AWWA water science最新文献

With increasing interest in using stannous chloride without filtration to achieve hexavalent chromium maximum contaminant level compliance in California, there is new urgency to quantify its effects on water quality and risks to public health manifested in distribution and premise plumbing systems. Accordingly, a 12-week groundwater pilot study was completed using ubiquitous premise plumbing materials under flowing (to waste) and stagnating conditions of hexavalent chromium-containing groundwater following stannous chloride addition without filtration. Results quantified the accumulation and release of chromium and tin, with total chromium concentrations exceeding regulatory or acceptable levels under stagnating conditions. Sediment with elevated chromium, tin, arsenic, and manganese concentrations was also observed. Given these observations would likely occur and worsen over time in distribution systems that cumulatively serve large populations, the use of stannous chloride without filtration represents an unacceptable risk to public health compared to other, more well-established, best available technologies.

Disasters can prompt hydrocarbon contaminants to reach building water systems, and ultimately customer fixtures. Here, seven water supply connectors (e.g., ice-maker lines, faucet connectors, washing machine hoses) were exposed to contaminated water, and were subsequently decontaminated by water flushing. After a 24 h contamination period, water samples were collected after three consecutive 72 h exposure periods. Samples were characterized for volatile organic compound, semi-volatile organic compound, and total organic carbon concentrations. New, uncontaminated, PVC tubing leached phenol at concentrations that exceeded the health advisory. All materials sorbed more than 90% of hydrocarbon contaminants during the initial exposure period. All materials then released the contaminants into the water during decontamination, at times above health-based limits. The majority of sorbed mass remained in the plastics at the end of the decontamination effort, indicating the products posed continued leaching risks. Public health guidance considerations and research needs were identified.

Hydrophobic ionizable organic compounds (HIOCs) like per- and polyfluoroalkyl substances (PFAS), pharmaceuticals, and surfactants have been detected in water supplies. Anion exchange is an effective process for the removal of HIOCs from water. Regeneration solution comprising methanol (ca. 75% v/v) and brine is used to effectively desorb HIOCs from resins to overcome the combination of electrostatic and non-electrostatic interactions. This research investigated different mono- and polyhydroxy alcohol cosolvents with brine to regenerate resins saturated with HIOCs to understand the effects of cosolvent properties on regeneration. For PFAS desorption using 25% v/v alcohol in 5% NaCl solution, regeneration efficiency increased in the order methanol < ethanol < 1-propanol. Experiments with the pharmaceutical diclofenac and surfactant dodecylbenzene sulfonate showed similar regeneration efficiency using 75% v/v methanol in 5% NaCl solution and 25% v/v 1-propanol in 5% NaCl solution and higher regeneration efficiency using 1-propanol than ethanol or methanol at the same volume fraction.

Chloraminated drinking water systems commonly use free chlorine conversions (FCCs) to prevent or control nitrification, but unintended water quality changes may occur, including increased disinfection by-product and metal concentrations. This study evaluated water quality in a chloraminated drinking water system and residential locations before, during, and after their annual, planned FCC. Water quality alternated between relatively consistent and variable periods when switching disinfectants. During the FCC, regulated four trihalomethane and five haloacetic acid concentrations increased by four and seven times, respectively, and exceeded corresponding maximum contaminant levels. Implications of disinfection by-product sampling during an FCC were assessed, and an approach to account for increased FCC disinfection by-product concentrations was proposed. For metals, the FCC had minor impacts on distribution system concentrations and did not appear to impact residential concentrations. Overall, observed variable water quality appeared primarily associated with switching disinfectants and depended on distribution system hydraulics.

US Environmental Protection Agency (EPA) requires public water systems (PWSs) that disinfect to maintain a detectable disinfectant residual throughout the distribution system (DS) to protect consumers against risks from microbial pathogens. The EPA is tasked with proposing revisions to the Microbial, Disinfectant, and Disinfection Byproduct rules by July 2025. Potential revisions could include a numeric minimum disinfectant residual level in place of the “detectable” requirement. Twenty-three states have defined a required DS numeric minimum disinfectant residual level. Only three such states, Louisiana, Colorado, and Pennsylvania, have made recent changes and have sufficient data available to assess implications. These states were used as case studies to assess the impact this regulatory change had on disinfectant residual levels and microbial and disinfection byproduct (DBP) occurrence in PWS DSs. Results included increases in disinfectant residual levels, decreases in total coliform positive occurrences and violations, and temporary increases in DBP occurrence and violations.

Ductile iron and copper coupons were aged 137–189 days and 2 days, respectively, with 2 mg Cl₂ L⁻¹ monochloramine under four water chemistries (pH 7 or 9 and 0 or 3 mg L⁻¹ orthophosphate). Subsequently, microelectrode profiles of monochloramine concentration, oxygen concentration, and pH were measured from the bulk water to near the coupon reactive surface, allowing estimation of flux and apparent surface reaction rate constants for monochloramine and oxygen. Both metals showed similar trends with orthophosphate where orthophosphate decreased metal reactivity with monochloramine (pH 9) and oxygen (pH 7). Comparing iron and copper coupons, apparent surface reaction rate constants for monochloramine and oxygen were one and two orders of magnitude greater, respectively, for iron coupons under all conditions. Overall, this research provides the first insights into monochloramine concentration, oxygen concentration, and pH by direct measurement near ductile iron and copper reactive surfaces aged in the presence of monochloramine.

Conventional metrics such as total organic carbon (TOC) and ultraviolet absorbance at 254 nm (UV₂₅₄) may oversee aspects of natural organic matter (NOM) reactivity in drinking water treatment. The novel photoelectrochemical oxygen demand (peCOD) analyzer indirectly measures the oxygen consumed during NOM oxidation with photo- and electrochemical methods, quantifying NOM reactivity. peCOD was valuable for tracking NOM degradation in nine drinking water treatment facilities, particularly in processes where conventional metrics failed to capture changes in NOM from partial oxidation (e.g., biofiltration and oxidation). However, peCOD exhibited moderate correlations with TOC (R² = 0.67) and UV₂₅₄ (R² = 0.48), indicating the need for its concurrent use with conventional methods. While peCOD was not a significant predictor of disinfection by-product formation potential (R² < 0.20), its inclusion alongside standard NOM metrics improved the performance of multivariable regression models. Thus, peCOD provided a rapid, standardized, operator-friendly, environmentally conscious, concentration-based approach for evaluating NOM characteristics in drinking water samples.

A data-driven approach is developed and proven for ranking the risk of low disinfection residual in water distribution storage tanks, 1 month ahead. The forecasting methodology uses water quality data collected from drinking water treatment plants, storage tank outlets, and rainfall data as inputs. This methodology was developed and tested with data from a water utility serving more than 5 million people. Results show high-risk category prediction accuracy of 75%–80%. Using a final year of unseen validation data, more than 90% of the storage tanks ranked in the top 20 by the forecasting methodology experienced low disinfectant residual in the following month. Storage tanks are critical water distribution system infrastructure that are currently managed reactively. The adoption of such readily transferable machine learning approaches enables direct proactive management strategies and efficient interventions that can help ensure drinking water quality.

The effectiveness of chemical oxidation depends on the type of cyanotoxins present in the water and varies with the water quality parameters. This study investigated four cyanotoxins to understand their reactions with conventional drinking water treatment plant oxidants and with advanced oxidation. Kinetic rate constants between saxitoxin, and two variants (dcSTX and neoSTX), and nodularin-R with chlorine, monochloramine, permanganate, ozone, and hydroxyl radicals (UV-H₂O₂) were developed under different pH and temperature conditions. Nodularin-R kinetic rate constants were comparable to peer-reviewed microcystin-LR rate constants with reaction rates in the order of OH radicals > ozone >> chlorine > permanganate >> monochloramine. The speciation of saxitoxins with pH had a dominant effect on their reaction rates with the listed oxidants. Chlorine was the only oxidant effective for saxitoxins removal. The reaction rates of saxitoxins with OH radicals varied slightly with pH but were around two orders of magnitude less than microcystin-LR's.