Anaerobic Digestion of Biodiesel Residues for Energy and Revenue Generation

Abstract

Biodiesel from inedible oilseeds is considered as a promising alternative to the non-renewable petroleum fuels which is facing an existential crisis. The comparatively higher selling price of biodiesel with respect to petro-diesel due to higher costs of oilseed kernel makes it expensive and uncompetitive in the current scenario, yet India has promised to shift to 20% biodiesel blends by 2020 and these wastes will soon be found in cities. The life cycle of biodiesel production also leads to the production of 5.83 and 7.88 kg residues per kg of biodiesel production from Pongamia pinnata (PP), Jatropha curcas (JC), respectively. The residues are mainly organic in nature and constitute 3.46 and 2.63 times the energy of biodiesel recovered. Anaerobic digestion (AD) of these residues was carried out in order to harvest the energy and convert the solid wastes to clean gaseous fuel. AD process carried out in a plug flow reactor (PFR) was estimated to reduce the net production costs of biodiesel by 30–80% in PP at a buy-back period of 2.29 years. Similarly, the net production costs reduced by 19–40% in JC with the returns in 6.02 years.