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

In this study, Bacillus cereus isolate efficiently remediated 57% PCP and 74% Cr⁶⁺ simultaneously with uptake rate of 0.65 mg Cr⁶⁺ g^?1 biomass h^?1 at initial 200 mg Cr⁶⁺ and 500 mg PCP l^?1 concentration under optimized 0.4% glucose, 0.2% NH₄Cl, pH 7.0, 35 °C, 1.0% inoculum during 60 h incubation. Optimization of agitation (100 rpm) and aeration (0.6 vvm) 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 36 h. 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.