Dewatering Chlorella Algae through Carbon Dioxide Hydrate Formation

With ever-increasing energy needs and climate change, there is great interest in implementing low-carbon, sustainable energy sources. Biofuels are of great interest because of their adaptability into liquid transportation fuels. Algae is an abundant, fast growing potential biofuel source that would not affect our food supply; however, a method to efficiently remove water from an algal needs to be determined. This study utilizes carbon dioxide (CO2) gas hydrates as a novel, nontoxic tool to dewater-water-saturated algae slurries. Gas hydrates are crystalline solids formed when a gas is entrapped in a water cage under high pressure and low temperature conditions. A stainless-steel reactor was built and used to perform proof of concept experiments using Chlorella and freshwater algae growth solutions. Experiments were performed with an initial pressure of 450 psig [32 bar] in a refrigerated circulator cooled to 2 degrees C for three or more days with occasional agitation to encourage CO2 hydrate formation. After performing several experiments, it was found that between 0.2 and 14.7 wt % of free water was converted into gas hydrates, which is in line with the theoretically possible range of water conversion based on experimental conditions. Extreme pressure and temperature conditions did affect the viability of the algae, as the algae only survived for about 3 days after being returned to atmospheric conditions. Overall, the results show that gas hydrates can form in an algal slurry; therefore, there is potential for the use of gas hydrates to dewater a water-saturated algae slurry.