Role of drinking water biofilms on residual chlorine decay and trihalomethane formation: An experimental and modeling study

Increased flushing frequency of a model plumbing system initially promoted the formation of viable but non culturable cells but ultimately reduced the concentration of culturable and total Legionella DNA

Legionella is the causative agent of Legionnaires' disease, and its prevalence in potable water is a significant public health issue. Water stagnation within buildings increases the risk of Legionella. However, there are limited studies investigating how stagnation arising through intermittent usage affects Legionella proliferation and the studies that are available do not consider viable but non culturable (VBNC) Legionella. This study used a model plumbing system to examine how intermittent water stagnation affects both VBNC and culturable Legionella. The model plumbing system contained a water tank supplying two biofilm reactors. The model was initially left stagnant for ≈5 months (147 days), after which one reactor was flushed daily, and the other weekly. Biofilm coupons, and water samples were collected for analysis at days 0, 14 and 28. These samples were analysed for culturable and VBNC Legionella, free-living amoebae, and heterotrophic bacteria. After 28 days, once-a-day flushing significantly (p < 0.001) reduced the amount of biofilm-associated culturable Legionella (1.5 log10 reduction) compared with weekly flushing. However, higher counts of biofilm-associated VBNC Legionella (1 log10 higher) were recovered from the reactor with once-a-day flushing compared with weekly flushing. Likewise, once-a-day flushing increased the population of biofilm-associated Vermamoeba vermiformis (approximately 3 log10 higher) compared with weekly flushing, which indicated a positive relationship between VBNC Legionella and V. vermiformis. This is the first study to investigate the influence of stagnation on VBNC Legionella under environmental conditions. Overall, this study showed that a reduction in water stagnation decreased culturable Legionella but not VBNC Legionella.

Tracking the changes of dissolved organic matter throughout the city water supply system with optical indices

Dissolved organic matter (DOM) is important in determining the drinking water treatment and the supplied water quality. However, a comprehensive DOM study for the whole water supply system is lacking and the potential effects of secondary water supply are largely unknown. This was studied using dissolved organic carbon (DOC), absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC). Four fluorescent components were identified, including humic-like C1-C2, tryptophan-like C3, and tyrosine-like C4. In the drinking water treatment plants, the advanced treatment using ozone and biological activated carbon (O3-BAC) was more effective in removing DOC than the conventional process, with the removals of C1 and C3 improved by 17.7%-25.1% and 19.2%-27.0%. The absorption coefficient and C1-C4 correlated significantly with DOC in water treatments, suggesting that absorption and fluorescence could effectively track the changes in bulk DOM. DOM generally remained stable in each drinking water distribution system, suggesting the importance of the treated water quality in determining that of the corresponding network. The optical indices changed notably between distribution networks of different treatment plants, which enabled the identification of changing water sources. A comparison of DOM in the direct and secondary water supplies suggested limited impacts of secondary water supply, although the changes in organic carbon and absorption indices were detected in some locations. These results have implications for better understanding the changes of DOM in the whole water supply system to help ensure the supplied water quality.

Performance of public drinking water purifiers in control of trihalomethanes, antibiotics and antibiotic resistance genes

Point-of-use water purifiers are widely applied as a terminal treatment device to produce drinking water with high quality. However, concerns are raised regarding low efficiency in eliminating emerging organic pollutants. To enhance our understanding of the reliability and potential risks of water purifiers, the removal of trihalomethanes, antibiotics, and antibiotic resistance genes (ARGs) in four public water purifiers was investigated. In the four public water purifiers in October and November, the removal efficiencies of trichloromethane (TCM) and bromodichloromethane (BDCM) were 15%-69% (averagely 37%) and 6%-44% (averagely 23%). The levels of TCM and BDCM were lowered by all water purifiers in October and November, but accelerated in effluent compared to the influent in one public water purifier in December. The removal efficiencies of twelve antibiotics greatly varied with species and time. Out of twelve sampling cases, the removal efficiencies of total antibiotics were 25%-75% in ten cases. In the other two cases, very low removal efficiency (6%) or higher levels of antibiotics present in effluent compared to the influent were observed. Two public water purifiers effectively remove ARGs from water, with log removal rates of 0.45 log-3.89 log. However, in the other two public water purifiers, the ARG abundance accidently increased in the effluents. Overall, public water purifiers were more effective in removing antibiotics and ARGs compared to household water purifiers, but less or equally effective in removing trihalomethanes. Both public and household water purifiers could be contaminated and release the accumulated micro-pollutants or biofilm-related pollutants into effluent. The production frequency and standing time of water within water purifiers can impact the internal contamination and purification efficacy.

DBP-FP change of biofilm in drinking water distribution system induced by sequential UV and chlorine disinfection: Effect of UV dose and influencing mechanism

The issue of biofilm-related disinfection byproducts (DBPs) in drinking water distribution system (DWDS) has garnered significant attention. This study sought to examine the changes in biofilm-originated halogenated DBP formation potential (biofilm DBP-FP) in simulated continuous-flow DWDSs subjected to sequential UV and chlorine disinfection (UV-Cl2) treatments with varying UV doses and to propose the underlying mechanism. The formation potential of trihalomethanes (THMs), haloacetic acids (HAAs), and the total organic halogen (TOX, X = Cl and Br) produced by biofilm were measured. Results showed that the biofilm TOCl-FP was at a minimum with a UV dose of 80 mJ/cm2, corresponding to the lowest amounts of protein and polysaccharides in the extracellular polymeric substances (EPS). Sphingobium, Methylobacterium, and Sphingomonas played a crucial role in protein and polysaccharide biosynthesis. Bacterial community composition characterization together with metabolic function analysis indicated that dominant bacteria varied and metabolic function shifted due to UV-Cl2 disinfection, with Alphaproteobacteria increasing in relative abundance and Bacteroidia showing the opposite trend with increasing UV doses. Correlation analysis suggested that the UV-Cl2 disinfection process led to changes in the water matrix, including organics, inorganics, bacteria, and components that provide environmental pressure for the biofilm. These changes ultimately influenced the properties of the biofilm EPS, which had a direct impact on biofilm DBP-FP.

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Impact of prolonged hotel closures during the COVID-19 pandemic on Legionella infection risks

In general, it is accepted that water stagnation and lack or poor maintenance in buildings are risk factors for Legionella growth. Then, in theory, the prolonged hotel closures due to the COVID-19 pandemic may have increased the risk of Legionella infections. However, there are very few field studies comparing the level of Legionella colonization in buildings before the pandemic and the new situation created after the lockdown. The objective of this study was to analyze these differences in a group of hotels that experienced prolonged closures in 2020 due to the COVID-19 pandemic. We have studied the Legionella spp. results, analyzed by standard culture, from the domestic water distribution systems of 73 hotels that experienced closures (from 1 to >4 months) during 2020, immediately after the reopening. The results were compared with those obtained in similar samplings of 2019. For the comparative analysis, we divided the hotels in two groups: Group A that have suffered closures for ≤3 months and Group B that remained closed for more than 3 months, both in relation to the opening period of 2019. In the Group B (36 sites), the frequency of positive samples in the hot water system increased from 6.7% in 2019 to 14.0% in 2020 (p < 0.05). In the Group A (37 sites), no significant differences were observed. No statistically significant differences were observed in terms of positive sites (defined as hotels with at least 1 positive sample), Legionella spp. concentrations and prevalence of Legionella pneumophila sg1 between the samplings of the two periods studied. The results suggest that hotels that suffered the longest prolonged closures (> 3 months) could have carried a higher risk of exposure to Legionella in the domestic hot water system. These findings highlight the importance of adequate preopening cleaning and disinfection procedures for hotel water systems, and the convenience of considering the most effective disinfection methods especially for hot water systems and after prolonged closure periods.

Insights into the role of prechlorination in algae-laden raw water distribution process: Algal organic matter and microcystin-LR release, extracellular polymeric substances (EPS) aggregation, and pipeline biofilm communities

Prechlorination routinely applied for the treatment of algae-laden raw water has received extensive attention due to its influence on water quality and aquatic microbes. In this study, prechlorination experiments with different doses were conducted in sets of model raw water distribution systems. With the elevated dose of chlorine and prolonged hydraulic retention time (HRT), the ratio of intact algal cells decreased, and the stability of water enhanced. Dissolved organic carbon (DOC) and nitrogen (DON) increased when chlorine dose elevated from 0 to 0.5 mg/L but decreased with elevations from 0.5 to 2.0 mg/L, while UV₂₅₄ showed a monotonically increasing tendency. DOC, DON and extracellular microcystin-LR increase initially and decrease thereafter with the prolonged HRT. Notably, the effects of prechlorination on extracellular polymeric substances aggregation behavior on pipe walls and microbial community composition was revealed, providing more profound understanding of the community dynamics in this engineered system. This study helped optimize strategies to improve the stability and efficiency of pretreatment of algae-laden water.

Spatiotemporal distribution of opportunistic pathogens and microbial community in centralized rural drinking water: One year survey in China

Centralized water supply in rural areas, supported by small waterworks (small-central mode) and by municipal water treatment plants (urban-extension mode), is an important guarantee to implement the Rural Revitalization Strategy Plan (2018-2022) in China. Opportunistic pathogens (OPs) could not be evaluated by the national drinking water sanitation standards in China (GB 5749-2022), posing potential microbial risks in rural drinking water. In this study, the spatiotemporal distribution of OPs, microbial community and the associated functional composition under two central water supply modes were investigated by molecular approaches. The results indicated that OPs were widely presented in the rural drinking water regardless of water supply modes, and were more abundant than those in the urban tap water. The insufficient residual chlorine and higher turbidity triggered more microbial proliferation, posing a seasonal variation of OPs gene copy numbers and bacterial community compositions. In warm seasons of summer and autumn, the gene copies of E. coli, M. avium, Pseudomonas spp. and the amoeba host Acanthamoeba spp. achieved up to 4.92, 3.94, 6.75 and 3.74 log₁₀ (gene copies/mL), respectively. Potential functional prediction indicated higher relative abundance of pathogenic genes and infectious risks associated with the rural drinking water under small-central water supply mode. This one-year survey of the spatiotemporal distribution of OPs and microbial community provided scientific insights into microbial safety of rural drinking water, prompting attention on small-central water supply mode against OPs risks.

Trihalomethanes in drinking water from three First Nation reserves in Manitoba, Canada

Previous research indicates that the water distribution system used has a significant impact on the microbial quality of tap water sampled in First Nations reserves in Canada. This study tested tap water from homes in three First Nations reserves to compare the concentrations of four trihalomethanes and related water quality parameters between homes receiving piped water from a water treatment plant (WTP) versus homes equipped with cisterns that are filled by a water truck. Of all the samples collected across time from household taps, 75% of piped samples and 70% of cistern samples had TTHM concentrations exceeding Health Canada's maximum acceptable concentration (MAC) of 100 µg L^-1 total trihalomethanes (TTHMs) in treated water. In all communities and across sampling times, trichloromethane (CHCl₃) was the dominant trihalomethane (42-96%) followed by bromodichloromethane (CHBrCl₂) (3-37%) and dibromochloromethane (CHClBr₂) (1-18%). Tribromomethane (CHBr₃) always accounted for < 5% of TTHMs. Within each of the three First Nations reserves, the water distribution system had no significant effect on TTHM concentration at the household level. Sampling month had a significant effect on TTHM concentration due to temporal changes in dissolved organic carbon of the source water. Results suggest that families in the studied First Nations reserves receive drinking water with high TTHM concentrations and that improvements to the water treatment plant might be the most effective way to minimize trihalomethane formation.

Aspartame-Sweetened Tap Water: Transformation Products and 2,6-Dichloro-1,4-Benzoquinone Formation

Aspartame (APM), a dipeptide of aspartic acid (ASP) and phenylalanine (PHE), is a widely used artificial sweetener in beverages. It is unclear whether residual chlorine in tap water can react with APM to form disinfection byproducts (DBPs). Therefore, we investigated the formation of DBPs from the reaction of APM with residual chlorine in authentic tap water. APM and a commercial sweetener (CS) packet containing APM were studied under authentic and simulated tap water conditions. Eight chlorinated products of APM were detected using solid-phase extraction (SPE) and high performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS). These new chloro-products were tentatively identified based on accurate masses, isotopic patterns of 35,37Cl, and MS/MS spectra. Furthermore, we identified APM as a precursor to 2,6-dichloro-1,4-benzoquinone (DCBQ). DCBQ significantly increased to 2.3-12 ng/L with the addition of APM or CS in tap waters collected from different locations compared to 1.4-1.8 ng/L in the same tap water samples without sweetener. DCBQ and two of the chlorinated transformation products were identified in cold prepared tea containing APM. DCBQ formation was eliminated when the residual chlorine in tap water was reduced by ascorbic acid or boiling prior to the addition of APM or CS. This study found that eight new DBPs and DCBQ were produced by the reactions of residual chlorine with APM and CS. These findings show an unintended exposure source of emerging DBPs via APM sweetened beverages.

An Automated Toolchain for Camera-Enabled Sensing of Drinking Water Chlorine Residual

Chlorine residual concentration is an important parameter to prevent pathogen growth in drinking water. Disposable color changing test strips that measure chlorine in tap water are commercially available to the public; however, the color changes are difficult to read by eye, and the data are not captured for water service providers. Here we present an automated toolchain designed to process digital images of free chlorine residual test strips taken with mobile phone cameras. The toolchain crops the image using image processing algorithms that isolate the areas relevant for analysis and automatically white balances the image to allow for use with different phones and lighting conditions. The average red, green, and blue (RGB) color values of the image are used to predict a free chlorine concentration that is classified into three concentration tiers (<0.2 mg/L, 0.2-0.5 mg/L, or >0.5 mg/L), which can be reported to water users and recorded for utility use. The proposed approach was applied to three different phone types under three different lighting conditions using a standard background. This approach can discriminate between concentrations above and below 0.5 mg/L with an accuracy of 90% and 94% for training and testing data sets, respectively. Furthermore, it can discriminate between concentrations of <0.2 mg/L, 0.2-0.5 mg/L, or >0.5 mg/L with weighted-averaged F1 scores of 79% and 88% for training and testing data sets, respectively. This tool sets the stage for tap water consumers and water utilities to gather frequent measurements and high-resolution temporal and spatial data on drinking water quality.

Chlorine decay and disinfection by-products formation during chlorination of biofilms formed with simulated drinking water containing corrosion inhibitors

Corrosion inhibitors used to reduce pipe corrosion can alter the physical structure and biochemical components of the biofilm in premise plumbing systems. We studied the effects of corrosion inhibitors on chlorine decay and associated disinfection by-products (DBPs) formation by biofilms grown with simulated drinking water amended with silicate, phosphate, and the phosphate blends. Experiments were conducted with either intact biofilms or biofilm materials dispersed in solution during sonication (referred to as biomass). While there was no significant difference in chlorine decay among biomass from different biofilms, biomass from the phosphate blend biofilm showed the lowest trihalomethane (THMs) and haloacetic acids (HAAs) formation. The chlorine decay rate constants from the biofilm experiment were ranked as: phosphate blends > phosphate ≈ groundwater (GW) > silicate. The kinetics of chlorine decay and formation of DBPs were successfully described by pseudo-first-order kinetics. These fitting parameters were used to predict the DBPs formation in a realistic premise plumbing system. The results showed that biofilm-derived THMs and HAAs increased with increasing chlorine concentration, while THMs and HAAs first increased and then stabilized to a maximum with increasing biofilm total organic carbon (TOC) concentration. In general, the biofilms grown with phosphate-based corrosion inhibitors resulted in lower DBPs formation yield but higher bacterial release, which could potentially increase the risk of user exposure to opportunistic pathogens in drinking water. The silicate biofilms showed the largest yield coefficient of DBPs formation but had the least biomass and lower bacterial release.

Influence of point-of-use filters and stagnation on water quality at a preschool and under laboratory conditions

A local preschool installed NSF/ANSI 42 and 53 certified point-of-use (POU) filters in its classroom sinks and drinking fountains to protect children from the possibility of elevated lead (Pb) levels in drinking water. We examined the effects of these filters during flowing water and immediately following stagnation periods on Pb, chlorine, and bacterial concentrations in the field and the laboratory. Before and after typical school stagnation periods, we collected samples from filtered classroom sinks, a filtered drinking fountain and nearby unfiltered sinks for a year. No unfiltered samples exceeded Illinois State limits of 5 µg/L for Pb in pre-K through 5th grade schools. However, following stagnation periods as short as overnight (14.5 h), over half of post-stagnation filtered samples from classroom sinks exceeded 5 µg/L while post-stagnation unfiltered samples remained below 5 µg/L. Laboratory testing showed no significant increases in Pb with stagnation, suggesting that the preschool classrooms may have had Pb-bearing plumbing downstream of the filters which released Pb into the filtered drinking water. The filters effectively removed free chlorine (99% decrease) in both the preschool and laboratory. Installing the filters had the unintended consequence of significantly increasing the bacterial concentrations (as measured by qPCR) in the preschool's drinking water and in laboratory filter effluent. Legionella pneumophila, Pseudomonas aeruginosa, and Mycobacterium spp. were not detected in pre-stagnation unfiltered and post-stagnation filtered samples. These results suggest that the installation of POU filters be considered as one component of an overall strategy to decrease Pb concentrations in school drinking water that holistically considers the premise plumbing system. A 5-minute flush significantly decreased concentrations of Pb and bacteria in filtered sinks. Replacing Pb-bearing plumbing components downstream of a POU filter may also be needed to combat Pb levels in drinking water.

Effects of pipe materials on the characteristic recognition, disinfection byproduct formation, and toxicity risk of pipe wall biofilms during chlorination in water supply pipelines

There are growing concerns over the contributions of biofilms to disinfection byproduct (DBP) formation in engineered water systems (EWSs). Three kinds of water supply pipes, ductile iron (DI), cement-lined stainless steel (SS) and polyethylene (PE) pipes, were selected for the experiment conducted in this study. Based on test results, the three pipe biofilms showed relatively obvious differences in growth, morphological characteristics, organic components and bacterial diversity. Secreted extracellular polymeric substance (EPS) accounted for more than 90% of the biofilm and had greater disinfection byproduct formation potential (DBPFP) than the cell phases. DI pipe wall biofilms had the highest DBPFP, which to a certain extent means that denser and richer organic matter can be produced as the precursor of different types of DBPs. UHPLC-Q Exactive was used to identify the types of DBPs generated from the chlorination of histidine (His), alanine (Ala) and tryptophan (Trp) shared by the three pipe materials and their formation pathways. Compared to carbonaceous disinfection by-products (C-DBPs), nitrogenous disinfection by-products (N-DBPs) had a significant advantage in toxicity generation potentials in the biofilms, especially dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM). DCAN and haloacetic acids (HAAs) were the key to cytotoxicity in biofilms, while TCNM was dominant in biofilm genotoxicity.

Effect of disinfectant exposure and starvation treatment on the detachment of simulated drinking water biofilms

Biofilms were one of the main habitats of microbes in the drinking water distribution system. The variation of environmental conditions can lead to the detachment of biofilms and the deterioration of water quality. In this study, the effects of disinfectant exposure and starvation treatment on the detachment of biofilms were investigated. The results showed that detaching rate increased with the concentration of chloramine in the inlet water and 1.0 mg/L of chloramine led to the largest detached biomass. The starvation treatment resulted in less biofilm biomass but the detaching rates of treated biofilms were higher than those without starvation. The 16S rRNA sequencing results showed that detached and stubborn biofilms had a significant difference in microbial diversity and richness. The microbial community composition of the two types of biofilm showed the difference in the abundance of Nitrospira, Bryobacter, Hyphomicrobium, and Pedomicrobium. Chloramine exposure did not have a significant impact on the microbial community while the starvation treatment led to a higher abundance of chemolithotrophs bacteria. Metagenomic results indicated that detached biofilms had higher abundances of ARGs and starvation treatment could enrich the ARGs. The results of this research could provide the knowledge of biofilm sloughing and help understand the health risk of antibiotic resistance in drinking water.

Bacterial community change and antibiotic resistance promotion after exposure to sulfadiazine and the role of UV/H2O2-GAC treatment

Effects of sulfadiazine on bacterial community and antibiotic resistance genes (ARGs) in drinking water distribution systems (DWDSs) were investigated in this study. Three DWDSs, including sand filtered (SF) DWDSs, granular active carbon (GAC) filtration DWDSs, and UV/H₂O₂-GAC DWDSs, were used to deliver sand filtered water, GAC filtered water, and UV/H₂O₂-GAC treated water, respectively. UV/H₂O₂-GAC filtration can remove the dissolved organic matter effectively, which resulted in the lowest bacterial diversity, biomass and ARGs in effluents and biofilm of DWDSs. When sulfadiazine was added to the sand filtered water, the dehydrogenase concentration and bacterial activity of bacterial community increased in effluents and biofilm of different DWDSs, inducing more extracellular polymeric substances (EPS) production. The proteins increasement percentage was 26.9%, 11.7% and 19.1% in biofilm of three DWDSs, respectively. And the proteins increased to 830.30 ± 20.56 μg cm^-2, 687.04 ± 18.65 μg cm^-2 and 586.07 ± 16.24 μg cm^-2, respectively. The increase of EPS promoted biofilm formation and increased the chlorine-resistance capability of bacteria. Therefore, the relative abundance of Clostridium_sensu_stricto_1 increased to 12.22%, 10.41% and 0.33% in biofilm of the three DWDSs, respectively. Candidatus_Odyssella also increased in the effluents and biofilm of the three DWDSs. These antibiotic resistance bacteria increase in DWDSs also induced the ARGs promotion, including sul1, sul2, sul3, mexA and class 1 integrons (int1). However, UV/H₂O₂-GAC filtration induced the lowest increase of dehydrogenase and EPS production through sulfadiazine removal efficiently, resulting in the least bacterial community change and ARGs promotion in UV/H₂O₂-GAC DWDSs.

Optimal Placement and Operation of Chlorine Booster Stations: A Multi-Level Optimization Approach

Chlorine demand as a disinfectant for water utility impacts on unintended energy consumption from electrolysis manufacture; thus, diminishing the chlorine consumption also reduces the environmental impact and energy consumption. Problems of disinfectant distribution and uniformity in Water Distribution Networks (WDN) are associated with the exponential urban growth and the physical and biochemical difficulties within the network. This study optimizes Chlorine Booster Stations (CBS) location on a network with two main objectives; (1) to deliver minimal Free Residual Chlorine (FRC) throughout all demand nodes according to country regulations, and (2) to reduce day chlorine mass concentration supplied in the system by applying an hour time pattern in CBS, consequently associated economic, energy and environmental impacts complying with regulatory standards. The application is demonstrated on a real-world WDN modeled from Guanajuato, Mexico. The resulting optimal location and disinfectant dosage schedule in CBS provided insights on maintaining disinfectant residuals throughout all the WDN to prevent health issues and diminishing chlorine consumption.

Domestic drinking water management: Quality assessment in Oforikrom municipality, Ghana

Drinking water in Ghana is estimated at 79%, but this only represents the proportion of the population with access to improved drinking water sources without regard to the quality of water consumed. This study investigated the quality of household drinking water sources in the Oforikrom municipality where potable water requirements are on the rise due to an ever-increasing population. Both quantitative and qualitative methods were employed in this study. One Hundred households were randomly selected and interviewed on the available options for drinking water and household water treatment and safe storage. A total of 52 points of collection (POC) and 97 points of use (POU) water samples from households were collected for physicochemical and microbial water quality analysis. Amongst the available drinking water options, sachet water (46%) was mostly consumed by households. Water quality analysis revealed that the physicochemical parameters of all sampled drinking water sources were within the Ghana Standards Authority (GSA) recommended values expected for pH (ranging from 4.50 to 7.50). For the drinking water sources, bottled (100%, n = 2) and sachet water (91%, n = 41) showed relatively good microbial water quality. Generally, POC water samples showed an improved microbial water quality in comparison to POU water samples. About 38% (n = 8) of the households practicing water quality management, were still exposed to unsafe drinking water sources. Households should practice good water quality management at the domestic level to ensure access to safe drinking water. This may include the use of chlorine-based disinfectants to frequently disinfect boreholes, wells and storage facilities at homes.

Derivates variation of phenylalanine as a model disinfection by-product precursor during long term chlorination and chloramination

Dissolved nitrogenous organic matter in water can contain precursors of disinfection by-products (DBPs), especially nitrogenous DBPs (N-DBPs). Amino acids are ubiquitous as dissolved nitrogenous organic matter in source water and can pass through drinking water treatment processes to react with disinfectants in finished water and in the distribution system. Phenylalanine (Phe) was selected as a model amino acid precursor to investigate its derived DBPs and their variations during a chlorination regime that simulated water distribution with residue chlorine. The 7-day DBPs formation potential (DBPsFP) test with chlorine revealed chlorination by-products of phenylalanine including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and halonitromethanes (HNMs), but not trichloronitromethane (TCNM) which was a significant N-DBP detected during the first 48 h of chlorine contact. The formation of most carbonaceous DBPs (C-DBPs) increased with chlorination time; however N-DBPs and non-chlorinated byproducts of phenylacetonitrile and phenylacetaldehyde reached their highest concentration after 2 h of reaction, and then gradually decreased until below detection after 7 days. The chlorination influencing factors indicated that light enhanced the peak yield of DBPs; the pH value showed different influences associated with corresponding DBPs; and the presence of bromide ions (Br^-) generated a variety of bromine-containing DBPs. The DBPsFP test with chloramine reduced C-DBPs generation to about 1/3 of the level observed for chlorine disinfection and caused an increase in dichloroacetonitrile. Surveillance of DBPs during drinking water distribution to consumers should consider the varying contact times with disinfectants to accurately profile the types and concentrations of C-DBPs and N-DBPs present in drinking water.

The role of biofilms on the formation and decay of disinfection by-products in chlor(am)inated water distribution systems

This study investigated the role of biofilms on the formation and decay of disinfection by-products (DBPs) in chlorine (Cl₂) or monochloramine (NH₂Cl) disinfected reactors under the conditions related to drinking water distribution systems (DWDSs). Biofilm analysis results revealed that at 0.5 mg/L of disinfectant residual, both Cl₂ and NH₂Cl were not effective to remove biofilms. As the disinfectant residual increased, biofilms could be eradicated by Cl₂, while remaining biofilms were still present even under the highest allowable NH₂Cl dose (4 mg/L) for 25 days. Low DBP formation was observed under the recommended minimum Cl₂ residual (0.5 mg/L), which could be attributed to limited Cl₂ reactions with biofilms, as well as a combination of the volatilization and biodegradation of DBPs. However, when Cl₂ residuals reached 2 mg/L, DBP concentrations in bulk water increased sharply beyond the DBP formation of the feed solution, with trihalomethanes and haloacetic acids being the most prevalent DBP species. The sharp increase was temporary for 15 days because of the removal of biofilms. For unregulated DBPs, high levels of haloacetonitriles were observed as attached biofilms reacted with the increased Cl₂ dose and provided an additional organic nitrogen source for nitrogenous DBP formation. When maximum Cl₂ residual (4 mg/L) was applied, no further increase of DBPs was observed because of biofilm eradication. For NH₂Cl disinfection, the DBP levels were much lower than those of Cl₂ disinfection, with small differences in DBP formation for different NH₂Cl residuals. Overall, this study provides insights into optimizing disinfection protocols for water utilities by balancing the benefits of disinfection application for biofilm control with minimized toxic DBP formation in DWDSs.

THMs, HAAs and NAs production from culturable microorganisms in pipeline network by ozonation, chlorination, chloramination and joint disinfection strategies

Disinfection is an indispensable process to inactivate pathogens, while unexpected disinfection by-products (DBPs) would also be formed between the reaction of residual disinfectants and microorganisms in the water distribution system (WDS). However, there are few studies referring to the formation of DBPs and DBPs-associated toxicity under various disinfection methods based on microorganisms in the real WDS. In addition, the main contributors of bacterial communities or components that generate DBPs are unclear. In this study, the formation of trihalomethanes (THMs), halo-acetic acids (HAAs), nitrosamines (NAs) from culturable microorganisms in pipeline network by ozonation(O₃), chlorination (Cl₂), chloramination (NH₂Cl) and joint disinfection methods were compared, meanwhile, their calculated toxicities under different oxidation scenarios were also discussed. Moreover, 16S ribosomal ribonucleic acid (rRNA) gene sequencing was used to identify the main microbial communities. The results demonstrated that THMs and HAAs increased with increasing disinfectant dosages, while the quantity of NAs (mainly nitroso dimethylamine (NDMA)) was not significantly related to disinfectant dosages for each disinfection strategy. Chloroform (TCM) and dichloroacetic acid (DCAA) were the dominant THMs and HAAs species, respectively. NDMA existed in the samples before disinfections, which may due to the metabolic activity of microorganisms. Pre-O₃ increased THMs formation during subsequent Cl₂ and NH₂Cl treatment. However, pre-O₃ effectively reduced HAAs produced by subsequent chlorination. O₃/Cl₂ disinfection had the highest DBPs formation potential (DBPFP) (883.6 nM), while its calculated toxicity was similar to that in Cl₂ disinfection treatment. Pseudomonas was the most abundant bacterial genus in biofilm of WDS pipeline. This study can aid in an optimal disinfection strategy for water treatment plants to reduce the toxicity of DBPs caused by biomass in pipelines and ensure water quality safety.

Ferrate(VI) pretreatment before disinfection: An effective approach to controlling unsaturated and aromatic halo-disinfection byproducts in chlorinated and chloraminated drinking waters

Disinfection is an essential process of drinking water treatment to eliminate harmful pathogens, but it generates potentially toxic disinfection byproducts (DBPs). Ferrate (FeO₄^2-, Fe(VI)) was used to pre-oxidize natural organic matter (NOM, the precursor of DBPs) in source water to control DBP formation in subsequent chlorine or chloramine disinfection. Currently, it is unclear how Fe(VI) changes the structure of NOM, and no information details the effect of Fe(VI) pretreatment on the aromatic DBPs or the speciation of overall DBPs generated in subsequent disinfection of drinking water. In the present paper, Fe(VI) was applied to pretreat simulated source water samples at a Fe(VI) to dissolved organic carbon mole ratio of 1:1 at pH 8.0. ¹³C nuclear magnetic resonance spectroscopy was newly employed to characterize NOM in simulated source waters with and without Fe(VI) treatment, and it was demonstrated that Fe(VI) converted unsaturated aromatic C functional groups in NOM to saturated aliphatic ones. High-resolution mass spectrometry (HRMS) and high performance liquid chromatography/triple quadrupole MS were applied to analyze the DBPs generated in chlorination and chloramination of the source waters with and without Fe(VI) pretreatment. It was confirmed that Fe(VI) pretreatment followed by chlorination (or chloramination), generated DBPs containing less unsaturated, halogenated, and aromatic moieties than chlorination (or chloramination) without pretreatment by Fe(VI). Finally, the cytotoxicity of disinfected drinking water samples were assessed with the human epithelial colorectal adenocarcinoma Caco-2 cell line (a model of the intestinal barrier for ingested toxicants), and the results show that Fe(VI) pretreatment detoxified the chlorinated and chloraminated drinking waters.

Assessing the chemical compositions and disinfection byproduct formation of biofilms: Application of fluorescence excitation-emission spectroscopy coupled with parallel factor analysis

There are increased concerns over the contributions of biofilms to disinfection byproduct (DBP) formation in engineered water systems (EWS). However, monitoring the biomolecular characteristics of biofilms to understand their impacts on DBP formation has been a great challenge as it requires complex analytical techniques. This study aimed to examine the applicability of fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) to assess the chemical compositions and DBP formation of biofilms. Biofilms were collected from reactors grown on R2A media, as well as two drinking water-related organic substrates such as humic substances and algal organic matter. The chemical composition and formation of carbonaceous and nitrogenous DBPs of biofilms were continuously monitored every 21 days for 168 days and correlated with the derived EEM-PARAFAC components. Results indicated that all biofilm samples comprised mostly of protein-like components (∼90%), and to a lesser extent, humic-like components (∼10%). Strong correlations were generally found between tryptophan-like substances and the studied DBP formation (R2min ≥ 0.76, P < 0.05), indicating that they play a major role in producing biofilm-derived DBPs upon chlorination. Moreover, significant discrepancies between the chemical compositions and DBP formation of biofilms and their corresponding feed solutions were observed, likely due to biotransformation and biosorption processes. Overall, this work highlights that EEM-PARAFAC analysis is a promising tool to monitor the biomolecular characteristics of biofilm components and to predict the subsequent DBP formation in optimizing disinfection protocols for EWS.

Effect of disinfectant residuals on infection risks from Legionella pneumophila released by biofilms grown under simulated premise plumbing conditions

The ubiquitous presence of biofilms in premise plumbing and stagnation, which commonly occurs in premise plumbing, can exacerbate the decay of chlorine residual in drinking water. Using biofilms grown in a simulated premise plumbing setup fed directly with freshly treated water at two full-scale water treatment plants, we previously determined the mass transfer coefficients for chlorine decay in premise plumbing. These coefficients coupled with inactivation kinetics of L. pneumophila released from biofilms reported previously were integrated into a Monte Carlo framework to estimate the infection risk of biofilm-derived L. pneumophila from 1 to 48 h of stagnation. The annual infection risk was significantly higher when water stayed stagnant for up to 48 h in pipes covered internally with biofilms, compared to clean pipes without biofilms. The decay of residual chlorine due to biofilms during 48-hour stagnation led to up to 6 times increase in the annual infection risk compared to the case where biofilms was absent. Global sensitivity analysis revealed that the rate of L. pneumophila detachment from biofilms and the decay of chlorine residual during stagnation are the two most important factors influencing the infection risks. Stagnation caused by water use patterns and water-saving devices in the premise plumbing can lead to increased infection risk by biofilm-derived L. pneumophila. Overall, this study's findings suggested that biofilms could induce chlorine decay and consequently increase L. pneumophila infection risk. Thus, reducing stagnation, maintaining residual chlorine, and suppressing biofilm growth could contribute to better management of L. pneumophila infection risk.

Formation of biofilms from new pipelines at both ends of the drinking water distribution system and comparison of disinfection by-products formation potential

The gradual updating of the water supply network is one of the crucial ways to ensure the safety of drinking water all over the world. The phenomenon and regularity of the biological risk and chemical risk of biofilms of the new pipes in drinking water distribution system (DWDS) is inadequate researched by now. In order to explore the biochemical risks of biofilms after new pipes are used, this paper studied the growth of biofilms, the content of disinfection by-products (DBPs) and the potential for disinfection by-products (DBPsFP) after 2-year use by establishing a pilot test platform at both ends of the DWDS in City S. The results showed that the total bacterial count in new pipelines was between 1.38 × 10⁸-9.97 × 10⁸/cm²; the DBPsFP at the front end and at the back end was subtly different. The overall DBPsFP of biofilms was the highest, followed by the ductile cast iron pipe and the galvanized pipe whereas the stainless steel pipe was the lowest. The HPC content of the 2-year-old pipe (1.68 × 10⁵-7.09 × 10⁶ CFU/cm²) was remarkably higher than that of the 1-year-old pipe (1.04 × 10⁵-8.76 × 10⁵ CFU/cm²), and the generation DBPsFP was about 50% higher. When a new pipeline was put into use in the urban drinking water distribution system, biofilms with certain biological hazards and risks of DBPs disinfection by-products would form in a short period of time.

Dynamics of the physiochemical and community structures of biofilms under the influence of algal organic matter and humic substances

Increased loading of algal organic matter (AOM) during harmful algal blooms not only burdens water treatment processes but also challenges safe drinking water delivery. While organic constituents promote biofilm growth in drinking water distribution systems (DWDS), the effects of AOM on biofilm formation in DWDS are not well understood. Herein, three parallel biofilm reactors were used to assess and compare how treated AOM- and humic substance (HS)-impacted bulk water, and R2A medium (a control) affect biofilm development for 168 days. The 16S rRNA gene sequencing analysis revealed that the bacterial communities in biofilms were clustered with the organic matter types in bulk water, where Family Comamonadaceae was the most dominant but showed different temporal dynamics depending on the organic matter characteristics in bulk water. Higher diversity was observed in the biofilms grown in AOM-impacted bulk water (BFAOM) than biofilms grown in HS-impacted (BFHS) and R2A-impacted bulk water (BFR2A) as the biofilms matured. In addition, some taxa (e.g., Rhodobacteraceae and Sphingomonadaceae) were enriched in BFAOM compared to BFHS and BFR2A. The biofilm image analysis results indicated that compared to BFHS, BFAOM and BFR2A had relatively thinner and heterogeneous physical structures with lower amounts of cell biomass, extracellular polymeric substances (EPS), and higher EPS protein/polysaccharide ratios. Overall, this study revealed how AOM- and HS-impacted bulk water shape the physiochemical and community structures of biofilms, which can provide insights into assessing biofilm-associated risks and optimizing disinfection practices for biofilm control in DWDS.

Characteristics of water quality and bacterial communities in three water supply pipelines

Many cities in China have implemented urban water supply pipe network renovation projects; however, at the beginning of new pipeline replacements, customers often complain about water quality problems, such as red water, odour and other water quality problems. To overcome these frequent water quality problems, this study selected a commonly used ductile cast iron (DCI) pipe, stainless steel (SS) pipe and high-density polyethylene (HDPE) pipe for laboratory simulations of the water quality regularity of new pipes, the variations in pipe inner walls, and the presence of microbial communities. Based on the research results, combined with actual water sample analysis, the stabilisation time of the interaction between the tubings inner walls and bulk water was determined, to allow pipeline cleaning and water quality maintenance. The results showed that the water quality change in the DCI was the most significant, while the SS and the HDPE pipes showed consistent changes with severe initial deterioration, then later stabilisation to meet the required standard. The DCI inner wall changed from a loose porous particle shape to a relatively dense and irregular three-dimensional shape, with the constituent elements mainly being O and Ca. The SS inner wall had a uniform structure in the early stage, but are obvious spherical balls of different sizes formed later, with the elemental composition here mainly being C and O. The HDPE inner wall was smooth and had small perforations in the early stage, while the perforation in the middle and late stages increased to become rough and scale-like at a much later stage. The proportion of Proteobacteria in effluents (72.82% to 86.87%) was significantly increased compared with the influent (48.45%), while the proportion of Proteobacteria (86.87%) in the DCI was significantly higher than in the SS (74.28%) and HDPE pipes (81.68%). Moreover, compared with the influent (23.33%), the Bacteroidetes (2.79% to 3.32%) levels in the effluents were significantly reduced, indicating that the pipe material affects the microbial abundance in water.

Factory water interacts with pipelines resulting in water quality deterioration. To stop this happening and to improve the selection of water supply pipes, it is important to study the water quality, the inner wall of the pipeline, and the microbial community.