由廢棄活性污泥萃取回收PHAs再製成生物可分解塑料系統之研發

目前國內外各地污水處理廠數量急遽增加，污水處理率也相對提高，然而每年所產生相當大量的污泥，需要委外處理，所需處理成本日漸提高，儼然已為污水處理業者最頭痛的問題。本研究基於廢物再利用的精神，以不同萃取方式來萃取廢棄污泥PHAs的含量，且找出最佳萃取條件，並將研發一套廢棄污泥回收PHAs系統，不僅可降低目前生產生物可分解塑料的成本，同時亦可使本來應該花錢處理的廢棄污泥，可以回收其生物可分解塑料成分，成為具有利用價值的物資，可解決污泥處理的問題，同時達到廢棄污泥資源化及減量化的目標，減少環境污染問題，建立永續發展。在廢棄污泥發酵產生揮發酸實驗得知，發酵溫度為40℃在第五天所得VFA濃度可達1350±38 mg C/L。經ADF馴養增加PHA含量實驗結果得知，在VFA進流濃度為400 mg/L，發酵溫度25℃及pH為9條件下，經過1107分鐘(約18小時)馴養後，可使污泥中PHA含量由2.3%提高70.6%。單純化學萃取法時，其最適操作條件分別為次氯酸鈉濃度60 v/v%，污泥液固比為1.00 mLmg-1，次氯酸鈉浸置時間為60 min；而高壓脈衝與化學複合萃取法時，次氯酸鈉濃度及浸置時間分別下降為10 v/v及5 min，將污泥先經高壓脈衝法後再做化學萃取，可以減少化學藥劑使用量；高壓脈衝與化學複合萃取法最適條件分別為伏特數100 V，反應時間30 sec，電壓頻率500 Hz，PHAs purity為83.1±1.75wt%，PHAs content為705±1.22 wt%。經由成本分析計算萃取每公斤PAH所需成本為421NTD，ADF馴養所成本為23.4NTD，迪化污水廠污泥量約為2,700公噸/月，每月委託清除處理費用約為27,000,000NTD，以平均含水率80%，每月污泥約可萃取出1,512,000公斤PHAs，以450 NTD/kg售價計，若廠區污泥回收萃取PHAs，不僅可以節省污泥處理成本，尚可經由販售PHAs (產值約680,400,000 NTD)原料至下游製造商而獲利，每月約有617,932,800 NTD的產值。

關鍵字

好氧動態進流；聚羥基烷基酸酯；廢棄污泥；過飽/過飢系統；高壓脈衝法

並列摘要

Currently, the number of sewage treatment plants at home and abroad is increasing rapidly and the treatment rate is relatively increased, while a considerable amount of sludge produced on annual basis, which requires outsourcing treatment, leads to increased cost, constituting it as the most troublesome problem for the sewage treatment industry. Based on the principle of recycling waste, the PHA content in waste sludge was extracted by different methods to identify the optimal extraction condition and develop a system for recovery of waste sludge to reduce the production cost of biodegradable plastic. In addition, the waste sludge, which was originally useless and costly, could be recovered for its biodegradable plastic ingredients to become valuable materials that simultaneously solve the accumulation and reutilization of waste sludge. It reduced environmental pollution and established a sustainable development in the industry. The result of waste sludge fermentation experiment showed that the concentration of VFA reached 1350±38 mg C/L at the fermentation temperature of 40℃ on day 5. The ADF domestication to increase PHA content showed that the PHA content in the sludge was increased by 70.6% after 1107 minutes (approximately 18 hours) of ADF domestication when the VFA inlet concentration was 400 mg/L at fermentation temperature of 25℃ and pH value of 9. In the pure chemical extraction method, the optimal operating conditions were as follows: sodium hypochlorite concentration at 60 v/v%, sludge liquid to solid ratio of 1.00 mLmg-1 and sodium hypochlorite immerse time of 60 min. In the case of pressurized pulse and chemical compound extraction, the concentration of sodium hypochlorite and the time of immersion were reduced to 10 v/v and 5 min, respectively, before the sludge was subjected to chemical extraction, in which the process reduced the chemical usage. The optimal conditions of pressurized pulse and chemical compound extraction were 100 V, 30 sec reaction time, 500 Hz voltage frequency, PHA purity at 83.1±1.75wt% and PHA content of 705±1.22 wt%. The cost per kilogram of PAH was estimated to be 421 NTD by cost analysis. The cost of ADF domestication was 23.4 NTD and the amount of sludge in the Dihua Sewage Treatment Plant was 2,700 metric tons per month, in which the commission fee was approximately 27,000,000 NTD per month. At an average water content of 80%, 1,512,000 metric tons of PHA could be monthly extracted from sludge. At a retail price of 450 NTD/kg, recovered sludge for extraction of PHA could save the treatment expense and the sales of raw materials to downstream manufacturers could be beneficial (commodity value of 680,400,000 NTD), yielding a monthly profit of 617,932,800 NTD.