Non-detoxified acid hydrolysate of de-oiled Pongamia seed cake as a low-cost solution to microbial oil synthesis

Abstract

• A lignocellulose residue, derived as a biodiesel byproduct, was used for microbial oil synthesis. • Acid pretreated biomass was used for lipid fermentation without detoxification. • The biomass and lipids in detoxified and non-detoxified media did not significantly differ. • A. ochraceus was resistant to inhibitors in the non-detoxified medium. • Avoiding the detoxification step may improve process economics. With rising energy demands, alternative transportation fuels are continually sought. The most recent advances in this area have been in the use of microorganisms to produce oils for biodiesel. When pretreated with dilute acid and used for microbial fermentation, the lignocellulosic sources currently preferred for microbial oil production require an additional detoxification step. In this work, microbial oil was produced from de-oiled Pongamia cake, a low-value residue from the biodiesel industry, to evaluate whether the detoxification step might be omitted during raw material processing. Non-detoxified acid hydrolysate (NDAH) and detoxified acid hydrolysate (DAH), when subjected to fermentation with Aspergillus ochraceus , produced comparable biomass and lipid concentrations, with a maximum biomass of 22.249 g/L and 21.445 g/L, and maximum lipid of 4.463 g/L and 4.106 g/L, in NDAH and DAH media, respectively, thus indicating that detoxification might be avoided. Detoxifying the medium decreased the concentrations of the fermentation inhibitors furfural, 5-hydroxymethyl furfural (HMF), and acetic acid; however, the microorganism was resistant to the inhibitors, thus demonstrating that bio-oil can be produced from acid-pretreated Pongamia cake without any detoxification procedure. Overall, these results may enable the elimination of additional process and operating costs.