Abstract
The study attempted to determine the hydraulic retention time (HRT) required for soil aquifer treatment (SAT) to reclaim water as potable water in an aspect of controlling disinfection byproduct (DBP) precursors. In order to evaluate the removal of DBP precursors, the uniform formation condition was used to estimate the formations of trihalomethanes (THMs) and haloacetic acids (HAAs). Effluent water from anaerobic-anoxic-oxic processes (A2O water) was fed through soil columns at different HRTs. Sand with low organic content and less specific surface area was selected to represent the ‘worst available case’ of subsurface environment in Japan. Overall, annual data (n ≥ 14) indicated that the average concentrations of THMs and HAAs for water passed through SAT with HRT less than 7 days were below the standard of drinking water. However, risks of exposure to THMs and HAAs were observed. Increasing HRT to 30 days resulted in the concentrations of regulated THM and HAA species lower than the 10% of the drinking water standard values, except for dichlorobromoform. Therefore, a treatment unit for bromide ion removal (e.g., anion exchanger) prior to chlorination is recommended to lower the risk levels of exposure to dichlorobromoform.
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