Value addition to Pongamia biodiesel industry through bioethanol production from pressed oil cake using Bacillus cereus

Pongamia pinnata, a tree bearing oil seeds, has been one of the prime focus among nonedible oil sources for biodiesel production in most parts of India. The oil cake obtained after the extraction of oil serves as an adequate source of cellulose, hemicellulose, proteins, lipids, and starch. The scarce literature data available suggest very low conversion rate of complex sugars to fermentable sugars and further to bioethanol. In the present work, a sulfuric acid hydrolysate obtained from Pongamia oil cake (POC) under microwave irradiation was anaerobically fermented using Bacillus cereus ATCC 14579. Under anaerobic and acidic conditions, the process parameters affecting the bioethanol production efficiency (BPE) were screened and optimized using statistical experimental designs. Of the seven parameters screened (glucose concentration, yeast extract as nitrogen source, agitation speed, pH, inoculum size, fermentation time, and temperature), only 3 were found to be significant and to increase BPE. The significant parameters were optimized using the Box-Behnken experimental design to obtain an optimal condition of 9 g/l reducing sugars, pH 4.6 maintained with acetate buffer, and fermentation period of 51 h that yielded 92% BPE with 4.2 g/l ethanol. Moreover, it was observed that the use of a buffer system to maintain broth pH, especially acetate buffer, significantly improved BPE. Low concentration of fermentation inhibitors is the key factor for improved BPE. The research outcome suggests that the production of dual fuel from Pongamia pinnata, viz. biodiesel and bioethanol, could not only improve the process economics but also reduce waste generation.