Integration of Microbial Electrolysis Cells (MECs) in the Biorefinery for Production of Ethanol, H2 and Phenolics

In a biorefinery, biomass is converted into a variety of chemicals, materials and energy. A typical example is the lignocellulosic ethanol biorefinery process, in which substrates such as wheat straw are used as a feedstock for production of ethanol. In this work, an integrated biorefinery procedure is proposed in which the ethanol biorefinery is coupled with a microbial electrolysis cell (MEC), with the aim to further process and valorize the waste stream of bioethanol production. A MEC is an electrochemical system capable of oxidizing reducing equivalents, which results in hydrogen production. The mass and energy balances as well as the economical evaluations, show that this strategy may be useful for additional generation of hydrogen and lignin, thereby increasing the final yield of this biorefinery. From one ton of straw, the yield of ethanol upon yeast fermentation is estimated at 177–190 kg, with a hydrogen yield corresponding to 19–23 kg H2. The remaining solid residue of 147–160 kg comprises primarily lignin. The estimated value of these products approximates the double of that of straw. Integrating a MEC in the biorefinery concept may also be useful for other applications such as polyphenol purification and targeted modification of fruit based phenolics. Examples of such high-value plant polyphenols include equol and resveratrol, which can be produced from soy and grape, respectively.