Enhanced Microbial Sulfate Removal Through a Novel Electrode-Integrated Bioreactor

Enhanced Microbial Sulfate Removal Through a Novel Electrode-Integrated Bioreactor

2018-07

In northeast Minnesota, elevated levels of sulfate in freshwater systems is a topic of great interest, due to potential adverse impacts to wild rice ecosystems. Sulfate may contribute to methylmercury production and eutrophication in certain conditions. Increased interest has emerged for developing low cost and efficient technologies to treat high levels of sulfate in mining and industrial waste water. The use of biological sulfate reduction is a promising and economically viable plan for maintaining low levels of sulfate and sulfide, but its performance is highly variable. This project developed a sediment bioelectrochemical batch reactor that used a low electrical potential to enhance and sustain biological sulfate reduction by continuously supplying electron donor substrates (electrolytic hydrogen) to sulfate reducing bacteria. The project aims to understand the effect of a low applied voltage on the efficacy of sulfate reduction and iron sulfide formation. Reactors contained creek sediment (Second Creek, MN) and an artificial mine water with a sulfate concentration of ~1000 ppm. The sulfur chemistry in the pore water of the reactors was assessed to determine sulfate reduction, resulting in over 90% reduction in porewater sulfate at the cathode in batch reactors, where electrolytic hydrogen gas was generated at a rate of 4.14 mmol/day. Simultaneously, ferrous iron was released into the reactor via iron electrodissolution and reacted with reduced sulfide ions to form iron sulfide precipitates. This level of hydrogen generation was sustained over a 14-day period and successfully showed that the application of a low voltage to sediment bioreactors is a promising technology to treat sulfate contaminated waste waters. The microbial community structure and relative abundance of different species associated with sulfate reduction were also examined. It was shown that relative abundance of sulfate reducing bacteria, specifically Desulfovibrio, a genus of deltaproteobacteria positively associated with sulfate reduction, which utilize hydrogen as their preferred electron donor, increased throughout batch reactor operation when operated at 2V. Finally, the sediment bioelectrochemical batch reactor served as a proof of concept for the application of low electrical potential to enhance and sustain biological sulfate reduction. The outcomes of this reactor operation laid the groundwork to develop a prototype flow-through bioelectrochemical reactor designed to handle larger volumes of waste water for an extended period of time. Preliminary results from this flow-through reactor demonstrated the ability to generate a constant supply of electrolytic hydrogen used by sulfate reducing bacteria. Through these experiments, recommendations have been made to improve efficacy of flow-through reactors.

Takaki, Daniel

University of Minnesota: Water Resources Science

University of Minnesota

University of Minnesota

66

Water Monitoring & Assessment

Bioreactor
Sulfate

2010-2019

Yes

https://conservancy.umn.edu/handle/11299/200161

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Takaki, Daniel