Abstract:
Crude glycerol, a by-product and major drawback of biodiesel, 10% by weight, once a valuable product is now considered a waste associated with disposal costs because of salts and methanol impurities. With an exponential increase of the biodiesel producers in South Africa and beyond, excess crude glycerol of concern as its supply exceeds its demand, creating excess glycerol of less value. Although purification is an option, South Africa does not have purification plants and exporting such negatively-valued glycerol is not economically viable. Innovative ways to dispose of crude glycerol are clearly necessary.
The study investigated the feasibility of upgrading crude glycerol as a carbon source in the aerobic production of ε-Poly-L-lysine using Streptomyces albulus (CCRC 11814). The polymer has a number of applications in food, biomedical and agricultural industries which exploit its water solubility, polycationic, biodegradability, edibility and non-toxicity to humans and the environment.
A total of 8 crude glycerol samples from 6 biodiesel producers around South Africa were analysed of elemental composition, as well as glycerol and methanol using an Inductively Coupled Plasma – Optical Emission Spectrometry and an HPLC respectively. The results of the only work of such analysis in South Africa showed that potassium salts were the main impurity, glycerol and methanol concentrations varied from one producer to the next.
This work compared growth and polymer production when S.albulus was grown in pure and crude glycerol. This work is important as it is the first to report Streptomyces albulus growing on crude glycerol (20g/l) (after reports that Escherichia coli and Clostridium glutamicum do not grow at all, with Sachoromyces. cerevisiae growing slowly) with remarkable biomass accumulating comparable to pure glycerol. Although, S. albulus grew slowly in methanol-containing glycerol (≤ 30g/l), the attribute could negate the costly methanol removal step. 0.219 g/l of ε-Poly-L-lysine produced is similar to 0.2 g/l from a wild strain reported in the literature.
These results show that biodiesel-derived crude glycerol is a promising, accessible and lowly-priced alternative carbon source for the industrial production of ε-Poly-L-lysine and its integration to an existing biodiesel business to reduce the production costs and hence increase its profitability and sustainability.
