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Insufficient treatments during bloom-forming seasons allow algae to enter the subsequent drinking water distribution system (DWDS). Yet, scarce information is available regarding the role escaped algae to play in the DWDS, and how they interact with the system. Thus, three scenarios were conducted: a pilot DWDS with algae (a), pipe water (b), and pipe water with algae (c). Experimental results showed that, compared to biofilm and bulk water, escaped algae required fewer disinfectants. Competition for disinfectants varied with algal strains (Microcystis aeruginosa, MA; Pseudanabaena sp., PS) and disinfectant types (chlorine, Cl 2 ; chloriamine, NH 2 Cl). Algae in the MA-Cl 2 group showed the highest demand (6.25%-36.02%). However, the low-concentration disinfectants distributed to algae could trigger distinct algal status alternations. Cl 2 diffused into intact MA cells and reacted with intracellular compositions. Damaged PS cells reached 100% within 2 h. Typical disinfection byproducts (DBPs), including trihalomethanes (THMs), haloacetic acids and halogenated acetonitriles were examined. Disinfectant types and algal strains affected DBP yield and distribution. Although disinfectants consumed by algae might not promote dissolved DBP formation, especially for THMs. DBP formation of the other components was affected by escaped algae via changing disinfectant assignment (reduced by 45.45% for MA-Cl 2 ) and transformation efficiency (by 34.52%). The cytotoxicity risks were estimated. Dissolved DBP-induced risks were not added when escaped algae occurred, whereas disruption and release of intracellular substances increased risks; the maximum cytotoxicity did not occur at 12 h rather than at the end (24 h). Overall, this study provided an innovative perspective on algal-related water quality issues in water systems., 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 © 2023 Elsevier Ltd. All rights reserved.)

O-methylated pollutants (OMPs) are emerging contaminants in drinking water and mainly produced through bacterial O-methylation. However, the information of OMP-producing bacteria (OMPPB) in drinking water treatment plant (DWTP) is largely unknown so far. In this study, the OMPPB in water samples from three DWTPs (XL, JX and NX) were investigated by using cultivation-dependent and cultivation-independent technologies. Four OMPs were detected and their odor and toxicity risks were assessed. Formation potentials (FPs) of 2,4,6-trichloanisole, 2,3,6-trichloanisole, 2,4,6-tribromoanisole, pentachloroanisole and diclofenac methyl ester were determined in water samples and their values shifted significantly among DWTPs. A most probable number (MPN) method was established to quantify OMPPB numbers and the relationships between total haloanisole FPs (HAFPs) (y) and OMPPB numbers (x) in three DWTPs could be described by the following functions: y = 0.496× 0.373 (XL), y = 0.041× 0.465 (JX) and y = 0.218× 0.237 (NX). Several genera like Bacillus, Ralstonia, Brevundimonas, etc. were newly found OMPPB among the cultivable bacteria, and their OMP products were evaluated in terms of quantity and environment risks (odor, toxicity and bioaccumulation). High-throughput sequencing revealed treatment process was the main driving factor to shape the OMPPB community structures and Mantel test showed HAFP profile was significantly influenced by Mycobacterium and Pelomonas. PICURSt2 analysis discovered four phenolic O-methyltransferases (OMTs) and four carboxylic OMTs which might be responsible for OMP formation. Several strategies were recommended to assess risk and control contamination brought by OMPPB in DWTPs., 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 © 2023 Elsevier Ltd. All rights reserved.)

The traditional methods of increasing the chlorine disinfectant dosage in the drinking water distribution system (DWDS) to control microorganisms and improve the safety of drinking water quality are subjected to several challenges. One noticeable problem is the unpleasant odor generated by chlorine and chloramines. However, the generally proposed chlorine dosage optimization model ignores the chloric odor distribution in the DWDS. This study proposes a comprehensive multi-parameter water quality model and aims to balance the trade-offs between: (i) minimize the flavor profile analysis (FPA) degree of the chloric odor produced by chlorine and chloramines in the DWDS, and (ii) minimize the economic investment (chlorine dosage and operation cost). EPANET and back propagation (BP) network integrated with the Borg algorithm were employed as innovative approaches to simulate the chlorine, chloramines, and chloric odor intensity in the DWDS. Moreover, the application of the multi-parameter model was demonstrated in a real-world DWDS case study. 0.5 mg-Cl 2 /L (mg/L) chlorine at 8 secondary chlorination points was added to the DWDS as an optimized chlorine dosing scheme considering the olfactory and financial objective functions simultaneously. When switching to a superior water source, the FPA of the chloric odor in DWDS increased by a maximum of 1.4 at most if the initial chlorine dosage remained as before. To avoid the occurrence of chloric odor and also control the residual free chlorine (residual chlorine) at a suitable value, the initial and secondary chlorine dosages were optimized to 0.4 mg/L and 0.3 mg/L, respectively. Under this condition, the initial chlorine dosage was reduced by 50% compared to the original operation scheme in City J, China, the qualification rate of the residual chlorine reached 97.2%, basically consistent with that before water source switching, and the chloric odor intensity of the DWDS was controlled below FPA 3.4., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Chlorine-based compounds have been used as a disinfectant in drinking water treatment plants for decades because of their excellent sterilisation efficiency and low cost. However, the formation of disinfection by-products during chlorination is a cause for concern. Peracetic acid (PAA) is a strong oxidant with a redox potential higher than that of chlorine and does not form harmful disinfection by-products. It is thus a potential alternative for chlorine-based disinfectants. However, PAA decomposes rapidly in water at a rate that is highly affected by many factors, such as organic compounds and pH. The aim of this study is to investigate the stability of PAA during drinking water disinfection. To accomplish this, we studied methods for rapid detection of residual PAA and PAA decay in drinking water. Residual PAA was detected in water by the spectrophotometry-total chlorine reagent (SPTCR) method with a PAA concentration range of 0.090-10 mg/L (R 2 = 0.9943). Decay tests of PAA in drinking water and other sources of water showed that the decay process conformed to the first-order kinetic model with fast and slow reactions. Among four factors, pH was the key factor in the decay process because an alkaline environment significantly promotes the decomposition of PAA. In addition, total organic carbon (TOC), conductivity, and initial PAA concentration also affected PAA decay. Experimental and statistical analyses suggested that these factors affected PAA decay in the following descending order of influence: TOC, initial PAA concentration, and conductivity. In real water matrices, the PAA decay rate increased with increasing initial PAA concentration.

Chlorination is essential to provide safe drinking water. However, this process leads to the formation of disinfection byproducts (DBPs). In this study, tryptophan (Trp) has been selected as a precursor to conduct the chlorine disinfection. Moreover, the factors that affect the formation of trihalomethanes (THMs) and iodinated trihalomethanes (I-THMs) are investigated. The formation pathway of Trp chlorination is proposed based on the intermediate products identified. According to the experimental results, the formation of THMs and I-THMs during Trp chlorination fitted a new first-order kinetic model. The dosage of chlorine, temperature, pH and the ratio of bromide and iodide had major influence on the formation of THMs and I-THMs during chlorination. In addition, the inhibition of luminescent bacteria Vibrio fischeri in the water sample increased during Trp chlorination., (Copyright © 2018. Published by Elsevier Ltd.)

2,4,6-Trichloroanisole (TCA) is an odorous compound that is often detected in tap water and is difficult to be removed via water treatment. In this study, the transformation efficiency of TCA in the presence of persulfate (PS) activated by iron (Fe 2+ , Fe 0 , and Fe 3+ ) was investigated for the first time. The effects of the activator dosage, oxidant dosage, pH, dosing method, chelating agents, humic acid, and temperature were evaluated. The degradation rate of TCA increased with increasing PS dosages (0.12-0.48 mM) and initial Fe 2+ concentrations (0.12-0.96 mM), while it decreased with higher Fe 2+ concentrations. Fe 2+ /PS and Fe 0 /PS systems achieved their best TCA removal efficiency at pH 7 and 2.5, respectively. According to the results of electron paramagnetic resonance (EPR), the contribution of SO 4 - • to TCA degradation was much higher than that of •OH. Gradual addition of Fe 2+ improved TCA degradation compared to single addition. Citric acid (CA) promoted TCA degradation under Fe 2+ /PS at the beginning of the reaction, but inhibited it after 10 min. Ethylenediaminetetraacetic acid (EDTA) improved the TCA removal rate with an EDTA/Fe 2+ molar ratio of 0.5:1, while it decreased it at higher EDTA/Fe 2+ molar ratios. Oxalic acid (OA) negatively affected TCA degradation with increasing OA/Fe 2+ molar ratios. Among all of the chelating agents, only CA increased TCA degradation by Fe 0 /PS. Humic acid promoted TCA degradation by Fe 2+ /PS at the proper dosage (1 mg/L). Under our specific conditions and over the temperature ranging from 10 to 25 °C, no change was observed in the reaction kinetics. It was found that 2,4,6-trichlorophenol (TCP) was the only detected oxidation product. The presence of an Fe 2+ -Fe 3+ redox cycle in iron-activated PS systems was confirmed by TCA degradation under the Fe 3+ /PS system.

Tap water quality is at risk for odor-producing algae. Besides being hazardous to source water and water treatments, these algae threaten drinking water distribution system (DWDS). Yet little information is available for odorous risks occurring, responding, and transforming in real DWDS. Hence, two algae (Microcystis aeruginosa , MA; Pseudanabaena sp., PS) were selected for pilot studies. Two ways were verified for algal occurrence, including insufficient water treatments and DWDS-biofilm attachment. MA survived moderate disinfectant exposures and restored odorants (β-cyclocitral). Also, MA could be attached to biofilm and its detachment occurred upon flushing (0.60 m/s). These occurrence ways were not seen for PS. Three factors were compared for living algae in DWDS. Flow velocities had minimal impacts on MA but affected PS odorant (2-methylisobropanol, 2-MIB) releases. Releasing rates increased by 115.79% with velocity from 0.05 m/s to 1.50 m/s. Disinfectants were the riskiest, maximizing risks for MA and PS, respectively at 0.30 mg/L NH 2 Cl and 1.00 mg/L Cl 2. Coexisting antibiotics showed selective effects and reduced risks, e.g., tetracycline reduced MA intensity and PS odorant production. For naked odorant transformation, 2-MIB in DWDS had reduced degradation ratios compared to beaker conditions. Overall, odorous risks by MA and PS were different. MA was tough and could resist water treatments and adverse stressors in DWDS, with partial odorants remaining within cells. PS was vulnerable to treatments and DWDS, and the released odorants were not degradable. Hence, customized management is required for various algal odorous problems in DWDS. [Display omitted] • Viable algae entered pipes and formed odorous risks due to insufficient treatments. • Microcystis cells were attached to pipe-biofilm, while Pseudanabaena cells were not. • Flow rates did not affect Microcystis ' integrity, but caused Pseudanabaena 's rupture. • Pipe-biofilm influenced disinfectants and antibiotics working on algal behaviors. • Transforming patterns of 2-MIB differed in pipe and beaker conditions. [ABSTRACT FROM AUTHOR]

Microcystis aeruginosa and Pseudanabaena are two common cyanobacterial species/genus and they can occur coincidently in many eutrophic lakes globally. These two cyanobacteria could produce Taste & Odor (T&O) compounds, and their production of T&O compounds might be changed when they are present coincidently. The amounts of T&O compounds and their producers may influence the effectiveness of water treatment processes. Therefore, the mutual interactions between Microcystis aeruginosa (FACHB-905, M) and Pseudanabaena sp. (FACHB-1277, P) on T&O compounds in co-cultures were evaluated in this study. Different initial cell concentrations of M and P, with ratios of M:P = 1:1, M:P = 1:2 and M:P = 2:1 were applied in the co-cultures. The growth of M was enhanced under all of the cyanobacterial cell ratios. The growth of P was enhanced under the ratio of M:P = 1:1, while it was inhibited under the ratios of M:P = 1:2 and M: P = 2:1. In addition, the growth of the two cyanobacteria and their production of β-cyclocitral and 2-methylisoborneol (2-MIB) in the filtrate of P were higher than those in the filtrate of M, which may be attributed to their associated secondary metabolites. The cell integrity and photosynthetic capacity of the two studied cyanobacteria are greatly affected by exposure to β-cyclocitral and 2-MIB. The results showed that β-cyclocitral and 2-MIB had the allelopathic effects on the two cyanobacteria species which might influence the composition of co-existing cyanobacteria and their production of T&O compounds. Image 1 • The growth of M. aeruginosa and associated β-cyclocitral is enhanced in co-cultures. • Allelopathy is crucial in the interspecific competition of co-existed cyanobacteria. • β-cyclocitral and 2-MIB could impact cyanobacterial growth and metabolism. [ABSTRACT FROM AUTHOR]