以超音波前處理改良SDS-次氯酸鈉法萃取廢棄污泥PHAs技術

台灣每年產生近四百萬噸污泥，而國內近年來廢水處理廠污泥的處置費用佔了廢水處理廠約50%左右，故以廢棄物再利用之觀點作為基礎，本研究擬利用兩階段的萃取步驟，針對生活污水處理廠廢棄污泥來進行PHAs（Polyhydroxyalkanoates, PHAs）萃取方法評估。實驗過程為，找出最佳的第一階段處理方式與參數，以此改良第二階段的SDS-次氯酸鈉化學萃取法為主軸，期能達到降低藥劑使用、降低廢水排放、減少操作時間、廢棄物減量並再利用之目標。單純SDS-次氯酸納萃取法時，最適操作條件分別為SDS濃度1 %，污泥液固比為1.00 mL/mg，藥劑停留時間15 min，分析其PHAs之含量為43.08±1.73 mg PHAs/g VSS。當超音波前處理加入SDS-次氯酸納萃取法時，SDS濃度得以降低至0.7 %、污泥液固比降低至0.83 mL/mg、藥劑停留時間降低至10 min，可以得知於化學萃取前加入一物理前萃取，能有夠有效降低其藥劑使用量與藥劑停留時間；並提升單位污泥處理量。污泥前處理最佳操作參數為：輸出功率20W、持續時間0.5 min。成本部分，經過物理前處理之化學法萃取1kg PHAs之成本約為202 US$，降低藥劑使用量後萃取1kg PHAs之成本約為154 US$，降低了24%之萃取成本。比較經馴養後污泥與純菌培養之萃取原料，廢棄污泥雖有原始含量過低之問題，但本研究關注面向為藥劑減量，故成本降低才是本文首要評估之指標。關鍵字：廢棄污泥、超音波前處理、SDS-次氯酸鈉萃取法、聚羥基烷酸酯

關鍵字

廢棄污泥；超音波前處理； SDS-次氯酸鈉萃取法；聚羥基烷酸酯

並列摘要

Taiwan produces nearly 4 million tons of sludge each year, the cost of sludge treatment has constituted approximately 50% of the budget of wastewater treatment plants. From the viewpoint of waste recovery, this study used a two-stage extraction method to extract polyhydroxyalkanoates (PHAs) from waste sludge from a domestic wastewater treatment plant; the extraction results were evaluated. The optimal procedures and parameters were determined in the first stage and then used in the second stage to improve sodium dodecyl sulfate (SDS)–sodium hypochlorite (NaOCl) extraction. The extraction method was expected to meet objectives of reducing the use of chemicals, minimizing wastewater discharge, shortening operating time, reducing waste, and enhancing waste circulation. For SDS–NaOCl extraction, the optimal operating conditions were a SDS concentration of 1%, sludge liquid-to-solid ratio of 1.00 mL/mg, and chemical retention time of 15 min. After the extraction, the observed PHA content was 43.08 ± 1.73 mg PHAs/g VSS. Ultrasonic pretreatment was added to the extraction method, and the SDS concentration was reduced to 0.7%, liquid-to-solid ratio of the sludge was reduced to 0.83 mL/mg, and retention time of the chemicals was shortened to 10 min. Therefore, the addition of a physical pretreatment process before chemical extraction can effectively reduce the amount of chemical use and the retention time of chemicals; it can also increase the per unit volume of treated sludge. The optimal operating parameter for the ultrasonic pretreatment process was an output power of 20 W for 0.5 min. The chemical extraction of 1 kg of PHAs after the physical pretreatment cost US$202. After the amount of chemical use was reduced, extracting the same amount of PHAs was estimated to cost US$154; the extraction cost decreased by 24%. A comparison of domesticated sludge and raw materials produced by pure cultures indicated that waste sludge contained an excessively low amount of PHAs. However, this study focused on reducing the amount of chemicals; therefore, cost reduction was the primary assessment indicator in this study. Keywords: West sludge, Ultrasonic pretreatment, SDS–sodium hypochlorite extraction, Polyhydroxyalkanoates