淨水前加氯之消毒效率及其對混凝沈澱的影響

Abstract

消毒效率的定義是指水中致病微生物在使用消毒劑後的失活率，為確保飲用水水質對消費者健康的安全無虞，歐美各國均將此一項目列入凈水廠凈水處理效能評估的重點；本國八十六年十一月所頒布『飲用水水源水質改善計劃書審核作業要點』中亦要求，使用不合於用水水源水質標準之原水凈水廠需提出凈水處理之消毒效率分析報告。在飲用水水質安全度要求日益嚴格下，加氯單元與現有水設備配合所能達到最佳消毒效率之研究實為當務之急。 國外凈水廠目前大都以後加氯消毒處理為主，故消毒效率的本關研究亦大都針對後加氯消毒，然由於臺灣地區原水氨氮偏高且多藻類的特性，水廠通常以原水前加氯配合水加氯使用之，此外，消毒效率亦與自然水體環境中水質環境有極相關，故國外消毒實務經驗並未能真正適用於國內的凈水工程上。 消毒效率的主要影響因子包括接觸時間與加氯劑量，綜合上述，實驗將分為兩方向進行並探討消毒效率影響，一為不同加氯劑量下，消毒效率的變化與接觸時間及餘氯形成的關係；其次為探討不同加氯點對消毒效率與混凝效率的影響。此外，藉由水廠各凈水單元處理後水的採樣水質分析結果，觀察前加氯在其他凈水單元的配合下，對於微生物去除及其他水質指標的處理效率。 實驗結果顯示，現場前加氯操作就消毒觀點而言，對於現行管制之總菌落數及大腸桿菌群密度皆能符合標準，然而前加氯量則有過量之虞；此外，結果亦顯示，當混凝劑與消毒劑同時存在時並不會降低消毒效率，但消毒劑若未充分混合即加入混凝劑則會降低混凝效率。

Disinfection efficiency is epresented by the inactivation rate of pathogenic microorganisms after the application of disinfectants. To ensure the drinking water safety, many countries have included this item in the assessment of drinking water treatment efficiency. On November, 1997, ERA in Taiwan, ROC, promulgated a policy that requires water facilities provide disinfection efficiency report when their source water does not comply with the standard for drinking water. Therefore, it is important to evaluate the existiong chlorination processes and other treatment facilities in order to achieve better disinfection efficiency and meet the increasingly strict safety drinking water standard. Most research about disinfection are focused on post-chlorination, because it is more commonly practiced in many countries. However, both pre- and pos-chlorination are practiced in Taiwan, due to the high contents of ammonia-nitrogen and algae in source water. Furthermore, since water quality can significantly affect the disinfection efficiency, the results from ther countriex may not apply to all situations. In this study, the variations on disinfection efficiency with the contact time and residual chlorine at various chlorine dosage were evaluated. The efficiencies of disinfection and coagulation by means of pre- and post-chlorination were also studied. Water samples were collected from various points in the water treatment plant , namely, after rapid mixing, sedimentation, filtration and finished tank to analyze microbial removal and other water quality treatment efficiency. The results showed that the current pre-chlorination could meet the disinfection standard required by the law. However, the application of chlorine in the process might be overdosed. The coexistence of the coagulate with the disinfectant did not decrease the disinfection efficiency, unless the coagulant was added before the complete mixing of the disinfectant.