Biofixation of CO2 and biomass production from model natural gas using microalgae: An attractive concept for natural gas sweetening

Abstract

Despite the fact that natural gases are the most vital source of energy, pollutants like carbon dioxide in natural gases cause sediment and erosion of equipment, catalysts poisoning, and the most important environmental pollution. Microalgae also have the ability to remove CO2 from some gas streams. In this work, for the first time, a species of microalgae is used to fix carbon dioxide from the natural gas stream that contain 7% (v/v) CO2. Therefore, the effect of different strategies of model gas injection, light intensity, and light/dark cycle on the biomass productivity, carbon dioxide fixation rate, and lipid and chlorophyll content of Chlorella sp. were investigated. The results showed that when the model gas was injected in the dark period, biomass productivity and carbon dioxide fixation rate reached the highest level. In point of fact, under light intensity of 300 µmol photon m-2s-1 the fixation rate has reached 240 mg L-1 day-1. In addition, both using nitrogen as a model gas balancer and higher level of light intensity arose increased productivity and fixation. Also, the combination of increased light intensity and model gas injection in the dark cycle provided a condition in which higher rates of lipid accumulation were induced. The highest lipid content observed in this condition was 42% obtained. Aeration using nitrogen as a model gas balancer decreased lipid production.