Rural Domestic Wastewater Treatment Research Articles

Occurrence of micropollutants in rural domestic wastewater in Zhejiang Province, China and corresponding wastewater-based epidemiology analysis

By 2021, rural regions in China were occupied by over 500 million residents, generating an annual volume of 19.5 billion m3 of rural domestic wastewater (RDW). This study aimed to investigate the occurrence and removal of micropollutants (MPs) in RDW treatment facilities and to perform a corresponding wastewater-based epidemiology analysis (WBE). Our findings indicated the significantly high levels of influent MPs, particularly pharmaceuticals, such as ofloxacin and diclofenac being most prevalent (ranging from several to tens of μg/L) across different facilities. After various treatments, regular water indexes in the effluent, like NH3 -N and COD, have basically satisfied the local discharge standard. However, the concentration of certain dominant MPs in effluent remained notably high, ranging from hundreds of ng/L to several μg/L. The risk quotients of MPs like diclofenac, ciprofloxacin, ofloxacin, sulfamethoxazole, diuron, and isoproturon were all above 1 in the effluent, signifying significant hazards to aquatic organisms. The quantitative meta-analysis revealed higher average standardized removal efficiency for membrane bioreactor (MBR) treatment (-11 %) compared to anaerobic/anoxic/aerobic (A2O) treatment (11 %), indicating the higher efficiency of MBR treatment in outperforming the A2O as a secondary treatment. Additionally, employing biofilter as a tertiary treatment proved to be more effective as compared to flocculation-air flotation and artificial wetlands. Moreover, the results of WBE analysis showed that diclofenac and ofloxacin emerged as the most commonly used pharmaceuticals (of seven), with consumption levels recorded at 1222 and 517 mg/(d·103 capita), with daily defined doses per day per 103 capita of 12.2/1000 and 1.29/1000, respectively. This study addresses the existing knowledge gaps regarding the occurrence and removal of MPs in RDW and offers valuable insights into pharmaceutical consumption patterns in rural regions, thereby improving our understanding of public health.

Pilot–scale vertical continuous–flow reactors applied to treat rural domestic wastewater at low temperature via aerobic granular sludge

A pilot–scale vertical–flow continuous flow reactors (VF–CFR) was investigated for the treatment of rural domestic wastewater in the cold areas of Northeast China. VF–CFR helps in the creating of aerobic granular sludge (AGS), which improves the sludge concentration and removal efficiency of pollutants. VF–CFR achieved a high removal efficiency of Chemical Oxygen Demand (COD), Ammonia Nitrogen (NH3−N), Total Nitrogen (TN) and Total Phosphorus (TP) with 90 %, 94 %, 75 % and 93 % under the condition of sharp fluctuation of influent quality and temperature. The high–throughput sequencing analysis of the AGS revealed that Flavobacterium was a functional bacterium in the AGS process that had the function of heterotrophic nitrification and denitrification. The field–scale experiment confirmed the superiority of VF–CFR in wastewater treatment efficacy and stability. During the experiment, the concentrations of COD, TP and NH3–N in effluent at different temperatures were well met with the first–class A discharge standard of China (GB 18596–2001). However, there was a risk of exceedance exists in the reduction of TN removal under low temperature conditions.

Exploration of sustainable driving path of rural domestic wastewater treatment-from the perspective of life cycle assessment

Most rural wastewater treatment facilities require electricity to maintain operation. Traditional fossil energy consumption increases the environmental load and greenhouse gas emissions. Wind-solar power generation is widely recognized as a renewable energy technology. However, conventional wind-solar power systems need batteries to store energy, which can lead to secondary pollution. Additionally, the alternating aerobic and anaerobic process were crucial for nitrogen and phosphorus removal, and some distributed wastewater treatment systems do not require continuity operation. Therefore, this study reports on a wind–solar power generation mode without batteries (Mode-II) to control and drive a bioecological rural domestic wastewater treatment system with a scale of 0.5 m³/day. By logic control, the inspired combination of power generation capacity and treatment process requirements was realized. The effluent CODcr, NH4+-N, and TN concentrations were 14.63 ± 7.02, 1.39 ± 1.63, and 8.65 ± 4.02 mg/L, with removal rates of 89.01 ± 4.15%, 88.58 ± 2.28%, 75.47 ± 8.84%, respectively. From the perspective of environmental load and carbon emissions, based on life cycle assessment theory, this novel approach was compared with the traditional wind–solar power generation driven mode with battery storage (Mode-I) and mains power driven mode (Mode-III). The environmental load and carbon emissions of Mode-II were 1.08 kPt and 2836 kg CO2 eq by end-of-life (25 years), the lowest of the three modes. Compared with the mains power drive mode, the environmental load and carbon emissions of Mode-II can be repayment until years 6 and 2. The supercapacitors and solar panels were the main source of environmental load and carbon emissions for Mode-II. Overall, Mode-II was found to be the most environmentally friendly mode all over the China, which is expected to be promoted in the field of rural wastewater treatment.

Disentangling microbial coupled fillers mechanisms for the permeable layer optimization process in multi-soil-layering systems

The multi-soil-layering (MSL) systems is an emerging solution for environmentally-friendly and cost-effective treatment of decentralized rural domestic wastewater. However, the role of the seemingly simple permeable layer has been overlooked, potentially holding the breakthroughs or directions to addressing suboptimal nitrogen removal performance in MSL systems. In this paper, the mechanism among diverse substrates (zeolite, green zeolite and biological ceramsite) coupled microorganisms in different systems (activated bacterial powder and activated sludge) for rural domestic wastewater purification was investigated. The removal efficiencies performed by zeolite coupled with microorganisms within 3 days were 93.8% for COD, 97.1% for TP, and 98.8% for NH4+-N. Notably, activated sludge showed better nitrification and comprehensive performance than specialized nitrifying bacteria powder. Zeolite attained an impressive 89.4% NH4+-N desorption efficiency, with a substantive fraction of NH4+-N manifesting as exchanged ammonium. High-throughput 16S rRNA gene sequencing revealed that aerobic and parthenogenetic anaerobic bacteria dominated the reactor, with anaerobic bacteria conspicuously absent. And the heterotrophic nitrification-aerobic denitrification (HN-AD) process was significant, with the presence of denitrifying phosphorus-accumulating organisms (DPAOs) for simultaneous nitrogen and phosphorus removal. This study not only raises awareness about the importance of the permeable layer and enhances comprehension of the HN-AD mechanism in MSL systems, but also provides valuable insights for optimizing MSL system construction, operation, and rural domestic wastewater treatment.

Organophosphate esters in rural wastewater along the Yangtze river Basin: Occurrence, removal efficiency and environmental implications

Organophosphate esters (OPEs) discharged from rural domestic wastewater were one of the important sources of OPEs in receiving water bodies, which has posed a potential threat to the ecological environment. However, very little information on the characteristics of OPEs in the rural domestic wastewater is available. Herein, the occurrence, removal efficiency and environmental implication of OPEs in rural domestic wastewater treatment facilities (RD-WWTFs) along the Yangtze River Basin were investigated. Results indicated that the median concentrations of ΣAlkyl-OPEs, ΣHalogenated-OPEs, ΣAryl-OPEs and the total OPE (ΣOPEs) in influents were 28.28, 99.25, 10.22 and 136.84 ng/L, while the median concentrations of them in effluents were 25.80, 141.86, 7.98 and 173.31 ng/L, respectively. Undoubtedly, halogenated OPEs were the most abundant in both influent and effluent, followed by alkyl and aryl OPEs, and they accounted for average proportions of 69.50%, 19.96%and 10.54% for influents, and 78.16%, 16.14%and 5.71% for effluents, respectively. Specifically, tris(2-chloroisopropyl) phosphate (TCPP, median: 55.17 ng/L in influents and 85.75 ng/L in effluents) was the dominant contributor to the ΣOPEs concentrations with average proportions of 37.75% and 47.33% for influents and effluents, respectively. Moreover, the concentration ranks for most OPEs except for aryl OPEs from high to low were upper reaches > lower reaches > middle reaches. However, negative values of tris(2-chloroethyl)phosphate (TCEP, −32.4%), TCPP (−55.4%) and tris(1,3-dichloroisopropyl) phosphate (TDCPP, −26.3%) were observed. The removal rates of alkyl OPEs (10–20%) and aryl OPEs (20–30%) were also not sufficient. Ecological risk values of ΣOPEs showed that there were 2.44% of high risk, 31.7% of moderate risk and 41.5% of low risk for effluents; while 0.00%, 48.8% and 46.3% were exhibited in high, moderate and low risk for influents, indicating that very slight reduction in risk was achieved by the RD-WWTFs.

Countermeasures for rural domestic wastewater based on ecological environment security: a case study of an MBR-integrated process based on the PVDF@ZrO2 flat membrane, China

Abstract The harmonious coexistence of humans and nature has reached a broad consensus in the world. Maintaining the health of the ecological environment is the foundation of the existence and development of human civilization, and is also the inevitable choice for human beings to deal with the global ecological environment crisis. As an important factor affecting ecological stability, rural domestic wastewater has been neglected and not treated effectively for a long time because of its special geographical location and development limitations. In this paper, an integrated process of an MBR was applied to rural domestic wastewater treatment, inside which the modified PVDF@ZrO2 membrane was used to replace the traditional PVDF membrane. A series of membrane analyses and project follow-ups have proven that the hydrophilicity, anti-fouling performance of the membrane, and the treated water quality were improved. Meanwhile, this research enlightens us to pay attention to the overall planning, the maintenance of the pipe network, and the stable investment of funds in the treatment of rural domestic wastewater.

Influence of inoculation ratio on the performance and microbial community of bacterial-algal symbiotic system for rural wastewater treatment.

In this study, co-culture of microalgae and activated sludge in photobioreactors (PBRs) was investigated at different inoculation ratios (0:1, 0.3:1, 0.7:1, and 1.3:1 sludge wt./algae wt.) for rural domestic wastewater treatment under direct solar radiation. Effluent qualities (such as pH, NO2 - , PO4 3- , and NH4 + -N concentrations) were assessed; bacterial and microalgal communities in co-culture system were compared. The microalgal and bacterial biomass fraction played a significant role in the performance and microbial community structure of the treatment system. In reactors with inoculation ratio of 0.3:1 and 0.7:1, the pH exceeded 9 or 10 under solar radiation, which led to some functional bacteria being missing. In the reactor with inoculation ratio of 1.3:1, activated sludge effectively prevented excessive increase in pH in the reactor. Similar observations were made for reactors with inoculation ratios below 1.3:1 by adding sludge halfway through the process. The results show that activated sludge can inhibit excessive increase in pH caused by algal photosynthesis, maintain the activity of nitrite-oxidizing bacteria in PBR, and reduce algae loss with the effluent. PRACTITIONER POINTS: Appropriate fraction of activated sludge can effectively inhibit the excessive increase in pH caused by algal photosynthesis in PBR. Adding activated sludge could maintain the activity of nitrite-oxidizingbacteria in PBR, and reduce microalgae loss with the effluent. Considering the stability of operation and biodiversity in PBR, a 1.3:1 inoculation ratio of activated sludge and microalgae is preferred.

A Modular Coupling System for Efficient Treatment of Rural Domestic Wastewater

A Modular Coupling System for Efficient Treatment of Rural Domestic Wastewater

Performance of the anaerobic baffled reactor for primary treatment of rural domestic wastewater in Iraq

Abstract The purpose of this work is to evaluate the performance of the anaerobic baffled reactor (ABR) for on-site primary treatment of domestic wastewater in rural areas of Iraq. The performance of the three-chamber ABR has been investigated at four different hydraulic retention times (HRTs) ranging from 6 to 36 h. The results showed that the chemical oxygen demand (COD) removal efficiency is enhanced with increasing HRT, where it was recorded at 75, 71, 63, and 56% removals rate of COD at HRTs of 36, 24, 12, and 6 h, respectively. The mean steady-state removals of total suspended solids are 91, 78, 72, and 67% at HRTs of 36, 24, 12, and 6 h, respectively. Also, it was shown that there was low-nutrients removal within the ABR. Consequently, the effluent ABR wastewater needs to be post-treated before being discharged to the receiving water bodies. In general, it is concluded that the ABR could introduce a solution for on-site primary treatment of domestic wastewater in rural communities in Iraq.

Insights into the occurrence, elimination efficiency and ecological risk of antibiotics in rural domestic wastewater treatment facilities along the Yangtze River Basin, China.

China is embarking on the treatment of rural domestic wastewater, but little information on the characteristics of antibiotics in the rural domestic wastewater is available. As one of the most important new-emerging pollutants, antibiotic has been explicitly proposed to be controlled and treated since the fifth plenary session of the 19th Central Committee of the Communist Party of China. Thus, the occurrence, elimination efficiency and ecological risk of antibiotics, as well as conventional wastewater quality parameters were investigated in influents and effluents from 41 rural domestic wastewater treatment facilities (RD-WWTFs) along the Yangtze River Basin. Results showed that elimination efficiencies of routinely monitored conventional pollutants in 33 RD-WWTFs (accounting for 80.5%) were effective based on conventional wastewater quality parameters. Of 39 target antibiotics selected, 26 ones were detected in the influents and effluents with a detection frequency (DF) between 2.4% and 100%. No significant decrease of antibiotics was observed in the effluents compared with that in the influents except chlortetracyclin (CTE) and tetracycline (TCs). The composition characteristics of antibiotics showed regional differences. Among the investigated antibiotics, ofloxacin (OFX), doxycycline (DOX), roxithromycin (ROX) and lincomycin (LIN) were the predominant, totally accounted for a median percentage of more than 60% of ΣAB concentrations in both influents and effluents. Ecological risk values of ΣABs showed that 11 effluents presented high risks (26.8%), 18 ones had moderate risks (43.9%), and the rest 12 ones showed low risks (29.3%). Moreover, oxytetracycline (OXY), norfloxacin (NOR), LIN and ROX was the dominant contributors to the ecological risk values. Overall, the elimination effect of antibiotics was limited in RD-WWTFs along the Yangtze River Basin, which was likely to pose potential adverse impacts on aquatic ecosystems.

Full-scale application and performance of a low-consuming system for decentralized village domestic wastewater treatment

Rural domestic wastewater (RDW) management has always been challenging due to the vast range and decentralized household distribution. This study constructed a full-scale system combined with source-separated pretreatment and terminal bio-eco treatment for a village RDW treating. The process of the application was designed from the perspective of low consumption in energy and device. The performance of the biological units consisted of an anoxic filter (ANF) and multi-stage waterwheel driving rotating biological contactors (ms-wdRBCs) was investigated. ANF/ms-wdRBCs with HRTANF 12 h and HRTms-wdRBCs 1.5 h performed best in pollutants' removal at 200% reflux ratio (RR). The maximum flow rate (FR) that the system could burden is 0.6 m3/h with a 42% increase from the designed FR 0.42 m3/h, which shows the potential in coping with the future increase of individual RDW generation. Meanwhile, the source separation and primary treatment could effectively reduce the pollutant load entering the biologic units. In the four consecutive seasons' operating, 84.9 ± 3.1% COD, 87.6 ± 3.5% NH4+-N, 44.2 ± 3.1% TN, and 28.2 ± 2.0% TP are removed, respectively. Seasonal water temperature (WT) variation is found to have a remarkable effect on biological treatment. NH4+-N removal is found the most sensitive index of pollutant removal to RR, FR, and WT variating. The system has shown the reliability of the year-round running. The full-scale application could serve as a sustainable prototype for the village RDW treatment.

Insights into the Occurrence, Elimination Efficiency and Ecological Risk of Antibiotics in Rural Domestic Wastewater Treatment Facilities Along the Yangtze River, China

Insights into the Occurrence, Elimination Efficiency and Ecological Risk of Antibiotics in Rural Domestic Wastewater Treatment Facilities Along the Yangtze River, China

Enhancement of algae ponds for rural domestic sewage treatment by prolonging daylight using artificial lamps

Algal ponds (APs) are widely used as treatment facilities for domestic sewage in sparsely populated rural areas. However, few AP studies have focused on daylight length to enhance pollutants removal. In this study, four algae ponds were set up, daylight was prolonged by 0, 2, 4, and 6 h with an illuminating intensity of 3000 lx. The highest removal efficiencies of total nitrogen, ammonium, and total phosphorus were 37.36%, 41.20%, and 21.56% due to the highest microbial abundance under optimum conditions (2 h PD), respectively. Excessive PD (4 h and 6 h) could inhibit the removal abilities. PD also increased the maximum relative electron transport rate of algae, leading to an increase in the photosynthetic capacity of APs. Meanwhile, the high microbial abundance indicates that chemoheterotrophic bacteria are the main influencing factor for the removal of nitrogen and phosphorus by the APs. Moreover, the system with PD using artificial lamps was proven to be feasible for engineering applications and potentially utilized in rural domestic wastewater treatment.

Constructed wetlands for rural domestic wastewater treatment: A coupling of tidal strategy, in-situ bio-regeneration of zeolite and Fe(Ⅱ)-oxygen denitrification

Constructed wetlands (CWs) offer a promising method to treat domestic wastewater in rural areas, but CWs usually limiting in nitrogen removal and large area. In this study, zeolite and pyrite were used to construct tidal wetlands to address the problems of insufficient oxygen supply and carbon source. The results show that the fully drained wetland achieved the highest ammonia removal load of 34.67 ± 1.72 g/(m2·d) with 8.57 ± 1.13 mg/L of effluent. Pyrite was found to compensate for the lack of carbon source in the denitrification process in half-drained wetland, which achieved a 78.36 ± 5.3% TN removal rate with 7.09 ± 1.85 mg/L effluent concentration. Pyrite released Fe(II) to promote nitrate reduction for denitrification in the subsequent flooded period. Microbial community analysis indicates that the tidal flow constructed wetlands simultaneously achieved nitrification and denitrification by the coupling of in-situ zeolite regeneration and Fe(II) oxidation denitrification.

Effects of Hydraulic Retention Time (HRT) and Packing Height on the Performance of Homemade Ceramsite-Soil Constructed Wetland for Rural Domestic Wastewater Treatment

Effects of Hydraulic Retention Time (HRT) and Packing Height on the Performance of Homemade Ceramsite-Soil Constructed Wetland for Rural Domestic Wastewater Treatment

Experimental Study on the Treatment of Rural Domestic Wastewater Using the Multi-Soil-Layering System Filled with Sludge-Based Biochar

This paper aims to improve the treatment effect of the multi-soil-layering system (MSL) on rural domestic wastewater. For this, sludge-based biochar materials were selected in the experiments to study its impacts on the treatment of rural domestic wastewater using the MSL. The comparative experiments were conducted for the three MSL systems filled with different materials: the sludge-based biochar (a), wood chips (b), and charcoal (c). The results showed that when the sludge-based biochar material was used as a filler, the removal effect of COD, NH4+-N, TN, TP is better than that of wood chips and charcoal, and the removal rates were 80%, 90%, 65% and 92%, respectively, meeting the Grade A standard specified in the Hebei Province Rural Domestic wastewater Discharge Standard (DB13/2171-2015); hydraulic loading rates (HLRs) have a great impact on the removal of pollutants, and the pollutant indicators in the system (a)re affected by the HLRs in different degrees, i.e., NH4+-N>TP>COD>TN from high to low; considering the treatment efficiency and pollutant removal effect, the HLRs should be selected between 800L/(m2·d) and 1200L/(m2·d). It’s concluded finally that the sludge-based biochar material can strengthen the removal effect of the MSL system. This study is of theoretical value for the further research on MSL system and resource utilization of the sludge.

Nitrification, denitrification and anammox process coupled to iron redox in wetlands for domestic wastewater treatment

Constructed wetlands (CWs) is widely used in rural areas as low-cost wastewater treatment technology. However, in rural domestic wastewater treatment using subsurface CWs, the lack of oxygen for nitrification and a carbon source for denitrification is often responsible for low removal of nitrogen. As organic carbon addition requires human and financial investment, which is not suitable for long-term utilization in rural areas. Other electron donors become the preferred choice. Compared to granulated iron materials, the iron scraps with fluffy structure could avoid clogging problem and be effective for nitrogen removal simultaneously. In this study, two CWs were constructed using gravel and iron scraps as substrate, respectively. After 6 months of operation, the total nitrogen and ammonia removal in CWs with iron improved to 71.46% and 70.44%, respectively. Enhancement of 24.08% organic nitrogen removal was observed in iron zone of CWs. Autotrophic denitrifying bacteria became the dominant genus in the system. Traditional nitrification-denitrification and anaerobic ammonia oxidation process could be the primary nitrogen removal pathway in CWs with iron. The presence of iron-reducing bacteria (Anaeromyxobacter, Geobacter, and Geothrix) provided the possibility of iron oxide reduction reactions. Electron transfer and products in iron oxidation and reduction processes significantly affected on nitrogen removal to complete the coupling of iron cycle and nitrogen cycle in CWs.

Distribution of Antibiotic Concentration in Domestic Wastewater Treatment Facilities in Villages and Towns

Antibiotics discharged into the environment cause increased environmental resistance. Four types of antibiotics (quinolones, tetracyclines, macrolides, and β-lactams) were selected for this study. In a comparison with the municipal wastewater plant, the concentration and removal of antibiotics in influent and effluent of domestic wastewater treatment facilities of different scales in villages and towns was investigated using high-performance liquid chromatography (HPLC) and tandem mass spectrometry (MS). The results showed that the highest amount of ofloxacin in rural wastewater treatment facilities reached 32663.5 ng·L-1. Due to the different situations of influent fluctuation, discharge requirements, and management between urban and rural wastewater plants, only 33% of the rural domestic wastewater facilities detected an antibiotics removal rate of more than 60%. The effective removal of some antibiotics can be achieved when the rural domestic wastewater treatment facilities maintain the standard discharge of conventional pollutants.

Effects of reaction conditions on products and elements distribution via hydrothermal liquefaction of duckweed for wastewater treatment

Wastewater treatment by duckweed is a naturally sustainable technology. However, its development is limited due to the lack of a follow-up treatment of duckweed. The duckweed was proposed for the treatment of rural domestic wastewater and agricultural wastewater, and it was further processed to produce bio-oil via hydrothermal liquefaction at various temperatures (250 °C–370 °C) and residence times (15–60 min). The highest bio-oil yield of 35.6 wt% was obtained at 370 °C, 45 min. The higher heating value of bio-oil was 40.85 MJ/kg, and the H/C ratio (1.72–1.98) was similar to that of petroleum (1.84). The gas chromatography-mass spectrometry analysis results revealed that the bio-oil mainly consisted of N-heterocycles, cyclic ketones, esters, amides, long-chain hydrocarbons, phenols, and aromatic intermediates. Valuable compounds (3-pyridinol, 2-pyrrolidinone, and its analogues) of high concentration were identified in the water-soluble organic matter. Compared with other materials, this study produced higher-quality bio-oil and water-soluble organic matter.

Management of rural domestic wastewater in a city of Yangtze delta region: Performance and remaining challenges

Wastewater samples from 267 rural domestic wastewater treatment systems in Yangtze River Delta region were collected and analyzed to investigate their treatment performance and identify potential problems. The influent wastewater was mainly affected by the treatment performance of septic tanks, the combined rainwater and wastewater collection, and the pipeline damage. Seven kinds of treatment processes were employed in the studied treatment systems, with constructed wetlands (CWs) being the main process accounting for 66% of all the systems. CWs had the best performance on NH4+-N and chemical oxygen demand removal, anaerobic/oxic (AO)-CWs had the best performance on total nitrogen and total phosphorus removal, and membrane biofilm reactors had the best performance on suspended solids removal. To improve treatment performance, recirculation and aeration are recommended for CWs, while AAO and AO should be combined with CWs. Training to gain more professional skills for the operation staff is needed.