Electrokinetic removal of aluminium and sulfates from a dairy sludge

Abstract

ABSTRACT Electrokinetic (EK) treatment of soil/sludge contaminated with metallic and organic pollutants has proven its success concerning efficiency and cost. The study carried out in the laboratory aimed at the feasibility of this technology for the simultaneous elimination of aluminium and sulphates from sludge obtained from the clarification of industrial dairy wastewater by coagulation-flocculation with aluminium sulphate. Work in this area is scarce due to the presence of bacteria in the sludge. The EK reactor comprises three compartments: the anode, the cathode, and the central part, which contains the sludge to be treated. A constant voltage of 15 V is applied between two platinum wire electrodes immersed in each electrolytic compartment. The EK treatment employed gave satisfaction despite the bacterial front in the 3/5 of reactor sludge fractions. Indeed, the removal rates are approximately 72% for aluminium and 92% for sulphates with current values below 5 mA, and relatively low energy consumption and cost (648 kWh/ton and 25.9 $/ton of sludge, respectively). For EK transport, the absence of hydraulic convection exerted on the sludge would favour the displacement of aluminium and sulphates by electromigration. Electroosmosis also contributes to this displacement. Thereby, analysis of sludge after this EK treatment predicts a possible valorisation but after liming. The sludge is rich in nutrients with low heavy metals concentrations. Although the study is more interesting for aluminium because of its toxicity, the behaviour of sulphates suggests the possibility of using EK to decontaminate soils or sludge from anions like nitrates, chlorides, etc.