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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]

Water quality deterioration of drinking water distribution systems (DWDSs) caused by water source switching has been reported previously. However, systematic investigation of the biostability of DWDS under water source switching is limited. Aged pipes, including three commonly used pipe materials dug out from a practical DWDS, were used to systematically investigate the biofilm stability mechanism of DWDS under water source switching to quality-improved water. An increase in adenosine triphosphate (ATP) concentration in the bulk water during the initial stage of the switching period was observed, indicating the risk of biofilm release through aged pipe surfaces after water source switching. Sloughing of biofilms might contribute to temporary instability. From day 35, the ATP concentration in the polyethylene (PE) and plastic stainless steel composite (PS) pipes were maintained at approximately 2.40 and 2.56 ng/L, respectively. In contrast, the ATP concentration in the ductile iron (DI) pipes was higher, at approximately 3.43 ng/L from day 42. The water quality variation could cause areas of the biofilm to slough and reduce the biomass of biofilm, causing partial alteration of the microbial community. 16S rRNA gene amplicon sequencing–based functional prediction revealed that the biofilm could increase the abundance of chlorine-resistant bacteria attributed to the increase in Pseudomonas and Methylobacterium after switching to quality-improved water. Moreover, the profiles of specific pathways linked to human diseases, antibiotic resistance, and antibiotic biosynthesis revealed that the safety of the biofilm could improve after switching to quality-improved water. Key points: • The PE and PS biofilm showed improved resistance to water quality perturbation. • Greater number of Methylobacterium was found in the biofilm after water source switching. • 3.16S gene–based metagenomics prediction revealed that the safety of the biofilm under water source switching. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Escaped algae had lower disinfectant demand than biofilm and bulk water. • Microcystis was intact even with chlorine entry, yet Pseudanabaena easily ruptured. • Algae impacted dissolved disinfection byproducts (DBPs) formation indirectly. • Chlorine diffusing into intact MA cells allowed extra DBP generation. • Algal entry in short-term (24 h) might not worsen pipe risks, yet algal rupture did. [ABSTRACT FROM AUTHOR]

Pipe breaks have significant impacts on the hydraulic and water quality performance of water distribution systems (WDSs). Therefore, it is important to evaluate these impacts for developing effective strategies to ultimately minimize the consequences of these events. However, there has been surprisingly limited research focusing on impact evaluation for pipe breaks so far. To address this gap, this paper proposes a framework to comprehensively evaluate hydraulic and water quality impacts of pipe breaks on a WDS using six quantitative metrics. These metrics primarily focus on identifying (i) break outflow volume, (ii) water shortage, (iii) nodes with reduced service quality, (iv) pipes with affected pressures, (v) pipes with reversed flow directions, and (vi) pipes with significantly increased velocities, for each breaking event within a WDS. Statistical behaviors, spatial properties, and pipe rankings of metric results are analyzed to reveal the underlying characteristics of impacts induced by pipe breaks. We illustrate the proposed framework using three WDSs with different properties. Results show that impacts of pipe breaks not only vary with pipe diameters but are also significantly influenced by pipe locations, when the break occurs, and the specific metric considered. The proposed framework greatly enhances the fundamental understanding of the underlying properties of breaking impacts on the hydraulic and water quality of WDSs, as well as the ranking of pipes based on the consequences of breaks. Such understanding offers important guidance to develop effective pipe management, resource planning, and break restoration strategies to minimize the impacts of breaking events on WDSs. Key Points: The proposed framework is effective to comprehensively evaluate impacts of pipe breaksBoth hydraulic and water quality impacts are influenced by diameters, locations, and occurring time of the breaking pipesPipes are ranked based on consequence levels of their breaks, which offers important guidance for effective management of pipe breaks [ABSTRACT FROM AUTHOR]

It is important for water utilities to provide esthetically acceptable drinking water to the public, because our consumers always initially judge the quality of the tap water by its color, taste, and odor (T&O). Microorganisms in drinking water contribute largely to T&O production and drinking water distribution systems (DWDS) are known to harbor biofilms and microorganisms in bulk water, even in the presence of a disinfectant. These microbes include T&O-causing bacteria, fungi, and algae, which may lead to unwanted effects on the organoleptic quality of distributed water. Importantly, the understanding of types of these microbes and their T&O compound-producing mechanisms is needed to prevent T&O formation during drinking water distribution. Additionally, new disinfection strategies and operation methods of DWDS are also needed for better control of T&O problems in drinking water. This review covers: (1) the microbial species which can produce T&O compounds in DWDS; (2) typical T&O compounds in DWDS and their formation mechanisms by microorganisms; (3) several common factors in DWDS which can influence the growth and T&O generation of microbes; and (4) several strategies to control biofilm and T&O compound formation in DWDS. At the end of this review, recommendations were given based on the conclusion of this review. [ABSTRACT FROM AUTHOR]

• Eight bacteria from biofilms were identified and could produce haloanisoles. • Sphingomonadaceae was firstly proved to be able to O -methylate halophenols. • The halophenol O -methyltransferases of some bacteria were inducible. • Trihaloanisoles have higher potential risks than less substituted haloanisoles. • A new drinking water 2,4,6-trichlorophenol criteria was proposed. Microorganisms in drinking water distribution systems (DWDSs) can O -methylate toxic halophenols (HPs) into earthy-musty haloanisoles (HAs). However, the dominant HA-producing bacterial species and their O -methylation properties are still unknown. In this study, eight bacterial strains from DWDS were isolated and the community abundances of the related genera in bulk water and biofilms as well as their O -methylation properties were investigated. Among the genera discovered in this study, Sphingomonas and Pseudomonas are dominant and play important roles in DWDSs. All bacteria could simultaneously convert five HPs to the corresponding HAs. Two Sphingomonas ursincola strains mainly produced 2,3,6-trichloroanisole (2,3,6-TCA) (2.48 × 10-9−1.18 × 10-8 ng/CFU), 2,4,6-trichloroanisole (2,4,6-TCA) (8.12 × 10-10−3.11 × 10-9 ng/CFU) and 2,4,6-tribromoanisole (2,4,6-TBA) (2.95 × 10-9−3.21 × 10-9 ng/CFU), while two Pseudomonas moraviensis strains preferred to generate 2-monochloroanisole (2-MCA) (1.19 × 10-9−3.70 × 10-9 ng/CFU) and 2,4-dichloroanisole (2,4-DCA) (3.81 × 10-9−1.20 × 10-8 ng/CFU). Among the chloramphenicol-susceptible strains, four strains contained inducible O -methyltransferases (OMTs), while the O -methylations of the others were expressed constitutively. All bacteria could use S -adenosyl methionine as methyl donor. Potential taste and odor (T & O) risks of five HAs in DWDS followed an order of 2,4,6-TBA > 2,4,6-TCA > 2,3,6-TCA > 2,4-DCA > 2-MCA. The recommended 2,4,6-TCP criteria for T & O control is 0.003−0.07 mg/L. [ABSTRACT FROM AUTHOR]

Thermal energy recovery from drinking water has a high potential in the application of sustainable building and industrial cooling. However, drinking water and biofilm microbial qualities should be concerned because the elevated water temperature after cold recovery may influence the microbial activities in water and biofilm phases in drinking water distribution systems (DWDSs). In this study, the effect of cold recovery on microbial qualities was investigated in a chlorinated DWDS. The chlorine decay was slight (1.1%–15.5%) due to a short contact time (~60 s) and was not affected by the cold recovery (p > 0.05). The concentrations of cellular ATP and intact cell numbers in the bulk water were partially inactivated by the residual chlorine, with the removal rates of 10.1%–16.2% and 22.4%–29.4%, respectively. The chlorine inactivation was probably promoted by heat exchangers but was not further enhanced by higher temperatures. The higher water temperature (25 °C) enhanced the growth of biofilm biomass on pipelines. Principle coordination analysis (PCoA) showed that the biofilms on the stainless steel plates of HEs and the plastic pipe inner surfaces had totally different community compositions. Elevated temperatures favored the growth of Pseudomonas spp. and Legionella spp. in the biofilm after cold recovery. The community functional predictions revealed more abundances of five human diseases (e.g. Staphylococcis aureus infection) and beta-lactam resistance pathways in the biofilms at higher temperature. Compared with a previous study with a non-chlorinated DWDS, chlorine dramatically reduced the biofilm biomass growth but raised the relative abundances of the chlorine-resistant genera (i.e. Pseudomonas and Sphingomonas) in bacterial communities. • Cold recovery did not influence the chlorine decay in a short contact time. • Heat exchangers slightly promoted the efficiency of chlorine disinfection. • More biomass and health risky functions were found in biofilm after cold recovery. • More Sphingomonas abundance was found in chlorinated pipe than non-chlorinated one. [ABSTRACT FROM AUTHOR]