- 學位論文
十二烷基硫酸鈉對電聚浮除法處理含氟廢水之效能探討
Effects of sodium dodecylsulfate on fluoride-containing wastewater treated by electro-coagulation-flotation (ECF) process
摘要
目前台灣半導體製造業主要是以傳統的化學沉降法作為氟系廢水的處理，其沉降劑為石灰、氯化鈣等含鈣鹽類，但由於化學沉降後所產生的晶體非常細小，故須以高分子聚合物或鋁鹽混凝後，才能有效去除。此外，由於氟化鈣仍有一定的溶解性，故通常都須加入過量的鈣鹽才能得到較佳的去除率。過量加藥不但增加藥品成本，殘餘的過量鈣離子會大量增加水的硬度，影響回收利用的可行性。 本研究利用偶極化鋁極板之電聚浮除反應槽處理含氟廢水，並以批次系統與連續系統測試其處理效能。先加入當量之鈣鹽降低氟離子濃度，之後再結合電膠羽浮除法(Electrocoagulation)與十二烷基硫酸鈉(SDS)去除懸浮微粒(SS)與殘餘氟離子，而將此結合的處理方法稱為電聚浮除法(Electrocoagulation-flotation)。 由實驗結果顯示，有添加SDS之SS去除率(80%以上)較無添加SDS(56.4%)高；處理500mg/L之人工含氟廢水時，批次式系統之最佳操作條件為：SDS添加量=5mg/L，操作電流＝0.6A，電聚時間＝4分鐘。在此操作條件下，殘餘氟離子濃度＝10.6mg/L；SS濃度＝40mg/L(去除率=95.2%)。連續式系統之最佳操作條件為：SDS添加量=30mg/L，操作電流＝1.0A，流量大小＝300ml/min，電聚時間＝1分鐘。在此操作條件下，殘餘氟離子濃度＝5.7mg/L；SS濃度＝44mg/L(去除率=94.7%)。 本系統中之共存陰離子(SO42-、HCO3-、H2PO4-)的干擾，可藉由增加鈣離子與SDS的加量克服。對於本系統中酸度的影響，當廢水之初始酸度接近於電聚前之氟濃度時，含氟廢水之去除效果最好。最後在處理半導體廠之含氟廢水時，添加之[Ca(OH)2]/[Ca2+]T ([Ca2+]T =Ca(OH)2+CaCl2•2H2O)比例，可藉由改變廢水之初始酸度加以調整而使氟離子與SS有最佳的處理效果。
並列摘要
Recently, the conventional defluoridation process of fluoride-containing wastewater of semiconductor manufactory is lime or other calcium precipitation. The calcium fluoride (CaF2) particles are usually so fine that they can only be removed effectively after coagulation of polymer or aluminum salt. However, CaF2 has still moderate solubility, so it usually has to add excess calcium salt. Therefore, over-dosing occurs frequently and increases the hardness in the effluent. The high level of hardness constrains the reuse of water . In this study, fluoride-containing wastewater was treated by a electro-coagulation reactor with bipolar aluminum electrodes. A bench-scale and a continuous system were used to evaluate the treatment performance. First, stoichiometric amounts of calcium salt would be added to decrease the fluoride concentration in aqueous solution. Then, electrocoagulation process and sodium dodecylsulfate (SDS) would be combined to remove suspended solids (SS) and residual fluoride ions. The treatment process of the combination is called electrocoagulation-flotation (ECF). The results indicated that the removal efficiency of SS with adding SDS (over 80%) is better than that without SDS (about 56.4%). When 500mg-F/L synthetic wastewater was treated, the optimal operating conditions of batch system were: the dosage of SDS= 5mg/L, the operating current= 0.6A, and the operating time= 4minutes. In this case, the concentration of residual fluoride ions and SS were 10.6mg/L and 40mg/L (removal efficiency about 95.2%), respectively. The optimal operating conditions of continuous system were: the dosage of SDS= 30mg/L, the operating current= 1.0A, the flow rate =300ml/min, and the operating time= 1minutes. In that, the concentration of residual fluoride ions and SS were 5.7mg/L and 44mg/L (removal efficiency about 94.7%), respectively. The interference of co-existing anions (SO42-、HCO3-、H2PO4-) can be overcome by increasing the dosage of calcium ions and SDS. The optimum initial acidity required for fluoride and CaF2 particle removal is close to the initial fluoride concentration after calcium precipitation. Finally, when fluoride-containing wastewater from a semiconductor manufactory was treated, the added [Ca(OH)2]/[Ca2+]T ([Ca2+]T =Ca(OH)2+CaCl2•2H2O) ratio can be modified by altering the initial acidity of the wastewater to make the best treatment efficiency of fluoride ions and SS.