Removal of heavy metal from sludge by the combined application of a biodegradable biosurfactant and complexing agent in enhanced electrokinetic treatment

•The combined biosurfactant and complexing agent were used to enhance heavy metals removal in the EK treatment.•GLDA and rhamnolipid could produce higher electric current and conductivity in the EK treatment.•The GLDA obtained higher pH at the anode, the rhamnolipid obtained lower pH at the cathode.•The combined chelating agent and biosurfactant to result in better heavy metals removal efficiencies.•Exchangeable and reducible fractions of heavy metals had an apparent reduction.

In this work, the heavy metal removal potentiality of an electrokinetic (EK) decontamination treatment enhanced by a biodegradable complexing agent Tetrasodium of N, N-bis (carboxymethyl) glutamic acid (GLDA) also in combination with a biodegradable biosurfactant (rhamnolipid) was investigated to decontaminate heavy metals from the sludge. The main results explored that the nature of sludge and their interactions with different improving agents significantly influenced the electrokinetic removal processes. A general increase of pH values from anode to cathode in the sludge-cell was observed due to the strong buffering capacity of carbonates. Compared with the deionized water, the use of GLDA as an electrolyte, Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 53.2 ± 3.12%, 67.4 ± 3.45%, 59.2 ± 4.78%, 45.4 ± 4.15%, 72.8 ± 3.68% and 45.0 ± 4.85%, respectively, whereas a further improvement heavy metals removal efficiencies (Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 64.8 ± 2.34%, 56.8 ± 4.12%, 49.4 ± 4.45%, 46.6 ± 2.35%, 60.4 ± 3.45% and 69.6 ± 3.54%, respectively) were achieved by repalcing rhamnolipid as the electrolyte. Significantly higher removal efficiencies (Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 70.6 ± 3.41%, 82.2 ± 5.21%, 89.0 ± 3.34%, 60.0 ± 4.67%, 88.4 ± 4.43% and 70.0 ± 3.51%, respectively) were obtained by the simultaneous use of GLDA and rhamnolipid due to their synergic action in electrokinetic process.