Electrokinetic removal of aluminum and chromium from industrial wastewater electrocoagulation treatment sludge

Abstract

Treatment of industrial wastewaters by electrocoagulation is very efficient to remove numerous types of pollutant (organic, mineral, colored, metal). However, few researches are devoted to the elimination of metals contained in the generated sludge. The objective of this paper was to study the possible simultaneous removal of aluminum (issued from the electrodes) and chromium (initially present in the effluent) contained in the sludge by electrochemical migration. Electrocoagulation treatment of textile industrial wastewater in which chromium has been added was carried out using aluminum electrodes. Turbidity, COD, and TOC could be efficiently removed with abatement yields, respectively, at 97, 93, and 90%. For chromium, only 62% of the initial amount was eliminated by applying the highest current with a long operating time. The generated sludge contained high amounts of Cr and Al (749 and 1,260 mg/kg of dry sludge), far above the maximum level allowed by legislation. The possibility of removing these pollutants from the resulting sludge using electrokinetic technique was investigated. Acetic acid at 1 or 3 M and citric acid at 3 and 6 M were used as catholyte solutions to enhance the removal of aluminum and chromium(III). Best results for aluminum removal were obtained using 3 M acetic acid: up to 82% of the initial Al was recovered in the cathode chamber, whereas citric acid was more effective in chromium removal: up to 79% was transported to the cathode chamber with 6 M citric acid. Specific energy consumption is also discussed.