Suchergebnisse

AbstractWildfires can abruptly transform forests, char vegetation and soils, and create an environment susceptible to postfire erosion and runoff to nearby surface waters serving as potable water supplies. The rising trend in wildfire activity increases the risk to source waters, while postwildfire implications on drinking water treatment are not well understood. A laboratory‐based approach was used to simulate the effects of forest floor heating during wildfire on water quality. Surface soil and litter samples were heated in a furnace and leached to evaluate changes to water‐soluble compounds. Leachates were diluted to a dissolved organic carbon (DOC) concentration of 5.0 ± 1.0 mgC/L. Heated and unheated (control) leachates were compared for dissolved organic matter (DOM) properties, treatability by alum coagulation, and disinfection byproduct formation. Size exclusion chromatography, optical property characterization, and organic nitrogen levels suggest that the DOM character shifted to lower‐molecular‐weight, nitrogen‐enriched aromatic compounds following heating. Raw water total trihalomethane and haloacetic acid precursor yields were not significantly different following heating; however, pairwise responses varied. Chloropicrin precursor yields increased by an average of 155% following heating, while haloacetonitrile precursor yields showed minimal changes. Even at high coagulant doses (>80 mg/L), the heated leachates consistently exhibited a poor coagulation response to turbidity and DOC removal. The DOC removal per mg alum was statistically lower for the heated leachates compared to the control samples (mean Δ = −0.06 mgC/mg‐alum). The adverse effect of heating on the DOC removal of the leachates might be explained by a lower‐molecular‐weight DOM composition. While findings suggest an altered DOM character, utilities may also experience an increase in influent DOC concentrations coupled with higher, or even extreme, sediment loads, resulting in compounding effects on water treatment.

AbstractThe widespread and successful use of coagulation, ozonation, biofiltration, and granular activated carbon (GAC) adsorption for the treatment of impaired drinking water sources makes them attractive as an economical approach for direct potable reuse. This study systematically evaluated these processes for the treatment of four secondary wastewater effluents with the objective of meeting U.S. drinking water disinfection byproduct (DBP) regulations and developing treatment objectives. Total trihalomethane (TTHM) and the sum of five haloacetic acids (HAA5) targets of 60 and 50 μg/L, respectively, were developed under uniform formation conditions and were related to a target total organic carbon (TOC) concentration of 2 mg/L. Ozonation, followed by biofiltration, was effective in decreasing HAA5 formation to below the target levels, but GAC treatment was needed to meet the target TTHM and TOC levels. Optimizing the TOC removal before GAC treatment extended the GAC run times similarily to those found in drinking water treatment. Drinking water–based DBP formation algorithms were very effective in predicting TTHM and HAA5 formation.

The effectiveness of granular activated carbon (GAC) for carcinogenic volatile organic compounds (cVOCs) has not been evaluated in the low‐ to submicrogram per liter range. Rapid small‐scale column tests were used to determine the GAC performance at empty bed contact times (EBCTs) of 7.5 and 15 min for 13 cVOCs at a target influent concentration of 5 μg/L in a typical groundwater matrix. Breakthrough was assessed for vinyl chloride, dichloromethane, 1,1‐dichloroethane (1,1 DCA), 1,2‐dichloroethane (1,2 DCA), 1,2‐dichloropropane, carbon tetrachloride, 1,3‐butadiene, 1,1,1,2‐tetrachloroethane, 1,2,3‐trichloropropane, trichloroethylene, and tetrachloroethylene. The throughput to breakthrough was found to be linearly correlated to capacities calculated with single‐solute equilibrium isotherm parameters. Modest decreases, 9–13% on average, in throughput to 50 and 75% breakthrough were found when the EBCT was increased from 7.5 to 15 min. The carbon use rate (CUR), when scaled to simulate full‐scale adsorption, indicated that GAC would be a viable technology for seven of the cVOCs evaluated, with a CUR threshold of less than 0.2 lb/1,000 gal. It may be possible to use 1,1 DCA and 1,2 DCA as surrogates for assessing chemicals near the feasibility limit.

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.

AbstractThis study examines the effect of pipe characteristics and stagnation time on nitrification, disinfectant loss, and organic carbon concentrations. Pipe racks consisting of different pipe materials (chlorinated polyvinyl chloride [CPVC], cross‐linked polyethylene [PEX‐B], and copper), diameters (0.75 and 0.5 in.), and water stagnation times (1 week and 12 hr) were set up in two cities with different disinfectants (chloramine and free chlorine) and different corrosion control (orthophosphate vs. pH/alkalinity adjustment). Copper pipe material had lower residual concentrations relative to plastic pipe in both water systems. In the chloramine system, residual concentrations were lower for smaller‐diameter pipes, whereas diameter did not strongly influence residual concentration in the chlorine system. Total organic carbon (TOC) increased during stagnation in the chloramine system. Nitrification was observed in the chloramine system for stagnation times of 1 week and 12 hr, indicating that flushing as frequently as every 12 hr may not be an effective mechanism for nitrification control in building plumbing.