Integrated processing of algal biomass: pathway towards biorefinery production of fuels and chemicals

Two model processes for algal biorefineries involve either lipid extraction of algal biomass followed by anaerobic digestion or hydrothermal liquefaction of the whole algal biomass into fuel intermediates.  Neither of these processes optimally valorizes all algal components. We report on a integrated processing regime that employs a dilute sulfuric acid pretreatment to hydrolyze algal biomass prior to extraction to fractionate the biomass into a carbohydrate rich liquid stream, amenable for fermentation, a lipid stream, and a solid fraction consisting primarily of denatured proteins.

 Screening experiments were conducted using an automated microwave reactor pretreating two algal strains, Scenedesmus and Chlorella, at 7% solids loading (w/w). Reaction conditions leading to enhanced carbohydrate and lipid release were scaled 20% solids loading (w/w) pretreated using a steam injected Zipperclave reactor.  After pretreatment the slurry was centrifuged with the liquor fraction fermented to ethanol with yields approaching 91% (w/w).  The protein and lipid component were collected into the solid fraction and later extracted for characterization. The process was further scaled to pilot scale utilizing 130-kg pretreatment reactor at 25% solids loading  (w/w). Ethanol yield of the algal hydrolyzate approached 79% (w/w) in less than 20 hours. Hexane extraction of the solid fraction yielded a lipid content in the solid fraction approaching 45% (w/w).   Based on these results we present an integrated approach to bioprocessing of algal biomass examining the impact of scale, % solids loading and reactor type on the pretreatment and fractionation process.