金門地區配水管網水質參數與微生物再生長之研究

Abstract

目前台灣地區之自來水廠，大多添加氯氣或次氯酸鹽等含氯消毒劑，來維護飲用水水質安全；因為加氯消毒具有成本低廉、使用技術成熟和殺菌力強等優點，同時適當的餘氯可以維持配水系統之消毒效果，故加氯消毒為台灣淨水場之主要消毒方式。但是含氯消毒劑會與水中之天然有機物發生反應形成消毒副產物（Disinfection By-Products, DBPs），如三鹵甲烷（Trihalomethanes, THMs）、含鹵乙酸（Haloacetic Acids, HAAs）等，對人體健康具有致癌、生殖危害之風險。 由配水管線將自來水運送至家戶的過程中，由於配水管線冗長導致滯留時間過長，使得配水管線中之餘氯常會被消耗殆盡，而無法消除或抑制水中微生物，造成管線內微生物再生長，甚至在配水管線管壁上形成生物膜，引發水質惡化的問題。本研究之目的為透過金門地區太湖淨水場和榮湖淨水場及其配水系統之實場採樣以及實驗室批次實驗，觀察飲用水經後加氯之後滯留於配水管線的過程中，其水質參數變化對於微生物再生長之影響；並探討消毒劑、微生物、消毒副產物三者之關聯性及其消長情形。 研究結果顯示，隨著配水管線中飲用水滯留時間的增加，造成自由餘氯逐漸被消耗殆盡；在缺乏自由餘氯的情形下進而導致微生物再生長的現象。消毒副產物三鹵甲烷則是隨著滯留時間的增加，水中三鹵甲烷前質和氯之接觸時間增長而持續形成三鹵甲烷；其中以氯仿濃度增加趨勢最為明顯，次之為一溴二氯甲烷和二溴一氯甲烷，而溴仿則是維持平穩的狀態。微生物降解作用為造成含鹵乙酸濃度下降之主要因素，且降解速率鹵乙酸之與含鹵素多寡有關，含鹵素越多者越不易被微生物所降解。根據批次實驗結果，當微生物總菌落數約達5×105 CFU/ml時，微生物可於短時間內迅速降解濃度為100 ppb之單鹵乙酸及雙鹵乙酸，而三鹵乙酸則不易被降解；其實驗分析結果與實場調查一致，微生物在未經馴養時難以利用多鹵素之含鹵乙酸。

Due to the requirement of 0.2 mg/L residual chlorine in the distribution systems, chlorination is the main disinfection method for waterworks in Taiwan. It has the advantages of low cost, effectiveness for inactivation of a wide range of pathogens, and a matured technology with extensive successful records. However, chlorination also produces disinfection by-products (DBPs) such as Trihalomethanes (THMs) and Haloacetic acids (HAAs), these DBPs could cause adverse health effects. After treatment, the tap water was transported to the households through the drinking water distribution system. Due to the complex pipe lines and the long residence time in the distribution systems, the residual chlorine in finished water may degraded. Meanwhile, the microorganisms will regrowth and the biofilms will accrue on the pipe walls, this may cause further deterioration of finished water quality. The objective of this research is to investigate the relationship among the concentrations of residual chlorine, the microorganisms and the disinfection by-product in distribution systems. The results will be helpful to elucidate the influence of residual chlorine on the microorganism regrowth and DBPs degradations in distribution systems. The results indicated the residual chlorine was decreased gradually after its residence in the distribution system. In the meanwhile the microorganism grew again, the THMs concentration were increase and the HAAs were degraded due to the biodegradation. Besides, the biodegradation rates of HAAs decreased as the number of halogen atoms increased. In warmer water and in the absence of enough residual chlorine, a large portion of dihalogenated HAA species degraded due to biodegradation. However, the rates of biodegradation are lower for trihalogenated HAAs.