Utilization of Drinking Water Treatment Sludge to Produce Aluminum Sulfate

Abstract

In Egypt, water treatment industry consumes about 365,000 tons of aluminum sulfate as coagulant and produces more than 100 million tons of semidried sludge per year. The common disposal system of alum sludge in Egypt is to discharge it into natural water bodies. Toxic nature of free and complexed aluminum species to aquatic life, stringent environmental regulations on disposal of sludge into water bodies and costs of the chemicals used in water treatment process and sludge treatment led to evaluate coagulant recovery and subsequent reuse. The present work aimed at aluminum metal recovery from sludge obtained from El-Shiekh Zayd water treatment plant by acidification method to produce aluminum sulfate coagulant. Sludge from drying beds was characterized and sulfuric acid was selected as the acidic leaching medium and effect of five variables were tested: acid concentration (N), sludge weight (g), mixing speed (rpm), temperature (o C) and leaching time (min) was studied. Moreover, the process efficiency was evaluated at different operating conditions. Then optimum conditions were applied to get maximum recovery for aluminum sulfate. Maximum recovery is 94.2 % at acid concentration 1.5 N, sludge weight 5 g, mixing speed 60 rpm, temperature 60 o C and leaching time 40 min.