Αcidogenic fermentation of wheat straw after chemical and microbial pretreatment for biofuel applications

Abstract

The anaerobic acidogenic fermentation of wheat straw was studied, after various chemical and microbial pretreatments, namely (a) chemical delignification, (b) hydrolytic pretreatment with T. viride of the chemically delignified straw to enhance the organic acid (OAs) yields in the subsequent acidogenic fermentations, and (c) microbial delignification by P. chrysosporium to enhance the biodegradability of the cellulosic material and avoid the chemical pretreatment. The subsequent anaerobic acidogenesis experiments of the wheat straw samples were carried out using a UASB culture free and immobilised on γ-alumina. Hydrolysis with T. viride was limited and slightly improved the result of the acidogenesis. On the other hand, delignification by P. chrysosporium produced satisfactory results, comparable to those of the chemical delignification process. The optimum substrate moisture content for the microbial delignification was 85%. In all cases the immobilised cells increased the OAs yields during the acidogenic fermentations by about 2-fold. Lactic, acetic and butyric acid were the prevailing OAs produced. The OAs could be then used as structural components of ester-based biofuels similar to biodiesel, an approach that has been recently proposed as a cost-effective and environmentally friendly alternative for 2nd generation biofuels production.