An evaluation of the bioconversion of woody biomass to calcium acetate deicing salt

Abstract

A competitive process is described using local woody biomass residues, which may also include associated pulp and paper wastes, or municipal solid waste, as potential feedstocks for bioconversion to calcium acetate, an alternative deicing salt. The process first involves “suppressed methane” fermentation of these woody biomass residues in a “packed bed” fermentor for the production of acetic acid. In earlier experimental work, operation of conventional anaerobic digestion systems in this suppressed methane mode has yielded a product of over 85% acetic acid, the remainder primarily being other organic acids such as propionic and butyric acids; operation at thermophilic conditions (60°C) yielded essentially all acetic acid. In the process described, recovery of the dilute organic acids (=3.5% acetic acid) will be by liquid ion exchange extraction. Product calcium acetate is formed by back extraction of liquid ion exchange with calcium hydroxide. After spray drying, this calcium acetate is ready for use as an organic deicing salt. Pretreatment of woody biomass may be by “steam explosion” or by mild alkali treatment to breakdown the lignin fraction for fermentation to acetic acid; however, if cellulosic wastes are used, no pretreatment step will be needed. Essentially, only technology transfer is involved in commercialization of this process, rather than the development of new technology. Our cost analysis, the objective of this present work, projects calcium acetate costs of 0.258 $US/kg ($0.117/lb) for a full-scale plant of 454 metric tons/day (500 U.S. tons/day).