- 學位論文
結合鈣鹽沉降及電聚浮除法處理砷系廢水之研究
Combining calcium precipitation and electro-coagulation-flotation to treat wastewater with high-concentration-arsenic
摘要
有鑑於半導體業中砷化鎵材料之興起，高濃度砷系廢水成為目前新興之污染物，砷已被證實和肺癌、肝癌及皮膚癌有關，濃度過高更會致人於死，因此，如何妥善處理此廢水是目前重要課題。 過去對砷之處理範疇，大多以低濃度為主，高濃度之研究較為有限，目前對於高濃度砷系廢水的處理，都是以鈣鹽固定為主，但是無法使廢水達到管制標準，需要再合併於其他程序進行處理，然砷酸鈣不易沉澱，污泥蒐集困難，砷污泥之處理費用更為一般污泥之五倍。因此本研究期望發展出一套可行又有效率之處理方法。 本研究主要結合鈣鹽沉降與電聚浮除法來處理500ppm之高濃度含砷廢水，就其可行性推估、主要去除機制、鈣鹽添加量、界面活性劑、電流密度、酸鹼度及干擾離子對除砷效率的影響進行探討。 實驗結果顯示，鈣鹽添加量對除砷效果有很大影響，當沒有添加鈣鹽對砷 僅有78.8%去除率，當添加鈣鹽，去除率可達99.9%，陰離子型界面活性劑(SDS)較有助於系統對膠羽之浮除，電流密度對砷之去除與浮除效果是重要操作因子，本研究之最佳操作條件為: 鈣鹽添加量=1.962g/L(Ca/As莫耳比=2)、SDS添加量=50mg/L、電流密度= 17.86mAcm-2、反應時間=15分鐘。在此操作條件下，殘餘砷濃度小於0.5ppm, SS小於30mg/L。 由酸鹼度影響實驗發現，最終pH對除砷效果較初始pH值重要。pH值改變也會造成顆粒表面界達電位改變，最佳浮除效果發生在零電位點，當廢水中存在陰離子，會與砷酸根離子競爭鈣鹽，及競爭SDS表面位置，整體來說影響之程度由大至小分別為：PO43-、SiO32-、SO42-、CO32-。
並列摘要
Because gallium arsenide (GaAs) becomes a new material in the semiconductor industry, the problem of treating high-arsenic-containing wastewater has newly risen. Arsenic has already been proved to be in relation to lung cancer, liver cancer and skin cancer. Excessive uptake of arsenide will cause death. Therefore, treating arsenic wastewater well is an important issue for environmental engineers nowadays. The treatment of arsenic is mostly aimed at low-concentration in the past and the process for high-arsenic-containing wastewater is limited. A common method for removing arsenic from wastewater is principally in calcium precipitation. But the treatment of calcium precipitation cannot reach the discharge standards of wastewater. It therefore needs to combine with other processes. Moreover, the sludge of calcium arsenates is very difficult to precipitate and collect. The costs of arsenic sludge treatments are five times to the ones of the normal sludge. Therefore, this study expects to develop a feasible and effective method to remove arsenic in high-arsenic-containing wastewater. This study combined precipitation of calcium, and electro-coagulation- flotation to treat the wastewater with 500ppm of As. The effects of the additions of calcium, type and concentration of the surfactants, current densities, pH, and interference ions on arsenic removal efficiency were eximed. The results indicated that the additions of calcium dramatically influenced the efficiency of arsenic removal. The removal efficiency increased from 78.8% to 99.9% as calcium was added. SDS facilitated to flotation efficiency. The current density is an important operating factor influencing arsenic removal and flotation efficiency. The best operating system of this study was the following, the dosages of calcium =1.962g/L(Ca/As molar ratio=2), the additions of SDS=50mg/L, the current density= 17.86mAcm-2, the reaction time=15 minutes. Under this operating system, the residual concentration of arsenic was less than 0.5ppm and SS was less than 30mg/L in the effluent. The final pH is more important than initial pH for arsenic removal. The changes of pH value caused the changes of zeta potential of particles. The optimum flotation efficiency occurs at the zero point of surface charged. The co-existing of anions compete the calcium with arsenate and the active cites with SDS. This fact cause the decrease the efficiencies of arsenic removal and SS removal. The series of the influence is PO43- > SiO32- > SO42- > CO32-.