Microbial electrolysis using aqueous fractions derived via tail-gas recycle pyrolysis of willow and guayule

Authors: SATINOVER, SCOTT - University Of Tennessee; Elkasabi, Yaseen; Nunez, Alberto; RODRIGUEZ JR, MIGUEL - Oak Ridge National Laboratory; BOROLE, ABHIJEET - University Of Tennessee

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2018
Publication Date: 2/1/2019
Publication URL: https://handle.nal.usda.gov/10113/6256321
Citation: Satinover, S.J., Elkasabi, Y.M., Nunez, A., Rodriguez Jr, M., Borole, A.P. 2019. Microbial electrolysis using aqueous fractions derived via tail-gas recycle pyrolysis of willow and guayule. Bioresource Technology. 274:302-312. https://doi.org/10.1016/j.biortech.2018.11.099.
DOI: https://doi.org/10.1016/j.biortech.2018.11.099

Interpretive Summary: In order to provide renewable energy, innovative methods will need to be employed that utilize sources that normally are of low value. To this end, biomass can be converted into oils that resemble petroleum, using a high-temperature process that breaks down biomass in the absence of oxygen (termed “pyrolysis”). The oils can be refined to produce liquid fuels. At the same time, pyrolysis produces an additional water-rich product that is contaminated with miscellaneous chemicals (about 10-20%), making it difficult to use as-is. One promising technology for utilizing this water fraction is to convert the chemical components into hydrogen gas using a combination of bacteria and electrochemical reactions. In this work, we looked at pyrolysis water produced from guayule plant bagasse (what remains after extraction processes) and willow biomasses. The two water products, although similar in the amount of components, were very different in terms of the types of compounds present. The compounds in willow pyrolysis water were more easily converted into hydrogen than those in guayule pyrolysis water. We attribute this difference in conversion to the differences in types of compounds produced from the biomasses. The results could enable users of pyrolysis systems to make better use and efficiency of biomass pyrolysis products through produced energy.

Technical Abstract: In order to improve the viability of renewable hydrogen for energy use, new methods must be demonstrated that are energy efficient and capitalize on unconventional sources of fuel to operate. Here, biological electrolysis of an aqueous phase waste product generated from tail gas recycle pyrolysis (TGRP) of two different biomass sources was investigated for renewable hydrogen production, one derived from guayule bagasse and another derived from willow. Microbial electrolysis cell (MEC) performance was investigated using these substrates at an organic loading rate ranging from 2 to 10 grams of chemical oxygen demand (COD) per liter of anode volume per day (g/L-day) and 0.2 to 0.5 g/L batch loading experiments. The highest average current density achieved was 4.97 ± 0. A/m2 and 1.80 ± 0.16 A/m2. A maximum hydrogen productivity of 4.99 ± 0.35 L/L-day was obtained from willow and 1.52 ± 0.22 L/L-day for guayule. The anode coulombic efficiency was 76.43 ± 7.29% for willow and 66.86 ± 22.5% for guayule and The cathode efficiency, was 99.25 ± 3.37 % and 84.39 ± 11.43 % for willow and guayule respectively. The maximum total hydrogen recovery in continuous loading was 66.33 ± 11.27 and 52.45 ± 21.88% for willow and guayule respectively. Both cells demonstrated significant degradation of organic acids, sugar derivatives, and phenolics, where most of the compounds investigated exceed 80% degradation. However, not all compounds were degraded effectively, as UHPLC-MS demonstrated the accumulation of a long chain amine not present in either substrate before treatment. UHPLC-MS also identified the persistence of several peptide residues resultant from the TGRP process. The results demonstrate potential for hydrogen production from a waste stream, which can improve the total biofuel or energy yield of future biorefineries.