應用醋酸萃取法與酵母菌生物吸附法回收畜牧污泥中銅及鋅之研究

Abstract

國內目前現有的廢水處理設施所產生之畜牧污泥常含有高濃度的銅及鋅，並導致堆肥中累積許多銅及鋅。應用此富含銅與鋅之堆肥可能會造成土壤表面含過高的銅及鋅，也不符合現有的法規。 首先，將畜牧污泥自污泥重力濃縮槽取出後，以105oC烘乾、過篩後以不同濃度之醋酸（1N、2N及4N）同時添加搭配2 %之過氧化氫水溶液，在不同時間（4、24及48 小時）的處理下，探討對於銅及鋅之去除率的影響。而酸萃取過後混合液，會使用離心的方式將其分離出上清液與殘餘物的部分。結果顯示，在添加2 %之過氧化氫水溶液可顯著促進畜牧污泥中銅及鋅的去除效率（p < 0.01），且最佳處理條件為使用4 N醋酸在48小時的處理下，對於銅及鋅的去除率分別為40及70 %，然而使用2N醋酸搭配過氧化氫水溶液的處理24小時後，與使用4N醋酸處理的組別無差異，然成本相對來說較低，故後續試驗採用此方法。 接著第二部分，將上述酸萃取之上清液經過濾後，使用1N之氫氧化鈉調整pH值至4.5、5.0及5.5，研究酸鹼值對於酵母菌生物吸附之影響。在生物吸附中，會添加少量糖蜜作為酵母菌之可利用碳源，本次酵母菌生物吸附試驗處理時間皆為4小時。研究顯示，在pH值5.5的條件下，麵包酵母可吸附濾液中90 %的鋅離子以及50 %的銅離子。接著在相同的條件下，接種不同比例（2.5%、5%及10 %）之酵母菌菌量，發現酵母菌接種比例對於酵母菌生物吸附效率並無顯著影響。 總而言之，結合上述兩方法可達到減少以及回收畜牧污泥中的銅與鋅，透過本研究所建立之醋酸萃取法及酵母菌生物吸附法的整合平台，可作為後續回收畜牧污泥中銅與鋅的方法之一，增加污泥回歸土地資源化之可利用性。

High concentrations of zinc and copper are often found in bio-sludge of livestock wastewater treatment facility and cause high zinc and copper accumulation in compost. Applications of zinc- or copper-rich compost to the field can result in high zinc/copper residues in the surface soil and violate the limitation of zinc and copper for land applications. The livestock bio-sludge was dried and treated with different concentrations of acetic acid (1N, 2N, and 4N). The acid-extracted sludge was then treated with or without addition of H2O2 during different time periods (4-, 24-, and 48-h) for investigating the efficiency of acid extraction of zinc and copper. The supernatant of the acid-extracted product was separated from the residues by centrifugation. Experimental results showed that the treatment set of the dried bio-sludge with 2% H2O2 significantly promoted the removal efficiency of zinc and copper from the bio-sludge (p < 0.01). Results showed that the best removal efficiency of copper and zinc from the bio-sludge was 40 and 70%, respectively, by 4N acetic acid in the 48-h group. The filtrated supernatant was adjusted to different pH values (i.e. 4.5, 5.0, and 5.5) with 1N NaOH for exploring the effects of acidity and alkalinity in the filtrate, containing the extracted zinc and copper, on the following bio-absorption by baker’s yeast. The molasses was added into the filtrate and used as the available carbon source to support the yeast’s growth during 4-h time course experiments for bio-absorption of the copper and zinc from the filtrate. Results of the study revealed that the removal efficiency of zinc from the filtrate was more than 90% by baker’s yeast, while of copper was about 50% at pH=5.5 and reaction time of 4 h. In summary, combination of these two approaches is expected to reduce and recycle the heavy metal in livestock sludge. The use of acetic acid with hydrogen peroxide can extract copper and zinc from the sludge. However, the use of 2N acetic acid with hydrogen peroxide solution under a 24-h time period can achieve the same effect by using 4N acetic acid. The yeast has the ability to absorb both copper and zinc in the filtrate at pH = 5.5. Hopefully, the achievement of this study can be applied to develop a machinery platform for recycling zinc and copper from livestock bio-sludge.