Managing exoelectrogenic microbial community development through bioprocess control for conversion of biomass-derived streams

Bioelectrochemical systems are an emerging technology capable of utilizing aqueous waste streams generated during biomass conversion of lignocellulosic feedstocks to produce valuable co-products and thus, have potential to be integrated into biorefineries. In a microbial electrolysis cell, organic compounds are converted to electrons, protons, and CO₂ by fermentative and exoelectrogenic bacteria in the anode compartment. By having the ability to extract electrons from waste streams, these systems can treat water while also producing hydrogen, and thus can improve the efficiency of biomass to fuel production by minimizing external hydrogen requirement and enabling water recycle. The overall goal of this research is to understand how changes in the way the reactors are operated affect the performance of the system, and the structure of microbial community within when converting a biomass-derived stream (BOAP). This can enable the design of optimal community structure for waste stream conversion, which can lead to improved and stable performance of the system.

An integrated approach was taken to test parameters such as flow-rate, recycle, organic loading rate, feeding regime, and electrode potential using a suite of electrochemical, metabolic and genomic techniques to unravel the biocomplexity of these systems and the impact on the reactor microbial communities. Faster flow-rates and recycle operation led to better conversion of BOAP, but efficiencies decreased as organic loading rates increased. Exposure to high concentrations during fed-batch feeding resulted in a substantial loss of electrons that was alleviated through continuous operation. Additionally, high loading/concentration conditions selected for different microbial species. Furthermore, exposing the microbial communities to different anode voltages provided evidence that the benefits of using more negative anode potentials to increase electrical efficiency can be capture through long-term enrichment without sacrificing substantial output. Lastly, the microbial community was characterized using deep sequencing techniques, revealing novel players directing a wide range of compounds to electrons. The resulting data was used to develop correlations that will serve as the foundation for operating these systems for commercial applications.