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Bacterial community structure and iron corrosion were investigated for simulated drinking water distribution systems (DWDSs) composed of annular reactors incorporating three different treatments: ozone, biologically activated carbon and chlorination (O 3 -BAC-Cl 2 ); ozone and chlorination (O 3 -Cl 2 ); or chlorination alone (Cl 2 ). The lowest corrosion rate and iron release, along with more Fe 3 O 4 formation, occurred in DWDSs with O 3 -BAC-Cl 2 compared to those without a BAC filter. It was verified that O 3 -BAC influenced the bacterial community greatly to promote the relative advantage of nitrate-reducing bacteria (NRB) in DWDSs. Moreover, the advantaged NRB induced active Fe(III) reduction coupled to Fe(II) oxidation, enhancing Fe 3 O 4 formation and inhibiting corrosion. In addition, O 3 -BAC pretreatment could reduce high-molecular-weight fractions of dissolved organic carbon effectively to promote iron particle aggregation and inhibit further iron release. Our findings indicated that the O 3 -BAC treatment, besides removing organic pollutants in water, was also a good approach for controlling cast iron corrosion and iron release in DWDSs. [ABSTRACT FROM AUTHOR]

The effects of biological activated carbon treatment using Fe 2 O 3 modified coconut shell-based activated carbon (Fe/CAC) were investigated on the occurrence of opportunistic pathogens (OPs) and formation of disinfection by-products (DBPs) in simulated drinking water distribution systems (DWDSs) with unmodified CAC as a reference. In the effluent of annular reactor (AR) with Fe/CAC, the OPs growth and DBPs formation were inhibited greatly. Based on the differential pulse voltammetry and dehydrogenase activity tests, it was verified that extracellular electron transfer was enhanced in the attached biofilms of Fe/CAC, hence improving the microbial metabolic activity and biological removal of organic matter especially DBPs precursors. Meanwhile, the extracellular polymeric substances (EPS) on the surface of Fe/CAC exhibited stronger viscosity, higher flocculating efficiency and better mechanical stability, avoiding bacteria or small-scale biofilms falling off into the water. Consequently, the microbial biomass and EPS substances amount decreased markedly in the effluent of Fe/CAC filter. More importantly, Fe/CAC did significantly enhance the shaping role on microbial community of downstream DWDSs, continuously excluding OPs advantage and inhibiting EPS production. The weakening of EPS in DWDSs resulted in decrease of microbial chlorine-resistance ability and EPS-derived DBPs precursors supply. Therefore, the deterioration of water quality in DWDSs was inhibited greatly, sustainably maintaining the safety of tap water. Our findings indicated that optimizing biological activated carbon treatment by interface modification is a promising method for improving water quality in DWDSs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Simulated drinking water distribution system (DWDS) treated with O 3 -BAC-Cl 2 (ozone-biological activated carbon-chlorine) was constructed to study its effects on the regrowth of five typical opportunistic pathogens (OPs). It was found that O 3 -BAC-Cl 2 could significantly reduce the regrowth of target OPs in the effluents of DWDS compared with Cl 2 and O 3 -Cl 2 with the same residual chlorine levels. However, the effect of O 3 -BAC-Cl 2 on the average numbers of target OPs gene markers in the biofilms of DWDS was not apparent, suggesting that OPs in the biofilms of DWDS were tolerant to the upstream disinfection process. The quantification of target OPs in the BAC-filter column demonstrated that OPs decreased with the increase of depth, which was likely due to the organic nutrient gradient and microbial competition inside the BAC-filter. Increase in the ozone dose could further reduce the OPs at the bottom of the BAC-filter. Spearman correlation analysis demonstrated that some significant correlations existed between target microorganisms, suggesting potential microbial ecological relationships. Overall, our results demonstrated that the BAC-filter may act as a "battlefield" suppressing the OPs through microbial competition. O 3 -BAC-Cl 2 could be an effective multi-barrier process to suppress the proliferation of OPs in the bulk water of DWDS. However, OPs protected by the biofilms of DWDS should receive further attention because OPs may be detached and released from the biofilms., (Copyright © 2018. Published by Elsevier B.V.)

Nanomaterials, such as ZrO 2 nanoparticles (ZrO 2 NPs), are very effective in water remediation. However, the safety issues related to nanoparticle release and toxicity to humans remain to be resolved. Here we evaluated the cytotoxicity of ZrO 2 NPs and their adducts with pollutants using a human cell panel containing stomach, intestine, liver and kidney cells. We found that different pollutants or ZrO 2 NP/pollutant adducts targeted cells from different organs, suggesting the necessity of a cell panel to model oral exposures. The cooperation of ZrO 2 NPs and pollutants was quite complex, consisting of synergistic, antagonistic, or additive effects. For example, ZrO 2 NPs enhanced the cytotoxicity of Pb 2+ in GES-1 cells and of Pb 2+ , Cd 2+ in FHC cells, while alleviating the toxicity of Pb 2+ and As (III) in HepG2 and Hek293 cells. Our results also indicated that even concentrations of pollutants that meet the national standard, the ZrO 2 NPs concentration should be kept below 17 μg/mL to avoid ZrO 2 NP/pollutant adduct synergistic toxicity., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The effects of O 3 /Cl 2 disinfection on corrosion and the growth of opportunistic pathogens in drinking water distribution systems were studied using annular reactors (ARs). The corrosion process and most probable number (MPN) analysis indicated that the higher content of iron-oxidizing bacteria and iron-reducing bacteria in biofilms of the AR treated with O 3 /Cl 2 induced higher Fe 3 O 4 formation in corrosion scales. These corrosion scales became more stable than the ones that formed in the AR treated with Cl 2 alone. O 3 /Cl 2 disinfection inhibited corrosion and iron release efficiently by changing the content of corrosion-related bacteria. Moreover, ozone disinfection inactivated or damaged the opportunistic pathogens due to its strong oxidizing properties. The damaged bacteria resulting from initial ozone treatment were inactivated by the subsequent chlorine disinfection. Compared with the AR treated with Cl 2 alone, the opportunistic pathogens M. avium and L. pneumophila were not detectable in effluents of the AR treated with O 3 /Cl 2 , and decreased to (4.60±0.14) and (3.09±0.12) log 10 (gene copies/g corrosion scales) in biofilms, respectively. The amoeba counts were also lower in the AR treated with O 3 /Cl 2 . Therefore, O 3 /Cl 2 disinfection can effectively control opportunistic pathogens in effluents and biofilms of an AR used as a model for a drinking water distribution system., (Copyright © 2018. Published by Elsevier B.V.)