Comparative Assessment of Fungal Consortium Ligninolytic Enzymes Versus Sequential Acid–Alkali Pretreatments for Bioethanol Production from Rice Straw

Abstract

The present study analyses the impact of biological pretreatment of rice straw on the degradation of recalcitrant lignin vis-à-vis chemical pretreatment. A fungal consortium was set up with Phanerochaete chrysosporium and Pleurotus ostreatus and the ligninolytic enzyme produced by it was used for biological pretreatment. The chemical pretreatment was achieved using a sequential treatment with H₂SO₄ followed by NaOH. The biological pretreatment showed promising results on par with the robust chemical pretreatment method. The biological and chemical pretreatment of rice straw resulted in 80.9% and 82.6% delignification, respectively. The saccharification of pretreated straw with 30 FPU/g of commercial cellulase yielded 49.2 g/100 g dry substrate and 56.6 g/100 g dry substrate reducing sugars from biological and chemical pretreated rice straw, respectively. The sequential fermentation under separate hydrolysis and fermentation (SHF) conditions with 10% (v/v) Saccharomyces cerevisiae and Pachysolen tannophilus achieved a maximum ethanol concentration of 9.25 g/L (fermentation efficiency; 73.8%) and 12.0 g/L (fermentation efficiency; 74.2%) from biological and chemical pretreated straw, respectively. The cost for the bioethanol production from 1.0 kg rice straw was calculated to be 31.92 Rs while it is 36.45 Rs for chemical pretreatment.