Mekwichai et al. [72] conducted a case study conducted in the Moe Sot District of Thailand, which had been reported to be contaminated over more than a 600‐hectare (ha) area of paddy field. Researchers in their study utilized the potential of biosurfactants (rhamnolipid (RL) and saponin (SP)) for Cd remediation.
Researchers utilized corn, which is a low cost agro waste for reduction of toxic Cd, for the contaminated site and corn biomass utilization. The Cd phytoextraction was enhanced by adding RL and SP., where 4 mmol/kg was set as the optimum dose for both RL and SP. To execute the phytoextraction experiment on corn, the optimum dose of biosurfactants had been applied at different growth stages of corn, i.e. the 7th, 45th, and 80th day from the sowing. On the 45th day of the experiment, the highest Cd uptake levels were recorded and RL showed a maximum Cd uptake capacity of 39.06 mg/kg. The recorded data was also validated by bioaccumulation factors, which reflected that RL increased soil Cd uptake by corn plants to the highest extent. Also, Cd leaching after biosurfactant addition was studied and results confirmed a lower level of leaching compared to EDTA applications.
The performance of an anionic biosurfactant from Candida sphaerica for the removal of heavy metal ions collected from soil of an automotive battery industry have been evaluated by Luna et al. [66]. They also evaluated metal remediation performance of biosurfactant from an aqueous solution. Multiple combinations of biosurfactant solution, sodium hydroxide, and hydrogen chloride were tested. Biosurfactant showed a very efficient removal rate with values of 95, 90, and 79% for Fe, Zn, and Pb, respectively. Treatment of biosurfactant solution with 0.1 and 0.25% HCl solution increased the metal removal rate. The recycled biosurfactant also showed 70, 62, and 45% of Fe, Zn, and Pb removal efficiency, respectively. In another study, Rufino et al. [32] extracted lipopeptide biosurfactant from C. lipolytica (UCP 0988). Both Zn and Cu metal ions were reduced by up to 96% of their initial concentration, and also there was significant reduction in the concentrations of Pb, Cd, and Fe.
Scientific communities for the production of biosurfactants have also utilized many species of Bacillus. In one study, surfactin extracted from B. subtilis have been tested for the removal of heavy metals from a contaminated soil (890 mg/kg Zn, 420 mg/kg Cu, 12.6% oil and grease) and sediments (110 mg/kg Cu and 3300 mg/kg Zn). Results showed that 25 and 70% of the Cu, 6 and 25% of the Zn, and 5 and 15% of the Cd could be removed by 0.1% surfactin with 1% NaOH, respectively, after one and five batch washings of the soil. Also, 15% of the Cu and 6% of the Zn could be removed after a single washing with 0.25% surfactin/1% NaOH from the sediment [67]. In their subsequent study, a batch study was performed by Mulligan et al. [17] to evaluate the feasibility of biosurfactants extracted from different strains for the removal of metal ions from sediments. Surfactin, rhamnolipids, and sophorolipid extracted from B. subtilis, P. aeruginosa and T. bombicola, respectively, were evaluated using sediment polluted with metals (110 mg/kg Cu and 3300 mg/kg Zn); 65% of the Cu and 18% of the Zn were removed by studied biosurfactant after a single washing with a concentration of 0.5% rhamnolipid, whereas 25% of the Cu and 60% of the Zn were removed by 4% sophorolipids. Compared to rhamnolipid and sophorolipids, surfactin was less effective, removing 15% of the Cu and only 6% of the Zn. Singh and Cameotra [68] utilized B. subtilis A21 species to synthesize lipopeptide biosurfactant, consisting of surfactin and fengycin, for the removal of petroleum hydrocarbons and heavy metals from contaminated soil. Soil washing with lipopeptide biosurfactant solution removed significant amounts of petroleum hydrocarbons (64.5%) and metals, namely Cd (44.2%), Co (35.4%), Pb (40.3%), Ni (32.2%), Cu (26.2%), and Zn (32.07%).
To evaluate the efficiency of environmentally compatible rhamnolipid biosurfactant produced by P. aeruginosa BS2 for the remediation of Cd and Pb from the artificially contaminated