台灣地區之公共給水水源約有65％來自湖床之蓄水。而湖床內常易滋生藻類。藻類會增進淨水程序各單元之負荷，如增加混凝劑之需求及阻塞濾床。如藻體未在淨水程序中去除，而隨清水進入配水管網內，則可能死亡，而釋出藻毒、臭味物質及其他有機物，而引起配水管網內水質惡化之問題。故如何增進淨水程序對藻體之去除，為一值得研究之課題。
　　本試驗承研究室所進行前氧化劑對藻類混凝增益之研究，以實驗室培養之純種藻類：綠藻(Chodatella sp.)及矽藻(Navicula sp.)為研究對象，進一步的使用高分子凝集劑作為助凝劑，研究其對於混凝效果之影響與作用之機制。對於瓶杯試驗所形成的藻體膠羽以100 rpm之攪拌速度攪拌1分鐘，利用顆粒計數器進行藻體膠羽之粒徑分析，以所呈現之膠羽粒徑分佈描述膠羽破碎之情形。之後量測各種加藥條件下的膠羽進行膠羽特性分析，瞭解所形成之膠羽特性，最後以公式計算的方式推估出個別的膠羽強度。
　　試驗所得之結果顯示：使用臭氧及高錳酸鉀前氧化對於綠藻以明礬或高分子凝集劑混凝之效果均有助益。使用明礬作為混凝劑時，臭氧之效果優於高錳酸鉀。而高分子凝集劑作為混凝劑時，則以高錳酸鉀前氧化之混凝效果較佳。
　　使用臭氧及高錳酸鉀前氧化對明礬混凝矽藻之影響並不一致，經臭氧前氧化不利於混凝去除，可能為臭氧之氧化力，將矽藻外圍有助於凝集之胞外物破壞，降低矽藻之混凝效果。使用高錳酸鉀可增進矽藻之混凝效果。但加入足夠量之明礬，均可達到90%以上之去除效果。使用高分子凝集劑為混凝劑時，臭氧前氧化依然不利於矽藻混凝，而高錳酸鉀仍可增進混凝效果。
　　使用高分子凝集劑作為助凝劑，均可增進藻體混凝去除之效果，但使用在綠藻助凝之效果較明顯，對於矽藻之助凝效果有限。藻類混凝去除之機制以沈澱絆除時有較佳之去除效果，可大幅降低所需明礬之劑量，即使僅添加低劑量的明礬亦有非常好之效果。綠藻在有前氧化劑的條件下，添加高分子凝集劑能明顯增進混凝效果，但高分子凝集劑對經前氧化矽藻之混凝增進效果則較不明顯。
　　對於藻體膠羽特性之分析，加入前氧化劑所形成的膠羽較為鬆散，且沈降速度較慢。就膠羽強度而言，前氧化劑會使膠羽強度降低，且以高錳酸鉀前氧化所形成的膠羽強度最弱。高分子凝集劑可增進未前氧化矽藻之膠羽沈降速度及膠羽密度，使用臭氧及高錳酸鉀前氧化之膠羽密度皆下降。
　　綜合上述之結果，可知對原水中藻體之去除，應考量佔優勢藻種之不同。譬如綠藻佔優勢時，可使用臭氧作為前氧化劑，或硬度存在時以高錳酸鉀為前氧化劑，而以帶正電之高分子凝集劑為助凝劑，若矽藻佔優勢時，則應避免使用臭氧。

　　In Taiwan, over 65% of source water for public water supply is from reservoir. Owing to eutrophication, the growth of algae in the reservoir is quite common. Algae can cause water quality problems such as taste and odor and/or toxicity. During water treatment, if algae are not removed by coagulation and sedimentation, some species may clog filter. While other species can penetrate filter media, and cause water quality deterioration in distribution system.
　　In this research, pure-culture of green algae (Chodatella sp.) and diatom (Navicula sp.) were used to prepare algal suspensions. Both alum and polyelectrolyte were used as coagulant. Polyelectrolyte was also used as coagulant-aid, while alum was the primary coagulant. The effect of preoxidation with ozone and potassium permanganate on coagulation removal of algae was also studied. The algal floc size distribution after various mixing conditions were measured with particle counter, and the data used to look into floc strength.
　　The results show that preoxidation with ozone or potassium permanganate improved coagulation removal of green algae with either alum or polyelectrolyte as primary coagulant. However, ozone worked better when alum was used, and potassium permanganate was the choice of preoxidant when polyelectrolyte was the primary coagulant.
　　For diatom, ozone preoxidation had detrimental effect on alum coagulation. It is speculated that this may be due to the high oxidation power of ozone, which could oxidize those extracellular polymeric substances(EPS) of algal cells. EPS was said to be helpful to cell aggregation. Potassium permanganate preoxidation was found to improve the diatom coagulation by alum. The results also indicate that if alum doses were high enough, diatom removal rate could be higher than 90%, no matter if preoxidation was practiced or not. When polyelectrolyte was used as primary coagulant, potassium permanganate preoxidation still was beneficial to diatom coagulation removal, and preozonation also had bad effect.
　　When polyelectrolyte was used as coagulation-aid to alum, the cell removal rates of both green algae and diatom were improved. However, it was more significant for green algae than that of diatom. It could significantly reduce the required alum dosage.
　　As far as floc characteristics is concerned, the floc formed with preoxidation were more loosely packed, with lower density and settling velocity. Preoxidation also reduced floc strength, especially with potassium permanganate. When polyelectrolyte was used as coagulant-aid to alum, it generally formed larger floc with lower density and lower settling velocity. However, its effect on floc strength was mixed.
　　Based on the results from this study, it can be said that the strategy for algae removal from source water should be based on the dominant algae species. For example: when green algae dominate, either ozone used as preoxidant, or potassium permanganate couples with cationic polyelectrolyte can be adopted to enhance alum coagulatioin. However, preozonation should be avoid if diatom is the dominant species.

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