Efficient coproduction of butanol, ethanol, and biohydrogen from municipal solid waste through a cocultivated biorefinery

Abstract

The cocultivation of Clostridium acetobutylicum and Mucor indicus was evaluated for the first time to take the advantages of both microorganisms for fully exploiting the energy potential of the organic fraction of municipal solid waste (OFMSW), generating high yields of acetone-butanol-ethanol (ABE) and hydrogen through a biorefinery scheme. Unlike M. indicus, C. acetobutylicum can ferment unhydrolyzed starch and pentose sugars. However, the low biofuel titer through ABE fermentation makes the bioprocess uneconomical. The fungal-bacterial symbiosis led to high ethanol titer along with high butanol and hydrogen yields without the need for starch hydrolysis. The effects of most influencing factors, i.e., initial pH, bacterium to fungus biomass ratio, and solid loading, on ABE and hydrogen production were investigated. The fermentation of organosolv pretreated OFMSW hydrolysate at initial pH of 5.5 and solid loading of 5% with 1:1 bacterium to fungus biomass ratio produced 80.2 g butanol, 30.2 g acetone, 108.1 g ethanol, and 96.3 L hydrogen from each kg raw OFMSW. From the bioenergy point of view, 7.2 MJ energy was generated, which was significantly higher than those obtained via the mono cultivation of C. acetobutylicum (6.2 MJ) and M. indicus (4.4 MJ), indicating the great potential of the fungal-bacterial cocultivation for bioenergy production from OFMSW. The economic potential of the cocultivated biorefinery was 0.16 $/kg OFMSW.