AWWA water science最新文献

Spray aeration is a comparatively low-cost option to reduce trihalomethane (THM) concentrations in distribution system storage. The effect of spray aeration on unregulated, toxic disinfection by-products was investigated in a bench-scale apparatus in closed-tank and open-tank experiments. In the closed-tank experiments, initially over 90% of THMs, trichloroacetonitrile, and chloropicrin were removed, while 36% of dihaloacetonitriles were removed. However, due to the buildup of concentrations in the tank headspace, removal rates for all compounds decreased significantly with time, falling to 44% removal of THMs, 76% removal of trichloroacetonitrile, and 58% removal of chloropicrin. Removal of dihaloacetonitriles decreased to zero. In the open-tank experiments, THM removal rates were high and did not decrease with time. Considering the results with open and closed tanks as approximate bounds for performance expected under real-world conditions in storage tanks, the findings suggest that spray aeration may not significantly reduce haloacetonitrile-related toxicity while halonitromethane-related toxicity may be reduced.

Two commonly used methods for cyanotoxin analysis are enzyme-linked immunosorbent assay (ELISA) and liquid chromatography/tandem mass spectrometry (LC–MS/MS). Two rounds of interlaboratory comparisons of ELISA and LC–MS/MS analyses were conducted with 12 participating laboratories to evaluate method performances in various matrices, including cyanobacterial bloom and drinking water samples. Fifteen cyanotoxins, including 12 microcystin variants, nodularin, anatoxin-a, and cylindrospermopsin were evaluated. The impact of sample matrices, preservatives, and quenching reagents was assessed, and no substantial effects were observed. Overall, comparable results were obtained among laboratories performing ELISA and LC–MS/MS analyses, respectively. ELISA results for fortified samples matched more closely with those from LC–MS/MS when microcystin cross-reactivities were considered, providing data 26% closer to theoretical values on average. This study demonstrates that understanding the effect of cross-reactivities when comparing ELISA and LC–MS/MS results and considering potential variabilities in commercial standards is important when interpreting data from these two methods.

Harmful algal blooms (HABs) have incurred numerous health problems through drinking water or exposure. A better understanding of the growth kinetics and toxin production under different environmental conditions will help develop tools for early-warning indicators for predicting HABs. Lab-scale experiments were performed with Microcystis aeruginosa PCC 7806 under varying N:P ratios and temperatures. We observed different growth behaviors for cultures growing at the three temperatures (20, 25, and 30°C). M. aeruginosa exhibited higher growth rates at higher N:P ratios during the incubation at 25 and 30°C. Microcystis 16S rRNA gene abundance correlated well with the cell growth parameters. Based on RT-qPCR data, the transcripts of mcyA, mcyD, and mcyE were occasionally detected with N:P of 76.86 showing highest detections of all gene transcripts. Intracellular microcystin (MC) production corresponded well with the presence of gene transcripts, while no extracellular MC was detected. These findings would provide valuable insights and beneficial guidance to further explore and predict the impacts of cyanobacterial blooms in freshwater systems.

This case study compared microcystins in tap water from 18 public water systems (PWSs) and 46 households with private intakes or nearshore wells (called self-supplied water systems [SSWS]) from Clear Lake, California during a major cyanobacterial bloom in 2021. Microcystin concentrations were below the US EPA health advisory (HA; 0.3 μg/L) for PWS with Clear Lake intakes and for SSWS drawing from wells. However, for SSWS with Clear Lake intakes (intake SSWS), 24 of 79 microcystin samples collected were at or above the HA (maximum 3.9 μg/L). Further, microscopy showed that 20 of 28 tap samples (post-treatment) from intake SSWS contained either cyanobacteria or algal cells. This demonstrates that robust multi-barrier treatment systems at PWS reliably removed microcystins, while the less sophisticated treatment systems at intake SSWS were compromised during a major cyanobacterial bloom. Intake SSWS should consider alternative sources of drinking water, including physically connecting to an adjacent PWS or drilling a well.

Managing the aging infrastructure of water distribution systems presents a challenge for many utilities. With various asset types competing for limited dollars, designing an effective asset management program is a resource allocation problem. Mobilization of equipment and crew is a significant cost (typically 2%–10%) within any capital improvement program. Therefore, selecting projects that target multiple asset classes together can reduce mobilization and help utilities stretch their budgets further. This research presents a process for modeling the joint renewal planning of multiple asset classes. The problem is framed as a dual-objective optimization, where the selection of project areas aims to maximize lead service line removal and water meter changeout together. A case study from a Midwest utility is presented, and empirical data suggests the dual-objective approach effectively reduces duplicate interventions in the same regions. Equity considerations are also examined, where constraints are added to enforce system-wide project selection. Results show that the sensitivity of the objective toward equity is dependent on the underlying spatial distribution of the target asset itself, where uneven spread of the target asset leads to greater negative impact on model performance.