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.