Characteristics of organic pollutants in source water and purification evaluations in drinking water treatment plants

The release of contaminants of emerging concern (CECs) into water bodies has aroused wide concern in recent years. Little information on the characteristics of CECs to pose potential risks even at low concentrations in urban water systems of Shanghai is available. This study investigated the occurrence and spatial distribution in source water, as well as the fates by drinking water treatment processes for organic compounds including 35 pesticides, 17 antibiotics, 7 microcystins (MCs), and 10 disinfection by-products (DBPs). The similar trends across seasons for COD and TOC, the indicators for organic pollutants, indicated that the water qualities in three targeted reservoirs were relatively stable. COD in the R3 reservoir inlet was 1.3-2.4 times greater than that in the R1 and R2 reservoirs, possibly resulting from the inflow of the Taipu River as a tributary. Pesticides, particularly methamidophos and metabolites, macrolide and sulfonamide antibiotics, particularly roxithromycin, were frequently detected in Shanghai source water inlets. Pesticide concentrations were 2.58-3.66 μg/L much higher than antibiotics (8.6-47.6 ng/L). The results showed that MCs (ng/L) and DBPs (haloacetic acids, HAAs μg/L; N-nitrosodimethylamine, NDMA ng/L) were found to be in low detection frequencies. It was found that 51.1-74.6% of organic matters in source water were composed of molecular weight (MW) <1 kDa. The removal rates for the part of MW <1 kDa were only 11.7-12.3% through the conventional treatment processes, compared with higher removal rates of 23.5-28.5% by advanced treatment processes. Pesticides, antibiotics and MCs can be significantly removed by six drinking water treatment plants.