| 摘要: | 對灰渣及骨材而言，水洗是常採用的前處理方法，具有從材料表面洗出某些無益於利用之物質功效。但至目前為止，仍缺乏水洗廢水性質的相關文獻資料，故本研究主要目的在於瞭解垃圾焚化底渣水洗所衍生之廢水特性。另外，本研究更進一步以沉澱及過濾等傳統廢水處理方式，探討水洗廢水處理成效，同時並評估廢水循環再利用之可行性。 研究結果顯示，水洗廢水均維持高鹼性且pH大多大於11，且隨水洗時間增加，廢水SS、COD及總重金屬(如Pb、Zn、Cu、Cd、Cr)等濃度，基本上呈現增加的現象。且經水洗180分鐘後，濃度分別可達最高之31429 mg/L、3000mg/L及近百餘mg/L。在高液固比條件下水洗時，對廢水明顯具有稀釋的效果，且除COD外，各濃度稀釋倍數大致與液固比增加成正比關係。 若以L/S=5、水洗時間25分鐘之條件水洗時，廢水之SS、COD及總重金屬等之沉澱去除率分別為99%、76%及96%。且與沉澱+過濾之去除率差異不大。底渣水洗後，由質量平衡計算可知，重金屬約有8%分佈於廢水中，而經沉澱處理後，廢水中重金屬幾近完全沉澱於污泥中。沉澱污泥氧化態主要為SiO2及CaO，同時重金屬溶出濃度亦符合國內TCLP溶出標準。 以廢水經沉澱後之上澄液，回收再利用於底渣水洗時，廢水及上澄液之SS、COD及重金屬隨循環水洗次數增加，濃度有累積的現象，與初次水洗相較，廢水溶解性COD及Cl-濃度最高可提升2倍以上，但重金屬濃度增加幅度僅在10%內。至於廢水處理中之沉澱單元，對循環水洗所衍生廢水，大致仍維持穩定的去除率。對底渣而言，單位底渣之TDS及Cl-洗出量，隨重複水洗次數增加而降低，不過，單位底渣之重金屬洗出量，則較不受循環水洗次數增加而影響。 Water-washing process is a common pre-treatment because of the advantage of washing out undesired substances from the surface of ash and aggregate for improving their applications. However, little information concerning the properties of derived wastewater from water-washing process has been found in literature. Therefore, the main objective of this study was to examine the characteristics of wastewater derived from water-washing municipal solid waste incinerator (MSWI) bottom ash. In addition, the treatability of the wastewater by sedimentation/filtration and the feasibility of recycle and reuse the treated wastewater were evaluated. The results of this study indicated that the water-washing wastewater was high alkaline with pH greater than 11. The concentrations of SS, COD, and total heavy metals (e.g. Pb, Zn, Cu, Cd, and Cr) in wastewater were basically increased with the increase of water-washing time, and the maximum concentrations after 180 min of washing were 31429 mg/L, 3000 mg/L and hundreds of mg/L, respectively. Increasing the ratio of liquid-to-solid (L/S) for washing, the concentration dilution effect was significant for the derived wastewater. Also, the dilution ratio of wastewater concentrations was proportioned to L/S ratio, except for COD. For wastewater derived from water-washing under the conditions of 25 min of washing at L/S ratio was 5, the removal efficiency of SS, COD, and total heavy metals by simple gravity sedimentation was 99%, 76%, and 96%, respectively. The additional removal was insignificant if followed by filtration. According to the mass balance calculation, about 8% of total heavy metals were distributed in the wastewater when MSWI bottom ash was washed. However, most of the total heavy metals in wastewater were removed and settled down as a part of the sludge after sedimentation. The main oxide forms of settled sludge were consisted of SiO2 and CaO. In addition, the results of sludge leaching test revealed that the heavy metals concentration in leachate could meet the TCLP limits of Taiwan. When the supernatant of treated wastewater by sedimentation was recycled and reused as the water for bottom ash washing, it found that the concentrations of SS, COD, and heavy metals in the following derived wastewater and treated supernatant were accumulated gradually with the increase of the recycle number. The maximum concentrations of soluble COD and chloride in wastewater became two times higher than that in original; however, the concentration of heavy metals was only 10% higher. Nevertheless, the removal efficiency of sedimentation could still maintain a stable performance for treating the recycle-derived wastewater. Based on the unit weight of bottom ash, the amounts of TDS and chloride washed out were reduced with the increase of the recycle number, but the effect was insignificant for heavy metals. |
