都市垃圾焚化飛灰水洗廢水全回收與模廠試驗之研究

焚化處理為國內目前最主要的廢棄物處理方式，焚化飛灰因含有大量重金屬，被歸類為有害廢棄物，目前多以穩定化或固化後掩埋。根據許多國內外研究及實務經驗，發現飛灰水萃可萃取出大量氯鹽及部分重金屬，對於後續再利用大有助益，因此水洗也已成為許多飛灰安定化之前處理步驟。飛灰水洗液傳統物化處理難度不高，但仍有有害污泥產生，對於掩埋場及水資源不足的台灣，及因應多數焚化廠採廢水零排放設計，飛灰水洗液全回收確實有其必要性。因此本研究秉持循環經濟之想法，對焚化飛灰水洗液零排放全回收進行研究。根據本實驗室過去研究之結果，已成功分別對鈣及鉛進行回收，因此本研究期望能統合過去經驗使最終廢液符合排放標準。水萃液以CO2曝氣沉降回收Pb，將過濾之重金屬沉降污泥以HCl進行酸萃固液分離後即得到高純度PbCl2，此法預計能以水洗液吸收焚化排放之CO2，達到減碳之效果；經重金屬沉降後之水萃液以石灰蘇打軟化可獲得CaCO3之沉澱物；將鈣回收後之回收水以電解法進行處理，以鐵作為犧牲金屬，預計能獲得FeCl2，以及利用惰性電極，預計產生次氯酸溶液。在CO2曝氣程序中以pH 8.5左右為最佳操作條件，並得到良好的鉛去除效果。以理論蘇打加藥量之Ca去除率為99.6 %。酸萃後汙泥之Pb之重量百分比由1.73 %提升到6.72 %。飛灰水洗液經CO2曝氣沉降重金屬及石灰蘇打軟化法回收Ca後，水質已達放流水標準。回收FeCl2實驗中，2A條件下水中Fe2+濃度為19.72g/L，電流效率78.60%；10A條件下水中Fe2+濃度為17.00g/L，電流效率67.76%。電解產生次氯酸溶液所建議使用之參數為，電解時間4 hr、電解液氯離子濃度3 %、極板間距1 cm ，電流密度0.13 A/cm2以及蘇打軟化時以理論加藥量處理，可以產生 11,236 mg/L的自由餘氯量。模廠試驗之電解效率良好，自由餘氯濃度所測得之4小時電解效率為76.3 %，自由餘氯濃度約303 mg/L。

關鍵字

垃圾焚化飛灰；水萃程序； CO2曝氣；鉛回收；鈣回收；電解

並列摘要

Washing pretreatment is helpful to the recovery of incinerator fly ash, nevertheless, the treatment of its wastewater will produce hazardous sludge due to the high concentration of Pb, besides, the high concentration of Cl- is harmful to the receiving water body. So the recovery of fly ash washing wastewater is an important issue. The study on the recovery of Pb and Ca from the fly ash washing wastewater has been proved feasibly in the past, while the Cl- recovery technologies has not been studied. The Pb metal in the fly ash washing wastewater was recovered by CO2 aeration and sedimentation firstly, then the sludge was extracted by HCl, which can obtain high-concentration of PbCl2. This operation is expected to absorb the CO2 in the flue gas of the incinerator, to achieve carbon capturing. After then, the wastewater was softened by lime-soda method to obtain pure CaCO3 precipitate, finally, the recovered water was treated by electrolysis, iron was used as the sacrificial anode, FeCl2 was expected to be obtained to recovery as coagulant. Another study was recovery of hypochlorous acid solution by using inert anode. In the CO2 aeration operation, pH 8.5 is the optimum condition, and a good lead recovery is obtained, after the acid extraction, Pb concentration of the sludge increased from 1.73 to 6.72 %. The removal of Ca based on the theoretical soda dosage is 99.6 %, and the effluent could satisfy the discharge standards. In the FeCl2 recovery experiment, the Fe2+ concentration and the current efficiency were 19.72 g/L and 78.60 % under 2 A, while 17.00 g/L and 67.76 % under 10A electrolysis. The parameters recommend for producing hypochlorous acid solution are: electrolysis time 4 hr, chloride concentration 3%, electrode spacing 1 cm, current density 0.13 A/cm2, which can produce 11,236 mg/L of free residual chlorine. The electrolysis by the pilot tested was good, the current efficiency was 76.3 %, and the free residual chlorine concentration was 303 mg/L in the 4-hours electrolysis operation.