정수장 슬러지는 수 처리 역 세척 과정에서 발생되는데, 기계적인 방법 또는 자연건조방법으로 탈수된 후 주로 해양투기, 매립등의 방법으로 처리한다. 최근에는 런던협약에 의해 해양투기가 상당히 제약을 받고 있다. 탈수된 정수장 슬러지를 위생매립장의 복토재로서의 활용가능성을 파악하기 위하여 실내실험을 통하여 정수장슬러지의 물리 화학적 특성과 지반공학적 특성을 파악하였다. 슬러지의 지반공학적 특성을 향상시키기 위하여 슬러지에 일반토사를 혼합한 시료에 비중계실험, 액 소성한계실험 비중실험, 다짐실험. 일축압측 실험등을 실시하였다. 슬러지에 일반토사를 혼합한 혼합토는 정수장슬러지와 비교하여 최대건조단위증량은 증가하고, 최적함수비는 감소하였고, 최대압축응력과 마찰각을 증가한 반면 점착력은 감소하였다. 미국환경청의 복토재 기준을 확보하기 위해서 슬러지와 일반토사를 3:7로 혼합하여야 하며, 혼합토의 압축강도는 3.6kg/cm2이다.

Waste oil sludge was generated from waste oil purification process, oil bunker, or the ocean plant. Although it has high calorific values, it should be treated as a designated waste. During the recycling process of construction and demolition wastes or the trimming process of woods, a lot of sawdust is produced. In this study, the feasibility of BOF (biomass and waste oil sludge Fuel) as a source of renewable energy was estimated. To estimate combustion characteristics, a lab scale batch type combustion reactor was used and temperature fluctuation and the flue gas composition were measured for various experimental conditions. The results could be summarized as follows: the maximum CO2 concentration in the flue gas was increased with increasing waste oil sludge content in BOF. SO2 concentration in the flue gas was showed a tendency such as the highest CO2 concentration in the flue gas. With increasing waste oil sludge content in BOF, the combustion time was rather shorter although the increase of the CO2 concentration in the flue gas was delayed. Because the carbon conversion rate showed small difference with increasing the mixing ratio of waste oil sludge in BOF, BOF with the mixing ratio of waste oil sludge of 40% was effective for combustion. With decreasing the air/fuel ratio and the mixing ratio of waste oil sludge in BOF, activation energy and frequency factor were increased. The optimal air/fuel ratio for the combustion of BOF was 1.5.

The large amount of waste oil sludge was generated from waste oil purification process, oil bunker, or the ocean plant. Although it has high calorific values, it should be treated as a designated waste. During the recycling process of construction and demolition wastes or the trimming process of woods, a lot of sawdust is produced. In this study, the feasibility of BOF (biomass and waste oil sludge fuel) as a renewable energy source was estimated. For manufacturing a BOF, a press type pelletizing was better than an extruder type and also 40 ~ 60% of mixing ratio in waste oil sludge was appropriate to produce a pellet. The pellet was 13 mm in diameter and 20 mm in length. There was no fixed carbon in waste oil sludge, and its carbon content and higher heating value were 63.90% and 9,110 kcal/kg, respectively. With an increse of mixing ratio of sawdust, the carbon content and heating value of the BOF were dropped, but fixed carbon content was increased. The heating value of BOF was in the range of 6,400 ~ 7,970 kcal/kg at the mixing ratio of 40 ~ 60% in waste oil sludge. It means that the BOF can be classified as the 1stgrade solid fuel. In TGA experiment carried out at heating rate of 10oC/min and under nitrogen atmosphere, thermal decomposition of sawdust was occurred in two steps, but waste oil sludge was destructed in one step. The initiated cracking temperature of sawdust and waste oil sludge was 300 and 280oC in respective and after 450oC the thermal decomposition process of sawdust was slowly progressed by 800oC in contrast to waste oil sludge. Thermal decomposition of waste oil sludge was finished around 600oC. It can be considered that this difference is due to the fixed carbon content. Thermal decomposition pattern for the pellet of mixing ratio over 50% in waste oil sludge was similar to that for waste oil sludge and thermal cracking was occurred between 300 and 350oC. As the mixing ratio of waste oil sludge in the pellet increased, the reaction of thermal cracking became fast.

Sludge minimization from wastewater treatment plant is becoming more important to save disposal costs and to contribute to sustainable development. For the reduction of sludge production, solubilization and dewaterability of sludge are important factors in sludge processing. Ultrasonic treatment has been used to enhance sludge solubility and dewaterability with anaerobic digestion sludge, primary sludge, and activated sludge. At the ultrasonic power of 0.2 kW/L for 1 hour, anaerobic sludge and activated sludge showed higher solubilization efficiency than the primary sludge in terms of COD, proteins, and suspended solids. Ultrasonic treatment decreased sludge dewaterability and sludge settling characteristics up to 720 kJ/L of ultrasonic energy. In conclusion, ultrasonic treatment was effective for sludge solubilization but it deteriorate dewaterability (specific resistance) and settling characteristics (SVI) of sludge at the experimental conditions.