Increasing microalgal carbohydrate content for hydrothermal gasification purposes

Abstract

Abstract This research examines the growth of Chlorella sp. microalgae under nutrient limitation (10–200 mg NaNO 3 L −1 and 10–70 mg K 2 HPO 4 L −1 ) and different light intensities (60–450 μmol photons m −2 s −1 ) for achieving maximum carbohydrate content and biomass productivity using Response Surface Methodology (RSM) technique. According to the results, nutrition limitation had considerable effect on carbohydrate accumulation especially phosphorus concentrations; as in constant light intensities, maximum carbohydrate content was obtained in minimum concentration of K 2 HPO 4 . Under favorable circumstances; i.e. K 2 HPO 4 = 10 mg L −1 , NaNO 3 = 105 mg L −1 , and light intensity = 255 μmol photons m −2 s −1 the highest carbohydrate content by 60.9% was achieved. Moreover, Supercritical Water Gasification (SCWG) of carbohydrate enriched microalgal biomass is able to produce much more hydrogen gas in comparison to the basic microalgal biomass. In addition, a 1.85 times increase in amount of produced gas is appeared as a result of a change in biochemical composition of the microalgal biomass.