate that even simple decentralized wastewater treatment systems, combined with facility management practices, can substantially reduce permitted wastewater characteristics. The facility with the best BOD removal had an effluent value of 71.3 mg/L, representing a 96% reduction. The facility with the best TN removal had an effluent value of 20 mg/L, representing a 92% reduction prior to discharge.

Critical evaluation of electroactive wetlands: traditional and modern advances.

In the field of sustainable wastewater management, electroactive wetlands (EW), or constructed wetland-microbial fuel cells (CW-MFC), are an emerging technology. With the growing problem of untreated wastewater, the emphasis must shift to decentralisation of wastewater treatment infrastructure, and CW-MFC can be an excellent choice. This review provides a chronologically organized account of the design and configuration of CW-MFCs developed between 2010 and 2023. The research on CW-MFC has mainly focused on material, positioning and number of electrodes; use of electroconductive media and filler materials; flow regime; algal-based CW-MFC and multistage setups. Compared to traditional constructed wetlands (CW) and microbial fuel cells (MFC), CW-MFCs have a number of advantages, including better treatment efficiency, faster organic matter utilisation, lower capital and land requirements and a smaller carbon footprint. However, there are some limitations as well, such as upscaling and viable electricity generation, which are covered in more detail in the article. Moreover, the economics of this technology is also evaluated. The microbiology of a CW-MFC and its influence on its performance are also elaborated. Recent advancements in this field in terms of design, configuration and performance are discussed. Finally, the knowledge gaps that must be addressed before this technique can be successfully implemented on a large scale are highlighted, along with specific recommendations. This article aims to advocate for EWs as an ideal decentralised wastewater treatment technique, while also shedding light on the areas that still need to be worked on.

Assessing the determinants of scale effects on carbon efficiency in China's wastewater treatment plants using causal machine learning

The debate over the merits of centralized versus decentralized wastewater treatment plants (WWTPs) has gained prominence considering pressing sustainable development objectives and the need to reduce greenhouse gas (GHG) emissions. This highlights the importance of innovative analytical tools to shape forthcoming policies. Using causal machine learning, we evaluate the impact of WWTP scale on GHG emission intensities and investigate contributing factors. Results show GHG intensity typically decreases as WWTPs scale up. However, this trend varies based on regional environmental, economic, and infrastructure elements. Specifically, regions with fewer industrial wastewater contributions, increased rainwater composition, and elevated temperatures show smaller scale effects. This suggests limited GHG reductions from merely expanding WWTPs in such areas, as the benefits of handling fluctuating inflow volumes, tackling heavy pollution, and operating in cooler conditions offered by larger WWTPs are compromised. This research lays the foundation for comprehensive models promoting sustainable wastewater treatment strategies.

Removal of anionic surfactant from aqueous solutions by adsorption onto biochars: characterisation, kinetics, and mechanism.

Biochar, a waste biomass-derived adsorbent, holds promise for decentralised wastewater treatment. However, limited research exists on its efficacy in adsorbing anionic surfactants in wastewater. To address this, the adsorption of sodium dodecyl sulphate (SDS), a common anionic surfactant, was studied using various biochar types: rice husk biochar (RH-550 and RH-700), wheat straw biochar (WS-550 and WS-700) produced at 550°C and 700°C, wood-based biochar (OB), and activated carbon (AC) as a control. The study investigated the impact of pH (3-9), adsorbent loading (1-10 g/L), adsorbent size (<0.5-2.5 mm), contact time (5-180 min), and initial concentration (50-200 mg/L) on SDS removal. Under optimised conditions (100 mg/L SDS, 4 g/L adsorbent, 1-2 mm particle size, pH 8.3, and 180 min contact time), maximum SDS removals were RH-550 (78%), RH-700 (82.4%), WS-550 (89.5%), WS-700 (90.4%), AC (97%), and OB (88.4%). Among the tested adsorbent materials, WS-550 exhibited the highest SDS adsorption capacity at 66.23 mg/g compared to AC (80.65 mg/g), followed by RH-550 (49.75 mg/g), OB (45.87 mg/g), RH-700 (43.67 mg/g), and WS-700 (42.74 mg/g). SDS adsorption followed a pseudo-second-order kinetic model, indicating chemisorption on the adsorbent surface. The Freundlich isotherm model exhibited a better fit for the experimental data on SDS adsorption using all tested adsorbents except for RH-550. This study showed that biochars produced from agricultural and forestry residues are effective adsorbents for SDS in aqueous solutions and can be a promising sustainable and low-cost material for the treatment of greywater containing anionic surfactants (e.g. handwashing, laundry, kitchen, and bathroom greywaters).

Biological pretreatment coupled gravity-driven membrane filtration for purifying decentralized domestic wastewater toward resource reuse

Membrane bioreactor (MBR) is an effective technology for the decentralized wastewater treatment; however, its high energy consumption and complex operation & maintenance limit its intensive application. This study introduced an innovative membrane-based process, gravity-driven membrane (GDM) filtration, to treat the decentralized wastewater without any cleaning procedures, and different biological pretreatments were constructed, including (I) tubular filler (TF-8), (II) tubular filler (TF-4), (III) fiber bundle filler (FBF), and (IV) sole aeration (control) to improve the filtration performance. The results indicated that the flux of GDM control can be maintained during long-term filtration in treating the real decentralized wastewater, and introducing the biological pretreatment processes could improve the stabilized flux of GDM without any influence on its stability. The average flux of TF-8/GDM was 3.69 ± 0.89 L m−2 h−1 during long-term filtration. Furthermore, coupling pre-treatment to GDM can effectively improve permeability quality and withstand the shock of water quality fluctuations. The average removal rates of chemical oxygen demand (COD) and dissolved organic carbon (DOC) by TF-8 were 59.7% and 48.3%, respectively. Besides, the organic contaminants could be further removed by the following GDM process owing to the biodegradation function of the self-formed biofilm on the membrane surface, and the DOC concentration in the GDM effluent can be reduced to as low as 4.5 mg L−1. Additionally, the elements of nitrogen (N) and phosphorus (P) could be effectively retention through the coupling process, with a retention rate of 84.3%–94.6% for total nitrogen (TN) and 99.8%–104.8% for total phosphorus (TP), respectively. Therefore, these findings can benefit to develop of new strategies to provide stable effluent quality, resource recovery, and energy consumption reduction in the membrane-based decentralized domestic wastewater treatment.

Occurrence and fate of CECs (OMPs, ARGs and pathogens) during decentralised treatment of black water and grey water

Decentralised wastewater treatment is becoming a suitable strategy to reduce cost and environmental impact. In this research, the performance of two technologies treating black water (BW) and grey water (GW) fractions of urban sewage is carried out in a decentralised treatment of the wastewater produced in three office buildings. An Anaerobic Membrane Bioreactor (AnMBR) treating BW and a Hybrid preanoxic Membrane Bioreactor (H-MBR) containing small plastic carrier elements, treating GW were operated at pilot scale. Their potential on reducing the release of contaminants of emerging concern (CECs) such as Organic Micropollutants (OMPs), Antibiotic Resistance Genes (ARGs) and pathogens was studied. After 226 d of operation, a stable operation was achieved in both systems: the AnMBR removed 92.4 ± 2.5 % of influent COD, and H-MBR removed 89.7 ± 3.5 %. Regarding OMPs, the profile of compounds differed between BW and GW, being BW the matrix with more compounds detected at higher concentrations (up to μg L−1). For example, in the case of ibuprofen the concentrations in BW were 23.63 ± 3.97 μg L−1, 3 orders of magnitude higher than those detected in GW. The most abundant ARGs were sulfonamide resistant genes (sul1) and integron class 1 (intl1) in both BW and GW. Pathogenic bacteria counts were reduced between 1 and 3 log units in the AnMBR. Bacterial loads in GW were much lower than in BW, being no bacterial re-growth observed for the GW effluents after treatment in the H-MBR. None of the selected enteric viruses was detected in GW treatment line.

Conceptual Feasibility of a Portable Containerized and Decentralized Wastewater Treatment System for Rural Regions: A Case Study in Palestine

The necessary implementation of decentralized wastewater treatment systems in densely populated rural regions is a viable alternative to constructing a large centralized system. Therefore, this study aims to assess the conceptual feasibility of implementing a portable containerized and decentralized wastewater treatment system as a case study in Palestine that can help in treating wastewater in rural areas efficiently generated by up to 4,000 individuals. The conceptually proposed system is comprised of two stages. The initial stage includes a standalone primary sedimentation tank located outside the container. The subsequent stage consists of a container housing all the equipment utilized in the treatment process beginning with aeration, followed by secondary sedimentation, and ending with filtration and chlorination. Although the system is designed as a single container, in practice, it will consist of two containers with identical units. The second container will ensure continuous operation mode in case of maintenance in the first container. An initial cost evaluation was conducted, and the projected cost for one container is roughly $9,800, which is reasonable. Indeed, adopting this proposed system would result in a significant cost-saving of approximately 40 million dollars compared to the current west wastewater treatment plant in Nablus. Additional research can be undertaken to explore the running cost and the level of efficacy attained

Estimates of Renewable Energy Recovery from Biogas in Residential Buildings: Economic Feasibility Analysis

Increasing of energy demand and climate change have hampered sustainable development. This article aimed to study the potential of biogas recovery for energy generation from compact wastewater treatment plants in buildings. Three buildings were selected and an economic feasibility analysis was carried out. The net present value (NPV) was positive and the economic internal rate of return (EIRR) was higher than the minimum attractive rate in five of six cases, showing that energy savings were sufficient to cover implementation, operation, and maintenance costs, with two to four years of payback time for biogas structures. The anaerobic reactor was responsible for the main expenditure, which indicates the importance of developing low-cost and compact units for decentralized wastewater treatment. Finally, the results indicate that biogas may be a promising and viable energy source in residential buildings.

Tracking performance and disturbance in decentralized wastewater treatment systems with fluorescence spectroscopy

Fluorescence spectroscopy holds promise as a rapid tracer of performance in decentralized wastewater treatment systems (DEWATS) that may reduce the monitoring burden on communities.