Quantifying drought-driven temperature impacts on ozone disinfection credit and bromate control
ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY(2024)
摘要
Climate change and drought can lead to unprecedented changes in surface water temperature requiring utilities to examine their ozone system's disinfection capability while minimizing bromate production. This pilot-scale study investigated temperature (15-30 degrees C) as a single/isolated variable affecting ozone operating performance (demand, decay rate, exposure (CT)) and the ability to achieve a Cryptosporidium log reduction value (LRV) of 0.5-1.5 logs, as defined by the United States Environmental Protection Agency (USEPA). When dosing 3.0 mg L-1 of ozone into a surface water with 2.5 mg L-1 of total organic carbon, an increase in temperature from 15 degrees C to 30 degrees C increased ozone demand in the dissolution zone from 1.0 mg L-1 to 1.6 mg L-1 (60%) and ozone decay rate from 0.07 min(-1) to 0.27 min(-1) (385%). Despite more rapid demand/decay, the required ozone dose to achieve an LRV of 1.5 logs remained at 2.4-2.8 mg L-1 due to the reduction in USEPA's CT requirement at higher temperatures (9.35 mg min L-1 at 15 degrees C vs. 2.31 mg min L-1 at 30 degrees C). Bromate formation exceeded the USEPA maximum contaminant level of 10 mu g L-1 when ozone was dosed to achieve LRV > 0.5 log at all temperature conditions. Chlorine-ammonium pretreatment (0.5 mg L-1 Cl-2, 0.1-0.5 mg L-1 NH4+-N) lowered bromate formation to <5 mu g L-1 under ambient (80 mu g L-1) and elevated (120 mu g L-1) bromide concentrations at all temperatures. These results were applied to evaluate a full-scale ozone system designed to achieve an LRV of 1.5 logs if drought increases temperature from 13 degrees C to 26 degrees C. The study systematically examined the role of temperature on ozone system performance, which can assist utilities planning for future drought-driven changes.
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