探討脫氯對模擬建物自來水配管生物穩定性之影響

Abstract

供應穩定且安全的飲用水在現代社會是相當重要的議題。當自來水進入建物配管中，時常停滯的條件使餘氯與水中有機物反應出許多消毒副產物。尤其在台灣的公寓社區多數會使用水塔，因而增加了自來水在建物配管的停留時間。為了減少消毒副產物對人體暴露的風險，許多住戶使用全戶型脫氯淨水裝置去除水中的餘氯。本研究目標將探討脫氯之行為對於自來水生物穩定性之影響。研究期間定期於模擬間接供水系統採樣並分析水質，並比較脫氯前後水質之差異。總異營菌數(HPC)與生物可利用有機碳(AOC)為本次研究採用的生物穩定性指標參數。研究結果顯示脫氯後，系統出流水之消毒副產物濃度下降但水中總異營菌數顯著增加至10^5 CFU/ml。然而出流水之生物可利用有機碳降低至可抑制微生物再生長之閾值濃度(< 10 μg/L)，因此出流水之總異營菌數於一個月後達到穩態而非持續上升。最後利用進流水之生物可利用有機碳計算之理論總異營菌數與實際檢測值相近，證明了出流水之總異營菌數之增加主要源自於進流水中的生物可利用有機碳。總結若是進流水之生物可利用有機碳高於閾值濃度，於建物配管前脫氯便會衝擊飲用水之生物穩定性。

The biological stability of drinking water is a crucial part for public health. In Taiwan, indirect water supply with extra water storage tank increases hydraulic retention time in premise plumbing and may increase disinfection byproduct (DBP) formation. Therefore, dechlorination devices are commonly used to reduce chlorine residual. The objective of this research was to explore the impact of point-of-entry dechlorination device on biological stability. A simulation of indirect water supply system was established and the water quality parameters were sampled and analyzed. Heterotrophic plate count (HPC) and assimilable organic carbon (AOC), carbon source directly support the microbial regrowth, are the main methods to access the biological stability. The results show that concentrations of DBPs in effluent were decreased and HPC were significantly increased to 10^5 CFU/ml after dechlorination. AOC in the effluent reached to the threshold of the nutrient scarcity (< 10 μg/L) that resulted in stable effluent HPC after one month. The theoretical HPC, calculated from the consumed AOC, was similar to the actual detected value. The result indicates that high amount of HPC in effluent is controlled by AOC in influent. To sum up, point-of-entry dechlorination could result in biological instability if AOC in influent is above the threshold of the nutrient scarcity.