Increasing microalgal carbohydrate content for hydrothermal gasification purposes

This research examines the growth of Chlorella sp. microalgae under nutrient limitation (10-200 mg NaNO3 L−1 and 10-70 mg K2HPO4 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 K2HPO4. Under favorable circumstances; i.e. K2HPO4 = 10 mg L−1, NaNO3 = 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.