Associação de Bactérias Fototróficas para o Tratamento de Efluentes com Metais Pesados

Abstract

Bioremediation has been seen as a promising method for removing heavy metals in contaminated effluents. Using different microorganisms, researchers affirm its efficiency for the treatment of effluents, which guarantees the reduction of costs and the increase of sustainability concerning conventional processes. In this context, this study aimed to evaluate the potential of purple non-sulfur bacteria Rhodobacter capsulatus and Rhodospirillum rubrum to remove hexavalent chromium, total chromium, cadmium, and lead. In addition, pigments (bacteriochlorophyll and carotenoids) production and biomass increments. A composite central design was proposed and analyzed to obtain models describing the behavior of the dependent variables (initial concentration of chromium, cadmium, and lead) and independent variables (chromium, cadmium, and lead removal). Then, the co-culture (R.capsulatus: R. rubrum), were inoculated in 500 mL Erlenmeyer flasks in the presence of a synthetic effluent consisting of RCV medium plus heavy metals with initial concentrations of 20 mg/L of chromium (VI), 10 mg/L of cadmium and 10 mg /L of lead – an optimal condition found by the experimental design 23 - under anaerobic conditions, the light intensity of 5760 lux and biological treatment duration of 216 hours. For the co-culture, the maximum removals were 83.2 % for total chromium, 30.1 % for cadmium, and 80.2 % for lead. After 216 hours the bacterial biomass increased by 68 % about the initial value of the cell concentration of 1.0 g/L. Evaluating the levels of bacteriochlorophyll a, an increase of 44% was observed. Finally, for the initial and final levels of carotenoids a obtained, an increase of 49% was observed for the co-culture in the experiments containing the initial concentrations of metals in the optimal condition found.