消毒副產物於淨水流程中之生成與宿命研究

Abstract

經處理之汙水放流水已知為消毒副產物及其前驅物的來源之一，放流水的排放更可能影響下游水質以及增加下游自來水淨水廠的操作負擔。 為了解各項淨水流程對於消毒副產物的生成與宿命之影響，本研究調查傳統汙水處理廠及自來水處理廠處理流程中消毒副產物、消毒副產物前驅物之降解效率以及相關水質參數的變化。並以人工模擬受放流水汙染之天然水樣於實驗室模擬傳統自來水處理流程，以評估受放流水汙染之天然水樣將對淨水流程造成何種程度的衝擊。本研究評估之消毒副產物包含傳統消毒副產物：三鹵甲烷(Trihalomathanes；THMs)、含鹵乙酸(Haloacetic acids；HAAs)，以及新興消毒副產物：N-亞硝基二甲基胺(N-Nitrosodimethylamine；NDMA)。 研究結果顯示，家庭廢水因水中有機物濃度較高，有機碳、有機氮、UV吸光值等水質參數與消毒副產物生成潛能呈現相關性。實廠調查結果顯示二級生物處理能移除絕大部分的有機前驅物，生物處理對於THMs、HAAs以及NDMA的前驅物移除效率分別為：83.7%、79.0%、97.5%。但NDMA濃度於汙水處理流程中無明顯變化趨勢，其濃度介於13 ng/L至23 ng/L之間。 傳統自來水淨水流程也觀察到消毒副產物之前驅物濃度以及有機碳隨著處理流程而漸漸降低。由於部分有機前質被移除，NDMA生成潛能由原水之114.3-194.58 ng/L降至清水之32.9-49.6 ng/L，在自來水淨水流程當中所產生的NDMA濃度皆低於10 ng/L。因為自來水水源相較於家庭汙水相對乾淨，有機氮濃度並無觀察到顯著地變化趨勢。 而添加汙水放流水之天然水樣則因為廢水的添加而使得不同水質參數與消毒副產物前驅物濃度顯著增加。與傳統淨水流程相同的是，THMs與HAAs之前驅物濃度經淨水流程處理後濃度皆顯著下降。但因實驗設備的限制與水源特性稍有不同，NDMA前驅物實驗結果與傳統自來水處理流程稍有差異。

The treated wastewater effluent has known to be a source of disinfection by-products (DBPs) and DBP precursors. The discharge of effluent may also impact the quality of source water and raise the burden of drinking water treatment plant in the downstream area. To gain a better understanding for the effects of the different treatment processes on the formation and fate of DBPs, this study investigated the degradation profiles of DBPs precursors and related water quality parameters within the wastewater and drinking water treatment plants. Furthermore, laboratory synthetic wastewater impaired natural water was prepared to assess the impacts from treated wastewater effluent and treatment efficiency after conventional drinking water treatment processes. The DBPs investigated in this study included: (1) traditional DBPs: trihalomathanes (THMs) and haloacetic acids (HAAs), and (2) emerging DBPs: N-nitrosodimethylamine (NDMA). The results showed that in wastewater treatment plant, the concentrations of DBPs precursors were correlated with concentration of dissolved organic carbon, dissolved organic nitrogen, and UV absorbance due to the presence of the high concentrations of organic contents in wastewater. Moreover, the biological treatment could remove a great portion of organic precursors, where the precursor removal efficiencies (measured as DBP formation potential, DBPFP) of THMs, HAAs, and NDMA were 83.7%, 79.0%, and 97.5%, respectively. The concentration of NDMA in wastewater was around 13-23 ng/L in each treatment unit, but there was no obvious trend for concentrations of NDMA within the wastewater treatment processes. In conventional drinking water treatment plant, the concentrations of DBPs precursors and organic carbon were found to be reduced after treatments. Indeed, the NDMAFP were decreased from 114.3-194.6 ng/L to 32.9-49.6 ng/L. Because of the great reduction of organic precursors, the NDMA concentration in finished water was very low (<10 ng/L). However, it was difficult to characterize the trend of dissolved organic nitrogen concentration in drinking water treatment units because of its relatively low concentration (0.6-1.1 mg/L as N) as compared with those observed in wastewater (17.2 mg/L as N). The results of simulated drinking water treatment process showed that the concentrations of water quality parameters and DBPs precursors were significantly increased after spiking wastewater effluent into the natural water. The significant reductions of THMs and HAAs precursors after conventional treatment processes were similar to those obtained in full scale conventional drinking water treatments. However, different results of NDMA precursor removals were observed between simulated treatment tests and conventional drinking water treatment plant operation; and it was resulted from the different properties of raw waters used and the limitations between laboratory and full scale operations.