低溫處理對污泥脫水特性之影響

Abstract

近年來由於自來水使用之普及化及政府當局對廢水處理日益嚴格之要求，致使自來水之需求量及污水處理量明顯上升，也造成污泥年產量大幅增加。如何有效地作污泥調理以減少污泥之最終體積，並做好最終處置之預備，將是一日益重要的研究目標。傳統之污泥調理方法為添加高分子調理劑作化學調理，但由於相關之環保法規日趨嚴格，對淨水廠中能使用之高分子聚合物之種類及劑量有諸多限制，因此，多年來已有許多學者積極尋求一取代高分子調理之方法。本研究之目的為探討低溫處理及搭配化學調理對污泥調理脫水之影響，探討項目包含以冷藏溫度、時間及降溫速率之影響，期以低溫處理替代化學調理，或以低溫調理搭配化學調理作污泥調理，以減少高分子調理劑之加藥量。 研究結果顯示低溫處理之關鍵在於污泥結冰與否。在冷藏溫度未使污泥結冰時，低溫處理對污泥調理脫水並無明顯改善效果，但在搭配化學調理時，脫水速率之改善效果則遠優於單作化學調理，並可以低溫處理減低化學調理所須之加藥量。若將溫度降至使污泥結冰，其脫水性、過濾性、沉降性及脫水速率皆有顯著之改善效果，且較慢之降溫速度、較長之冷藏時間及較低之溫度有較佳之調理效果。

Currently, approximately one hundred and seventy thousand tons of sludge is produced annually from the water treatment plants in Taiwan. This amount is expected to increase astronomically due to the increasing demand for more quality water and the more stringent regulations regarding wastewater treatments implemented by the Government. How to minimize the sludge volume and optimize the sludge condition for final disposal in an efficient way has become the focus of many studies. Traditionally, sludge is conditioned chemically by using polymers. The current law forbids the discharge of wastewater containing certain types of polymers into water bodies, which limits the use of polymers. Other disadvantages of using polyelectrolytes include their significant cost and safety concerns. Therefore, it is necessary to search for other options for sludge conditioning. In this study, the feasibility of low-temperature treatment was evaluated. Cationic polyelectrolyte was also applied with the low-temperature treatment. Experimental conditions such as temperature, duration of cold storage, and the rate of lowering the temperature of the sludge are manipulated to find the most efficient conditioning. Experimental results indicate that the success of low-temperature treatment relies on the degree of freezing. After the freezing/thawing stage, the dewaterability, filterability and settling properties were all improved greatly. Better performance was observed at slower freezing rates, lower temperatures and longer period of freezing time. If the temperature was not low enough to freeze the sludge, no significant change in dewatering characteristics was observed. When low-temperature treatment was combined with polyelectrolyte conditioning, the improvement in dewatering rate was better than chemical conditioning alone, suggesting that low-temperature treatment may replace the use of polymer to some extent.