NITROGEN AND PHOSPHORUS REMOVAL FROM SEWAGE EFFLUENT IN AMENDED SAND COLUMNS

Column experiments were conducted to examine the removal of phosphorus and nitrogen from sewage effluent by passage through sand amended with bauxite refining residue (red mud). Red mud was neutralized with 5% gypsum. The study was conducted in two parts. In Part 1 the removal of nitrogen and phosphorus in mixtures of 30, 20 and 10% red mud in sand was compared. Cycles of 10 days flooding with secondary effluent and 18 days drying were used. An average of 24% nitrogen removal was obtained with 30% red mud, 9% removal with 20% red mud and very little removal with 10% red mud. An average of 91% phosphorus removal was obtained with 30% red mud, 63% removal with 20% red mud and 50% removal with 10% red mud. The decrease in phosphorus and nitrogen removal with decreasing red mud content was caused by a decrease in the adsorption capacity of the soil and an increase in the infiltration rate. In Part 2 the use of primary and secondary effluents was compared. Phosphorus removal was excellent using both primary and secondary effluents in columns packed with 30% red mud. Nitrogen removal continued to be poor using secondary effluent (16%) but was significantly greater using primary effluent (74%).