The long-distance transport of wastewater in sewers inevitably leads to the formation of biofilms on the inner wall of sewers. Numerous studies have focused on analyzing the hydrogen sulfide, methane production, and emission patterns associated with sewer biofilms in sewer systems. This study employed bibliometric methods to analyze the research progress in the field of sewer biofilms from 1995 to 2025, and revealed the associated development trend, international cooperation network, and research hotspots. The results demonstrate a substantial increase in the number of annual publications over the past decade, with China and Australia as the primary contributors. The journal Water Research has been found to exert a significant influence. The research hotspots concentrate on the generation and control of hydrogen sulfide and methane, sewer corrosion mechanisms, and microbial community dynamics, with chemical dosing, sulfate-reducing bacteria, and biofilm metabolism as the key directions. The evolution of keywords demonstrates that early research focused on organic matter transformation, and in recent years, there has been a shift towards microbial ecology and wastewater epidemiology, along with other emerging areas. Recent years have seen China as well as China’s institution and authors emerge as the primary contributors in the sewer biofilm field, a development attributable to the country’s policy support, which has precipitated the development of green technologies and smart monitoring systems. This study demonstrates the necessity of international cooperation and provides theoretical references and technological directions for future sewer biofilms research.

Spinel-type metal oxides NiCo2O4 represents a promising catalyst, yet the agglomeration and inadequate exposure of active sites limit their catalytic effectiveness. Herein, this work proposes an effective method of supporting NiCo2O4 nanoparticles on Chrysotile Fiber (CF), focusing on the reinforcement mechanism and degradation pathways. Results indicated that NiCo2O4@CF-90 exhibited exceptional catalytic performance in activating peroxymonosulfate (PMS) for the degradation of norfloxacin (NOR). The reaction rate constant of the NiCo2O4@CF-90 was 3.98–folds higher than that of the NiCo2O4 without CF support. NiCo2O4@CF-90 exhibited an outstanding degradation efficiency of 99.96% for NOR, attributable to a 96.14% contribution from 1O2 radical. Potential degradation pathways of NOR were included defluorination, decarboxylation, and transformations of the piperazine and quinolone moieties. Toxicity assessment confirmed that a significant reduction in the biological toxicity of degradation products. Further analysis indicates that the CF framework provides a large surface area for loading, which prevents the agglomeration of NiCo2O4 nanoparticles and facilitates their uniform dispersion. This increases the density of accessible active sites for PMS activation, thereby enhancing catalytic performance. Overall, this study demonstrates the effectiveness of the CF framework in enhancing the catalytic performance of NiCo2O4, highlighting its potential application in activating PMS for treating antibiotic-polluted water.

To investigate the recovery mechanisms of anaerobic ammonium oxidation (anammox) systems under long-term yttrium (Y) stress, we established two recovery strategies: natural recovery (R1) and biochar-mediated recovery (R2). Compared with natural recovery, biochar addition significantly enhanced total nitrogen removal and anammox activity by 20.85% and 55.72 mg N/(gVSS·d), respectively. Extracellular polymeric substances in the sludge increased by 115.72 mg/g VSS, with polysaccharides contributing an additional 80.13 mg/g VSS, serving as a biological barrier against Y-induced stress. Zeta potential decreased by 2.5 mV, promoting sludge aggregation. Microbial community analysis revealed that biochar selectively enriched anammox bacteria (Candidatus_Brocadia) and symbiotic genera (Exiguobacterium and Norank_f_Aggregatilineaceae), whose relative abundances increased by 13.82%, 19.55%, and 4.17%, respectively, establishing a stable ”core–defense–structure” consortium that enhanced system resilience under Y stress. Functional gene analysis indicated that biochar alleviated Y-induced electron flux limitations by upregulating genes involved in quinone pool synthesis (ubiE), complex III function (petB/C), and cytochrome c-associated pathways (ccoP, cycB). Differential protein and metabolite enrichment analyses further demonstrated that biochar promoted ribosomal protein translation, enhanced quorum sensing, enriched ABC transporters, increased antioxidant metabolites (3',4'-Dimethoxy-2'-Hydroxychalcone and Dihydrolipoate), and reduced intracellular toxin accumulation (Neosaxitoxin). These synergistic effects repaired damaged anammox cell structures, mitigated intracellular oxidative stress, improved substrate utilization and Y efflux, and redirected more energy toward anammox metabolism, thereby restoring bacterial functional performance. This study provides a theoretical and technical foundation for sustainable, low-carbon treatment of yttrium-laden wastewater in southern Jiangxi.

Spinel-type metal oxides NiCo2O4 represents a promising catalyst, yet the agglomeration and inadequate exposure of active sites limit their catalytic effectiveness. Herein, this work proposes an effective method of supporting NiCo2O4 nanoparticles on Chrysotile Fiber (CF), focusing on the reinforcement mechanism and degradation pathways. Results indicated that NiCo2O4@CF-90 exhibited exceptional catalytic performance in activating peroxymonosulfate (PMS) for the degradation of norfloxacin (NOR). The reaction rate constant of the NiCo2O4@CF-90 (0.1580 min-1) was 3.98–folds higher than that of the NiCo2O4 without CF support. NiCo2O4@CF-90 exhibited an outstanding degradation efficiency of 99.96% for NOR, attributable to a multiple mechanism involving free radicals (·OH and SO4·-), non-free radicals (1O2), and direct electron transfer. Potential degradation pathways of NOR were included defluorination, decarboxylation, and transformations of the piperazine and quinolone moieties. Environmental Chemistry and SAR Tool (ECOSAR) prediction indicated a significant reduction in the biological toxicity of degradation products. Further analysis indicates that the CF framework provides a large surface area for loading, which prevents the agglomeration of NiCo2O4 nanoparticles and facilitates their uniform dispersion. This increases the density of accessible active sites for PMS activation, thereby enhancing catalytic performance. Overall, this study demonstrates the effectiveness of the CF framework in enhancing the catalytic performance of NiCo2O4, highlighting its potential application in activating PMS for treating antibiotic-polluted water.

Partial nitrification (PN) is an energy-efficient autotrophic nitrogen removal bioprocess, yet ensuring the PN stability under high organic loading is not simple. Herein, low- intensity ultrasound was introduced to improve the stability of PN under high organic loading. The results showed that when subjected to a high organic load of 0.63 kg/(m³·d), the PN system achieved a nitrite accumulation rate of 80% in the presence of low-intensity ultrasound. Low intensity ultrasound enhanced the tolerance of autotrophic microorganisms to high organic loads. Besides, the stable cavitation effect of ultrasound preventing heterotrophic bacteria from proliferating preferentially under high organic concentration conditions, and inhibiting heterotrophic bacteria from constantly competing with ammonia-oxidizing bacteria for oxygen. Low- intensity ultrasound enhances the permeability of the cell membrane and increases oxygen affinity, giving ammonia-oxidizing bacteria an advantage when competing with heterotrophic bacteria for oxygen; stimulates the secretion of extracellular polymeric substances, promoting the formation of a specialized sludge structure. These effects collectively create a protective niche and a favorable microenvironment, thereby consolidating and enhancing the competitive advantage of ammonia-oxidizing bacteria, which in turn inhibits the uncontrolled proliferation of heterotrophic bacteria. This reshaping of microbial competition ultimately establishes a stable and resilient PN microbial community. In summary, this work presents an effective method for improving the stability of PN systems under high organic loading, and sheds light on the mechanisms by which low-intensity ultrasound reshapes microbial competition.

Urban sewer systems function as active subsurface bioreactors, where dynamic biofilms drive significant methane (CH ₄ ) and nitrous oxide (N ₂ O) emissions. Redox-stratified microenvironments within biofilms enable concurrent fermentation, methanogenesis, methane oxidation, and nitrogen transformations, linking hydraulic conditions to greenhouse gas generation. CH ₄ derives mainly from anaerobic micro-zones regulated by substrates and retention time, whereas N ₂ O forms under micro-aerobic conditions via nitrification and incomplete denitrification. Current mitigation strategies, including physical cleaning, chemical dosing, and electron acceptor adjustments, often target isolated pollutants, neglecting inter-gas trade-offs. Methanotroph-mediated methane oxidation, including aerobic and nitrite-dependent anaerobic pathways, provides an additional biological route for mitigating sewer CH ₄ emissions. This review synthesizes biofilm-mediated emission mechanisms and control measures, advocating a shift from single-pollutant interventions toward precision, system-wide strategies. Integrating high-frequency monitoring, multi-omics, and dynamic modeling is essential to reconcile drainage functionality with climate goals and advance low-carbon, resilient urban wastewater infrastructure.