The ballasted flocculation effects of the mill scale and magnetite on activated sludge were investigated. Both ballasted flocculants (BF) could remarkably improve the sludge settleability in terms of zone settling velocity (ZSV) and sludge volume index (SVI). With the BF dosage of 0.2 to 2.0 g-BF/g-SS, the magnetite particles showed better efficiency on improving settling behavior of activated sludge than the mill scale due to higher surface area and hydrophobic property. The efficiency of SVI30 with magnetite injection was 2.5 to 11.3% higher than mill scale injection and that of the ZSV appreciated from 23.7% to 44.4% for magnetite injection. Averaged floc size of the BF sludge with magnetite dosage (0.5 g-BF/g-SS) was 2.3 times higher than that of the control sludge. Dewaterability of the sludge was also greatly improved by addition of the BF. The specific resistance to filtration (SRF) was reduced exponentially with increasing the dosage of BF. However, the BF’s particle size effect on the SRF looks to be marginal. Consequently, for improving the dewaterability, the BF played a physical role to remove the pore water of the biological flocs by intrusive attachment and a chemical role to induce aggregation of the flocs by charge neutralization.

This study aimed to investigate the feasibility of improving dewaterability and settleability of sewage sludge using coagulation sludge. When mixed with sewage sludge and coagulation sludge at 1:1 ratio, capillary suction time(CST) and specific resistance to filtration(SRF) decreased by about 56% and 68%, respectively. It is found that total solids(TS) and volatile solids(VS) of mixing sludge are increased by about 59% and 53%, respectively. Also, the turbidity of the mixing sludge supernatant was reduced from 99 to 16 NTU. It is observed that the mixing of sewage sludge and coagulation sludge at 1:1 showed better effect than using poly-aluminum chloride(PAC) coagulant at 25 mg/L.

Recently, production of sewage and wastewater sludge have increased sharply with the population density and related industrial activity. As a result, studies of sludge treatment and reduction have been conducted and a pre-treatment method that uses thermal hydrolysis has emerged as a solution to this problem. To address problems with the thermal hydrolysis pre-treatment process, the deaeration and nitrogen recovery processes have been set up together, thus generating factors that inhibit dewaterability. In this study, the effect of pre-treatment, deaerated sludge on dewaterability-inhibiting factors (pH, temperature, aeration rate) was evaluated and alternative solutions were prepared. First, the dewaterability improvement effect increased rapidly at 190°C or higher when thermal hydrolysis pre-treatment was applied. Then, 1 L of thermal hydrolysis pre-treatment reactants at 190°C were injected into 1, 5, and 10 L/min air flows at 50°C, but no significant difference in capillary suction time (CST) or time to filter (TTF) was found. The dewaterability improved when the temperatures of the pre-treatment reactants varied between 30, 50, and 70°C under aeration at 5 L/min. However, when the pH was increased to 7, 9, or 11 at 5 L/min and 50°C, the dewaterability worsened by at least 10 times relative to the hydrolysis pre-treatment reactants. The zeta potential decreased from -30 mV to -50 mV as the pH increased. Thus, the stabilities and dispersities of the reactants increased due to the repulsive force of the particles. This was confirmed to be the cause of poor dewaterability. A coagulant can be used to solve to this problem, or the deaeration process can be placed after solid-liquid separation and the heat of thermal hydrolysis can be extracted via heat exchanger.

최근 런던협약 96의정서 발효에 따라 하수 슬러지의 해양투기가 금지되고 환경 정책 강화와 향후 에너지 자원 부족을 대비하기 위해 녹색 성장이 강조되면서 슬러지를 재이용화 및 자원화 시키려는 처리 기술방법들이 개발되고 있다. 하수슬러지 처리 공정의 중점은 발생량의 감량화와 개량화를 통해 탈수 효율을 높이기 위함이며 대표적인 전처리 방법으로 물리적인 방법과 화학적인 방법으로 약품 처리하는 것이 일반화되어 있다. 본 논문에서는 폴리머 응집제를 사용하여 총 4종류의 생, 잉여, 소화, 혼합슬러지에 대해서 적합한 유기 및 무기 응집제를 주입한 후 최적의 응집 조건을 선정하여 최종적으로 슬러지 탈수성의 효율을 비교 및 평가하도록 하였다. 혼합슬러지는 생슬러지와 잉여슬러지를 같은 부피 비율로 혼합하여 제조하였다. 최적의 응집 조건을 선정하기에 앞서 기본적으로 Jar Test 실험을 시행하였으며 200rpm에서 1 ~ 3분 완속 교반, 50rpm에서 5분 급속 교반 조건을 제시하였고, 유기 폴리머와 무기 폴리머 응집제의 단일 및 이액 주입 방식에 따라 응집 반응의 특성을 비교하였다. 실험결과는 슬러지 탈수성 및 최적 응집 조건 선정의 지표로서 응집을 형성시키고 방치 후, 고액 분리를 통해서 상등수의 탁도, pH, ORP, SS, 흡광도 (330nm), floc size와 TTF 실험을 하여 탈수성을 측정하였다. 따라서 응집제 주입 방법에 있어서 유기 응집제의 단일 방식 주입과 무기 응집제를 첨가하여 floc의 응결도를 높이는 이액 주입 방식으로부터 탈수성 효율에 미치는 결과를 본 논문에 나타내었다.