Optimization of Chromium(VI) Detoxification byPseudomonas aeruginosaand Its Application for Treatment of Industrial Waste and Contaminated Soil

The reduction of Cr(VI) to Cr(III) is a potential detoxification process. In this study, seven Pseudomonas spp. were isolated and screened for chromium reduction. Isolate P4 was able to grow in the presence of 8000 μM chromium, in spite of the fact that the isolate was not previously exposed to any metal stress. Isolate P4 was identified as Pseudomonas aeruginosa strain SRD chr3 by 16S rDNA sequence analysis. Shake flask study showed 78% reduction of 1000 μM Cr(VI) after 6 h of incubation. The optimum pH for chromium reduction by the isolate was between 6 and 8. Isolate Pseudomonas aeruginosa gave 50–80% Cr(VI) reduction even in the presence of 100 mM of Cu, Mn, Ni, and Zn and 300–800 mM NaCl in 24 h, compared with the absence of any of these metals. In a 5-L reactor, the isolate showed 84.85% reduction of Cr(VI) even at the 70th cycle, with a hydraulic retention time of 24 h from the effluent of a hard chrome plating (electroplating) industry, which contained 2100 mg L−1 hexavalent chromium. The chromate-amended soil inoculated with the isolate showed 2800 μM chromium removal from 4000 μM Cr(VI) kg−1 of soil, which corresponds to 70% removal. The isolate had the ability to degrade stimulated waste containing 10,000 μM chromium.