Small diameter gravity sewers (SDGSs) have a wide range of applications in rural wastewater collection due to their low construction costs, fast implementation, and simple operation and maintenance. However, the mechanism of sediment accumulation urgently needs to be solved. This study investigated the sedimentation mechanisms in different components of SDGS through pilot-scale experiments and computational fluid dynamics (CFD) simulations. The results indicate that the sedimentation rate of SDGSs decreased as the flow velocity increased, with sediment primarily accumulating at the end section of upstream pipes and within manholes, accounting for 90.37 +/- 5.15% of the total accumulation. Areas with relatively high sedimentation rates exhibited lower turbulent kinetic energy (TKE), and this trend became more pronounced as the flow velocity decreased. TKE and flow velocity were identified as the key factors influencing the sedimentation process in the SDGSs. This study provides important theoretical foundations and technical support for the design and maintenance of SDGSs.

污水处理填料能够提高污水处理效果，但其堵塞问题会降低处理能力、恶化运行工况，亟待解决。为提高污水处理填料的抗堵塞能力，综述了污水处理填料堵塞的相关研究，从填料特性、应用场景、物质分类、堵塞特点、发展机制和影响因素等方面总结了污水处理填料堵塞的形成机理，从事前、事中、事后三个方面讨论了针对污水处理填料堵塞问题的7项常用控制措施，并根据研究现状提出了堵塞形成机理、堵塞控制措施、填料设计优化等方面的研究建议，以期为污水处理填料及配套工艺的后续研究和技术开发提供支撑，提高污水处理填料的应用效益。

Determining the rural domestic water consumption (RDWS, L/person-day) and rural sewage production (RSP, L/person-day) of rural residents at the county scale can provide decision support for rural domestic sewage treatment. However, methods for predicting county-scale RDWS and RSP based on geographical, social, and governance factors are rarely reported. This paper proposes an RDWS and RSP prediction method based on Automated Machine Learning (AutoML) for the Inner Mongolia Autonomous Region. The RDWS and RSP in the Inner Mongolia Autonomous Region were successfully predicted from multi-source data. The AutoML model accurately predicted RDWS (mean absolute error = 1.7072, R2 = 0.7759) and RSP (mean absolute error = 0.6580, R2 = 0.65107). Average years of education (AYOS), proportion of resident population, and proportion of elderly and children (POEAC) were key driving factors related to RDWS prediction. The most important factors associated with RSP prediction were AYOS, POEAC, and annual average precipitation (AAP). An explanatory analysis further revealed dependence between the input variables, RDWS, and RSP. The framework was demonstrated to be a practical tool for qualitative and quantitative analyses of rural domestic water consumption and domestic sewage production in the Inner Mongolia Autonomous Region. Overall, this study provides a solution for predicting county-level RDWS and RSP, providing a reference for the design of rural domestic sewage treatment.

The traits of rural domestic sewage emission are unclear, negatively affecting rural domestic sewage treatment and sewage management. This study used data from the Second National Pollution Source Census Bulletin to establish a data set. The spatial distribution characteristics and main factors influencing rural sewage discharge in the Northern Region were studied using spatial autocorrelation analysis and structural equations. The findings demonstrated that (1) a significant Spearman correlation between drainage water volume (DWV), chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP) and that the correlation coefficients between DWV and COD, NH3-N, TN and TP were 0.87**, 1.0**, 0.99**, 0.99**, respectively; (2) rural sewage discharge showed spatial autocorrelation, and rural domestic sewage discharge in the districts and counties with an administration was significantly higher than in the surrounding areas; and (3) social development was the main driver rural domestic sewage changes (path coefficient was 0.407**), and the main factors influencing rural domestic sewage discharge were the urbanization rate, years of education, and population age structure. This study obtained the spatial variation law and clarified the main influencing factors of rural domestic sewage to provide data support and a theoretical basis for subsequent rural sewage collection and treatment. Use of the Inner Mongolia Autonomous Region in northern China as a typical case, provides a theoretical foundation for scientific decision-making on rural domestic sewage treatment at the national and regional levels and offers new perspectives for managing pollutants.

The amount of rural sewage varies greatly, which easily affects the normal operation of sewage treatment facilities. The application of waste bricks to construct rural sewage treatment type household manholes can realize front pollution control, improve the stability of the rural sewage treatment system, and realize the resource utilization of rural construction wastes, which has a broad prospect. However, the influencing factors and parameter selection of this technology are not clear, which affects its popularization and application. To solve the above problems,this study adopted small and pilot devices, combined with material characterization, single factor analysis and response surface analysis to study the influence of waste brick particle size, pollution control effect and parameter optimization process of waste brick-based rural sewage treatment type household manholes. It was found that waste brick-based rural sewage treatment type household manholes had good sewage treatment effects, and waste brick fragments with particle size of 0.5-<1.0 cm were more suitable. Filling height, baffling depth and drop height had influences on the pollution control effect of household manholes. With the increase of filling height and baffling depth, and the decrease of drop height, the removal rate of pollutants increased. Under the optimal conditions of household manholes, the removal rates of chemical oxygen demand, suspended matter, ammonia nitrogen, total nitrogen and total phosphorus reached 58%, 68%, 60%, 52% and 58%, respectively. The filling height of 90 cm, the baffling depth of 64 cm, and the drop height of 12 cm were desirable for the in-site reuse scenario. This study could provide a feasible technical solution for the pollution control of rural sewage and a reference for rural sewage treatment technology.

Significant differences existed in microbes from different rural sewers. Lots of denitrifying bacteria and lack of sulfate-reducing bacteria were found in rural sewers. Certain abundance of pathogenic bacteria were detected in rural greywater sewer.

Perfluorooctanoic acid (PFOA) as nonbiodegradable organic pollutant, its presence and risks in wastewater treatment system has aroused wide concern. This study investigated the effect and underlying mechanism of PFOA on anaerobic digestion sludge (ADS) dewaterability. Long-term exposure experiments were set up to investigate the effect with various concentration of PFOA dosed. Experimental results suggested that the existence of high concentration PFOA (over 1000 μg/L) could deteriorate ADS dewaterability. The long-term exposure to 100,000 μg/L PFOA of ADS increased specific resistance filtration (SRF) by 81.57%. It was found that PFOA promoted the release of extracellular polymeric substances (EPS), which was strongly associated with sludge dewaterability. The fluorescence analysis revealed that the high PFOA concentration could significantly improve the percentage of protein-like substances and soluble microbial by-product-like content, and then further deteriorated the dewaterability. The FTIR results showed that long-term exposure of PFOA caused loose protein structure in sludge EPS, which led to loose sludge floc structure. The loose sludge floc structure aggravated the deterioration of sludge dewaterability. The solids-water distribution coefficient (Kd) decreased with the increase of initial PFOA concentration. Moreover, PFOA significantly affected microbial community structure. Metabolic function prediction results showed significant decrease of fermentation function exposed to PFOA. This study revealed that the PFOA with high concentration could deteriorated sludge dewaterability, which should be highly concerned.

New low-cost rural sewage collection and treatment technologies should be developed to solve the problem of conventional rural sewage technology caused by rural sewage characteristics. In this study, a novel facility, the construction waste ditch, was established to collect and treat household rural sewage, making use of the collection capacity of ditches and the treatment capacity of construction wastes, and the structure parameters were optimized. Results show that the construction waste ditch achieved pollutant removal phenomenon (average removal rates were above 25

Bacteria in rural sewage collection systems have the important influences on operation and maintenance risks, such as sedimentation blockage and harmful gas accumulation, and pollutant pre-treatment ability. It is necessary to analyze and interpret the influence on bacterial communities caused by the location (sewage, biofilms, and deposits), season (winter and spring, summer and autumn), and system type (sewers and ditches) to better understand the bacterial characteristics in rural sewage collection systems. To achieve the above purpose, 96 samples obtained from practical rural sewage collection systems in eight villages were analyzed by 16S rRNA whole region sequencing methods. The results indicate that locations and seasons caused significant influences on the overall bacterial communities, which were mainly affected by temperature, sewage quality and bacterial survival preference, and 13 genera of sulfate-reducing bacteria (SRB), 2 genera of ammonia-oxidizing bacteria (AOB), 2 genera of nitrite-oxidizing bacteria (NOB), and 9 genera of water-related pathogenic bacteria (WPB) were detected in rural sewage collection systems. SRB, AOB, NOB, and WPB tended to inhabit in biofilms or deposits rather than in sewage. The total relative abundance of SRB in summer and autumn (∼2.19%) was higher than in winter and spring (∼0.41%), and the WPB distribution in different seasons showed significant distinction. Additionally, some of SRB, AOB, NOB, and WPB also showed significant differences in sewers and ditches. Overall, this study provided a deeper understanding of bacteria in rural sewage collection systems and could further provide the basic parameter for the operation and maintenance risk control.

To investigate the differences in the bacterial communities of biofilms in the appurtenant facilities of rural sewage collection systems, a pilot research setup was constructed. A study was conducted using real sewage collected in a rural area, and the bacterial communities of biofilms in different appurtenant facilities were characterized using Illumina HiSeq high-throughput sequencing technology. The results showed that there were significant differences in biofilm bacterial communities among the different annexes. The biofilms from all four ancillary facilities (drop manhole, turning inspection well, mud trap, and direct inspection well) contained some amounts of denitrifying bacteria (relative abundance >6 %), but lacked ammonia- and nitrite-oxidizing bacteria (relative abundance <0.1 %). The relative abundance of sulfate-reducing bacteria was high (6.32 %), with Desulfobulbus being dominant (4.12 %) owing to the prolonged low dissolved oxygen environment in the sedimentation wells, which are at high risk of accumulating H2S relative to other ancillary facilities. All four ancillary facilities had high abundances of potential disease-causing bacteria (e.g., Acinetobacter and Arcobacter) in the biofilm and in the overwater. Therefore, the biosafety of the effluent should be taken into account in the collection process.

In order to investigate the potential health risk of odor escape from rural vacuum sewer system to the surrounding residents, the odor escape law of the whole process of rural vacuum sewer system, household sewer,vacuum well and vacuum station was studied by using the vacuum sewer experimental device combined with odor zoning monitoring and correlation analysis, etc. The results showed that the average H 2 S mass concentrations in toilet black water（TBW）, toilet gray water（TGW）, and kitchen gray water（KGW） sewer in rural households were 0.08, 0.06, and 0.06 mg·m -3 , respectively, all of them reached the standard limit(0.06mg·m -3 ) of class 2 plant boundary for malodorous pollutants（GB 14554-1993）. The peak odor mass concentrations of NH 3 、 C 3 H 9 N、 C 2 H 6 S 2 and OU in the TBW sewer were 5.79, 2.58, 0.18, 337 mg·m -3 ,respectively, which were significantly higher than the peak mass concentrations in the TGW and KGW sewers(0.32 and 0.62 mg·m -3 , 0.18 and 0.31 mg·m -3 , 0.06 and 0.05 mg·m -3 , 136 and 170 mg·m -3 ). The peak mass concentrations of NH 3 and H 2 S around the vacuum wells are 2.80 and 17.56 times higher than the standard limits of level 3 plant boundary(4.0 mg·m -3 , 0.32 mg·m -3 ), respectively, and the peak mass concentrations of NH 3 and H 2 S decreased by 72.3% and 65.1%, respectively after the transformation of the anti-fall water structure of vacuum wells. The correlation coefficients between the changes in mass concentrations of OU, H 2 S, CS 2 , C 8 H 8 ,and C 2 H 6 S 2 around the vacuum station and their changes in operating electrical power were-0.370,-0.452,-0.169,-0.426 and-0.379, respectively. This showed that over standard phenomenon occurred for the mass concentration of H 2 S and other odorous gases in the rural vacuum sewer system, different water quality pipes had different odor characteristics, the vacuum well was the area with the highest odor quality concentration in the whole vacuum sewer system, the anti-fall structure modification of vacuum wells could significantly reduce the odor quality concentration around vacuum wells, and the change of odor quality concentration around vacuum stations significantly correlated with the change of its operating power. The research results can provide a reference for the improvement design and parameter optimization of rural drainage technology.

Truck-wash facilities have become popularized globally on construction sites, and the wastewater was frequently treated by three-stage sedimentation basins. The wastewater and bacterial characteristics in three-stage sedimentation basins need to be studied, which might affect the treatment cost and reuse security. In this study, the wastewater characteristics, bacterial communities, and pathogenic bacteria distribution of three-stage sedimentation basins on four construction sites were investigated. Results indicated that truck-wash wastewater contained a high concentration of suspended solids (29-211 mg/L) and bacteria (4.2x10(3) to 2.7x10(4) colony forming units/mL). Proteobacteria (mean at 72.3%), Firmicutes (mean at 11.3%), and Bacteroidetes (mean at 10.6%) were the predominant bacterial phyla and Acinetobacter (mean at 18.4%), Chryseomicrobium (mean at 6.3%), and Paracoccus (mean at 6.1%) were the predominant bacterial genera. Truck-wash wastewater contained pathogenic bacteria, identified by the Illumina sequencing method. Acinetobacter, Shigella, or Escherichia (about 0.2%) and Legionella (about 0.2%) were the main pathogenic bacteria and Legionella should be a concern due to the wastewater reuse method. Traditional three-stage sedimentation basins should be simplified and further improved because of the lower suspended solids or pathogenic bacteria removal effect. The practical technology for suspended solids and pathogenic bacteria control in truck-wash wastewater should be further studied, and disinfection facilities should be applied to protect construction workers. (C) 2022 American Society of Civil Engineers.

Biological contact oxidation process is attractive and widely used in rural sewage treatment, due to its simplicity and relatively superior pollutants elimination efficiency. However, the effluent total nitrogen (TN) and excess sludge yield during the biological contact oxidation process still need to be intensified to stably satisfy the discharge standard. In the current study, an enhanced rural anoxic/oxic (A/O) biological contact oxidation process with air-lift reflux technique was properly established, which achieved better pollutant removal efficiency and lower excess sludge yield. Under the pathway of air-lift reflux technique, the TN and ammonia nitrogen (AN) removal capacity of A/O biological contact oxidation process were obviously increased from 66.5% and 73.8% to 95.3% and 80.6%, respectively, which should be attributed to the increasement of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Denitratisoma, Thauera, and Dechloromonas). The excess sludge yield was also decreased from 0.19 kg MLSS/kg COD (no reflux model) to 0.11 kg MLSS/kg COD (air-lift reflux model) since the degradation of returned oxic sludge in the anoxic tank, which was verified by stable isotope tracer analysis. The rural A/O biological contact oxidation process with air-lift reflux technique had great potential to strengthen TN removal and reduce sludge generation, which could provide a useful and easy-implement technology for rural sewage treatment.

目前农村灰水系统在技术和管理上存在问题，不利于灰水资源化。农村灰水收集系统分为管道系统和沟渠系统；处理系统主要采用生物转盘、曝气生物滤池、膜生物反应器等生物处理工艺，人工湿地等生态处理工艺和物理过滤等物化处理工艺；回用系统以加氯消毒和紫外消毒较为常见。农村灰水系统的工程应用中，管道系统造价高、处理系统冬季运行效果差是常见问题，技术上应优化灰水收集管道管径以降低造价，改进处理与回用技术以提升运行效果，并在回用前进行科学消毒，结合管理提升和制度优化协同推进农村灰水资源化。分析了农村灰水收集-处理-回用系统的现状及问题，从技术、管理和制度层面提出建议并展望了发展趋势。未来应研究灰水系统中物质和微生物的迁移转化规律，研发低温适用的灰水处理技术，并科学评估灰水管道和沟渠的综合效益，推进农村灰水有关理论和技术的进一步发展。

采用化肥驱动正渗透(fertilizer driven forward osmosis,FDFO)工艺处理生活污水,不仅有效降低受纳环境风险或减少水体污染,同时经稀释后的化肥汲取液可直接用于周边农田灌溉,实现了生活污水处理与农田灌溉水肥一体化协同效应,具有良好的应用前景.目前,FDFO处理生活污水处于实验室小试和部分现场中试验证阶段,规模化应用的关键核心在于高效正渗透膜的开发、膜装置设计的改进、膜表面水力学参数的优化及膜污染缓解技术水平的提升.文章综述了近10年FDFO工艺在处理生活污水中的应用,重点阐述了FDFO工艺的膜装置类型与工艺流程、评价指标及其影响因素等3方面,并展望了未来FDFO工艺规模化处理生活污水面临的挑战,以期推动FDFO工艺在处理污水领域的应用.

Channels and sewers are commonly used to collect sewage during extensively rural areas. The sewage and bacterial characteristics of rural sewage collection systems can influence their operation and maintenance performance which further affect appropriate system decision. In this study, eight rural sewage collection systems (four each of channels and sewers) were applied to evaluate the sewage quality, bacterial characteristics, and their differences of two kinds of collection systems. The results indicate that significantly distinction existed between the rural sewage collection systems of channels and sewers. Sewage in channels had higher suspended solid (SS) concentration but lower sulfide concentration than that in sewers. The SS, sulfate, and chemical oxygen demand (COD) removal capacity in channels was nearly 3.5, 4.0, and 0.6 times than those in sewers. At least 14 genera and 18 species of bacteria showed significantly distinction between channels and sewers even their main phylum, genus, and species of bacteria communities was Proteobacteria (∼70.3%), Acinetobacter (∼22.3%), and Pseudomonas fragi (∼13.8%), respectively. The structural characteristics and bacterial function caused the difference between channels and sewers. Overall, this study revealed the intrinsic and essential differences of channels and sewers, providing basic and meaningful data for rural sewage collection systems decision.

Sewage and construction waste in rural areas are urgently needed to be effectively treated with low cost as the higher environmental demand and lower economic level in rural areas. In this study, unpowered baffle rural sewage reactors filtered with different construction wastes, autoclaved aerated concrete (ALC), composite mortar (CM), and red brick (RB), were established and operated to achieve the cooperative governance of rural sewage and rural construction wastes. The pollutant removal effect and bacterial communities were revealed and the mechanism of pollutant removal caused by construction wastes was discussed. Unpowered baffle rural sewage reactors filtered with construction wastes had evident removal effect on COD (31.57%-55.07%) and SS (27.57%- 41.36%) during the 3 h retention time and cement based construction wastes (ALC and CM) showed evident TP removal effect (16.71%-35.26%). The bacterial communities of construction wastes (e.g. Chlorobium, Coma-monas, and Acinetobacter) were complex and differed with waste type. However, the pollutant removal related functions of the bacteria on different construction wastes were similar. The different pollutant removal effect of construction wastes was mainly caused by their physicochemical characteristics, but not their bacterial com-munity characteristics. ALC and RB can be used to COD removal, CM can be used to SS removal, and ALC and CM can be used to TP removal in rural sewage treatment. Overall, this study provided an effectively and low-cost method to co-governance of rural sewage and rural construction wastes which is suitable for rural areas and has development potential.

Pyrite tailings can cause serious pollution to the surface water as the strong acidity, high iron and sulfate concentration in the leachate. The bacterial communities of pyrite tailings polluted area were still unclear which could restrict the recognition of the pyrite tailings pollution effect and further impede the development of microbial or ecology treatment technologies. In this study, the bacterial communities in the polluted area of pyrite tailings, from the upstream, pollutant source, and to the downstream, were analyzed with Illumina HiSeq sequencing. Results showed that Acinetobacter and Flavobacterium were abundant in the water and sediment of upstream and downstream while Bacteroides, Lactobacillus, and Akkermansia were abundant in the pollutant source. Sulfur-metabolizing or iron-metabolizing bacteria extensively existed in the polluted area in which Acidiferrobacter, Ferrithrix, and Desulfovibrio played crucial roles on the whole communities. Sulfur-metabolizing bacteria (e.g. Thiomonas, Sulfurospirillum, and Desulfobulbus) and iron-metabolizing bacteria (e.g. Ferrimicrobium, Ferrithrix, and Ferrovum) were introduced to the river polluted by pyrite tailings. Pyrite tailings can remarkably change the physicochemical characteristics and bacterial communities of river water and sediment.

High cost of sewer systems usually restricts the sewage collection in rural areas. Many rural areas take traditional sewer scheme whose private-secondary-main sewer diameter is 110-200-300 mm without hydraulic calculation and increased the total cost of sewers. The rational utilization of small diameter sewers might contribute to sewer cost reduction. In this study, rural sewer length and cost models were established taking sewer diameter, household number, and length/width ratio of village as parameters to evaluate the cost benefits of using small diameter sewers. Hydraulic calculation of sewers was applied by Storm Water Management Model to ensure the small diameter sewers were feasible. The results indicate that household number and length/width ratio cause obvious impact on sewer length and cost. Main sewer with 200 mm diameter is suitable for the village with less than 1000 households. Using small diameter sewers can reduce the sewer cost by 6-15% compared with traditional sewer scheme and 110-110-200 might be the better scheme to rural areas because of the low cost (including construction cost and operation and maintenance cost) and high tolerance of sewage flow fluctuation. This study provided the suitable diameter of rural sewers based on cost model and hydraulic calculation which might be helpful for the application of rural sewers.

Rural sewers are applied widely to collect rural sewage and biofilm characteristics in rural sewers may be different with municipal sewers. The succession of bacteria communities, sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) need to be studied since rural sewers have a potential risk of sulfide and methane accumulation. In this study, lab-scale rural sewer facilities were established to analyze the characteristics of sewer biofilm and the generation of sulfide and methane. The results indicate that the variation tendency of biofilm thickness in rural sewers was different with municipal sewers. Time-based bacterial succession existed in rural sewer biofilms and the predominant genus was changed from Acinetobacter (approximately 19.10%) to Pseudomonas (approximately 12.61%). SRB (mean 1.49 × 106dsrA copies/cm2) were abundant than MA (mean 2.57 × 105mcrA copies/cm2) while MA were eliminated gradually in rural sewer biofilms. The tendency of sulfide and methane generation was similar with the number variation of SRB and MA, indicating sulfide accumulation might be more serious trouble than methane accumulation in a long-run rural sewer. Overall, this study deeply analyzed the succession of rural sewer biofilms and found that MA and methane were automatically inhibited in rural sewers.