Suchergebnisse

AbstractMany organic chemicals occur in reclaimed water at higher concentrations than in conventional drinking water sources. Some of these chemicals are known to occur at concentrations that pose chronic health risks. The toxicity or occurrence of other chemicals may not yet be known. Thus, potable reuse systems should achieve robust removal of known and unknown chemicals to ensure public health protection. Here, criteria were proposed for performance‐based indicators that could cost‐effectively verify this robust removal. The selection process was then demonstrated for a hypothetical system using ozonation, granular activated carbon, and direct ultraviolet photolysis. A set of indicators (e.g., acesulfame, meprobamate, perfluoroheptanoic acid, sucralose, iopromide, benzotriazole, and iohexol) was recommended on the basis of original and literature review data. However, the concentrations of some of these indicators are sufficient at certain locations only or decrease over time. Thus, indicators should be site‐specific, periodically reevaluated, and the topic of further research.

AbstractHydraulic performance issues in drinking‐water biofilters have sometimes been associated with phosphorus limitation and increased production of extracellular polymeric substances in previous bench‐scale studies. However, field studies utilizing phosphorus supplementation to improve biofilter hydraulic performance have produced mixed results. Here, we determined the ratio of activities for phosphatase to glycosidase (PHO:GLY), which are enzymes involved in acquiring orthophosphate and biodegradable organic carbon from complex organic substrates, to assess phosphorus limitation in 21 pilot‐ and full‐scale biofilters. Supplementation of the pilot‐scale biofilter influents with 37 μg/L orthophosphate‐P reduced the PHO:GLY from 1.8–40.3 (mean 14.8) to 0.3–15.9 (mean 5.3), demonstrating that increased orthophosphate availability decreases PHO:GLY. In the absence of phosphorus supplementation, the PHO:GLY of the pilot‐ and full‐scale biofilters ranged from 0.3 to 40.3 (mean 10.1), and no hydraulic performance issues were noted. Thus, severe phosphorus limitation appears uncommon in the field, suggesting that phosphorus supplementation is unlikely to improve hydraulic performance in typical drinking water biofilters.

AbstractAdsorption of perfluoroalkyl acids (PFAAs) by granular activated carbon (GAC) was evaluated in bench‐, pilot‐, and full‐scale studies to determine effects of PFAA characteristics and background organic matter on carbon use rates. Rapid small‐scale column tests (RSSCTs) were conducted according to the proportional diffusivity (PD) design to assess their suitability to predict full‐ or pilot‐scale GAC performance. PFAA removal from groundwater (GW) and coagulated surface water (SW) was studied with two sub‐bituminous coal‐based GACs. In batch tests conducted with pulverized GAC, the GACs performed similarly in GW, but the GAC with the larger mesopore volume was more effective for PFAA removal from SW. In column tests, carbon use rates decreased with increasing PFAA chain length and were lower for GW (total organic carbon [TOC] = 0.7 mg/L) than for SW (TOC = 2.0–2.7 mg/L). The volume of SW that could be treated to 10% or 50% PFAA breakthrough was about 50–60% of the volume of GW that could be treated when comparing pilot‐scale data for SW with full‐scale data for GW. Consistent differences in PFAA adsorption capacity were not observed for empty bed contact times of 13 and 26 min in full‐scale adsorbers treating GW. The PD‐RSSCT simulating PFAA removal from GW consistently overpredicted full‐scale adsorption capacity, on average by ~70%. Using a carbon use rate of <25 mgGAC/Lwater treated) as a criterion for the feasibility of GAC treatment, full‐ and pilot‐scale GAC adsorber data suggest that GAC is a viable treatment option (carbon use rate < 25 mgGAC/Lwater treated) for perfluoroalkylcarboxylic acids with six or more carbon atoms in SW and five or more carbon atoms in GW. For perfluoroalkyl sulfonic acids, GAC treatment is viable for compounds containing four or more carbons based on results obtained with both SW and GW.