Conversion of aluminium anodizing sludge into aluminium potassium sulphate for use as a coagulant in wastewater treatment

Abstract

During the process of aluminium surface treatment, a large quantity of aluminium-rich sludge is generated but its disposal is a great challenge. The main objective of this study was to investigate the potential to recover aluminium from the anodizing sludge for use in. Both wastewater and dumped sludge from various sampling locations in the wastewater treatment plant were characterized. Temperature, pH, total suspended solids, total dissolved solids, turbidity, dissolved oxygen, biological oxygen demand and chemical oxygen demand were analyzed. The final effluent temperature was 28.7±5.8 oC which was within permitted levels while the pH was 5.8±0.4. The total suspended solids and total dissolved solids were significantly high at 690.6±183.7 and 4,619.8±0.23 mg/l, respectively. The sludge from the dumpsite had solids content ranging from 13.73 % to 16.80 %. Recovery of aluminium from sludges obtained from the dumpsite, wastewater treatment plant and from mixed effluent emanating from process tanks were 87.1%, 77.4% and 64.26%, respectively. Low temperature favoured crystallization of the alum. The alum crystallization yield at 4 oC and 60 oC were 92.6 % and 65.3 %, respectively. The prepared alum had higher content of heavy metals especially aluminium and chromium than commercial alum but coagulation performance that compared well with that of the commercial alum. Jar tests gave reduction in wastewater pollution and the optimum settling dosage, pH, temperature and time were 8 g/L, 6.5, 40 oC and 20 minutes, respectively. These results demonstrate the potential of reducing the pollution posed by anodizing sludge and related wastewater.