Optimization of sulfide production by an indigenous consortium of sulfate-reducing bacteria for the treatment of lead-contaminated wastewater.

Biological treatment with sulfate-reducing bacteria (SRB) is considered to be an excellent option to remove heavy metals from wastewater. In this study, the optimization of sulfide production for an enhanced removal of lead by a consortium of SRB was carried out based on central composite design and analyzed using response surface methodology (RSM). The sulfide production process was investigated as a function of three independent variables: solution pH (6.5-8.5), lactate concentration (32-96 mM), and sulfate concentration (16-32 mM). RSM analysis showed that the optimum conditions for a high sulfide concentration (14.2 mM) occurred at a pH of 7.5 and at lactate and sulfate concentrations of 53.4 mM and 22.6 mM, respectively. The lead removal efficiency of the SRB consortium using optimum conditions was determined in four parallel anaerobic continuous moving bed biofilm reactors (V = 2 L) that were fed with synthetic wastewater containing dissolved lead at concentrations of 0, 100, 150, 200 mg L(-1) and operated with a hydraulic retention time of 5 days. 99-100 % was removed from synthetic wastewater with lead concentrations of 100 and 150 mg L(-1) during 40 days of operation. For the highest lead concentration of 200 mg L(-1), a decrease in efficiency of removal (96 %) was observed at the end of the experiment.