Recycling of Waste Alum Sludge for Phosphorus Removal in Effluents

Waste alum sludge from water treatment plants can be successfully recycled to produce an aluminium-rich solution which is effective in reducing phosphorus concentrations in treated sewage effuents. A batch recycling process is proposed whereby the alum sludge is acidified using either sulphuric acid or waste pickle liquor. Aluminium recoveries greater than seventy percent are achievable. Overall sludge volumes needing disposal are reduced by seventy five percent. The laboratory study indicated that the cost of recycled aluminium liquor would be less than that of commercially available alum, although chemical transport and labour costs have not been allowed for. It is likely that the overall viability of the process in a given location would depend upon the distance from the acid source and the diligence of the relevant pollution control authority with respect to wastewater phosphorus, standards and acceptable means of disposal of water treatment sludges. Pilot scale trials are proposed.