Microalgae cultivation using biogas and digestate carbon sources

Anaerobic digestion produces biogas and digestate containing CO2 and volatile fatty acids, respectively that might need to be removed if they are to be used or discharged. Algae cultivation would remove the carbon in biogas and digestate. The present work used a textile desizing wastewater digester's biogas and digestate effluent to cultivate microalgae Scenedesmus sp. The tested biogas CO2 and digestate chemical oxygen demand (COD) concentrations were 22% and 3-7 g L-1, respectively. It is shown that Scenedesmus sp. could simultaneously assimilate biogas CO2 and organic carbon in the digestate. A digestate concentration of 5 g COD L-1 resulted in peak algal biomass concentration, COD removal and bio-CO2 fixation efficiency with values of 1.79 g L-1, 69.1% and 98.2%, respectively in 10 day algae cultivation. Based on the experimental results, a diagram was proposed to show a wastewater treatment to give an algae and methane bioenergy production concept as an example of circular economy.