Avaliação do uso de bactéria fototrófica Rhodobacter capsulatus na recuperação de efluente contaminado com cromo (VI)

Abstract

This study aimed to evaluate the potential of the non-sulfur purple photosynthetic bacterium Rhodobacter capsulatus in the removal of hexavalent chromium and total chromium, together with the production of biomass and pigments, through different light intensities (dark, 800 lux, 3,200 lux, 5,670 lux, and 8,000 lux) and different wavelengths (white, blue, green, yellow and red light sources). For this, the bacteria were inoculated in 250 mL Erlenmeyers in the presence of synthetic effluent of initial concentrations of hexavalent chromium of 10, 30, 60, 90, and 110 mg/L under anaerobic conditions and a duration of biological treatment of 192 hours. The results show that there was complete removal of hexavalent chromium in all tests performed, and the increase in light intensity reduced the time for removal of hexavalent chromium. Concerning total chromium, it was verified that the maximum removals occurred under a luminous intensity of 5,670 lux for the synthetic effluent conditions of low initial concentrations of hexavalent chromium of 10, 30, and 60 mg/L, being 80.2 %, 89.3 %, and 77.0 %, respectively. Furthermore, the increase in light intensity up to 5,670 lux favored cell growth under these conditions, as well as pigment production, and above this light intensity value, there was stabilization in the biomass content and the production of pigments. It was reported that for this condition of 5,670 lux there was a 230 % increase in biomass content in the synthetic effluent condition with an initial concentration of 60 mg/L of hexavalent chromium and the final bacteriochlorophyll and carotenoid contents were 2.22 and 1.44 mg/m³, respectively. However, in synthetic effluent conditions with high initial concentrations of hexavalent chromium of 90 and 110 mg/L, cell growth was inhibited. Regarding the different wavelengths, it is observed that the blue light source performed better about the biomass content, while for the production of pigments the yellow, white and blue light sources stood out. For total chromium removal, it was found that the highest removal percentages were achieved in white and blue light sources, reaching a maximum removal of 88.9 % in the synthetic effluent condition with an initial hexavalent chromium concentration of 10 mg/L under the influence of the blue light source.