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The biofilm stress response of biological activated carbon (BAC) was investigated under prolonged exposure to sulfadiazine and 2,4-Dichlorophenoxyacetic acid, simulating complex emerging organic contaminants (EOCs) that are mainly involved in the formation of nitrogenous disinfection byproducts (N-DBPs) and antibiotic resistance genes (ARGs). Under trace complex EOCs condition (2 µg/L), N-DBP precursors and abundance of ARGs increased significantly in BAC effluent. The total formation potential of haloacetonitriles (HANs) and halonitromethanes (HNMs) was 751.47 ± 2.98 ng/L, which was much higher than the control group (440.67 ± 13.38 ng/L without EOCs). Similarly, the relative abundance of ARGs was more than twice that in the control group. The complex EOCs induce excessive extracellular polymeric substance secretion (EPS), thereby causing more N-DBP precursors and stronger horizontal gene transfer. Metagenome analysis revealed that functional amino acid and protein biosynthesis genes were overexpressed compared to the control group, causing more EPS to be secreted into the external environment. Complex EOCs promote Cobetia , Clostridium, and Streptomyces dominance, contributing to the production of N-DBP precursors and ARGs. For the first time, in addition to the direct hazards of the EOCs, this study successfully revealed the indirect water quality risks of complex EOCs from the microbial stress response during BAC treatment. Synergistic regulation of EOCs and microorganisms is important for tap water security. [Display omitted] • Trace complex emerging organic contaminants exacerbated the risk of DBPs and ARGs after BAC treatment. • Excessive EPS secretion contributed to DBP precursors and horizontal gene transfer. • The amino acid/protein-encoding functional genes overexpressed to counteract micropollutants stress. • Cobetia , Clostridium, and Streptomyces were the dominant bacterial genera associated with DBPs and ARGs. • The indirect effect of micropollutants on microbial stress response should receive more attention. [ABSTRACT FROM AUTHOR]

The effects of ozone-biologically activated carbon (O 3 -BAC) treatment with various phosphate doses (0, 0.3 or 0.6 mg/L) were investigated on the formation of disinfection by-products (DBPs) and occurrence of opportunistic pathogens (OPs) in drinking water distribution systems (DWDSs) simulated by annular reactors (ARs). It was found that the lowest DBPs and the highest inactivation of OPs such as Mycobacterium spp. , Mycobacterium avium , Aeromonas spp. , Pseudomonas aeruginosa and Hartmanella vermiformis , occurred in the effluent of the AR with 0.6 mg/L phosphate addition. Based on the results of different characterization techniques, for the AR with 0.6 mg/L phosphate-enhanced O 3 -BAC treatment, dissolved organic carbon in the influent exhibited the lowest concentration and most stable fraction due to the improved biodegradation effect. Moreover, the total amount of suspended extracellular polymeric substances (EPS) in the bulk water of the AR decreased greatly, resulting in the lowest chlorine consumption and DBPs formation in the AR. In Fourier transform infrared spectra of the suspended EPS, the amide II band (1600-1500 cm −1 ) disappeared and the protein/polysaccharide ratio decreased remarkably, indicating the destruction of protein and a decrease in hydrophobicity. Moreover, β-sheets and α-helices in the protein secondary structures were degraded while the random coils increased sharply as phosphate addition increased to 0.6 mg/L, inhibiting microbial aggregation and hence weakening the chlorine-resistance capability. Thus, most of the OPs in suspended biofilms were more easily inactivated by residual chlorine, resulting in the lowest OPs occurrence in the effluent of the AR. Our findings indicated that enhancing the efficiency of the BAC filter by adding phosphate is a promising method for improving water quality in DWDSs. [ABSTRACT FROM AUTHOR]

Effects of sulfadiazine and ciprofloxacin on the occurrence of free-living and particle-associated opportunistic pathogens in bulk water of simulated drinking water distribution systems (DWDSs) were investigated. It was found that sulfadiazine and ciprofloxacin greatly promoted the occurrence of opportunistic pathogens including Pseudomonas aeruginosa , Legionella pneumophila , Mycobacterium avium and its broader genus Mycobacterium spp., as well as the amoebae Acanthamoeba spp. and Hartmanella vermiformis, in bulk water of DWDSs. Moreover, sulfadiazine and ciprofloxacin exhibited much stronger combined effects on the increase of these opportunistic pathogens. Based on the analysis of the antibiotic resistance genes (ARGs) and extracellular polymeric substances (EPS), it was verified that EPS production was increased by the antibiotic resistant bacteria arising from the effects of sulfadiazine/ciprofloxacin. The combined effects of sulfadiazine and ciprofloxacin induced the greatest increase of EPS production in DWDSs. Furthermore, the increased EPS with higher contents of proteins and secondary structure β -sheet led to greater bacterial aggregation and adsorption. Meanwhile, large numbers of suspended particles were formed, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in bulk water of DWDSs with sulfadiazine/ciprofloxacin. Therefore, sulfadiazine and ciprofloxacin promoted the occurrence of particle-associated opportunistic pathogens in bulk water of DWDSs due to the role of EPS produced by the bacteria with ARGs. [ABSTRACT FROM AUTHOR]

Change in water quality was investigated with laboratory-scale ozone-biological activated carbon filters using copper-modified granular activated carbon (Cu/GAC) and unmodified granular activated carbon (GAC). In the first seven days of the experimental period, Cu/GAC removed organic matter more efficiently owing to its enhanced adsorption capacity. As the running time increased, the amount of disinfection by-products (DBPs), dissolved organic carbon, and extracellular polymeric substances (EPS) increased sharply in the effluent of the Cu/GAC filter (CCW). More importantly, the EPS suspended in the CCW exhibited weaker flocculating efficiency and hydrophobicity, causing more active chemical reactions between chlorine and EPS substances. The copper species significantly limited the microbial biomass (0.01 nmol/L adenosine triphosphate) but stimulated the secretion of significant amounts of EPS by microorganisms for self-protection. Furthermore, the microbial community in the bulk water was successfully shaped by Cu/GAC, resulting in a continuous supply of EPS-derived DBP precursors and a sharp rise in chlorine consumption in the downstream drinking water distribution. Therefore, use of modified GAC materials, similar to Cu/GAC, as carrier materials for biological activated carbon (BAC) treatment remains controversial, despite enhanced pollutant adsorption capacity. This is the first study to reveal the mechanism of BAC-modified materials for water quality stability. The study potentially contributes to a comprehensive understanding of the effects of biofilm transformation and microbial community succession on drinking water quality. These results showed that tap water safety risks could be reduced by improving BAC pretreatment in drinking water treatment plants. [Display omitted] • Effect of biofiltration with Cu/GAC on DBPs and pathogenic bacteria were investigated. • Cu/GAC exhibited enhanced organic pollutants adsorption capacity compared with GAC. • More DOC, DBPs precursors, and EPS were detected in the effluent of Cu/GAC biofilter. • Cu/GAC successfully shaped the microbial community in the bulk water. • It is controversial that Cu/GAC can be used as BAC carrier materials. [ABSTRACT FROM AUTHOR]

Abstract Effects of sulfadiazine and ciprofloxacin on microorganisms in biofilm of drinking water distribution systems (DWDSs) were studied. The results verified that the increases of 16S rRNA for total bacteria and bacterial genus Hyphomicrobium were related to the promotion of antibiotic resistance genes (ARGs) and class 1 integrons (int1) in DWDSs with sulfadiazine and ciprofloxacin. Moreover, the bacteria showed higher enzymatic activities in DWDSs with sulfadiazine and ciprofloxacin, which resulted in more production of extracellular polymeric substances (EPS). The higher contents of EPS proteins and secondary structure β -sheet promoted bacterial aggregation and adsorption onto surface of pipelines to form biofilm. EPS can serve as a barrier for the microorganisms in biofilm. Therefore, the biofilm bacterial communities shifted and the 16S rRNA for total bacteria increased in DWDSs with antibiotics, which also drove the ARGs promotion. Furthermore, the two antibiotics exhibited stronger combined effects than that caused by sulfadiazine and ciprofloxacin alone. Graphical abstract Image 1 Highlights • Response of biofilm to sulfadiazine and ciprofloxacin in DWDSs was studied. • Bacterial community shift and total bacteria increase related to ARGs promotion. • The bacteria exhibited higher enzymatic activity and produced more EPS. • The higher contents of proteins and β -sheet in EPS promoted biofilm formation. • Sulfadiazine and ciprofloxacin exhibited stronger combined effects on biofilm. [ABSTRACT FROM AUTHOR]

The effects of cast iron pipe corrosion on nitrogenous disinfection by-products formation (N-DBPs) in drinking water distribution systems (DWDSs) were investigated. The results verified that in the effluent of corroded DWDSs simulated by annular reactors with corroded cast iron coupons, typical N-DBPs, including haloacetamides, halonitromethanes, and haloacetonitriles, increased significantly compared with the influent of DWDSs. In addition, more dissolved organic carbon, adenosine triphosphate, and iron particles were simultaneously detected in the bulk water of corroded DWDSs, thereby indicating that abundant iron particles acted as a "protective umbrella" for microorganisms. Under the condition of corroded DWDSs, the extracellular polymeric substances gradually exhibited distinct characteristics, including a higher content and lower flocculation efficiency, thereby resulting in a large supply of N-DBPs precursors. Corroded cast iron pipes, equivalent to a unique microbial interface, induced completely distinct microbial community structures and metabolic functions in DWDSs, thereby enhancing the formation of N-DBPs. This is the first study to successfully reveal the interactions among iron particles, biofilms, and chlorine in DWDSs, which may help to fully understand the biofilm transformation and microbial community succession in DWDSs. [Display omitted] • Effect of cast iron pipe corrosion on N-DBPs formation in simulated DWDSs was investigated. • More N-DBPs, DOC, ATP and iron particles were detected in the bulk water of corroded DWDSs. • Corroded cast iron pipes were equivalent to a unique microbial interface in DWDSs. • The EPS characteristics of corroded DWDSs caused a large supply of N-DBPs precursors. • The interaction among iron particles, biofilms, and chlorine in DWDSs significantly affected water quality stability. [ABSTRACT FROM AUTHOR]