ENHANCING PHOSPHATE REMOVAL BY COAGULATION USING POLYELECTROLYTES AND RED MUD

摘要

Phosphate removal by chemical precipitation remains the leading technology today. In this research, phosphate removal using polyaluminium chloride (PAC) alone and in the presence of polydiallyldimethylammonium chloride (PDADMAC) and red mud were investigated. The results showed that PAC was effective in phosphate removal by coagulation via charge neutralization and adsorption of polymeric hydroxyl complexes. For synthetic wastewater, the phosphate removal efficiency reached 94.6% and for raw wastewater, the total phosphorus removal efficiency was as high as 96.6%. PDADMAC was not efficient in removing phosphate when used alone, at dosages of 0.1-0.3 mg/L, and it had little effect on enhancing phosphate removal by PAC as a coagulation aid, even when the dosage of PDADMAC was increased from 0.1 mg/L to 2 mg/L. Red mud, a by-product of bauxite processing in the alumina manufacturing industry, served as "nuclei for coagulation" resulting in large, rapid-settling floes. When 40 mg/L red mud was added, the phosphate removal efficiency of 3.18, 4.76 and 6.35 mg Al~(3+)/L PAC increased by 15.1, 20.5 and 13.0%, respectively. Adsorption and desorption experiments of phosphate on floes after coagulation showed that the addition of red mud not only decreased the required PAC dosage but also enforced the phosphate adsorption on floes.