Extraction and environmental risk assessment of heavy metal in the municipal dewatered sludge using rhamnolipid treatment

Abstract

ABSTRACTHeavy metal could lead to serious environmental risk to the ecosystem, destroy human health via the food chain. The heavy metal removal from sludge is an emergent issue. In this work, rhamnolipid, an environment-friendly material, was used to enhance heavy metal extraction from the sludge. The results showed that Cu, Zn, Cr, Pb, Ni, and Mn maximum extraction efficiencies were 35.10 ± 2.31%, 45.33 ± 3.24%, 27.58 ± 3.35%, 24.12 ± 3.51%, 43.31 ± 2.53% and 22.10 ± 2.11%, respectively; most of exchangeable and reducible fractions, and partly oxidizable and residual fractions have been extracted by the rhamnolipid solution. After treatment, IR values of heavy metals increased in the treated sludge, the IR values for Cu, Zn, Cr, Pb, Ni, and Mn were 0.24 ± 0.01, 0.25 ± 0.03, 0.21 ± 0.02, 0.32 ± 0.03, 0.22 ± 0.021 and 0.41 ± 0.03, respectively. MF values indicated that heavy metal mobility order was Zn>Ni>Cu>Mn>Cr>Pb in the treated sludge. According to the two risk assessment methods (risk assessment code, RAC and potential ecological risk index, PERI), the risk assessment of heavy metal was investigated in the after treatment sludge, which indicated that rhamnolipid could extract the mobility of heavy metal and lead to no or low risk to the ecosystem. Therefore, rhamnolipid was utilized to enhance heavy metal extraction from dewatered sludge in this study, which is a promising technique for heavy metal extraction from the dewatered sludge.