Co-remediation of pentachlorophenol and Cr6+ by free and immobilized cells of native Bacillus cereus isolate: Spectrometric characterization of PCP dechlorination products, bioreactor trial and chromate reductase activity

► High extent of PCP & Cr6+ removal at flask and bioreactor levels. ► Formation of PCP dechlorination products as evident by GC–MS analysis. ► Chromate reductase activity present both in culture supernatant and biomass. ► Immobilized biomass showed more Cr6+ removal than free bacterial cells. ► Possible use for in situ bioremediation of toxic Cr6+& PCP from tannery effluent. In this study, Bacillus cereus isolate efficiently remediated 57% PCP and 74% Cr6+ simultaneously with uptake rate of 0.65mgCr6+g−1biomassh−1 at initial 200mg Cr6+ and 500mgPCPl−1 concentration under optimized 0.4% glucose, 0.2% NH4Cl, pH 7.0, 35°C, 1.0% inoculum during 60h incubation. Optimization of agitation (100rpm) and aeration (0.6vvm) in bioreactor further enhanced PCP dechlorination by ∼5.0% and Cr6+ removal 7.5%. Presence of other heavy metals variedly affected bioremediation of both the toxicants. Maximum and minimum inhibition was exhibited by mercury and lead, respectively. Out of 74% Cr6+ remediated, 90% reduced to Cr3+, of which 52.8% was associated with cell biomass and 37.2% with culture supernatant. Maximum chromate reductase activity was evident in culture supernatant followed by cytosolic fraction and cell debris. A direct correlation existed between chromate reductase activity and reduced Cr3+ in different cell fractions. Among matrices, alginate was most suitable for biomass immobilization, which enhanced Cr6+ removal by 20.2% compared to free cells at 36h. Gas chromatography and mass spectrometry detected 2,3,4,6-tetrachlorophenol, 2,4,6-trichlorophenol, 2,6-dichlorophenol and 6-chlorohydroxyquinol as PCP dechlorination products. Our promising strain can be efficiently employed for simultaneous bioremediation of PCP and Cr6+ under wide environmental conditions.