Drinking Water Treatments for Arsenic and Manganese Removal and Health Risk Assessment in White Rock, Canada

Abstract

The City of White Rock, Canada has been facing challenges of elevated concentrations of arsenic and manganese in its drinking water supply. A pilot water treatment study was conducted to explore effective contaminant removal solutions for human health risk mitigation. The arsenic and manganese removal performance of four treatment processes, including ozonation-manganese greensand filtration (OSF), OSF-iron-based granular media adsorption (OSFIA), the Burgess Iron Removal Method (BIRM), and BIRM-iron-based granular media adsorption (BIA) were evaluated. The non-cancer health risks and the incremental lifetime cancer risks (ILCR) posed by arsenic in different water sources were also assessed. The results show that OSFIA treatment achieved the highest arsenic and manganese removal. An average arsenic removal rate of 68.5% (initial concentration = 9.3 μg/L) was observed using OSFIA during two months of treatment, while manganese (initial concentration = 133.9 μg/L) can be completely removed. The arsenic removal was mainly be attributed to the adsorption of iron-based granular media. The mean values of non-cancer health risks of arsenic exposure due to oral intake of treated water were identified to be lower than the critical threshold for different age groups. In addition, the probability of critical ILCR occurrence can be greatly reduced. Based on the results from the pilot study, OSFIA was selected to construct a full-scale water treatment plant. Arsenic and manganese concentrations in the effluent from the plant can be reduced to a low-to-undetectable level, achieving negligible health risks to the residents of the city.