加氯除藻對於混凝效率及消毒副產物生成之影響

Abstract

隨著工業的發展，水源污染日益嚴重，造成國內水庫普遍有優養化之現象。優養化水體中藻類的大量生長造成淨水程序處理上的負擔。藻類會造成淨水處理時阻塞濾池、縮短濾程、導致水質惡化、飲用水口感不佳與臭味等問題。此外，藻類細胞與細胞外產物也是造成水體中消毒副產物生成的前驅物質。因此本研究以純種藻類進行加氯混凝實驗，探討加氯除藻之影響及後續混凝效率的影響。實驗之純藻為水體中常見之綠藻（Chlorella sp.），混凝劑選用硫酸鋁及多元氯化鋁。 研究結果顯示，加氯對藻類的去除率和產生之溶解性有機物有高相關性，加氯同時會產生三鹵甲烷等有害健康物質。經由混凝沉澱可以去除大部分藻類及三鹵甲烷前驅物質，但對水體中溶解性有機物去除效率較差。而在加氯後混凝對於藻類去除效率皆有下降的趨勢，但對於三鹵甲烷前驅物質的去除率影響並不大。在混凝過程中藻類之去除率隨著加氯量增加而降低，需要過量的混凝劑才能達到良好的去除效果。不同的加藥方式會影響混凝效率，在經過前加氯反應後再進行混凝會對藻類去除效率造成影響，當同時加入氯和混凝劑進行混凝試驗時明顯會降低對藻類之去除效率。

Raw water quality is deteriorated because of the excessive development of industries, which promotes eutrophication and causes the blooming of algae in the reservoirs. Eutrophication makes the treatment of drinking water difficult. Algae cause uncomfortable taste and odor, clog the filter and penetrate the filter, leading to the deterioration of drinking water quality. In addition, Algae and its extracellular products are precursors of disinfection by-products. The goal of this study was to evaluate the effects of chlorination on algae and the subsequent coagulation. Algae used in this study was a green alga (Chlorella sp.). The coagulants used were aluminum sulfate and polyaluminum chlorides.

A high significant correlation was found between the removal efficiency of algae and the formation of dissolved organic compounds (DOC) on chlorination. Chlorination simultaneously produces the harmful trichloromethane compounds. With coagulation coupled to sedimentation, it can obviously remove the algae and precursor to trichloromethanes, but the DOC was difficult to remove by coagulation. On the other hand, prechlorination reduced the efficiency of algae coagulation, but no effect on the removal of the precursor of trichloromethanes. Algae removal decreased with the dosage of chlorine. Satisfactory removal occurred at overdosing only. The order of chemical dosing affected the removable efficiency of algae. Pre-chlorination had a detrimental effect on algae removal. Simultaneous chlorination and coagulation resulted in poor algae removal.