Anaerobic digestion of Chlorella vulgaris microalgae: slow nitrogen mineralization and partial COD removal

Abstract : Anaerobic digestion of Chlorella vulgaris produced in a lab-scale unit of microalgae production was investigated. The benefit of the proposed system is an intermediate settling device which allowed to concentrate the microalgae biomass by 30 fold compared to concentrations reached in the photobioreactor. A maximum methane production of 180 mL CH4.g-1CODinput was reached under the longest hydraulic retention time (HRT). The COD removal and nitrogen mineralisation increased by two and three fold respectively when increasing the HRT from 16 days to 28 days. Such results show that reaction rates of COD removal and nitrogen mineralisation are subject to different dynamics. Nevertheless even under high HRTs, 50% of the microalgae biomass did not undergo degradation which highlights the need to promote primarily hydrolysis to enhance the methane production of Chlorella vulgaris digestion.