Effective treatment of fermentation wastewater containing high concentration of sulfate by two-stage expanded granular sludge bed reactors

• Performance of fermentation wastewater treatment with two-stage EGSB reactors.
• Achieve sulfate and organic matters removal in the two reactors, respectively.
• Microbial community analyses in granular sludge by high-throughput sequencing.

The fermentation wastewater containing high concentration of sulfate was treated by a two-stage expanded granular sludge bed (EGSB) reactor system, which was primarily responsible for the removal of both sulfate and organics. The sulfate concentrations in the fermentation wastewater varied from hundreds to 5000 mg l−1 with an average of 1000 mg l−1. In the first EGSB reactor, the COD removal efficiency decreased from 93% to 65% with an increase in sulfate concentrations from 200 mg l−1 to 2000 mg l−1, and, at the same time, the sulfate removal efficiency increased from 90% to 95%. Moreover, ∼90% of COD were removed by the two-stage EGSB reactor system when the sulfate concentration was controlled at 2000 mg l−1. The removal efficiencies of COD and sulfate concentration declined obviously when the sulfate concentration was raised to 3000 mg l−1 in the influent, indicating that microbial activity was inhibited by sulfate; they declined to 83% and 40%, respectively, with a further increase in the sulfate concentration to 5000 mg l−1. The bacterial community analyzed by the high-throughput pyrosequencing method showed that the proportion of Desulfovibrio spp. increased from 2.8% to 10.8% in the anaerobic granular sludge after treating the fermentation wastewater. The results suggest that sulfate containing wastewater can be treated with properly configuration of the reactors so that both COD and sulfate can be removed.