Coagulant Replacement Study Using CaCl2 instead of Ca(OH)2 in a Dyeing Manufacturing Plant
|Keywords:||氯化鈣;混凝;氫氧化鈣;染料廢水;calcium chloride;coagulation,;calcium hydroxide;dye wastewater|
本研究以實廠單一染料製程廢水與綜合廢水進行實驗，比較氯化鈣與氫氧化鈣兩者之間的混凝效果。結果顯示在COD與色度去除效能比較上，添加氫氧化鈣與氯化鈣兩者差異不大，但添加氯化鈣卻無污泥過多以及加藥過量之風險。雖然實驗數據顯示氯化鈣添加量的多寡對於COD去除效能並無很明顯的幫助，但對於某些廢水添加氯化鈣是有助於去除色度。最後並以瓶杯實驗求得最適參數為氯化鈣劑量為2.6 g/L，硫酸亞鐵劑量建議為5.7 g/L，氯化鈣加藥點則在硫酸亞鐵之後加入。而於實廠測試中使用氯化鈣每噸廢水費用也比氫氧化鈣便宜，主要是因為污泥量減少了32%。且氯化鈣同樣具有幫助污泥脫水、提升膠羽沉降以及減少污泥量等優點。|
Dyeing industry which is one of the highly polluting industries produces a great quantity of high color and high salinity wastewater. Chemical coagulation is generally the most cost-effective process. In most factories, calcium hydroxide is extensively used as coagulants since it can provide alkalinity and absorb dye compounds resulting in significantly reducing color in dye wastewater. However, a large amount of waste sludge is produced during the addition of calcium hydroxide in dye wastewater. Moreover, during the preparation of calcium hydroxide coagulants, calcium hydroxide fine particles are easily suspended in the air which is harmful for the workers. Therefore, in this study, the feasibility of replacing calcium hydroxide by calcium chloride as an alternative coagulant was investigated in treating dye wastewater. In this study, a real stream of dye wastewater and composite dye wastewater were applied to compare the coagulation performance using calcium hydroxide and calcium chloride. The results showed that the removal performance of COD and color in addition of calcium hydroxide and calcium chloride as coagulants were similar in a single stream of dye wastewater or integrated dye wastewater. Nevertheless, in addition of calcium chloride resulted in less sludge production and prevention in over dosage. Although the experimental data showed that higher dosage of calcium chloride had little effect on COD removal, in some wastewater, addition of higher dosage of calcium chloride can improve decolorization. In jar tests, the optimal dosage of calcium chloride and ferrous sulfate were 2.6 g/L and 5.7 g/L, respectively. And the calcium chloride dosing point was right after adding the ferrous sulfate. In real wastewater application, it was found that the cost of treating per ton of dye wastewater was cheaper by using calcium chloride than calcium hydroxide, mainly due to a 32% reduction of sludge. Furthermore, by using calcium chloride as the alternative coagulant, it can improve the sludge dewaterability, floc settlement and reduce sludge production.
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