AWWA water science最新文献

Per- and polyfluoroalkyl substances (PFAS) occur widely in drinking water, and consumption of contaminated drinking water is an important human exposure route. Granular activated carbon (GAC) adsorption can effectively remove PFAS from water. To support the design of GAC treatment systems, a rapid bench-scale testing procedure and scale-up approach are needed to assess the effects of GAC type, background water matrix, and empty bed contact time (EBCT) on GAC use rates. The overarching goal of this study was to predict PFAS breakthrough curves obtained at the pilot-scale from rapid small-scale column test (RSSCT) data. The scale-up protocol was developed for pilot data obtained with coagulated/settled surface water (TOC = 2.3 mg/L), three GACs, and two EBCTs. Between 7 and 11 PFAS breakthrough curves were available for each pilot column. RSSCT designs were investigated that assumed intraparticle diffusivity is independent of GAC particle size (i.e., constant diffusivity [CD]) or linearly dependent on GAC particle size (i.e., proportional diffusivity [PD]). CD-RSSCTs effectively predicted the bed volumes of water that could be treated at the pilot-scale to reach 50% breakthrough (BV_50%) of individual PFAS. In contrast, PD-RSSCTs overpredicted BV_50% obtained at the pilot-scale by a factor of ~2–3. The shape of PFAS breakthrough curves obtained with CD-RSSCTs deviated from those obtained at the pilot-scale, indicating that intraparticle diffusivity was dependent on GAC particle diameter (d_p). Using the pore surface diffusion model (PSDM), intraparticle diffusivity was found to be proportional to (d_p)^0.25 when considering data up to about 70% PFAS breakthrough. This proportionality factor can be used to design RSSCTs or scale up existing CD-RSSCT data using the PSDM. Using pilot-scale data obtained with groundwater and wastewater-impacted groundwater as well as with additional GACs, the developed RSSCT scale-up approach was validated for PFAS breakthrough percentages up to 70%. The presented methodology permits the rapid prediction of GAC use rates for PFAS removal.

Cyanobacteria, also known as blue-green algae, are prokaryotic photosynthetic microorganisms present in freshwater and water supply systems worldwide. They are asexual phytoplankton species with gram-negative cell walls, and their pigmentation can vary from blue-green to red.

The accumulation of many excessively buoyant cyanobacterial cells or colonies (scum) at the surface of water bodies is called a “bloom event” or “proliferation.” In extreme cases, such agglomeration may become very dense and even acquire a gelatinous consistency and sometimes even looks like blue-green paint or jelly. The nature of cyanobacterial proliferation is very dynamic, and bloom events are followed by a dying-off phase.

Fast increase or accumulation in the population of cyanobacteria or algae in water systems can lead to harmful algal blooms (HABs) accompanied by the production of toxins. These events are exacerbated by climate change and population growth. It should be noted that harmful blooms caused by cyanobacteria are called “cyano-HABs,” but here we use the term HABs to also include cyano-HABs as well.

Cyanobacteria have long been recognized for their nitrogen fixing capacity (the ability to convert atmospheric N₂ to NH₃). It is estimated that they have been present in Earth's life cycle for more than 3.5 billion years. However, in the last 30 years, most of the literature covering cyanobacteria has focused on their ability to produce a variety of toxins responsible for intermittent but repeated, widespread poisoning of wild and domestic animals, aquaculture species and fish populations, and humans.

While many potentially toxic and/or nuisance species of cyanobacteria and their associated toxins have been detected, the mechanisms and drives for toxin production and release are not well understood. The increasing frequency and intensity of cyanobacterial proliferation leading to neurotoxin and hepatotoxin production is a problem for water utilities. The main toxins of interest are microcystins (e.g., MC-LR, MC-RR, MC-YR, MC-LA, MC-LW, MC-LF), nodularins, Anatoxin-a, Anatoxin-a(S), cylindrospermopsins, saxitoxins, aplysiatoxin, debromoaplysiatoxin, lyngbyatoxin-a, lipopolysaccharides, and most recently β-Methylamino-L-alanine. While microcystins such as MC-LR are the most frequently reported of the cyanobacterial toxins worldwide, other toxins are being detected more often than in the past, especially in more temperate climates.

Indeed, HABs can cause unpleasant taste and odor, which can decrease consumer confidence in the safety of their drinking water. Most often 2-methyl isoborneol (2-MIB) and geosmin, known for their signature earthy and musty odors, are the only two T&O compounds screened by laboratories in the United States. However, a range of compounds beyond those two can contribute to T&O issues. Less commonly studied classes, including sulfides, aldehydes, ketones, and pyrazines, can

Adding new unit operations to drinking water treatment systems requires consideration of not only efficacy for its design purpose but also costs, water quality characteristics, impact on overall regulatory compliance, and impact of other treatment unit operations. Here, pilot study results for ion exchange (IX) and granular activated carbon (GAC) are presented for a utility with both per- and polyfluoroalkyl substances (PFAS) and volatile organic contaminant removal needs. Specifically, the impact of upstream air stripping and phosphate addition on PFAS treatment performance was evaluated. Modeling was used to fit the IX and GAC pilot data and predict performance under different scenarios. GAC performance was generally consistent for treating water before or after the air stripper, but the addition of phosphate prior to air-stripping resulted in a loss of 15%–25% capacity for some PFAS on IX media, demonstrating the need to consider the entire treatment train before implementing PFAS removal unit operations.

Enhancing drinking water resilience has become increasingly important. However, a comprehensive analysis of drinking water emergency countermeasures is lacking. This study evaluated eight countermeasures including monitoring, local alternatives, reclaimed water, interconnection, bulk water, pre-packaged water, emergency treatment, and isolation valves from resilience and sustainability (i.e., life cycle cost) perspectives. While countermeasures such as interconnections perform relatively well from both perspectives, there is a clear trade-off between resilience and cost. Local alternatives and emergency treatment respond quickly and provide sustained supply during emergencies but may incur higher costs. Bulk water and pre-packaged water are typically inexpensive but have limited supply capacity and take time to distribute. As future threats are likely to become more frequent and prolonged, it is prudent for service providers to invest in countermeasures that perform well in both resilience and cost and use an integrated approach that combines high capital projects with bulk/pre-packaged water contracts.

Correction to https://doi.org/10.1002/aws2.1153.

Since publication of the article, a production error was identified in Table 1, where the last two column headings were swapped. The error had no effect on the analyses or conclusions reported in the study.

Correction to Table 1.