Activated sludge (AS) wastewater treatment generates substantial excess sludge which needs to be discarded and thereby increasing operational costs. Extracellular polymeric substances (EPS) within AS present a potential resource for recovery, reducing sludge volume and mass while adding value. Achieving this goal requires a better characterization of EPS, as the relationship between its composition and the microbial communities responsible for its production remains insufficiently understood. Here, we analysed extracted EPS from 16 wastewater treatment plants across 13 countries and 5 continents and found that alkaline extractable EPS yields varied widely (2.81–18.5 wt.% VSS). The microbial community composition of abundant species varied across plants and particularly across continents and did not correlate to the EPS yield. Only sludge retention time had a significant correlation with the EPS yield (p < 0.005). Traditional colorimetric assays failed to detect compositional trends of the EPS, but Fourier Transform Infrared (FTIR) analysis indicated that extracted EPS from biological phosphorus removal systems had higher lipid and polysaccharide content, while chemical phosphorus removal systems had higher relative protein content. Thus, FTIR proved effective for distinguishing extracted EPS composition, demonstrating its potential as a high-throughput characterization tool. These findings highlighted that the wastewater treatment design and operation may shape the functional groups in EPS when using the alkaline method. More investigations are needed to find possible correlations between the composition of extracted EPS and the microbial community structure. Overall, the study presents a baseline for the amount and overall composition of biopolymers that can be extracted from global AS plants for recovery.

The recovery of C, N, and P elements by sludge biorefinery potentially reduces operation costs and increases the extra benefits. Herein, we analyzed the elemental stoichiometry of C, N, and P and functional microbiome involved in enzymatic anaerobic fermentation. Enzymatic hydrolysis was observed to increase the release of C, N, and P into the sludge supernatants by 21.8 %–26.3 %. Metatranscriptome analysis indicated that enzymatic pretreatment enhanced the metabolism of the organic carbon degradation, ammonium conversion, and P solubilization in subsequent fermentation. Specifically, enzymatic pretreatment enhanced endogenous carbon hydrolase activity by 48.4 %–72.7 % and upregulated intra-C metabolic pathways, such as glycolysis and pyruvate metabolism. Ammonium transport and conversion were significantly increased by 4–6 fold, stimulating the synthesis of glutamine and endogenous amino acids. Additionally, enzymatic hydrolysis promoted phosphatase secretion and enhanced bacterial P uptake. These effects improved the recovery of C, N, and P as dentification carbon source and struvite by 13.7 %–41.8 % and the dry sludge production was reduced by 24.3 %–28.1 %. Life cycle assessment (LCA) indicated the shift of CO₂ emissions from net positive to net negative levels as compared to the conventional A²/O process. This study offers valuable insights into the redistribution and metabolism of various elements involved in the enzymatic anaerobic fermentation, and proposes the potential strategy to recovery C, N, and P from sewage via sludge biorefinery.

The post-pandemic world still faces ongoing COVID-19 infections, although international travel has returned to pre-pandemic conditions. Wastewater-based epidemiology (WBE) is considered an efficient tool for the population-wide surveillance of COVID-19 infections during the pandemic. However, the performance of WBE in post-pandemic era with travel restrictions lifted remains unknown. Utilizing weekly county-level wastewater surveillance data from June 2021-November 2022 for 222 counties in 49 states (covering 104 million people) in the United States of America, we retrospectively evaluated the correlations between SARS-CoV-2 RNA (CRNA) and reported cases, as well as the impacts of international air travel, demographics, socioeconomic aspects, test accessibility, epidemiological, and environmental factors on reported cases under the corresponding CRNA. The lifting of travel restrictions in June 2022, shifted the correlation between CRNA and COVID-19 incidence in the following 7-day and 14-day from 0.70 (IQR: 0.30–0.88) in June 2021-May 2022 (pandemic) to 0.01 (IQR: -0.31–0.36) in June-November 2022 (post-pandemic), and from 0.74 (IQR: 0.31–0.90) to -0.01 (IQR: -0.38–0.45), respectively. Besides, after lifting the travel restrictions, under the same CRNA, the reported case numbers were impacted by many factors, including the variations of international passengers, test accessibility, Omicron prevalence, ratio of population aged between 18 and 65, minority vulnerability, and healthcare system. This highlights the importance of demographics, infection testing, variants and socioeconomic status on the accuracy and implication of WBE to monitor COVID-19 infection status in post-pandemic era. Our findings facilitate the public health authorities to dynamically adjust their WBE-based tools/strategies to the local contexts to achieve optimal community surveillance.

Soil amendments and microbial inoculants can affect plant growth, water retention, and crop resilience. This study investigated the effects of two amendments, extracellular polymeric substances (EPS) and biochar, with and without bacterial inoculation, on maize (Zea mays) growth, irrigation needs, and physiological responses. Maize was cultivated in soil with 2.5 % and 5 % (w/w) of wet EPS (Kaumera®) or biochar and inoculated with a bacterial consortium consisting of Arthrobacter nicotinovorans EAPPA and Rhodococcus sp. EC35.

EPS-treated plants exhibited significantly higher shoot biomass, larger stem thickness, while soil plant analysis development (SPAD) values suggest improved nutrient availability and photosynthetic efficiency. In non-inoculated plants, EPS supplementation increased shoot dry biomass by 78 % and stem thickness by 9 % compared to control plants grown without amendments. This enhancement strongly correlated with nutrient uptake, especially in plants supplemented with 5 % of EPS. Particularly, Mg and Ca concentrations increased by 195 % and 73 %, respectively, compared to non-amended controls. Inoculation further amplified these benefits, underscoring its key role in plant development and resilience. In contrast, biochar-treated plants exhibited reduced growth, suggesting stress effects at the tested addition doses. Electrolyte leakage, a key indicator of plant stress, was significantly lower in soils amended with EPS, suggesting that EPS provides a protective effect to the plants. EPS also demonstrated remarkable water retention benefits, reducing irrigation requirements by 30 % with 5 % of EPS application, compared to 9 % reduction with biochar. The use of EPS, combined with microbial inoculants, represents a sustainable agricultural strategy for optimizing maize production in water-limited environments.

>50 % of the organic matter in sewage consist of particulate chemical oxygen demand (pCOD). This study used 250 μm fluorescent microbeads, 130±58 μm microparticles and 100 nm nanobeads to simulate sewage particles, and investigated the fate of these particles under both plug flow feeding and aeration phases in an aerobic granular sludge (AGS) system. Filtration performance was dominantly influenced by the particle size rather than the upflow velocity (V_upflow). The microbeads exhibited 95±3 % filtration efficiency with obvious accumulation around the AGS bed bottom, even as slight fluidization started at the V_upflow of 5.0 m·h^-1. In contrast, the nanobeads filtration efficiency was significantly lower (43±6 %). During the aeration phase, the attachment efficiency increased with the decrease of particle size. The microbeads attachment efficiency variated between 39–49 %, whereas the microparticles and nanobeads achieved better attachment of 89.4–95.2 % and 98.8–99.3 %, respectively. Furthermore, aeration batch tests showed both nanobeads and the irregular microparticles attachment by AGS was strong, and the detach-attach of nanobeads/microparticles between different sized AGS was very limited duration aeration. This work provides insight into the fate of particles in AGS system. The optimal sludge treatment was also evaluated in the scope of this removal of non-biodegradable, and potentially harmful particles.

The emphasis on phosphorus removal and recovery from wastewater treatment plants has intensified in recent years due to the urgent need to reduce dependency on nonrenewable phosphorus reserves. Enhanced biological phosphorus removal (EBPR), driven by a diverse community of polyphosphate-accumulating organisms with distinct metabolic capabilities, offers several advantages over chemical precipitation methods. These benefits include reduced chemical use, lower sludge volumes, decreased reliance on costly chemical precipitants, and improved phosphorus recovery quality. Recent advancements in recovery technologies now enable efficient phosphorus extraction from digester supernatant, dewatered digested sewage sludge, and sewage sludge ash, each yielding different recovery efficiencies. Despite these advances, a comprehensive assessment of the phosphorus recovery potential from these target streams in conjunction with EBPR remains crucial and has yet to be fully explored.

Extracellular Polymeric Substances (EPS) are ubiquitous in biological wastewater treatment (WWT) technologies like activated sludge systems, biofilm reactors, and granular sludge systems. EPS recovery from sludge potentially offers a high-value material for the industry. It can be utilized as a coating in slow-release fertilizers, as a bio-stimulant, as a binding agent in building materials, for the production of flame retarding materials, and more. P recovered within the extracted EPS is an intrinsic part of the recovered material that potentially influences its properties and industrial applications. P is present in EPS in different speciation (e.g., P esters, poly-P, ortho-P, etc.). Such P species are already intensively used in the chemical industry to enhance thermal stability, viscoelasticity, emulsification, water-holding capacity, and many other properties of some natural and petroleum-derived polymers. The translation of this knowledge to EPS is missing which prevents the full utilization of phosphorus in EPS. This knowledge could allow us to engineer EPS via phosphorus for specific target properties and applications. In this review, we discuss how P could affect EPS properties based on experiences from other industries and reflect on how these P species could be influenced during the EPS extraction process or in the WWTPs.

Municipal wastewater treatment plants are a ubiquitous source of microbial biomass for PHA production. Technological feasibility of directly using municipal activated sludge (WAS) for a PHA accumulation bioprocess is demonstrated in the literature. However, PHA contents and yields may be lower due to a coexistence of PHA-storing and non-PHA-storing microorganisms in WAS. This work focused on metabolic principles for stimulating selective growth of PHA-storing microorganisms during a PHA accumulation bioprocess to enhance PHA productivity. Two model substrates, butyrate and acetate, were used to evaluate conditions and principles that may regulate this selective growth response. Conditions promoting selective growth of the PHA storers were consistently observed in the fed-batch PHA production process fed with butyrate. Productivity was increased to 4 times more PHA produced over 48 h, wherein PHA contents and average yields were improved from 0.39 gPHA/gVSS and 0.25 gCODPHA/gCOD to 0.61 gPHA/gVSS and 0.47 gCODPHA/gCOD, respectively. Respiration monitoring and mass balances, with metabolic modelling, suggest that expected underlying differences in ATP yields between two tested substrates are the main mechanistic drivers of the observed selective growth. This study proposed that if conditions are created such that ATP is produced in sufficient excess of the demands for PHA storage and cell maintenance, then those PHA storers will further grow concurrently. The selective microbial growth allows extra conversion of substrates into PHA. These principles, concerning the metabolic basis of the PHA production pathway, provide a foundation that can be applied to a range of substrates or substrate mixtures for enhanced PHA accumulation.

Polyhydroxyalkanoate (PHA) production is a promising technology fostering the spread of the circular bio-economy approach. However, the environmental implication of the process is usually neglected. This paper shows the results of a membrane-based PHA production pilot plant fed with no-pretreated waste activated sludge (WAS). The system was monitored for effluent water quality, nitrous oxide (N₂O), and PHA production by dynamic accumulation over a long-term period to assess the consistency of the results over several fluctuations. The experimental study was characterized by three C/N ratios of 9, 4.5, and 4 g COD/g N. The system achieved a stable and high removal efficiency for carbon and nitrogen (96.3 ± 2.6 % and 89.9 ± 6.7 %, respectively), despite the only legislation limit respected being the biological oxygen demand concentration discharge limits imposed by 2020/741/EU. Low N₂O gaseous and liquid concentrations were achieved over the 200-day experimental period, never exceeding 0.52 mg N₂O-N/L. Despite the high concentration, the N₂O emission factor accounted for only 0.21 ± 0.14 % of the influent nitrogen. Finally, the system produced an average of 36.3 ± 1.8 % g PHA/g VSS with a storage yield of up to 0.42 g COD_PHA/g COD_VFA. The system revealed a high stability over a long-term experimental period, achieving a considerable amount of PHA while maintaining a low N₂O emission. Promising effluent water quality was achieved, highlighting the potential of applying the water reuse practices.

The hydrolysis of structural extracellular polymeric substances (St-EPS) is considered a major limiting step in the anaerobic fermentation of waste activated sludge (WAS). However, the degradation of heteropolysaccharides, characterized by complex monomers of uronic acids and neutral saccharides in St-EPS, has rarely been reported. In this study, microbial-produced xanthan-like heteropolysaccharides, characterized by a blue filamentary film, were identified. The xanthan-producing bacteria comprised ∼7.2% of total genera present in WAS. An xanthan-degrading consortium (XDC) was enriched in an anaerobic batch reactor. This consortium could degrade Xanthan for over 90% and disrupt the gel structure of xanthan while promoting methane production from WAS by 29%. The xanthan degradation network consisting of extracellular enzymes and bacteria was elucidated by combining high-throughput sequencing, metagenomic, and metaproteomic analyses. Five enzymes were identified as responsible for hydrolyzing xanthan to monomers, including xanthan lyase, β-D-glucosidase, β-D-glucanase, α-D-mannosidase, and unsaturated glucuronyl hydrolase. Seven genera, including Paenibacillus (0.2%) and Clostridium (3.1%), were identified as key bacteria excreting one to five of the aforementioned enzymes. This study thus provides insights into the complex conversions in anaerobic digestion of WAS and gives a foundation for future optimization of this process.

Understanding the relative influence of immigration and species sorting in wastewater treatment systems is essential, as bacteria in influent wastewater can significantly impact treatment system functionality. This study investigated the contribution of immigration to the community assembly of different-sized microbial aggregates in a full-scale aerobic granular sludge (AGS) system using genome-resolved metatranscriptomics. Our novel analysis revealed that negative-net-growth-rate populations, which persist due to immigration, can exhibit substantial activity and potentially contribute to the AGS system’s functionality. The results also highlighted that sulfate-reducing and fermenting bacteria, along with some nitrifiers and glycogen-accumulating organisms (GAOs), were more active in the influent wastewater, serving as a continuous source of both beneficial and competing immigrants to the AGS system. Granular sludge (size >0.2 mm) demonstrated a robust capacity to resist immigration effects from competing immigrants, whereas flocculent sludge (size <0.2 mm) was more susceptible. Importantly, flocculent sludge harbored functional microbial groups such as active nitrifiers and fermentative polyphosphate-accumulating organisms (PAOs) belonging to Ca. Phosphoribacter, while granular sludge enriched for active conventional PAOs such as Ca. Accumulibacter. These findings provide valuable insights for engineers to design and operate AGS systems by optimizing microbial aggregate sizes and emphasizing the importance of influent microbial characterization in the design of wastewater treatment plants to enhance the functionality and activity of AGS systems.

The implementation of mainstream anaerobic ammonium oxidation (anammox) can facilitate the realization of carbon-neutral wastewater treatment. However, this technology remains challenging owing to the inability to stably provide nitrite. In this study, we developed a novel nitrification and elemental sulfur-based partial autotrophic denitrification/anammox (NS⁰DA) process for mainstream nitrogen removal. The NS⁰DA system consists of a nitrification reactor and a combined elemental sulfur-based denitrification and anammox (S⁰DA) reactor. Each reactor was independently initiated and optimized before being integrated. At mainstream nitrogen levels (48.5 ± 1.7 mg NH₄⁺-N/L) and 25 °C, the NS⁰DA system achieved 89.1 ± 5.7 % total nitrogen (TN) removal efficiency, with an effluent TN concentration of 5.4 ± 2.8 mg N/L. The system exhibited a low N₂O emission factor (0.23 %), significantly lower than other anammox-based systems. The S⁰DA reactor achieved a nitrogen removal rate of 0.53 kg N/(m³·d) with a short hydraulic retention time (2 h). Anammox accounted for 87.3 ± 7.0 % of the TN removal in the S⁰DA reactor. Isotope experiments and kinetic analysis revealed the cooperation between anammox and denitrification for nitrogen removal. Polysulfides formed in the S⁰DA reactor enhanced the utilization rate of elemental sulfur. High-throughput sequencing identified Thiobacillus and Candidatus Brocadia as the dominant genera of sulfur oxidation and anammox, respectively. The nitrogen and sulfur metabolic pathways were further verified through metagenomic analysis. Overall, the NS⁰DA process provides a stable and efficient nitrogen removal process, minimizing oxygen demand, eliminating organic carbon requirements, and reducing N₂O emissions compared to conventional nitrification/denitrification. This approach offers a promising solution for mainstream nitrogen removal in wastewater treatment.

To meet the increasing drinking water demand, membrane technologies are used to treat previously unavailable water sources. A byproduct of membrane technologies is the concentrate stream, containing valuable resources in higher concentrations. We studied the recovery of iron from different groundwater matrices and anaerobic reverse osmosis (RO) concentrates via precipitation of vivianite and the co-removal of other common groundwater divalent cations Mn²⁺, Mg²⁺ and Ca²⁺ during vivianite precipitation. The formed precipitates were characterized using X-Ray Diffraction and Scanning Electron Microscopy. Vivianite precipitation removed a maximum of 89 % of Fe²⁺ in raw groundwater and 52 % Fe²⁺ from RO concentrate. Substantial co-removal of Mn²⁺ (max 91 %) and limited co-removal of Mg²⁺ (max 7 %) were found, without hindering Fe removal efficiencies or altering morphological changes of the vivianite crystal. In contrast, co-removal of Ca²⁺ occurred at the expense of iron removal, forming amorphous calcium phosphate precipitates. This study shows the potential of vivianite precipitation for iron recovery across a wide range of groundwater matrices and highlights the need for further research to optimize this novel method to treat concentrate streams that are challenging to dispose of.

The removal of nitrogen from the mature leachate landfills is a major challenge. In this study, a novel aeration control strategy combined with step-wise influent addition was used to successfully implement simultaneous partial nitrification, anaerobic ammonia oxidation and denitrification (SNAD) in a single-stage Sequencing Biofilm Batch Reactor (SBBR) used for nitrogen removal and carbon removal of mature landfill leachate with a low C/N ratio. The SNAD process was rapidly initiated by transitioning from aeration to aeration-anaerobic (OA) phases and stabilized under anaerobic-aeration-anoxic (AOA) conditions. The relative abundance of nitrite-oxidizing bacteria (NOB) in the reactor was consistently suppressed (<0.1 %), while the dominant genus of anaerobic ammonium-oxidizing bacteria (AnAOB), Candidatus Jettenia, reached a relative abundance of 10.9 % in the biofilm. During 160 days of operation with influent NH4+-N up to 600.9 mg/L and COD/TIN of 2.3 ± 0.3, the system achieved 98.3 ± 1.1 % nitrogen removal efficiency and effluent TIN of 10.8 ± 1.3 mg N/L, demonstrating robust synergy among ammonia-oxidizing bacteria (AOB), anammox bacteria, and denitrifying bacteria (DNB). This strategy provides a scalable approach for SNAD system cultivation and sustainable treatment of mature landfill leachate.

The role of high-pH conditions in anaerobic digestion (AD) has traditionally been confined to it's use in pre-treatment processes. However, operating AD at elevated pH and alkalinity offers significant advantages, including in-situ upgrading of biogas to biomethane. This study examines the potential and scalability of AD under these conditions (pH ∼ 9.3; alkalinity ∼ 0.5 eq/L). The substrate used was the alkaline waste generated from the extraction of extracellular polymeric substances (EPS) from aerobic granular sludge (AGS), and the inoculum used was a haloalkaliphile microbial community from soda lake sediments. To evaluate the system’s performance, the organic loading rate (OLR) was incrementally increased. The highest methane production obtained was 8.4 ± 0.1 mL/day/gVSadded at a hydraulic retention time (HRT) of 15 days and an OLR of 1 kgVS/day/m3. At this loading rate, methanogenesis became the rate limiting conversion. The maximum volatile solids conversion was 48.1 ± 1.1 %. Throughout the reactor operation, methane purity in the biogas consistently exceeded 90 % peaking at 96.0 ± 0.2 %, showcasing the potential for in-situ biogas purification under these conditions. In addition, no ammonia inhibition was observed, even with free-ammonia (NH3) concentrations reaching up to 14 mM. This study underscores the potential of high-pH anaerobic digestion as a sustainable method for both waste treatment and energy recovery.

Sensor availability and costs are nowadays no longer limiting data gathering at wastewater treatment plants (WWTPs). However, one should be aware that a higher amount of measured data gathered does not necessarily imply that also more information is obtained. In this light, this contribution assesses the general applicability and the added value of a structured experimental design approach for planning measurement campaigns at WWTPs, in view of mass-balance-based data reconciliation. To this end, the results from full-scale WWTP case studies available in the literature were compared to those obtained with the developed structured experimental design procedure. Planning measurement campaigns comprises the selection of (additional) measurements to meet a pre-set main goal. The need for a structured experimental design procedure replacing past expert judgment approaches became clear from the fact that three out of five case studies available in the literature failed to meet the main goal and/or performed unnecessary additional measurements. Translating the main goal into specific key variables was found essential in this respect. The general applicability of the procedure was proven with three outcomes. First, the procedure, involving well-defined steps, could be applied to different WWTP layouts. Second, it ensured the fulfilment of various main goals. Third, it provided useful outcomes, i.e., optimal measurement campaigns, which reduced the need for additional measurements (40-70% less) compared to expert knowledge approaches, hence more information could be obtained with less analytical data. Overall, the experimental design procedure proved a fast and useful tool ensuring the success of subsequent mass-balance-based data reconciliation.

Water treatment facilities are bound to incorporate resource recovery in the near future, necessitating novel economic assessments that capture the full economic potential of these systems. This study evaluates three cost calculation methods—Non-allocation, Economic allocation, and Dual allocation— to improve the accuracy of the Levelized Cost for multi-product desalination and brine treatment plants. The methods were tested across three technical scenarios: Sc1) maximum water recovery, Sc2) integrated desalination with brine treatment for resource recovery and Sc3) electricity-based desalination for chemical recovery. Results reveal that the traditional Non-allocation method tends to overestimate production costs by uniformly applying fixed costs across products, leading to inflated levelized costs. The Economic allocation approach reduces the levelized costs of water and other recovered products by up to 81 %, enhancing competitiveness with conventional production methods. The Dual allocation approach is most effective for recovered salts and chemicals, ensuring fair cost distribution and fostering competitiveness with linear systems. Sc2 is the most economically feasible under both novel approaches due to its balanced mix of high-value products and moderate operational costs. These findings suggest that cost calculation methods should align with plant objectives: Economic allocation for scenarios prioritizing water recovery and Dual allocation for maximizing the value of salts and chemicals. This study provides a foundation for tailored economic assessments and guides plant design and investment decisions.

Aerobic granular sludge (AGS) process is an effective wastewater treatment technology for nutrient and organic matter removal and is being widely applied worldwide. To date, its performance in removing organic micropollutants (OMPs), particularly under wet weather conditions when operation differs, remains poorly understood. This study evaluated the occurrence and removal of OMPs, including 19 pharmaceuticals and 2 industrial compounds, in a full-scale AGS plant during one year under both dry and wet weather conditions. Under dry weather conditions, influent concentrations of 5 pharmaceuticals and 1 industrial compound exceeded 1 μg L−1. Rainfall resulted in diluted OMP influent concentrations, but also caused a significant increase in the influent load of 6 OMPs with positively charged functional groups, likely due to mobilization of sewage sediments that had adsorbed these OMPs. Under dry weather conditions, average removal efficiencies of 14 compounds were greater than 20 %, with 6 of these compounds detected in the sludge phase, and thus likely removed through sorption. Under wet weather conditions, OMP removal efficiencies decreased by 8 % to 38 %. Shortened aeration reaction time significantly reduced (p-value<0.05; R2>0.5) the removal of 8 potentially biodegradable compounds, while the impact on sorption-driven removal was limited for 6 compounds. Effluent OMP load increased under wet weather conditions, mainly due to reduced removal efficiency, rather than the discharge of OMPs adsorbed onto suspended solids. Under dry weather conditions, the AGS plant exhibited comparable or slightly higher OMP removal efficiencyies than activated sludge plants; however, differences in performance under wet weather conditions remain unclear due to limited data on activated sludge systems. Overall, this study is the first to assess OMP removal in a full-scale AGS plant under wet weather, showing the impact of increased flow on the sorption and biotransformation of OMPs.

城市污水集中收集率是城市污水系统运行效率的关键指标，城市污水污染物排放量是计算城市污水集中收集率的必需参数，但城市污水系统较高溢流量和缺乏溢流监测带来计算城市污水排污量的困扰。为此，应用城市污水系统模型和用水、污水处理、常住人口数等常规市政数据，首次提出了根据污水处理厂进水流量和负荷计算城市污水污染物排放量和污水集中收集率的2种方法。以面积约110 km2、常住居民近100×104 人口的城区污水系统为例，展示了应用2种方法的所需数据、具体步骤和计算结果，分析了2种方法各自的适用性。对流动人口、工商业活动和人日排污量等因素对城市污水污染物排污量的影响和估算进行了讨论。2种方法对当下国内和国外一些国家的城市污水排污量、污水集中收集率的计算和城市污水系统运行效率的评估，具有现实意义。

The centralized collection rate of urban sewage is a key indicator of the operational efficiency of urban sewage systems, urban sewage pollutant loading is an essential parameter for calculating the sewage collection ratio. The high overflow of urban sewage systems and lack of monitoring data pose difficulties in calculating sewage collection ratio. By using the urban sewage system model and regular domestic water consumption and sewage treatment information, this study first time proposed two methods, which were based on the influent flow and pollutant loadings of the sewage treatment plant to calculate the urban sewage pollutant loadings and sewage collection ratio. The applicability of two methods was demonstrated including the required data, specific steps, and calculation results by a case of an urban area with almost 110 km2 square meters and nearly 100×104 inhabitants in a city in the Yangtze Delta area. The applicability of each method was discussed. Furthermore, the effects of the commuters, industry and commercial activities, personal discharge load on the estimation of sewage collection ratio in the cities at different levels of economic development are discussed and analyzed. The methods introduced in this study had practical significance for calculating the sewage collection ratio and evaluating the operation efficiency of urban sewage systems in China and part of the other countries.

The authors wish to make a rectification of authorship, adding Dr. Peter. J.T. Verheijen as an author. Dr. Peter. J.T. Verheijen (ORCID 0000-0003-2649-1189) introduced the methodological approach regarding statistics and data reconciliation on which this paper was built, was actively involved in the formal analysis, the software and the reviewing and editing of the original drafts. The correct author list reads as follows: Q.H. Le1, P.J.T. Verheijen2, P. Carrera1, M.C.M. van Loosdrecht2, E.I.P. Volcke1* 1 BioCo research group, Department of Green Chemistry and Technology, Ghent University, 9000 Ghent, Belgium 2 Department of Biotechnology, Delft University of Technology, 2600 AA Delft, The Netherlands> *Corresponding author: The authors sincerely apologise for this mistake, arising from a most unfortunate miscommunication.Quan Hong Le: Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft, Writing-review & editing Peter J.T. Verheijen (ORCID 0000-0003-2649-1189): Formal analysis, Methodology, Software, Supervision, Writing – original draft, Writing-review & editing Paula Carrera (ORCID ID 0000-0003-0893-5663): Investigation, Validation, Visualization, Writing-review & editing Mark C.M. van Loosdrecht (ORCID ID 0000-0003-0658-4775): Conceptualization, Supervision, Writing-review & editing Eveline I.P.