Evaluation of different waste streams as fermentation substrates for microbial biopolymer production

Abstract

The growing reliance on synthetic polymers has raised a number of environmental and human health concerns. Most plastic materials are derived from nonrenewable resources and not biodegradable. Their distinguishing properties like durability and strength also ensure their persistence in the environment and complicate their disposal. Replacing synthetic polymers with biopolymers offers advantages in terms of biodegradability and biocompatibility however still suffers from high production costs. Therefore most research has shifted towards development of cost-effective ways of producing these biopolymers. Levan is a homopolymer of fructose with many outstanding properties like high solubility in oil and water, strong adhesivity, good biocompatibility and film-forming ability. However its industrial use has long been hampered by costly production processes which rely on mesophilic bacteria and plants. Halomonas sp. AAD6 halophilic bacteria were found to be the only extremophilic species producing levan at high titers and hence considerable research effort has been directed to combine the advantages of osmoadaptation and halophilicity to favor high yield levan production. As part of this on-going research, in this thesis work, the potential uses of different waste streams like sugar beet and starch molasses, cheese whey powder, sugar beet pulp, olive mill wastewater, and orange bagasses were investigated and based on EPS yields, pretreated sugar beet molasses was found to be superior to others. FT-IR analysis showed that EPSs produced under different conditions were all levan-type polymers and rheological studies revealed that these EPSs have shown the characteristic of low viscosity and appeared to exhibit pseudoplastic behaviours. Flocculating activity of these EPSs were dynamically monitored with a photometric dispersion analyser and one sample was found to exhibit flocculation performance and particles removal efficiency comparable with commercial synthetic polyelectrolytes. Finally, a rough economic analysis revealed that replacing pure sucrose with molasses not only increased the production yields but also resulted in five-fold lower costs of fermentation medium per gram of levan produced.