(409f) Optimization of Extracellular Polymeric Substance (EPS) Production by Activated Sludge Via Fermentation of Glucose

Authors with affiliation:  Hien Nguyen, Patrisha Pham, Rafael Hernandez, Todd French, Andro Mondala

Abstract

The use of activated sludge micro flora 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.  The nature and composition of EPS makes it potentially useful as a biofloculant and/or a matrix for other bioproducts.  Studying EPS production along with lipid formation could result in a process to produce feedstocks for biofuel production and multiple specialty products.

             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 fourteen 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. 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 EPS % (g/g cell dry weight) were observed during the incubation period in all treatments. Increasing the carbon loading while maintaining the same C:N ratio increased lipid % and increased specific EPS %. However, for a low C:N ratio, lipid concentration remained constant while specific EPS concentration increased. These results will be useful for manipulation of EPS and lipid production and consequently enable development of valuable strategies to enhance the technical and economic feasibility of the activated sludge to biofuels and bioproducts process.