The Potential for Biomimetic Application of Rumination to Bioreactor Design

Authors: WEIMER, PAUL - University Of Wisconsin; Hall, Mary Beth

Submitted to: Biomass and Bioenergy
Publication Type: Review Article
Publication Acceptance Date: 10/7/2020
Publication Date: 10/20/2020
Citation: Weimer, P.J., Hall, M. 2020. The Potential for Biomimetic Application of Rumination to Bioreactor Design. Biomass and Bioenergy. 143. Article 105822. https://doi.org/10.1016/j.biombioe.2020.105822.
DOI: https://doi.org/10.1016/j.biombioe.2020.105822

Interpretive Summary: Rumination, or "chewing the cud", is the process by which cows and other ruminants (cud chewing animals like sheep and goats) re-chew the fibrous plant feeds they've eaten to open up the plant structure and make the fiber more accessible for the microbes in their rumen to digest. Rumination rends apart the fibrous cell walls in forage grasses and legumes opening up the more easily fermentable fiber for microbes to access. Cows and other ruminants have evolved specialized forms of teeth that do an effective, energy efficient job of grinding and rending the plants during rumination. Biomass processing to make biofuels also relies on breaking apart fibrous plant materials for microbes to ferment. A comparison of the energy efficiency of rumination vs. other forms of milling used on biomass indicate that rumination requires less energy. Ruminants have evolved rumination and their tooth structure over the millennia in order to obtain nutrition from fibrous feeds. People have been working on processing fibrous feeds for biofuel production for many fewer years than that. We may be able to improve on the energy and overall efficiencies of current biomass processing for biofuel production by incorporating some of the ruminants' strategies of sample rending and particle size sorting during rumination, using the form of cow molar surfaces in developing grinding surfaces, and applying the concept of wet grinding within biofuel fermentation tanks rather than processing dry materials.

Technical Abstract: Rumination is the process by which ruminant animals regurgitate their food – largely cellulosic biomass – for re-chewing to reduce particle size and accelerate its biodegradation by the animal’s mutualistic microbial community. Detailed examination of the process reveals that it is a unique and unusually effective and energy-efficient type of physical pretreatment or co-treatment. Effectiveness and energy efficiency are gained by several unappreciated aspects of the process, including: full wetting of the biomass prior to its exposure to re-chewing; a hypsodont dentition pattern and jaw movement designed to maximize shearing and delamination (rather than cutting) of the biomass; and an effective feed sorting mechanism that results in a preferential processing of the larger particles that are in need of further grinding, rather than smaller particles whose additional grinding would provide little benefit. These nuances of the rumination process suggest several designs for accomplishing similar particle size reduction and surface area increases directly within bioreactors fermenting cellulosic biomass.