Hydrothermal processing as pretreatment for efficient production of ethanol and biogas from municipal solid waste

Organic fraction of municipal solid waste (OFMSW) is dominated by carbohydrates, including starch-based and lignocellulosic materials. The OFMSW was hydrothermally pretreated at 100-160 °C for 0-60 min, and then assessed for enzymatic ethanol production, followed by biogas production from the stillage. The highest glucose yield of 520 g/Kg of dry OFMSW, corresponding to 131% increase compared to that of the untreated OFMSW, was obtained after the pretreatment and enzymatic hydrolysis. Through ethanolic fermentation by an inhibitory tolerant fungus, Mucor indicus, 191.10 g ethanol/Kg of dry OFMSW was obtained, which was a 140.9% improvement in the ethanol yield compared to that from the untreated one. Methane production from the stillage (waste residues) resulted in 156 L/Kg OFMSW. In other words, a total of 10,774 KJ energy/Kg of dry OFMSW was generated at the best conditions.

Optimization of fermentation conditions for efficient ethanol production by Mucor hiemalis

Background

Mucor hiemalis is a dimorphic fungus that efficiently produces ethanol from different sugars; however, the yield of ethanol production highly depends on the fermentation conditions.

Objective

The conditions for obtaining a high ethanol production yield were optimized in this study.

Materials and methods

A response surface methodology was used to optimize pH, temperature, and time of ethanolic fermentation by M. hiemalis. Additionally, wheat flour was enzymatically hydrolyzed and the hydrolysate solution with high glucose concentration was fermented by the fungus.

Results

The optimum pH, temperature, and time were 5.5, 30°C, and 36 h, respectively. Maximum ethanol and glycerol yields were 0.48 and 0.06 g/g, respectively. The biomass yield was between 0.01 and 0.16 g/g of consumed glucose. The results showed that the fungus was able to produce ethanol in a medium containing 5.5% (v/v) ethanol, while higher ethanol concentration prevented further production of ethanol.

Conclusion

At the optimized conditions, the fungus was able to consume glucose with the concentration of 140 g/L and produce ethanol with a yield of 0.45 g/g, which was comparable to that by Saccharomyces cerevisiae.