Avaliação da utilização de nitrato por cultura mista enriquecida com bactérias redutoras de sulfato (BRS) em efluente contendo sulfato

Abstract

This work analyzed the decrease of sulfite production in a sulfate rich synthetic effluent. A mixed culture was used, isolated from the water used in petroleum production in Carmópolis, Sergipe State, Brazil, enriched with sulfate reducing bacteria (SRB). Initially, the microbial culture was acclimated to rising concentrations of Carbon, (0.1 - 5.0 g/L), and growth could be observed in all tested concentrations. A Central Composite Design was used to study the influence of the concentrations of sulfate, carbon and nitrate on the decrease of sulfite production in anaerobic condition. The response parameters evaluated were the sulfite production, the growth of anaerobic and sulfate reducing bacteria and the consumption of sulfate and nitrate. The minimization points for the sulfite production were obtained with the process optimization using the response surface methodology. The results from the optimization for minimization of sulfite production showed that the point of SO42-: C: NO3- de 3,6: 1: 5,1, lead to a minimum sulfite production (8.2 mg/L). The influence of carbon concentration on the sulfite production was studied for the optimized conditions of sulfate and nitrate, proving through this study that the concentration of carbon does not have substantial influence on the production of sulfite. Another study was carried out about the behavior of the microbial culture with intermittent addition of nitrate at pre-established intervals, and it could be observed that the rate of nitrate consumption was only significant when there was a larger number of anaerobic bacteria, a larger concentration of nitrate and when nutrients and carbon source had been added to the medium. This must have happened due to the number of Nitrate Reducing Bacteria (NRB) present in the microbial culture. The data from the optimized conditions were then evaluated in two kinetics of sulfite production, one in the presence and the other in the absence of nitrate.