To centralize or to decentralize? A systematic framework for optimizing rural wastewater treatment planning

The ecological role of microbiome at community-, taxonomic - and genome-levels in black-odorous waters

Black-odorous waters (BOWs) are heavily polluted waters where microbial information remains elusive mechanistically. Based on gene amplicon and metagenomics sequencing, a comprehensive study was conducted to investigate the microbial communities in urban and rural BOWs. The results revealed that microbial communities' assembly in urban and rural BOWs was predominantly governed by stochastic factors at the community level. At the taxonomic level, there were 62 core species (58.48%) in water and 207 core species (44.56%) in sediment across urban and rural areas. Notably, significant differences were observed in the functional genetic composition of BOWs between urban and rural areas. Specifically, rural areas exhibited an enhanced abundance of genes involved in nitrogen fixation, Fe2+ transport, and sulfate reduction. Conversely, urban areas showed higher abundances of some genes associated with carbon fixation, nitrification and denitrification. A sulfur-centered ecological model of microbial communities was constructed by integrating data from the three levels of analysis, and 14 near-complete draft genomes were generated, representing a substantial portion of the microbial community (35.04% in rural BOWs and 29.97% in urban BOWs). This research provides significant insights into the sustainable management and preservation of aquatic ecosystems affected by BOWs.

Electrocoagulation enhanced gravity driven membrane bioreactor for advanced treatment of rural sewage

The daily discharge of rural sewage in China occupies 30 % of the national wastewater discharge, and developing an energy-efficient, easy to operate, and decentralized rural sewage treatment technology becomes an important task. In this work, a novel rural sewage treatment technology, Electrocoagulation enhanced Gravity-Driven Membrane Bioreactor (EC-GDMBR) was exploited for the rural sewage treatment under long-term operation (160 days). Two EC-GDMBRs with various module structures of ceramic membrane (horizontal module and side module) not only displayed the desirable effluent quality, but also sustained the stable flux (8-13 LMH). The electrocoagulation, electrooxidation, biodegradation, and separation in EC-GDMBRs were able to synergistically remove the particle matter, organic (CODCr effluent <11.6 ± 1.2 mg/L) and nutrients (NH3-N effluent <0.1 mg/L, TN effluent <8.5 mg/L, TP effluent <0.05 mg/L). Besides, the high permeability of ceramic membrane and large porosity of biofilm on its surface improved the sustainability of stable flux during the long-term operation. Moreover, by analyzing bacterial abundance, Extracellular Polymeric Substances, Adenosine Tri-Phosphate and Confocal Laser Scanning Microscopy, a large number of microorganisms grew and accumulated on the carrier, as well as formed the biofilm (23.46-659.9 μm), while Nitrobacteria (1.6-4.1 %) and Nitrate (0.01-0.06 %) exited in the carrier biofilms, promoting the nitrogen removal. Compared with EC-GDMBR with side module of ceramic membrane, EC-GDMBR with horizontal module of ceramic membrane has advantages in flux behavior, organic/nutrient removal, microbial abundance/activity, abundance of nitrogen removal functional bacteria and water permeability of biofilm, because the ceramic membrane of horizontal module can promote the uniform growth of biofilm and improve the uniformity of flow penetration distribution. In general, the findings of this work verify the reliability of EC-GDMBR for the sustainable operation of wastewater treatment and improve its application value of rural sewage treatment.

Full-scale application and performance of a new multi-self-reflow decentralized Wastewater treatment device: Impact of hydraulic and pollutant loads

Decentralized treatment of wastewater in rural areas usually has several challenges, which include large fluctuations in pollutant concentration and water quantity, complicated operation and maintenance of conventional biochemical treatment equipment, resulting in poor stability and a low compliance rate of the wastewater treatment process. In order to solve the above problems, a new integration reactor is designed, which uses gravity and aeration tail gas self-reflux technology to realize the reflux of sludge and the nitrification liquid, respectively. The feasibility and operation characteristics of its application for decentralized wastewater treatment in rural areas are explored. The results demonstrated that, under constant influent, the device showed strong tolerance to the shock of pollutant load. The chemical oxygen demand, NH₄⁺-N, total nitrogen and total phosphorus fluctuated in the ranges of 95-715 mg/L, 7.6-38.5 mg/L, 9.32-40.3 mg/L and 0.84-4.9 mg/L, respectively. The corresponding effluent compliance rates were 82.1%, 92.8%, 96.4% and 96.3%, respectively. When the wastewater discharge was non-constant and the maximum single-day Q_max/Q_min reached 5, all indicators of the effluent met the relevant discharge standard. The integrated device also demonstrated high phosphorus enrichment levels in its anaerobic zone; the concentration of phosphorus reached a maximum of 26.9 mg/L, which created a good environment for phosphorus removal. The microbial community analysis showed that sludge digestion, denitrification, and phosphorus-accumulating bacteria all played an important role in pollutant treatment.

A new paradigm of sewage collection in rural areas

Rural sewage collection networks play extremely important roles in rural sewage treatment, and the lack of a suitable collection model makes this task difficult. Hence, there is an urgent need to develop a new method to collect and deal with rural sewage. This paper establishes a rural sewage optimal collection model (RSOCM) with critical distance (d) and sewage quota per unit area (q_s) as the constraint factors. The implementation of critical distance for rural sewage collection pipeline networks was demonstrated for 38 rural areas in the Huicheng District, Huizhou City, Guangdong Province of China. The average critical distances of 22 m, 38 m, 29 m, 29 m, 41 m, and 55 m were demonstrated for Sandong Town, Ma'an Town, Luzhou Town, Ruhu Town, Hengli Town, and Shuikou Subdistrict, respectively. The q_s is used to create the best possible pipe network layout, determine the appropriate treatment method, and reduce construction costs. This model can be widely applied to sewage collection in rural areas of China, where the overall sewage collection system can implement different regional strategies to maximize rural pollution control and protect the environment.

Evaluation of the treatment performance and reuse potential in agriculture of organized industrial zone (OIZ) wastewater through an innovative vermifiltration approach

Vermifiltration (VF) is a natural and sustainable biofilter that has many advantages, including being energy-free, cost-effective, and allowing ease of application and maintenance. In this study, the effectiveness of a lab-scale VF system was assessed by the removal efficiency of total suspended solids, electrical conductivity, chemical oxygen demand, total nitrogen, total phosphorus, fecal coliform, and heavy metals in organized industrial zones (OIZ) and domestic wastewater (DW) for the first time. Additionally, the reuse suitability of the treated wastewater was determined by comparing different countries' and global irrigational criteria. The lab systems were built with four layers: one worm-bed and three varying filtering materials, and operated at an optimum hydraulic loading rate of 1.8-2 m³/m²/day for 45 days with Eisenia fetida as the earthworm species. The results demonstrated that removal efficiencies of total suspended solids and chemical oxygen demand were found to be 95% and 80% in OIZ wastewater and 90% and 88% in DW, respectively. Total nitrogen and total phosphorus were removed at rates of 69% and 67% in OIZ wastewater, respectively, and 84% and 74% in DW. Besides, the VF system has shown satisfactory removal performance for heavy metals ranging from 51% to 77% in OIZ wastewater that has met Turkish national wastewater discharge limits. Although the final characterization of treated wastewater was suitable, heavy metal and fecal coliform levels have not met many countries' irrigation water quality criteria. To meet global irrigation standards and to enhance the VF performance, further experimental studies should be carried out, including parameters such as bed material type in the reactor, worm type, and different operating conditions.

An Evaluation of Pumping Stations for Pressure Sewers System Made from Concrete Coils, Polymer Concrete, and High-Density Polyethylene (HDPE)

A deficiency in accurate and current regulations, along with a lack of experience in sanitary construction, makes the installation of sewers challenging. Using models, it was determined that if the pumps were operated simultaneously, the service would last for a long time over the entire sewer system. With a daily sewage inflow of 468 dm³, the system was found to run 14.4-14.7% longer than expected at 100 pumping stations. Each month, the pressure-sensitive sewer system receives more than 51 min of extended service from the city's central sewer system. Increasing wastewater inflow and the number of pumps decrease centrifugal pump capacity. In the study, the main findings were related to the number of pumps. With 100 centrifugal pumps simultaneously, the pressure-based system was most effective. An increase in operation time of 18.4-19.1% was observed over a period of 30 days and an average sewage inflow of 705 dm³ for each. In place of gravity sewerage, sewerage can be used. Pressure sewer systems should be designed in a way that addresses technical as well as economic concerns. Accordingly, this study indicates that pressure sewerage is a viable alternative to gravity sewerage in villages with scattered drinking water supplies.

Effect of aeration on water quality and sediment humus in rural black-odorous water

Black-odorous water, which exists widely in rural areas of China, affects the living environments of residents and causes a loss of ecosystem functions, and improper treatment may even cause secondary pollution. Moreover, the transformation relationships among the components of humus in the sediments of black-odorous water are largely unknown. Therefore, it is necessary to select appropriate methods for treating black-odorous water in rural areas and to understand the characteristics of humus in sediment during the treatment process. In this study, the use of aeration in treating black-odorous water and interstitial water in rural areas was studied and the effects of different treatment methods on the contents and spectral characteristics of humus components in sediments were explored. It was found that the quality of the treated water improved from severe black-odorous to nonblack-odorous, the colour of the sediment changed from black to greyish-brown to turquoise, and the odour changed from strong to weak. The removal rates of ammonia nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand in the sediment aeration group reached more than 50% in the upper water, and more than 70% in the interstitial water. After treatment, the content of fulvic acid, the main black substance in sediment, decreased by 0.36-1.58 g/kg, and the molecular structure of the humus was simplified.

What's the cost-effective pattern for rural wastewater treatment?

Inadequate sanitation infrastructure is a global problem that is particularly impacting rural areas. And decentralized wastewater management system is considered as the feasible solution for rural sewage treatment (RuST). However, determining the cost-effective (CE) pattern for decentralized RuST is methodologically challenging because of scarce decision-support tools. In this research, a RuST optimization model (RuST-OM) was developed to gain an insight into the CE pattern of RuST based on the greedy algorithm. This model involves tradeoffs in the economy-of-scale and technology of wastewater treatment system versus the cost and energy consumption of the sewage collection system. The investment associated with the CE pattern for RuST is closely linked to the environmental demand, RuST coverage, topographic complexity, and degree of household dispersion. The cost of the CE pattern falls between the onsite-B and community-based pattern, and this range represents the optimized interval for RuST planning. Nature-based technology is a sustainable alternative for RuST in areas characterized by low or moderate environmental demand. To ensure applicability of the RuST-OM in other countries/regions, built-in datasets (e.g., technology and pipeline design parameters) are designed based on rural area features that can be modified as necessary. This research highlights the utility of the CE pattern for RuST planning, and can serve as a reference for RuST planning around the world.

Sustainability Assessment for Wastewater Treatment Systems in Developing Countries

As the assessment of the economic, environmental, institutional, and social sustainability of wastewater treatment systems may have several conceivable goals and intended recipients, there are numerous different approaches. This paper surveys certain aspects of sustainability assessment that may be of interest to the planners of wastewater treatment systems. Here, the key criteria assess the system’s costs and financing, including its affordability for the users, the environmental impact, the benefits for health and hygiene, the cultural acceptance of the system and its recycled products, the technical functioning, and the administrative, political, and legal framework for its construction and operation. A multi-criteria approach may then be used to analyze possible trade-offs and identify the most suitable system for a certain location.