Biotreatment of hexavalent chromium in a rectangular column using municipal wastewater sludge as a bioreactive barrier

Abstract

Contamination of the environment with hexavalent chromium [Cr(VI)] containing waste discharged from the production of alloys and stainless steel, dye industries, leather tanning, metal plating amongst others, it is a well-known global problem. Cr(VI) is highly mobile, soluble and bioavailable in the environment, it is the most toxic among chromium species, and is a known carcinogen. In contrast, trivalent chromium, [Cr(III)], is immobile, less stable in water and is an essential dietary element. As a results Cr(VI) has been placed under strict control measures by most national and international lists of high toxic materials. Bioremediation of Cr(VI) contaminated effluents appears to be more economical and environmentally friendly treatment method. This study investigates Cr(VI) removal in a bench-scale bioreactor using municipal dried sludge as permeable bioreactive barrier. Two series of experiments were conducted using two parallel bench-scale bioreactors under a hydraulic loading of 200 mL/h. During the first experiment, one system was used as a control, while the other received Cr(VI) concentrations equal to 40 mg/L. Experimental showed that the 20 cm thick permeable bioreactive barrier with a 30% sludge and 70% sand was able to achieve complete Cr(VI) removal during 30 operational days. The bioremediation technology proposed in this study significantly demonstrated the effectiveness of the permeable bioreactive barrier system in treating Cr(VI) containing process effluent streams. Fundamental knowledge and understanding of kinetic processes taking place within the bench-scale permeable bioreactive barrier system will be valuable in designing a proper pilot scale system.