Rice removal of pollutants in parboiled paddy wastewater

Abstract

Rice is the staple diet in Sri Lanka where parboiled rice is becoming fast popular. The parboiling process involves three main steps namely soaking, steaming and drying which improves various characteristics of rice. A significant amount of water is consumed in soaking operation. The wastewater generated from this operation is mostly discharged to inland water bodies and surface lands. The continuous discharge, of this effluent is of environmental concern. Lab scale experiments were carried out to investigate the effectiveness of different wastewater treatment methods for removal of pollutants in soak water resulting from hot soaking of red rice variety named LD 356. Biological treatment methods such as aerobic, anaerobic and physical treatment methods such as coagulation and adsorption were investigated. Removal of pollutants by aquatic plants and biological treatment using various microbial sources such as cow dung, rice straw, pond water and paddy field soil were also investigated. Results show that microbial sources from pond water and paddy field soil were able to reduce COD in soak water by 96% and 94% respectively at pH 8 under aerobic and dark conditions. In seven days, 62% and 65% COD removal were observed by water hyacinth and salvinia respectively. Combined treatment of anaerobic digestion and coagulation was able to remove 94% COD while the combination of anaerobic digestion and adsorption removed 95% COD.