Two-stage cultivation of N-rich and N-deprived Acutodesmus obliquus biomass: Influence of cultivation and dewatering methods on microalgal biomass used in anaerobic digestion

Abstract

Microalgae can be manipulated to accumulate certain cellular compounds of interest without the need for genetic modification - simply by controlling growth parameters such as nitrogen (N). Therefore, A. obliquus was batch-cultivated in a sleevebag photobioreactor system in N-deprived and N-rich medium to test the effect of N-status on CH4 yield under anaerobic digestion. Two different dewatering methods, i.e., centrifugation and sedimentation were applied to each resulting biomass. For the N-deprived biomass, cellular protein content dropped by 42–49%, and lipids increased up to 20% relative to the N-rich biomass. The highest CH4 yields were achieved with N-deprived, sedimented biomass (391Nm3t−1 VS=normalized gas volume in m3 corrected to norm temperature and pressure per unit volatile solids), followed by N-rich sedimented biomass (361Nm3t−1 VS). Centrifugation led to lower CH4 yields, where N-deprived biomass achieved 280 compared to 200Nm3t−1 VS for N-rich microalgae. Our data indicate that valuable organic material was lost to the supernatant during the centrifugation step. We conclude that not only the N-status of cultivation, but also the biomass dewatering method has an instrumental effect on CH4 yield of microalgal biomass in anaerobic digestion.