Anaerobic Conversion of Lignocellulose to Materials for Biofuel Production: Volatile Fatty Acids and Ethanol

Abstract

The processes of oxidative depolymerization and acidic hydrolysis have consistently been used for the pretreatment of lignocellulosic biomass (wheat straw, sawdust, and lignin), which makes it possible to obtain a high content of soluble organic compounds in the hydrolysate (44–94 g COD/L) and to enhance the concentration of reducing sugars from 1 to 36%. The introduction of Clostridium acetobutylicum bacteria to an acidogenic biocatalyst resulted in an even greater increase in the content of volatile fatty acids and ethanol in the end product. The maxima among the studied substrates yields of butyric acid and ethanol were observed when the pretreated straw was hydrolyzed (27% (0.82 g/L) and 17.4% (0.44 g/L), respectively). It was shown that the addition of glycerol as a substrate makes it possible to increase the yields of butyric and acetic acids as a result of the conversion of the pretreated biomass; the addition of glycerol to straw in a 1 : 1 ratio enhanced the maximum butyric acid and VFA yields up to 32% (0.96 g/L) and 72% (2.67 g/L), respectively.