不同混凝藥劑用於染料製程廢水色度去除之評估

Abstract

染料工業屬於高污染行業，對於其製程廢水高色度、高鹽類的特質，混凝操作一般被評估是最具經濟效益的前處理程序。使用硫酸亞鐵及石灰於高pH值進行混凝是許多工廠普遍使用的操作方式，然而其耗費大量酸鹼劑，且由於石灰的加入而產生了大量易於設備中結垢的污泥。 本研究以實廠綜合廢水進行實驗，比較硫酸鐵、硫酸亞鐵與多元硫酸鐵等鐵鹽在石灰增重劑幫助下之混凝效果，結果顯示使用硫酸亞鐵的混凝效果明顯優於硫酸鐵及多元硫酸鐵，對於色度一般可達到85%以上的去除率且膠羽具良好沈降性。進一步分析其混凝機制，並非以往所認定之亞鐵氧化成三價鐵之故，而可能是利用亞鐵離子與染料分子先行產生錯合，進而吸附於石灰顆粒表面而被沈降去除。於實驗中發現如結合硫酸亞鐵及多元硫酸鐵進行混凝，由於所能處理的目標染料分子不盡相同，故可大幅降低水中殘餘色度。 同時並評估硫酸亞鐵、石灰混凝法加藥操作變數對混凝沈澱效能的影響。結果顯示硫酸亞鐵劑量對色度去除影響明顯，而石灰劑量除能對色度去除有所助益，適量石灰可增加膠羽層界面沈降速度。此外硫酸亞鐵與石灰的加入順序亦影響了混凝結果，先加入石灰的色度去除較先加入硫酸亞鐵為佳，然而具較低的沈降速度。最後針對不同批次廢水水樣使用應答曲面實驗設計法，利用望想函數探討混凝程序最適加藥劑量，建議硫酸亞鐵加藥劑量範圍在8 g/l ~ 9 g/l，石灰劑量範圍在3.5 g/l ~ 3.6 g/l。

Dyestuff manufacturing is a highly polluting industry which produces wastewater of high color and high salt content. Many plants adopt coagulation to pretreat the wastewater by adding ferrous sulfate and lime at high pH. The drawback of this method is that it consumes large quantities of acids and bases, and produces large amounts of sludge which causes the scale problem in the treatment facilities. In this study, we evaluated the coagulation efficiencies of various types of iron sulfate, including ferrous sulfate, ferric sulfate, and polyferric sulfate, with the aid of lime. The results showed that ferrous sulfate was significantly better than ferric sulfate and polyferric sulfate in that more than 85% color removal and flocs with better settling characteristics. After analyzing the mechanism for coagulation, it is proposed that the soluble pollutants first complex with the ferrous ion. The complex ion is then adsorbed on the surface of the lime particle to form larger flocs. Results also indicate that by combining ferrous sulfate, lime and polyferric sulfate, various dyestuff molecules can be removed and consequently the residual color are significantly lowered. The effect of dosage and the dosing sequence of ferrous sulfate/lime addition on coagulation were also investigated. The results indicated ferrous sulfate was effective in color removal, while lime aided in both color removal and floc blanket settling velocity. Coagulation of lime followed by ferrous sulfate addition was better in color removal but poorer in floc blanket settling velocity. Finally, the response surface methodology and desirability function were used on several batches of effluent of different water quality to determine the optimal dosage. By considering the cost for. ferrous sulfate, it is recommended that the optimal dosage for ferrous sulfate is between 8 g/l ~ 9 g/l and lime is between 3.5 g/l ~ 3.6 g/l.