Efficiency of co-composting process to remove genotoxicity from sewage sludge contaminated with hexavalent chromium

• We assessed the genotoxicity of Cr(VI) from activated sewage sludge
• Genotoxic effects of Cr(VI) were demonstrated in liquid approach (compost aqueous extract).
• We revealed a significant increase of mitotic index in vicia faba and compost maturity.

This study focuses mainly on the genotoxicity of sewage sludge contaminated with hexavalent chromium (Cr(VI)). The effect was assessed by the micronucleus (MN) induction in Vicia faba roots, after exposure to solid co-composting matrix and aqueous extracts. Two different concentrations of co-composting of sewage sludge/palm waste were tested: mixture A:1/3 sludge + 2/3 palm waste and mixture B:1/2 sludge + 1/2 palm waste.No effect was detected at different concentrations of solid matrices. However in the co-compost aqueous extracts, the MN frequency was significantly higher than in the direct contact. The evaluation of Cr(VI) toxicity showed a positive relationship (R2 = 0.77) with MN frequency. After six months of co-composting, the MN rate decreased significantly by 70.4 and 77.2% with decreasing of Cr(VI) concentration with 58 and 58.6% for A and B respectively. These results indicate the efficiency of co-composting process to decrease the sludge genotoxicity by Cr(VI) stabilization.