Phosphate removal from wastewater using spent alum sludge

A small-scale continuous flow system, which allows recycling of effluent, has been set up to study the phosphate adsorption ability of air-dried alum sludge from wastewater effluent, and the variation of nitrogen species in wastewater associated with phosphate removal. Initial phosphate removal was rapid, with phosphate levels being reduced by approx. 55% in the first 20 minute of the experiment. The variation of nitrogen species present in the wastewater showed a negative correlation with the concentration of phosphate. Thus, the concentration of ammonia increased from 0 ppm to 16 ppm, while the concentration of nitrate increased from 0 ppm to 98 ppm in the first 20 minutes; nitrite concentrations were found to be insignificant. Very similar phosphate removal patterns and changes in nitrogen species concentrations were exhibited for different batches of alum substrate; the adsorption capacity of spent alum was found to be approx. 0.30–0.33 mg phosphate per 1 g of air-dried spent alum.