| 摘要: | 由於自來水供應水源中可能含有危害人體健康及引起人類疾病的病原體，因此為確保飲用水安全無虞，消毒是任何水處理系統的關鍵程序。而消毒程序不但需消減病菌數，同時要防止其再成長，以符合環保署飲用水品質標準之要求，確保人民之飲水安全與身體健康。飲用水的消毒方法眾多，大致有太陽光、臭氧、二氧化氯、過錳酸鉀、銀、碘、溴、輻射、氯銨、微過濾、慢過濾、紫外線、加熱、氯化等消毒程序，其中氯化消毒因具有合理的設備及消毒費用、廣範圍的殺菌力量、消毒能力佳、自來水品質穩定、餘氯值容易偵測及控制等諸多優點，是目前最廣為世界各國所接受及使用的飲用水消毒方法；若與過濾及沈澱等傳統水處理方法結合使用，可得到高品質的自來水。氯化消毒目前最常使用的消毒劑包括氯氣、氯化生石灰、次氯酸鈣及次氯酸鈉等，其中次氯酸鈉因較容易取得及處理，以及餘氯值容易偵測及控制等特色；因此，本研究採用此種消毒劑，針對台灣自來水公司所屬美濃營運所所轄之四個淨水場（美濃、廣興、六龜及梅蘭淨水場）的地下水及河川水等水體進行加氯量消毒與病菌數消減之研究。
當自來水的供應水源中含有某些有機物質時，可能與特定型式的氯反應，產生有害人體健康的消毒副產物，因此，環保署為維護民眾飲水的安全品質，對於這些消毒副產物訂定其上限標準規範。據此，本研究深入探
討加氯量與處理水量之間的最適比例，期望使處理後之水可達到環保署所訂定的飲用水安全標準，並減少消毒之操作成本，以及減輕消毒劑及消毒副產物對於用戶及環境之衝擊。自來水消毒效果之良窳，本研究依國家標準規範，以大腸桿菌及總菌落數作為指標。此外，對於自來水消毒效果的主要影響變因，諸如供應水源的濁度、含有有機物質的種類及濃度，以及消毒時消毒劑的劑量、作用時間、水之溫度及pH值等一併深入研究探討。
實驗結果顯示，在0.3~ 0.4 ppm自由餘氯值下，於溫度298oK消毒兩小時，具有較佳的消毒效果
Because pathogens that can harm human health and cause disease in humans can be present in drinking water supplies, disinfection is a key process of any water treatment system in ensuring that water is safe to drink. The dual objective of disinfection of drinking water is to provide the required level of organism destruction or inactivation and prevent bacterial regrowth in a distribution system, to protect health and to comply with the Taiwan Environmental Protection Agency regulations. Several disinfection treatment methods and technologies, such as solar disinfection, ozone, slow filtration, minifiltration ultraviolet light, chlorine dioxide, potassium permanganate, bromine, silver, iodine, radiation, chloramine and chlorination have been successfully used to produce safe drinking water. Water disinfection by chlorination is the most widely used technology in the world for providing acceptable quality drinking water. When combined with conventional treatment, such as sedimentation and filtration, good results have been obtained. The keys to its success are its easy accessibility in almost all of the world’s countries, reasonable cost, broad-spectrum germicidal potency, capacity for oxidation, and residual effect. For these reasons, chlorination is used in the present work to disinfect water obtained from river bed water supplies and groundwater sources in all four areas (Meinong, Kaun-Shin, Liouguei and Me-Lan drink water treatment plants). Primary disinfectants of chlorination are gaseous chlorine (Cl2), chlorinated lime (CaO• 2CaCl2O• 3H2O), calcium hypochlorite (Ca(ClO)2• 4H2O), and sodium hypochlorite (NaClO) solution. Because Sodium hypochlorite that is easier to handle and obtain than the other disinfectants, and is an easily measured residual in the treated water, it is used in the present work as disinfectants to disinfect drinking water.
Also, since certain forms of chlorine react with organic material naturally present in the raw water sources to form harmful chemical by-products, the Environmental Protection Agency has proposed maximum levels for these contaminants. For this reason, the amount of disinfectant that will be needed will depend upon the water flow to be treated, the required dosage according to the water quality and the country’s drinking water standards. In the present work, the effectiveness of disinfection is judged by analyzing for an indicator organism (total coliform bacteria and Escherichia coli). Furthermore, a number of factors can influence the formation of disinfection by-products. These comprise the types and concentrations of organic materials present when disinfectant is added, the dosage of disinfectant, the temperature and pH of the water, and the reactiontime. The relationships between these factors and drinking water quality are also discussed in the present work.
The experimental results revealed that the optimum conditions of disinfection were achieved by using 0.3- 0.4 ppm free available residual chlorine for about 2 h at 298 K. |
