Scientific Publications
Bioethanol production from spent mushroom compost derived from chaff of millet and sorghum
Biotechnology for Biofuels, 10, 195
Background: In Uganda, the chaff remaining from threshed panicles of millet and sorghum is a low value lignocellulosic by-product. Currently it is used in the production of substrates for the cultivation of Oyster mushrooms (Pleurotus ostreatus) that are harvested as a food. The aim of this study has been to assess the potential for exploiting the residual compost post-harvest for saccharification and fermentation to produce ethanol.
Results: Sorghum and millet chaff-derived spent oyster mushroom composts minus large mycelium particles were assessed at small scale and low substrate concentrations (5% w/v) for optimal hydrothermal pretreatment severity, enzyme loading and fermentation with robust yeasts to produce ethanol. These conditions were then used as a basis for larger scale assessments with high substrate concentrations (30% w/v). Millet-based compost had a low cellulose content and, at a high substrate concentration, did not liquefy effectively. The ethanol yield was 63.9 g/kg DM of original material with a low concentration (19.6 g/L). Compost derived from sorghum chaff had a higher cellulose content and could be liquefied at high substrate concentration enabling selected furfural-resistant yeasts to give an ethanol yield up to 186.9 g/kg DM of original material and an ethanol concentration of 45.8 g/L.
Conclusions: Spent mushroom compost derived from sorghum chaff has the potential to be an industrially useful substrate for producing second generation bioethanol. This might be improved further through fractionation and exploitation of hemicellulosic moieties, and possibly the exploitation of the mycelium-containing final residue for animal feed. However, that derived from millet does not provide a suitably high concentration of ethanol to make it worth-while. Further research on the difficulty in quantitatively saccharifying cellulose from composted millet chaff and other similar substrates such as rice husk is required.
Biotechnology for Biofuels, 10, 195
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