Aluminum and Organic Contaminant Removal from Drinking Water Treatment Sludge

Coagulation process using aluminum sulfate (Al2SO4) or alum as coagulant at a drinking water treatment plant generates a large volume of alum sludge. The alum sludge contains high concentrations of aluminum and organic matter, which are harmful to the environment. Organic contaminants can decrease the conductivity and mobility of ions in electrolyte, so it can reduce the effectiveness of electrolysis to remove the aluminum. Aims of this study are: (1) to determine the aluminum and COD removal in electrolysis process using carbon-silver electrodes and (2) to measure the efficiency of COD removal by H2O2 oxidation and UV light exposure. The sludge was acidified to pH 3 and 4 and centrifuged prior to electrolysis. The electrical current was 300 mA, based on polarization test using carbon silver as anode and cathode electrodes. Electrolysis was carried out in a batch recirculation one-compartment reactor for 10 hours. Deposited matter of alum at cathode was weighed and analyzed by Inductively Coupled Plasma. The electrolysis pretreatment was meant to remove high organic contaminants in electrolyte. The pretreatment was carried out by oxidation with addition of H2O2 with a ratio of [H2O2]/[COD] = 1/2 and 254 nm UV light exposure for 4 hours. This study resulted in low aluminium deposit of 3.19 mg at the cathode with COD removal of 11.11% at initial pH 3 using electrolysis. The highest COD removal efficiency by oxidation with addition of H2O2 and UV light exposure was 75%. It can be concluded that H2O2 oxidation and UV light exposure could be applied prior to electrolysis for optimizing aluminum removal.