HYDROLYSIS REACTION OF NUTREINTS FROM MICROALGAE

Abstract

This work investigated the efficiency of the hydrothermal hydrolysis reaction of Scenedesmus sp. and Ankistrodesmus sp. carbohydrate before/after lipid extraction. The carbohydrate was converted to sugar using hydrolysis under hydrothermal condition in a small autoclave. Firstly, the investigation was carried out to find suitable conditions for hydrolysis before lipid extraction. The hydrolysis conditions were varied in terms of biomass loading (10-40 g/L), incubation temperature (180–220oC), reaction time (0.5-2 h), acid categories (HCl, HNO3 and H2SO4) and acid concentration (0-2%wt). The maximum glucose content of Scenedesmus sp. and Ankistrodesmus sp. were 5.96 and 2.38 g/L, respectively, at 0.75%wt H2SO4, reaction temperature of 180oC and retention time 180 min. Acetic acid, furfural, HMF, levulinic acid and formic acid of both microalgae were generated and increased with acid concentration. At optimum condition, the total sugar acids were 0.63 g/L for Scenedesmus sp. and 1.30 g/L for Ankistrodesmus sp. The protein content in Scenedesmus sp. and Ankistrodesmus sp. were 5.68 and 5.22 g/L, respectively. The lipid contents of hydrolyzed residue were 13.78 (Scenedesmus sp.) and 24.88%wt (Ankistrodesmus sp.).

Secondly, the microalgae was extracted for their lipid contents where were 28.14%wt for Scenedesmus sp. and 14.9%wt for Ankistrodesmus sp. Hydrolysis of the lipid extracted residue gave the highest glucose contents of 6.08 and 1.89 g/L, respectively, at 0.5%wt H2SO4, reaction temperature of 200oC and retention time 120 min for Scenedesmus sp. and Ankistrodesmus sp. In this case, sugar acids were similar to hydrolysis before lipid extraction except that formic acid was not observed. At optimum condition, the total sugar acids were 0.99 g/L for Scenedesmus sp. and 1.16 g/L for Ankistrodesmus sp. The protein content in Scenedesmus sp. and Ankistrodesmus sp. were 5.93 and 5.85 g/L, respectively. Compared to hydrolysis before lipid extraction, the hydrolysis of solvent pretreated microalgae could decrease acid concentration and retention time.