본 연구는 냉동전처리 기술이 분리막 기반의 슬러지 탈수공정에 미치는 영향에 대해 연구하였다. 냉동법은 응집법이나 원심분리법과는 달리, 슬러지 Cell lysis를 통해 Cell의 체액을 유출시킬 수 있음을 확인하였다. Cell lysis 이후 슬러지를 정밀여과법으로 분리하여 슬러지 탈수효율을 증가시키고자 하였으나, 냉동전처리로 인해 슬러지의 모세관 흡입시간과 여과소요시간이 약 13배 증가함으로써 슬러지 탈수효율이 감소하였다. 이는 슬러지로부터 방출된 유기물에 의한 슬러지 케이크 형성과 작은 슬러지 입자에 의한 세공차단현상에 의한 것이다. 적절한 공극 크기 및 슬러지 흡착에 내성을 갖는 분리막의 개발이 이루어 진다면, 냉동전처리와 분리막 공정의 혼성화기술은 슬러지 탈수에 적용 가능할 수 있을 것으로 보인다.

The dewatering characteristics of the sewage sludge was investigated through the experimental observations and model simulations. The activated sludge and the anaerobically digested sludge were examined for the dewaterability evaluation within the pressure range of $0{\sim}10^6N/m^2$. Modified Buchner funnel test and compression test by the consolidometer were conducted to evaluate average specific resistance, porosity, and moisture percentage of filter cake. Shirato's technique of compression-permeability test was followed for the pressure range lower than about $10^2N/m^2$. The flocculation effects on sludge dewatering was also examined for ferric chloride and polymeric flocculant. The application of hydrated lime which can be used for flue-gas desulfurization showed improved moisture percentage, and was thought to have positive feasibility in combined system of sludge dewatering and incineration. Determined characteristic constants were applied to Tiller's cake filtration model to simulate liquid pressure distribution and porosity distribution in cake. Model simulations showed a sharp drop of the porosity close to the cake-medium interface for the highly compressible material such as the activated sludge and the anaerobically digested sludge.

This study was carried out to investigate the economic and environmentally friendly process of drying sludge by combining a mechanical dewatering filter press and thermal dryer. The dryer for 40 kg/hr of dewatered sludge consisted of a main dryer, a heat exchanger, a pre-dryer, and supplementary equipment. During the dewatering process, 100 kg of sludge with 80.11% water content was diluted and mixed with 400 kg of water and ferric chloride solution was added as a sludge conditioner. The average water content of dewatered sludge cake was 60.9% and the energy consumption rate (ECR) for removing water was 226.9 kcal/kg-H2O. Hot flue gas generated from the main dryer was utilized as heating air for the pre-dryer in the heat exchanger. When 36 kg/hr of dewatered sludge cake was dried, the ECR was 1,009 kcal/kg-H2O with 3.96% water content. The combined operation of the dewatering and the thermal drying processes showed that the ECR was reduced sharply to 521 kcal/kg-H2O. The high humidity gas generated from each drying unit in the main dryer was recirculated to the odor decomposition chamber in the main dryer to destroy odor components at a high temperature. The odor concentration of humid gas generated by the pre-dryer was very low due to the relatively low operating temperature.

The effect of sewage sludge irradiation and addition of starfish as a dewatering agent on the efficiency of composting was investigated using saw dust as a bulking agent. Results indicates that the temperature of EB sludge cake (electron beam irradiated sludge cake) and EB-SF sludge cake (electron beam irradiated sludge cake mixed with star fish powder) composting piles rose up to 62 ~ 66oC within 1 day and maintained high temperature of 52 ~ 55oC for more than 3 days, which was much higher than that of the control. The electron beam irradiation and addition of star fish accelerate the composting. The control sludge cake composting pile needed 35 days to reach the criteria of mature rate for composting, (Final C/N ratio)/(Initial C/N ratio) of 0.75, while EB-SF sludge cake composting plie required 11 days. This means that maturing compost could be highly improved by irradiating sludge cake or by adding star fish powder. The pH of the composting pile of sludge cake with addition of waste star fish powder rose 1 pH unit higher than that of the control during the entire operation, showing that the star fish has a good buffering capacity. The pH of the final matured compost was above pH 7, satisfying the standard of soil conditioner. The G.I. values of Chinese cabbage and lettuce with composts from EB sludge cake and EB-SF sludge cake composting pile ranged 88 ~ 99, satisfying a safety level (G.I. 80) in plant growth. After 60 days operation for composting 4 different types of sludge cakes, each compost was able to meet the Ministry of Agriculture's Standards of Compost.

This study aimed to investigate the influence of the conditioning properties such as pH, mixing speed and reaction time on the dewaterability of sewage sludge and compare the performance with the derived conditions at the different solid concentrations. Performance parameters including time to filter test (TTF), specific resistance to filtration (SRF) and water content showed the optimum result at the pH value of 3, the rapid mixing speed of 200 rpm, and the slow reaction time of 20 min. In case of 20,000 mg/L of TS, a dosage of 1.0 g inorganic conditioner/L-sludge decreased TTF, SRF, water content of dewatered sludge cake, turbidity of the supernatant from 146 to 22 sec, 2.0 × 1014 to 0.4 × 1014 m/kg, 81.6 to 74.8% and 112 to 51 NTU, respectively.