By constructing feature metagenome database of complete ammonia oxidizing bacteria (CAOB), their abundance and diversity in 56water treatment systems, e.g., urban wastewater nitrogen systems and drinking water treatment systems, were quantitatively analysed. The significant influencing factors were determined by statistical analysis and the influential mechanism were analysed. It was revealed that CAOB were accounted for 8.2%~99.6% of the ammonia oxidation community and 1.4%~48.6% of the Nitrospira in the surveyed urban wastewater nitrogen removal systems. Phylogenetic analysis revealed that CAOB metagenome assembled genomes (MAGs) were associated with Ca.Nitrospira nitrosa, with ANI value higher than 94%. CAOB community were more homogeneity than those in drinking water treatment systems, speculating that Ca.Nitrospira nitrosa cluster were specific adaptable to urban wastewater nitrogen removal systems. According to correlation analysis, pH value was significantly positively while COD was significantly negatively correlated with the abundance and diversity of CAOB. They were more likely to be dominant nitrifiers in low NH₄⁺, high sludge retention time, and low dissolved oxygen conditions. In conclusion, this study reveals that Ca.Nitrospira nitrosa cluster are dominant CAOB, and their distribution influencing factors in urban wastewater nitrogen removal systems.

To investigate the overall effects of carbon source types on wastewater treatment plant (WWTP) performance, this study compared the impacts of three external carbon sources—a composite carbon source, sodium acetate and glucose—on the overall operational process. The results demonstrated that different carbon sources led to variations in the metabolic performance of heterotrophic microorganisms. Under the influence of the three carbon sources, the heterotrophic yield coefficients Y_H were 0.703 (composite carbon source), 0.676 (sodium acetate), and 0.889 (glucose), respectively. The heterotrophic decay coefficients b_H were 0.405, 0.433 and 0.775d^-1, while the maximum heterotrophic growth rates μ_mH were 2.146, 3.071 and 6.078d^-1 respectively. Using GPS-X software, a model of the target WWTP was constructed and calibrated. The kinetic parameters under each carbon source were incorporated into the model for simulation. The results indicated that changes in kinetic parameters directly affected the treatment efficiency, energy consumption, sludge production, and greenhouse gas (GHG) emissions of the WWTP. In terms of total nitrogen removal efficiency, the composite carbon source and sodium acetate exhibited more significant advantages, albeit with increased energy consumption and GHG emissions. In contrast, while glucose was more energy-efficient and reduced carbon emissions, it resulted in lower nitrogen removal efficiency and potentially higher sludge production. After considering market pricing, the composite carbon source was found to be a more competitive option for denitrification.

This study integrated biological phosphorus removal into the PN-SAEPD process, establishing a PNPR-SAEPD system. To allocate the limited carbon source reasonably, the experiment gradually adjusted the two-stage anaerobic time ratio from 3:1 (90min:30min) in the S1stage to 1:1 (60min:60min) in the S2 stage, and then to 1:3 (30min:90min) in the S3stage. The study investigated the impact of the two-stage anaerobic time ratio on the conversion of influent organic matter, nitrogen and phosphorus removal performance, and microbial community structure of the PNPR-SAEPD system. The results showed that in the S2 stage, with a two-stage anaerobic time ratio of 1:1, the allocation of inflow organic carbon sources was most reasonable. The average COD consumed by the SAEPD and PNPR reactors for storing internal carbon sources was (89.3±8.4)mg/L and (82.6±7.7)mg/L, respectively. The phosphorus removal contribution of the PNPR reactor was (79.1%±8.5%), creating phosphorus starvation conditions for the subsequent anaerobic stage of the SAEPD reactor. The contribution of DPAOs in the SAEPD reactor to the storage of internal carbon sources was only 15%, consuming (10.1±4.0)mg/L of COD. The relative abundance of DPAOs dropped to 3.01%, enhancing the synergistic denitrification of DGAOs and AnAOB. Integrating biological phosphorus removal into the PN reactor improved the stability of short-cut nitrification, with the relative abundance of NOB gradually decreasing from 3.86% to 0.64% and NAR maintaining at around (82.1%±4.0%). In the S2stage, the superior PN performance of the PNPR reactor and the EPD pathway dominated by DGAOs in the SAEPD reactor provided sufficient electron acceptors for AnAOB. The anaerobic ammonium oxidation denitrification contribution remained at about (81.8%±3.6%), the total nitrogen removal rate was maintained at around (88.3%±1.6%), and the effluent total nitrogen concentration was below 10mg/L. The TP removal rate could reach up to 93.7%, and the effluent TP concentration was basically reduced to below 0.5mg/L.

This study proposes a strategy to inhibit nitrite-oxidizing bacteria (NOB) in the completely autotrophic nitrogen removal over nitrite (CANON) process by alternating long and short operational cycles. During long cycles, in-situ free ammonia (FA) was used to suppress NOB, while in short cycles, substrate inhibition was employed to continuously suppress NOB activity when FA concentrations fall below the inhibitory threshold for NOB. Two sets of SBR, R1 and R2, were operated with different long-short cycle alternation patterns. The results show that both R1 and R2 achieved good nitrogen removal efficiencies (NRE), with R2 slightly outperforming R1. The NRE for R1 and R2 were 78.73% and 85.41%, respectively, while the effluent NO₃^--N concentrations were 14.02mg/L and 7.21mg/L, respectively. At day 64, the specific nitrate production rates (SNPR) of R1 and R2 decreased to 2.88 and 1.95mgN/(gMLVSS·h), respectively, indicating effective suppression of NOB activity. Analysis of extracellular polymeric substances (EPS) revealed that the alternating long and short cycle strategy promoted microbial EPS secretion. The EPS content in R1 and R2 increased from 40.22mg/gVSS at inoculation to 86.41mg/gVSS and 97.79mg/gVSS, respectively. High-throughput sequencing results indicated that the dominant bacterial phyla in the system were Proteobacteria, Bacteroidota, and Planctomycetota. The growth of NOB, represented by Nitrospira and Nitrobacter, was inhibited in both R1 and R2. The relative abundance of Nitrospira decreased from 2.05% in the inoculated sludge to 0.18% in R1 and 0.11% in R2, while Nitrobacter abundance dropped from 1.97% to 0.06% in R1 and 0.05% in R2. Meanwhile, the abundance of AnAOB, (Candidatus_Brocadia) reached 8.92% (R1) and 9.14% (R2), and AOB, (Nitrosomonas) achieved abundances of 4.28% (R1) and 6.56% (R2), establishing a well-coordinated synergy.

An integrated fixed-film activated sludge system (IFAS) was used to treat simulated wastewater with high-strength ammonia and organics in this study. The shortcut nitrification and denitrification coupled with anammox was successfully achieved after 83d operation through stepwise increase of influent ammonia nitrogen concentration (50~300mg/L) and low oxygen control (DO: 0.15mg/L). With the increase of ammonia nitrogen concentration, effluent nitrite accumulated significantly. When the influent ammonia nitrogen concentration increased to 300mg/L, the removal efficiencies of COD, NH₄⁺-N and TN reached 95.3%, 100% and 93.1%, respectively, and the total nitrogen removal loading rate (NRR) reached 0.14kg/(m³·d). The microbial activity test showed that the anammox activity was higher in the biofilm phase, while ammonia aerobic oxidation activity was higher in the sludge phase. With the increase of ammonia nitrogen and COD concentrations, extracellular polymeric substance (EPS) secretion and protein/polysaccharide (PN/PS) increased, promoting stronger impact load resistance and biological stability of the system. Microbial community results found that heterotrophic nitrification and aerobic denitrifier (Acinetobacter), anammox bacteria (Candidatus Brocadia and Candidatus Jettenia) were mainly enriched in biofilm, while partial nitrification bacteria (Nitrosomonas) was distributed in sludge. The sludge-biofilm separation mode facilitates directed proliferation of different nitrogen-removing bacteria. Functional gene annotation (KEGG) suggests that collaborative nitrogen removal in the IFAS system is via heterotrophic nitrification/aerobic denitrification and partial nitrification denitrification/anammox.

The granulation process and pollutant removal performance of aerobic granular sludge (AGS) under conventional and micro-nano aeration modes were investigated, with focus on the roles of extracellular polymeric substances (EPS) and microbial community succession in mediating microstructural responses. Compared to conventional aeration, the micro-nano aeration exhibited superior oxygen mass transfer efficiency and higher hydroxyl radical (·OH) generation, leading to significantly enhanced pollutant removal. Ammonia and chemical oxygen demand (COD) removal efficiencies consistently exceeded95%, while total nitrogen removal remained at a high level of 78.81%. Micro-nano aeration also accelerated AGS granulation, with mean particle sizes surpassing300 μm within20days. XDLVO-based interaction energy calculations indicated favorable aggregation behavior under both aeration regimes. Due to the biofilm-promoting effects of micro-nano aeration system, AGS developed contained higher EPS content under this mode, with Hydrophobic TB-PN playing a key role in forming protein-based hydrophobic networks that promoted AGS granulation. In contrast, AGS stability in the conventional system was primarily maintained via ionic bridging by Ionic TB-PS. Distinct microbial community structures were observed between the two aeration modes. Conventional aeration favored typical denitrifying bacteria, whereas the intensified of micro-nano aeration system led to a proliferation of filamentous taxa, notably Neomegalonema, Thiothrix, and norank_f_Saprospiraceae. These filamentous bacteria contributed to EPS secretion and AGS structural integrity while maintaining stable nitrogen removal performance.

The typical low-C/N municipal wastewater (COD, ammonia, total nitrogen of 258.1, 30.5, 36.8mg/L) in South China was treated by membrane aerated biofilm reactor (MABR) process. By means of synchronously reducing hydraulic retention time (HRT) and increasing aeration pressure, the results showed that effluent COD met the discharge standard of level I class B, and effluent ammonia and total nitrogen met the discharge standard of level I class A at the individual HRT and selected aeration pressure combinations of 24h and 5kPa, 12h and 7kPa, 8h and 8kPa, 6h and 10kPa, 4h and 12kPa. The maximum surface and volume load removal of COD, ammonia nitrogen, total nitrogen achieved 19.2, 2.26, 2.53g/(m²·d) and 1.6, 0.19, 0.21g/(L·d), respectively, which showed significantly better performance of MABR than conventional biofilm and activated sludge processes. Oxygen transfer characterization showed that biofilm significantly enhanced the oxygen transfer rate (19.5~40.6gO₂/(m²·d)), oxygen transfer efficiency (30.9%~59.8%) and aeration efficiency (34.2~48.3kgO₂/kWh) of the investigated hollow fiber aeration membrane, implying the autonomous respiration of biofilm (i.e., automatically withdrawing the oxygen demand via aeration membrane to match the oxygen consumption caused by the influent load of ammonia nitrogen and COD). Thus, there is a significant potential for reducing pollution, carbon emission, energy consumption and cost for municipal wastewater treatment via MABR coupling intermittent aeration, synchronous coagulation, periodical detachment of excessive thick outer biofilm, adjustment of aeration flow and inlet/outlet pressure of membrane module to match the pollutants load.

Machine learning models, including multiple linear regression (MLR) and decision tree machine learning (LGB) algorithms, were used to predict the degradation efficiency of 57 organic pollutants in the Fenton process. Mechanistic interpretation of the models was performed by SHAP method to identify the key factors affecting the degradation efficiency. The results showed that the LGB model (R²_adj = 0.969, Q²_LOO = 0.925, R²_ext = 0.844) outperformed the MLR model (R²_adj = 0.831, Q²_LOO = 0.802, R²_ext = 0.861) in terms of prediction accuracy. The SHAP analysis revealed that temperature, molecular three-dimensional structure, and atomic ionization capacity were the main factors affecting the degradation efficiency. This study provides a scientific basis for optimizing the operating conditions of the Fenton process and enhancing the degradation efficiency, which is of great significance in guiding the research and practice in the field of water treatment.

Compared with the side-stream phosphorus recovery process based on enhanced biological phosphorus removal, biofilm phosphorus enrichment-recovery process has great application potential in the field of wastewater resource recovery due to the advantages of high phosphorus enrichment effect and phosphorus recovery rate. Enrichment and cultivation of biofilm predominated by phosphate-accumulating bacteria is the key to the operation of the process. However, the culture of phosphate-accumulating biofilms is affected by multiple factors, resulting in slow biofilm formation. Therefore, in order to realize the rapid cultivation of phosphate-accumulating biofilm, the operation control conditions, environmental influencing factors and formation mechanism of phosphate-accumulating biofilm was summarized in this paper. It was found that the aerobic aeration volume, sludge discharge time, as well as the type and concentration of carbon source are the key control conditions for the cultivation of phosphate-accumulating biofilm. The research direction for further achieving the rapid culture of phosphate-accumulating biofilm was prospected, with the expectation of providing a theoretical basis for the rapid start-up of phosphate-accumulating biofilm reactor.

Targeting the challenges in organic micropollutants (OMPs) detection and biotoxicity assessment, this study systematically evaluated four water pretreatment approaches and seven activated elution solvent combinations to improve the enrichment efficiency of residual organic matter in reclaimed water. The optimized procedure comprised: acidification to pH 2.5 with 5% (V/V) methanol addition; sequential SPE using HLB (500mg/6mL) and LC-18 (500mg/6mL) cartridges for broad-spectrum retention; ternary elution with 10mL methanol, 10mL ethyl acetate, and hexane (1:1V/V) to achieve polarity-balanced desorption. The optimized approach achieved 88% dissolved organic carbon (DOC) recovery, representing a 1.3~15.9-fold enhancement in OMPs recovery across compounds with logK_ow values ranging from 1.8 to 5.7 compared to conventional methanol-based methods. Notably, the optimized protocol reduced the sample volume required to reach EC50 in acute toxicity assays by 4.4-fold. The optimized method developed in this study significantly enhanced detection sensitivity and precision.