Biodiesel Production by Direct In Situ Transesterification of an Oleaginous Tropical Mangrove Fungus Grown on Untreated Agro-Residues and Evaluation of Its Fuel Properties

Abstract

Recent research has focused on use of waste agro- residues for growth of oleaginous microbial biomass as renewable feedstock for biodiesel. However, pretreatment of lignocellulosic biomass into fermentable sugar is necessary for microbial growth, increasing production costs. An oleaginous fungal isolate from the tropical mangrove wetlands, IBB G4, identified as Aspergillus candidus was assessed for its growth on waste agro-residues viz., banana peel, copra meal, corn cob, grape stalks and sugarcane bagasse,which had not been given any thermo-chemical or enzymatic pre-treatment. The resulting fungal biomass was subjected to in situ (direct) acid transesterification for fatty acid methyl esters (FAME) extraction. Maximal FAME production was obtained on raw untreated banana peel (420 mg/L) and sugarcane bagasse (400 mg/L) with the yields significantly higher (52–68 mg/g of fermented biomass) than those for glucose (32 mg/g). The FAMEs showed major presence of monounsaturated methyl esters (41.7 %; C18:1, C15:1, C17:1, C14:1) and methyl linoleate (C18:2, 36.8 %) and 20 % as saturated fraction when sugarcane bagasse was the substrate for fungal strain. For banana peel, the saturated fatty acid methyl esters (48.6 %; C16:0, C18:0) were abundant, methyl oleate (C18:1, 25 %) was the major monounsaturated fatty ester while methyl linoleate (C18:2, 19 %) and methyl arachidonate (C20:4, 3.8 %) were prevalent as polyunsaturated methyl esters. Biodiesel fuel properties (density, kinematic viscosity, iodine value, cetane number, free and total glycerol) were in accordance with international(ASTM D6751, EN 14214) and national (IS 15607) biodiesel standards, suggesting their suitability as biodiesel fuel.The results in our study indicate the potential suitability of A. candidus IBBG4 biomass grown on raw untreated banana peel and sugarcane bagasse waste and its conversion to FAME by direct in situ acid transesterification. This would help improve process economics for a green and sustainable production of biodiesel.