Bioremediation of multi-metal contaminated soil using biosurfactant - a novel approach.

An unconventional nutrient medium, distillery spent wash (1:3) diluted) was used to produce di-rhamnolipid biosurfactant by Pseudomonas aeruginosa strain BS2. This research further assessed the potential of the biosurfactant as a washing agent for metal removal from multimetal contaminated soil (Cr-940 ppm; Pb-900 ppm; Cd-430 ppm; Ni-880 ppm; Cu-480 ppm). Out of the treatments of contaminated soil with tap water and rhamnolipid biosurfactant, the latter was found to be potent in mobilization of metal and decontamination of contaminated soil. Within 36 hours of leaching study, di-rhamnolipid as compared to tap water facilitated 13 folds higher removal of Cr from the heavy metal spiked soil whereas removal of Pb and Cu was 9-10 and 14 folds higher respectively. Leaching of Cd and Ni was 25 folds higher from the spiked soil. This shows that leaching behavior of biosurfactant was different for different metals. The use of wastewater for production of biosurfactant and its efficient use in metal removal make it a strong applicant for bioremediation.

Study of speciation of metals in an industrial sludge and evaluation of metal chelators for their removal.

Leachability and mobility of metals were evaluated in sludge obtained from electroplating industry, using toxicity characteristic leaching procedure (TCLP) and diethylene triamine pentaacetic acid test (DTPA). Sequential leaching procedure was used to determine the chemical fractionation of metals. Further, removal of metals from sludge using various chelators (EDTA, citric acid, siderophore) was evaluated. The leaching test indicated that nickel in the sludge sample exceeded 5 ppm concentration. This categorized the sludge, as a toxic waste. The mobility of the metals in the sludge was in the following order: Ni, Fe, Zn, Cr, Pb. Metals were found to be associated with various fractions of sludge. The metal concentration in the sludge was very high as compared to normal abundance and thus not within the range to be used as a fertilizer. The low removal of metals from the sludge by various chelators may be due to overloading of metals and use of aged sludge rather than artificially contaminated one for the study. The results of this study bring forth the prospect of the use of siderophores for bioremediation, because it is biodegradable and ecofriendly. This can be achieved with further optimization of the method, exploration of more potent siderophores and by inclusion of metal bound sludge fraction specific treatments.

Biosurfactant technology for remediation of cadmium and lead contaminated soils.

This research focuses on column experiments conducted to evaluate the potential of environmentally compatible rhamnolipid biosurfactant produced by Pseudomonas aeruginosa strain BS2 to remove heavy metals (Cd and Pb) from artificially contaminated soil. Results have shown that di-rhamnolipid removes not only the leachable or available fraction of Cd and Pb but also the bound metals as compared to tap water which removed the mobile fraction only. Washing of contaminated soil with tap water revealed that approximately 2.7% of Cd and 9.8% of Pb in contaminated soil was in freely available or weakly bound forms whereas washing with rhamnolipid removed 92% of Cd and 88% of Pb after 36 h of leaching. This indicated that di-rhamnolipid selectively favours mobilization of metals in the order of Cd>Pb. Biosurfactant specificity observed towards specific metal will help in preferential elution of specific contaminant using di-rhamnolipid. It was further observed that pH of the leachates collected from heavy metal contaminated soil column treated with di-rhamnolipid solution was low (6.60-6.78) as compared to that of leachates from heavy metal contaminated soil column treated with tap water (pH 6.90-7.25), which showed high dissolution of metal species from the contaminated soil and effective leaching of metals with treatment with biosurfactant. The microbial population of the contaminated soil was increased after removal of metals by biosurfactant indicating the decrease of toxicity of metals to soil microflora. This study shows that biosurfactant technology can be an effective and nondestructive method for bioremediation of cadmium and lead contaminated soil.