Bioremediation of tannery wastewater using UV-treated bacteria in the free and immobilized form.

Aims: Heavy metals are significant environmental pollutants and toxic to life and chromium (Cr) (VI) is one of them being discharged in the environment due to many human activities. The leather industry uses Cr(VI) salt in the tanning process, which is discharged untreated and becomes a source of many diseases. The use of microbes to remove metals is a cost-effective and clean method. The present study aims to isolate local and native microbes for Cr(VI) removal from tannery wastewater and enhance their capacity to bioremediate the tannery wastewater. Further, efficiency in free and immobilized forms was also checked. Methodology and results: Microbes were isolated from a local tannery wastewater outlet and after many rounds of minimum inhibitory concentration, and concentration of 500 µg/mL was found to be that concentration at which microbes could survive, above which they died. The sequencing of 16S rRNA and its analysis showed that it was closely related to Staphylococcus saprophyticus and in the given study, it was named B6. At 37 °C, pH 7.5 and 120 h of incubation, it removed 77% Cr(VI) from the reaction mixture. B6 was exposed to UV to obtain mutant. Exposure of 15 min to a UV lamp gave mutant MB6, which showed a removal capacity of 77% after 72 h only. Cr(VI) removal capacity of the mutant was then analyzed in the free and attached form where coal and sodium alginate were used as solid surfaces. Mutants immobilized on coal showed 91% Cr(VI) removal after 96 h, while sodium alginate showed 58% Cr(VI) removal in 120 h, thus showing coal as a more effective surface for adsorption. Conclusion, significance and impact of study: Our present study shows the use of cheap and environmentally friendly methods to remediate tannery wastewater, which is a big problem in a country like Pakistan. Pakistan is the second largest producer of leather but lacks a wastewater treatment facility. So, this method offers in-situ wastewater treatment, which can be further enhanced in different ways. [ABSTRACT FROM AUTHOR]