Enhancement of flocculation performance during the intermediate treatment process of a construction sludge using gypsum powder

Abstract

During the coagulating sedimentation process of a construction sludge conducted in an intermediate treatment plant, polymeric flocculants are frequently used. However, since it is concerned with the toxicity of unreacted monomers included in the polymer coagulant, it is difficult for a construction sludge treated with a polymer flocculant to be accepted at the final disposal site. In order to reduce the amount of polymer flocculants to be added, the gypsum powder is employed as a material to assist the flocculation by combining a polymer coagulant with an inorganic coagulant during the coagulation sedimentation stage. Consequently, it was confirmed that the electric zeta potential of the clay slurry suspension was decreased by the addition of the gypsum powder and the aggregation performance was highly improved. In addition to this, it was confirmed that the addition of a gypsum powder to a sludge generated at a construction site including an arsenic material reduced the elution of an arsenic material originating from nature. It is expected for the employment of a gypsum powder to prevent the elution of naturally derived arsenic material from the soil generated by the underground construction.