Secondary water supply systems (SWSSs) are pivotal in urban water management. Municipal water entering SWSS storage tank undergoes hydraulic stagnation before being distributed to end users. This stagnation provides a stable microenvironment, facilitating a series of chemical reactions, particularly chlorine disinfectant decay resulting in favorable conditions for microbial proliferation. Elevated microbial loads within SWSSs directly compromise the microbiological safety of residential drinking water. In this review, we compile the findings from our studies and existing literature and systematically evaluate the latent microbial hazards in SWSSs serving both urban residential neighborhoods and self-built houses. SWSSs function as persistent reservoirs for pathogenic microbiota. We propose Legionella spp. as targeted supplementary microbiological indicators for routine water-quality monitoring in SWSSs. To mitigate the risks, we advocate implementing three-tiered interventions: 1) an optimized building layout and operation mode, 2) engineered secondary disinfection strategies, and 3) enhanced regulatory oversight through smart monitoring frameworks. In summary, we characterize the microbial contamination mechanisms in urban SWSSs and establish a vital scientific basis for advancing operational management and safety assurance.

Clinical surveillance for respiratory pathogens has traditionally been challenging in low-resource settings, such as Western China. A low-cost wastewater monitoring network offers an alternative solution. To explore this, we first compared the sensitivity of a MeltArray-based qPCR assay, which detects 25 respiratory pathogens, with singleplex qPCR using both mock and real wastewater samples. We then employed this MeltArray assay to detect these respiratory pathogens in wastewater from a low-income region in Xi’an city from September 2023 to January 2024. Following this, qPCR and MLST were employed to quantify the dynamics of positive respiratory pathogens and confirm their genotypes. Results showed unusual surges in sewage influenza A virus (IAV) and adenovirus levels starting in October 2023, persisting until late December. Additionally, influenza B virus (IBV) outbreaks were identified beginning in late December. These findings matched the positivity rates reported by a sentinel hospital. For coronaviruses, HCoV-229E/OC43 were consistently detected in wastewater, while SARS-CoV-2 was occasionally found. The qPCR assays revealed continuous increases in sewage Mycoplasma pneumoniae and Hemophilus influenzae concentrations since September, both peaking in October. Genotyping confirmed the circulation of specific bacterial genotypes in the region. Therefore, to the best of our knowledge, this study is possibly the first to evaluate the efficacy of qPCR assays for wastewater monitoring of respiratory bacterial pathogens. Thus, these findings provide significant insights into the co-circulation of various respiratory pathogens during the autumn and winter of 2023, thereby suggesting that wastewater surveillance could be a powerful tool for the early warning of respiratory diseases.

Pathogenic microorganisms pose a significant threat to water safety. Emerging disinfection processes that combine far-ultraviolet radiation with oxidants offer promising strategies for controlling these pathogens. This study investigated advanced disinfection processes (ADPs) that use 222 and 254 nm far-ultraviolet radiation in conjunction with hydrogen peroxide (H₂O₂), sodium percarbonate (SPC), and persulfate (PDS) to inactivate E. coli in water. The inactivation efficiencies of E. coli were measured as 6.50-log for UV₂₂₂ alone and 2.50-log for UV₂₅₄ alone at 0.0014 Einstein/L. When using UV₂₂₂-ADPs, the inactivation ranged from 5.20-log to 6.50-log, while UV₂₅₄-ADPs achieved inactivation levels of 2.55-log to 2.95-log. The inactivation occurred in the order of UV₂₂₂ ≥ UV₂₂₂-ADPs > UV₂₅₄-ADPs > UV₂₅₄, which was related to photon competition between E. coli and the oxidants, superiority of UV₂₂₂ radiation compared with UV₂₅₄ radiation, and the yields of radicals. When UV₂₂₂ was combined with H₂O₂, SPC and PDS, the absorption fractions of 222 nm photons by E. coli reduced from 13.7% to 13.1%, 12.4%, and 12.2%, respectively, and the actual inactivation also decreased. This reduction was attributed to the light shielding effect of the oxidants. In addition, intracellular organic matter released from ruptured bacterial cell membranes during UV₂₂₂-ADPs could be further damaged by UV₂₂₂ photons and radicals. The effectiveness of UV₂₂₂-ADPs was also demonstrated in real water samples. Moreover, it was shown that UV₂₂₂-ADPs are less susceptible to dissolved organic matter (DOM) than UV₂₂₂ alone. This study provides novel insights into disinfection by UV₂₂₂-ADPs in water.

Iron-based nanoparticles have recently been developed to mitigate cyanobacterial blooms. In this study, a method utilizing Mg(OH)₂ coated nanoscale zero-valent iron (Fe⁰@Mg(OH)₂) was applied to treat cyanobacteria (Microcystis aeruginosa) in natural water. The influence of initial cell densities, Fe⁰@Mg(OH)₂ dosages, and water matrix on the removal efficiency of M. aeruginosa was systematically explored. Higher removal efficiencies of M. aeruginosa were achieved with increased initial cell densities, probably because larger amounts of cells and associated dissolved algal organic matters (AOM) promoted the formation and sedimentation of cell-Fe⁰@Mg(OH)₂-AOM complexes. About 98.7% of M. aeruginosa cells (initial cell density = 1.0 × 10⁶ cells/mL) were removed after treatment with 20 mg/L Fe⁰@Mg(OH)₂ for 10 h, despite anions (e.g., SO₄^2–) in natural water reduced the removal efficiency in the first 1.5 h. Most of the M. aeruginosa cells maintained intact during Fe⁰@Mg(OH)₂ treatment, as confirmed by the observation of their ultrastructure and the measurement of K⁺ and Chlorophyll a concentrations. As a result, the release of microcystins and AOM was negligible during the treatment. This study demonstrates that Fe⁰@Mg(OH)₂ is a promising approach for effective treatment of waters with high concentrations of cyanobacteria, without posing increased ecological risks.

● A total of 3714 studies on ARB and ARGs removal techniques over 26 years were reviewed.

The spread of antibiotic resistance is a global threat, causing elevated death rates and economic costs. A growing number of studies have focused on the removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in environmental settings. However, summaries and reviews of removal techniques are limited. This study examined publications on ARB and ARGs removal from 1998 to 2023 through a bibliometric approach based on the Web of Science database. Research progress during the past 26 years was analyzed by collecting annual publications, countries, journals and keywords. The number of articles related to the removal of ARB and ARGs has increased annually. The main types of ARB and ARGs, their environmental milieus and the most commonly studied removal techniques were summarized by keyword clustering. The results revealed that tetracycline- and sulfonamide-resistant bacteria are the ARB of greatest concern; that sul1, sul2, and tetA are the most frequently studied ARGs; and that municipal sewage and drinking water are the most studied ARB and ARGs transmission sites. For treatment techniques, adsorption technology is the most widely studied, and the selection of adsorption materials is particularly important, with nanomaterials and biomodified materials having great prospects for development. The combination of membrane filtration with advanced oxidation treatment or biodegradation technology is the most promising technology in this field. Our findings can inform future efforts to further reduce the distribution risks of antibiotic resistance and improve removal techniques.

● The milestones underlying studies and mechanisms are summarized.

Current microbial control strategies face challenges in keeping up with the escalation of microbial problems due to the presence of biofilms. Therefore, there is an urgent need to develop effective and robust strategies to control problematic biofilms in water treatment and reuse systems. Nanozymes, which have intrinsic biocatalytic activity and broad antibacterial spectra, hold promise for controlling resilient biofilms. This review summarizes the milestones of nanozyme studies and their applications as antibiofilm agents. The mechanisms behind the antibacterial, quorum quenching, and depolymerizing properties of nanozymes with different enzyme activities are discussed. Notably, the surface and composition of nanozymes are crucial for their efficacy in biofilm control; thus, rationally designed nanozymes can increase their effectiveness. Additionally, the challenges of nanozymes as antibiofilm agents in realistic scenarios are investigated along with proposed strategies to overcome these challenges. Prospects of nanozyme-based biofilm control, such as machine learning-assisted nanozyme design, are also discussed. Overall, this review highlights the potential of nanozymes as antibiofilm agents and provides insights into the future design of nanozymes for biofilm control.

● We built a read-mapping framework to profile human microbes from sewages (HSM).

The human microbiome leaves a legacy in sewage ecosystems, also referred to as the human sewage microbiomes (HSM), and could cause potential risk to human health and ecosystem service. However, these host-associated communities remain understudied, especially at a global scale, regarding microbial diversity, community composition and the underlying drivers. Here, we built a metagenomic read mapping-based framework to estimate HSM abundance in 243 sewage samples from 60 countries across seven continents. Our approach revealed that 95.03% of human microbiome species were identified from global sewage, demonstrating the potential of sewage as a lens to explore these human-associated microbes while bypassing the limitations of human privacy concerns. We identified significant biogeographic patterns for the HSM community, with species richness increasing toward high latitudes and composition showing a distance-decay relationship at a global scale. Interestingly, the HSM communities were mainly clustered by continent, with those from Europe and North America being separated from Asia and Africa. Furthermore, global HSM diversity was shown to be shaped by both climate and socioeconomic variables. Specifically, the average annual temperature was identified as the most important factor for species richness (33.18%), whereas economic variables such as country export in goods and services contributed the most to the variation in community composition (27.53%). Economic and other socioeconomic variables, such as education, were demonstrated to have direct effects on the HSM, as indicated by structural equation modeling. Our study provides the global biogeography of human sewage microbiomes and highlights the economy as an important socioeconomic factor driving host-associated community composition.

● Class 1 integrons are prevalent in the isolates from drinking water.

Class 1 integrons are vital mobile genetic elements involved in the environmental transmission of antibiotic resistance genes (ARGs). However, knowledge about the diversity and abundance of class 1 integrons and gene cassettes during drinking water treatment and distribution is still limited. In this study, we aimed to uncover the prevalence of class 1 integrons in the drinking water treatment and distribution systems with the combination of culture-dependent and culture-independent methods. Further, we applied the nanopore sequencing method to characterize the diversity and arrangement of ARGs carried by class 1 integron-associated gene cassettes. A total of 42 isolates were intI1-positive among the 208 strains isolated from drinking water, which tended to confer multi-drug resistance compared with intI1-negative isolates. The absolute abundance of the intI1 average 1.15 × 10⁹ copies/L in the source water and underwent the most significant reduction of over 99.9% after liquid chlorine disinfection. Furthermore, nanopore sequencing revealed that the class 1 integron-associated gene cassettes carried 51 subtypes of ARGs in drinking water, mainly conferring resistance to aminoglycosides and trimethoprim. The treatment processes, especially liquid chlorine disinfection, reduced most of the ARGs carried by gene cassettes, though some of the ARG subtypes persisted along the treatment and distribution like aac(6')-II, aadA, and dfrB2. The antibiotic resistance gene cassette array |aac(6')-II|arr| was most frequently detected, especially in the chlorinated water. This study underlined that drinking water was potential reservoir for integron-mediated ARGs transfer, indicating that the health risks of resistance gene cassettes in class 1 integrons deserved urgent attention.

● The maximum coliforms concentration increased by 2 Logs during rainfall.

Climate change leads to an increase in both the frequency and intensity of extreme precipitation. Surface runoff generated by extreme precipitation has a significant impact on water. However, the impact of persistent precipitation on surface water quality is easy to neglect, due to its prolonged duration and lower-intensity rainfall. This study established eight sampling points within selected surface waters to observe the variation of microbial characteristics in a typical persistence precipitation event. The primary difference between Furong Lake (FL) and Chengqian Reservoir (CR) was: the concentrations of dissolved organic carbon (DOC) were 21.3 ± 0.7 and 8.3 ± 1.5 mg/L in FL and CR, respectively. The concentrations of R2A culturable bacteria and coliforms were 10^4.57 and 10^1.58 colony-forming units (CFU)/mL in FL, and were 10^5.46 and 10^2.64 CFU/mL in CR, respectively. During precipitation, the maximum increase concentrations of R2A, NA culturable bacteria, and coliforms were 10^0.75, 10^1.30, and 10^2.27 CFU/mL in FL, respectively. Furthermore, microbial concentration and rainfall did not increase simultaneously, and a delay phenomenon was observed in the increasing microbial concentrations. Through analyzing the concentration change trends and correlation of various water quality indicators during persistent precipitation, the significant correlation between the DOC concentration and the changes in the dominant species of microbial community structure was found in this study (p < 0.05). For example, as the DOC concentration declined, the abundance of hgcl_clade and CL500-29_marine_group increased. Consequently, although persistent precipitation might not obviously alter the water quality visibly, it could still pose potential microbial risks.

● The highest absolute abundance of ARGs in seawater reached 2.3 × 10⁴ copies/mL.

Antibiotic resistance genes (ARGs) might have great effect on ecological security and human health. Oceans are important reservoirs that receive tremendous amounts of pollutants globally. However, information on the proliferation of ARGs in seawater is still limited. This study performed field sampling to investigate the occurrence and distribution of ARGs in seawater of the South China Sea, which is the deepest and largest sea in China. The results showed that the total absolute abundances of ARGs in seawater samples ranged from 2.1 × 10³ to 2.3 × 10⁴ copies/mL, with an of 5.0 × 10³ copies/mL and a range of 2.2 × 10³–1.8 × 10⁴ copies/mL for those with mobile genetic elements (MGEs). Genes resistant to multidrug, aminoglycoside, tetracycline, and fluoroquinolone antibiotics accounted for 77.3%–88.6% of total ARGs in seawater. Proteobacteria and Cyanobacteria represented 32.1%–56.2% and 30.4%–49.5% of microbial community, respectively. Prochlorococcus_MIT9313 and Clade_la were the prevalent genera in seawater of the South China Sea. Complex co-occurrence relationship existed among ARGs, MGEs, and bacteria. Anthropogenic activities had critical influence on ARGs and MGEs. Hospital wastewater, wastewater treatment plant effluent, sewage, aquaculture tailwater, and runoff were determined as the important sources of ARGs in seawater of the South China Sea based on positive matrix factorization analysis.