USING BIOLOGICAL PROCESSES TO RECOVER SULFUR FROM CORN WET MILLING INDUSTRY WASTE STREAMS

A recent emphasis on pollution prevention and sustainable technology development in food processing industries has led to the desire to recover nutrients from coproducts and waste streams. The corn wet milling industry uses sulfur compounds as a steeping and antimicrobial agent. This sulfur is not recovered, but instead is released to the environment via air, waste streams, and solid coproducts. Sulfur recovery can be accomplished using anaerobic bioreactors to completely reduce sulfur compounds to sulfide. Subsequently, the produced hydrogen sulfide can be partially re-oxidized to elemental sulfur. However, the treatment of high-sulfate waste streams in anaerobic bioreactors is not straightforward since sulfidogenesis and methanogenesis are competing processes. In the current study operating conditions of a staged anaerobic bioreactor (anaerobic migrating blanket reactor [AMBR]) for the treatment of a high-sulfate wastewater were optimized to partly separate the processes of sulfidogenesis and methanogenesis, and thereby generate separate hydrogen sulfide-rich and methane-rich biogas streams. An upflow anaerobic sludge blanket (UASB) reactor was operated in parallel to compare the performance of the AMBR to a more established anaerobic process. Both reactors achieved similar sulfate removal efficiencies at a COD/SO4 2− ratio of 5, however the UASB reactor outperformed the AMBR in terms of SCOD removal. Process optimization strategies applied to the AMBR improved process performance, however the absence of granular sludge resulted in inhibition of the methanogens at levels of approximately 100 mg/L H2S-S. The UASB maintained lower effluent sulfide levels throughout the study. Process optimization must still be performed on the AMBR to more effectively strip H2S from the initial compartment, shielding the methanogens from inhibiting levels of H2S by promoting granulation, and allowing for greater sulfur recovery.