Long-term operation of anaerobic immobilized biomass reactor treating organic wastewater containing sulfate

This work evaluates the long-term performance (888 days) of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor fed with synthetic wastewater containing organic matter and sulfate. The HAIB reactor achieved stable performance, exhibiting high sulfate and organic matter removal efficiencies subjected to organic matter concentration (expressed as chemical oxygen demand - COD) of 1500 mg/L and sulfate of 500 mg/L. Sulfate removal efficiency close to 100% was obtained for COD/sulfate ratios equal to or higher than 2.6, decreasing to ∼80% for COD/sulfate ratio of 1.4. Sulfidogenesis was clearly dependent on the availability of electron donor; but not methanogenesis. The smaller COD removal efficiencies (∼93%) were observed at the higher sulfate (1980 mg/L) and organic matter (COD of 7000 mg/L) concentrations, with COD/sulfate ratio of 3.5. Under these conditions, the presence of volatile fatty acids in the effluent indicates the occurrence of methanogenesis inhibition probably due to sulfide. The fixed-film HAIB reactor did not present bed clogging throughout the entire long-term operation period, thereby leading the way to new perspectives to use the efficient treatment of sulfate-rich wastewater.