Simultaneous Extracellular Polymeric Substance (EPS) and Lipid Production by Activated Sludge Via Fermentation of Glucose

The use of activated sludge microflora to convert sugars, derived from the hydrolysis of lignocellulose biomass, into lipids for biofuel production is of current research interest in our group. Lipid accumulation in this system has been enhanced by manipulating the carbon-nitrogen (C:N) ratio and initial sugar loading on activated sludge bioreactors with glucose as the main carbon source. Activated sludge is a flocculated suspension composed of microorganisms that can also produce extracellular polymeric substances (EPS) in situ during fermentation. Microbial EPS which are secreted largely by bacteria in harsh environments are a matrix rich in polymers including polysaccharides, glycoproteins, proteins, nucleic acids and phospholipids. Thus, studying EPS production along with lipid formation is essential for understanding the technical and economic value of the whole process. In this study, samples were obtained from aerobic batch fermentation inoculated with 20 % (v/v) activated sludge. The total incubation time for the batch fermentation experiment was seven days. EPS from the collected samples were extracted using a Dowex cation exchange resin in phosphate buffered saline solution and precipitated with 95% v/v cold ethanol and dialyzed. Fourier transform-infrared spectroscopy of freeze-dried EPS revealed characteristic IR peaks for polysaccharides and proteins. Total polysaccharide and protein concentrations were estimated in each EPS sample using phenol-sulfuric and modified Lowry methods, respectively. An increase in lipid % (g/g cell dry weight) and a decrease in specific EPS % (g/g cell dry weight) was observed from day 0 to 7 in all treatments. Increasing the carbon loading while maintaining the same C:N ratio increased lipid % and decreased specific EPS %. However for a low C:N ratio, lipid % remained constant while specific EPS % decreased. These results will be useful for manipulation of EPS and lipid production and consequently enable development of valuable strategies for improving the process.