고탁도 건설폐수 처리시스템 개발

Abstract

Sediment and turbidity from construction sites are primary causes for surface water quality impairment. Much of the sediment leaving construction sites consists of silt an clay that can carry substantial amounts of nutrients and pollutants. Increased turbidity can limit sunlight penetration into water by both adsorbing and deflecting light. Coagulation is the most widely used for microparticle removal in water and wastewater treatment facilities. Coagulants are added to transform dispersed particles into aggregate floc for subsequent removal by sedimentation. Instead of impeller type mixer for coagulation, coagulants injection hydrocyclone and was used for coagulation. Hydrocyclone effluent and underflow are recycled in retention basin for flocculation and settling. To determine the optimum Chitosan dosage for treatment of construction sites high turbidity, tunnel construction site, aggregate extraction sediment, clay-silt soil samples were used for Jar test. Chitosan, obtained by deacetylation of chitin, is described as a cationic polyelectrolyte and is expected to coagulate negatively charged suspended particles found in turbid waters. The structure of Chitosan is very similar to that of cellulose, and is biodegradable. Chitosan coagulants also produced larger flocs of better quality and faster settling velocity, dewatering. Therefore, Chitosan has become necessary to develop more efficient and environment-friendly flocculants for removal of turbidity in waters. As the results of Jar test (rapid mixing 1min, slow mixing 3 min, settling 15 min), the optimum Chitosan dosage was 10~15 mg/L for clay silt soil. Because of the effectiveness of Chitosan in removing turbidity was independent on pH, the hydrocyclone coagulation system would be simple. The results of lab scale retention basin with hydrocyclone coagulation system test indicate that the ranges of removal efficiency of turbidity, SS were 81.5~96.1%, 84.9~95.1%, respectively. Hydrocyclone coagulation system would have possibility with compact design, because of the increase of floc size and reduces the settling time.