Dry and Wet Deposition of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans on the Drinking Water Treatment Plant

This study investigated the concentrations and congener profiles of polychlorinated dibenzo- p -dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in intake source water (source water) and tap drinking water (tap water) of drinking water treatment plants (DWTPs). In order to have a better understanding on the influence of atmospheric PCDD/F deposition on drinking water, PCDD/Fs in the ambient air of a DWTP (DWTP-LN) were measured and both dry and wet deposition on the water treatment facilities were assessed. The results of this study indicated that the mean PCDD/F concentration in tap water (0.0039 pg WHO-TEQ/L) was found to be approximately 55% of magnitude less than that in source water (0.0086 pg WHO-TEQ/L). In addition, the total deposition flux (dry + wet) of PCDD/Fs entering the DWTP-LN was 27.0 ng I-TEQ/m 2 -year, and wet and dry deposition contributed approximately 12.0% and 88%, respectively. It reveals that dry deposition is more important than wet deposition of PCDD/Fs in the ambient air of DWTP-LN. Atmospheric deposition of PCDD/Fs will increase the level in source water of DWTP-LN up to 8.91 × 10 -3 pg I-TEQ/L, which is approximately 92% of the PCDD/Fs in source water. If a removal efficiency of 87% is achieved by conventional treatment processes including coagulation, flocculation, sedimentation and rapid sand filtration, the water after treatment may increase 1.16 × 10 –3 pg I-TEQ/L, which is approximately 43% of the concentration level in tap water. These results indicate that in the DWTP-LN, the influence of atmospheric deposition of PCDD/Fs on the drinking water is of great significance, and water treatment facility with a cover is suggested.