Integrated Microbial Process for Bioconversion of Crude Glycerol from Biodiesel into Biosurfactants and PHAs

Abstract

Biodiesel production from oils and fats is continuously growing, raising the problem on how to dispose crude glycerol, the main byproduct, in an economic and ecofriendly way. On the parallel, the demand of green chemicals, such as polyhydroxyalkanoates (PHAs) and biosurfactants (BSs), is increasing, becoming a valuable economic perspective for new industrial processes. Some bacteria are able to synthesize PHAs and BSs by different carbon sources, therefore crude glycerol may be a suitable source for high-value added green chemicals. In this work, crude glycerol from Brassica carinata oil was converted into PHAs and BSs by Pseudomonas mediterranea 9.1. Addition of either meat or yeast extracts improved glycerol fermentation, minimizing the prolonged lag phase observed in mineral medium. The effects of nutritional requirements, pH, temperature and fermentation time on the PHA and BSs yields were evaluated by response surface methodology (RSM). A Box-Behnken experimental design was adopted to derive a statistical model for variables optimization. In order to establish an accurate control of PHAs and BSs yields and fermentation time, the data from RSM were applied to a mathematical mechanistic model, in order to simulate three distinct fermentative processes, which were verified experimentally, to obtain i) maximum production of PHA, ii) maximum production of BSs and iii) co-production of both. Results showed that P. mediterranea used crude glycerol as carbon source, at a concentration of 2.5%, and was able to convert it into PHA and BSs. The data from mathematical mechanistic model, experimentally confirmed by batch fermentations, indicated that maximum production of PHA (1.63 g/L) required 48 h with 2.5 mM (NH4)2HPO4, 0.1 % meat or yeast extracts, pH=6.9 and T=27°C, whereas maximum production of BSs (0.8 g/L) required 96 h with 8 mM (NH4)2HPO4, 0.1% meat or yeast extracts, pH=7.1 and T=33°C. In the co-production process, satisfactory yields of both PHA (1.1 g/L) and BSs (0.72 g/L) were simultaneously produced within 72 hours. The co-production strategy in a single integrated fermentative process looks as promising for industrial production of green chemicals at competitive costs.