Two-stage medium chain fatty acid (MCFA) production from municipal solid waste and ethanol

Chain elongation is an anaerobic fermentation that produces medium chain fatty acids (MCFAs) from volatile fatty acids and ethanol. These MCFAs can be used as biochemical building blocks for fuel production and other chemical processes. Producing MCFAs from the organic fraction of municipal solid waste (OFMSW) is attractive because it combines waste treatment with biochemical production. We investigated whether higher MCFA production rates can be achieved from OFMSW by applying a two-stage conversion, consisting of the OFMSW acidification step followed by chain elongation, compared to a single-stage system. We obtained higher MCFA production rates with a two-stage system than with a single-stage system. The obtained caproate concentrations were above the solubility of caproic acid in water. Furthermore, this work discussed competitive processes for MCFA production and shows how these processes can be controlled in a two-stage system. Finally an outlook was given on research required to prevent too much production of the intermediate co-product butyrate instead of MCFAs, which occurred several times during the experiment.