AWWA water science最新文献

Adsorption process modeling of drinking water systems can be a powerful tool for evaluating treatment performance, especially if the impact of natural organic matter (NOM), which can have a significant effect on system effectiveness, is considered. Models such as the pore and surface diffusion model (PSDM) in AdDesignS have been used extensively to model water treatment with granular activated carbon (GAC). PSDM can incorporate the impact of NOM on adsorption capacity; however, media fouling is only considered for five water types, limiting the extension of this approach or considering uncertainty in modeling results. A one-point derivation process to simplify parameter estimation is introduced to provide additional understanding about the mechanisms of fouling and how it could be implemented within the PSDM. This could allow users to consider other factors—specifically total organic carbon breakthrough—when incorporating fouling into their GAC performance predictions, leading to improvements in future modeling efforts.

With public water systems switching to chloramination for secondary disinfection, distribution system nitrification and diminished disinfectant residuals are a growing concern. While some states have adopted Nitrification Action Plans (NAPs), no comparative assessment exists on their impact on drinking water quality trends. This study uses causal impact analysis to evaluate the effectiveness of state-mandated NAPs in controlling nitrification. Chloraminated systems with residual challenges before NAPs showed increased residuals and at least a 26% reduction in total coliform detection post-mandate. Maintaining chloramine residuals above 1.5 mg/L can prevent nitrification and reduce violations without significantly increasing disinfection byproduct occurrences. In contrast, states with no notable challenges before the plan's enactment saw limited benefits. These findings offer policymakers valuable insights into the plan's implications, supporting informed decision-making, especially in areas where nitrate violation hotspots exist without a current plan.

With the publication of the toxicological review for hexavalent chromium, Cr(VI), the US Environmental Protection Agency may be initiating the process to develop a Maximum Contaminant Level (MCL) for Cr(VI) in US drinking water. This study developed national costs of compliance with Cr(VI) MCLs between 5 and 20 μg/L. All California water systems were excluded from the costs for MCLs of 10 μg/L and greater since California already adopted an MCL of 10 μg/L. For a national MCL of 10 μg/L, the minimum non-California capital cost is projected to be between $3.8B and $8.2B, with the minimum annual O&M cost ranging from $340M/year to $720M/year in 2024 dollars. The total population impacted by this MCL is projected at 4.36 million people. For communities smaller than 101 people, the minimum 2024 household cost for this MCL may have a 5th percentile value of $566/year and a 95th percentile value of $1611/year.

Workforce quality has been a major concern in the water utility sector for decades. While previous research presumes that workforce quality plays an important role in water utility performance, no research to date has explored this relationship empirically. This study represents a first attempt at quantifying the relationship between workforce quality and performance using a dataset containing water utilities in Texas serving over 500 customers, data on Safe Drinking Water Act (SDWA) violations, and water utility operator classes. The results of two negative binomial models, where the dependent variables are the count of SDWA health and SDWA monitoring and reporting violations between 2020 and 2024, show that workforce quality has a substantively large and statistically significant negative effect on SDWA compliance across both types of violations. An additional analysis explores the interactive effect of workforce quality and median income and workforce quality and water source on utility performance.

Permanent residential irrigation restrictions employed in locales, including Florida, are limited by poor awareness and compliance. To inform improved public communication, this electronic survey study, based on the elaboration likelihood model, tested three visual messages conveying varying levels of information (days, times, seasonality) surrounding irrigation restrictions. Nonprobability, quota-based sampling was used to recruit 2,615 Floridians and randomly assign message treatments to those subject to irrigation restrictions (n = 459). Treatments influenced information-seeking likelihood through some modalities; the most informative message prompted the greatest information-seeking likelihood. “Aware individuals” familiar with irrigation restrictions applicable to them, and thus motivated to engage more deeply with the message, reported greater intent to set their irrigation in alignment with policy, suggesting more information delivered to aware individuals could promote compliance. Potential negative effects among “unaware individuals” (who may have been less motivated to engage) suggest a need for cautious irrigation restriction campaign targeting and development.

Water systems using chloramine as a disinfectant are vulnerable to nitrification, which can degrade water quality by enhancing the loss of residual disinfectant, lowering pH, and providing substrates for the growth of heterotrophs, leading to a more active biofilm that may support opportunistic pathogen growth in the premise plumbing (i.e., piping within a building). This study examined the influence of a variety of domestic plumbing factors, specifically: use frequency (pipes used once per week vs. five times per week), pipe material (copper vs. CPVC vs. PEX-b), pipe diameter (3/8″ vs. 1/2″ vs. 3/4″), and flow rates (0.2 gal/min vs. 3.2–3.7 gal/min), on indicators of water quality and nitrification, specifically: residual disinfectant, ammonia, nitrite, nitrate, turbidity, pH, and adenosine triphosphate (ATP, a non-specific proxy for biological activity). Experiments were conducted on a set of 28 pipes connected to a chloraminated public drinking water supply. Fourteen of the pipes were operated at fast flow rates of 3.2–3.7 gal per minute (12.4–13.9 L/min), which corresponded to 2.7, 5.7, and 9.5 ft/s (0.81, 1.7, 2.9 m/s) for the 3/4, 1/2, and 3/8 in. pipes, respectively. The remaining 14 pipes were operated at slow flow rates of 0.2 gal per minute (0.8 L/min), which corresponds to 0.15, 0.36, and 0.56 ft/s (0.045, 0.11, and 0.17 m/s) for the 3/4 in. (19 mm), 1/2 in. (13 mm), and 3/8 in. pipes (9.5 mm), respectively. Faster velocity flows were associated with higher residual disinfectant, less degradation of ammonia, lower turbidity and lower ATP. These results suggest that the faster flow velocity altered the biofilm and reduced the amount of microbial activity and nitrification occurring. Differences were particularly strong in the 3/8 in. (9.5 mm) pipes, suggesting that a velocity of 9.5 ft/s (2.9 m/s) offered additional benefits in biofilm control, beyond those achieved at the velocities of 2.7 ft/s (0.81 m/s) and 5.7 ft/s (1.7 m/s) in 3/4 in. (19 mm) and 1/2 in. (13 mm) pipes, respectively. Pipes flushed once per week tended to reach a similar end state of loss of residual and progression of nitrification, with limited differences due to velocity, pipe material, or diameter. Better understanding of the conditions that are associated with nitrification offers the potential to better control nitrification. This in turn may help maintain residual disinfectant as a protection against harmful microorganisms in drinking water.

Effective biofilm recovery is essential when characterizing microbial communities on granular filter media in water treatment applications. This study evaluated (1) DNA extraction kit modifications to maximize DNA recovery and (2) low frequency sonication (40 kHz) durations to maximize recovery of viable cells for flow cytometry (FCM) considering filter media type (anthracite and granular activated carbon [GAC]), media age, and filter runtime. Both DNA and intact cell concentrations were greater for new GAC (< 12 months of full-scale operation) and anthracite compared to old GAC (> 20 years). Biomass yields for old GAC were improved by using a less aggressive bead-beating protocol (for DNA) and reduced sonication duration (for intact cells). Finally, collecting media at the beginning of a filter run (i.e., post-backwash) improved biomass recovery compared to sampling after long filter runtimes. Further study of carbon attrition during extraction is recommended.