Applicability of Euglena gracilis for biorefineries demonstrated by the production of α-tocopherol and paramylon followed by anaerobic digestion

Abstract

In this study the use of Euglena gracilis biomass for α-tocopherol, paramylon and biogas production in a value-added chain was investigated. Therefore, we analyzed the dry cell weight and product concentrations at different growth phases during heterotrophic, photoheterotrophic and photoautotrophic cultivation in a low-cost minimal medium. Furthermore, the specific biogas yields for differently derived biomass with and without product recovery were investigated. We demonstrate that growth phase and cultivation mode not only have a significant impact on product formation, but also influence the yield of biogas obtained from anaerobic digestion of Euglena gracilis biomass. The maximum dry cell weight concentration ranged from 12.3±0.14gL−1 for heterotrophically to 3.4±0.02gL−1 for photoautotrophically grown Euglena gracilis cells. The heterotrophically grown biomass accumulated product concentrations of 5.3±0.12mgL−1 of α-tocopherol and 9.3±0.1gL−1 of paramylon or 805±10.9mL of biogasgvs−1 (per gram volatile solids). The results for photoautotrophically grown cells were 8.6±0.22mgL−1 of α-tocopherol and 0.78±0.01gL−1 of paramylon or 648±7.2mL of biogasgvs−1. For an energy-saving downstream procedure the extracting agent methanol does not have to be removed strictly. Samples with residual methanol showed a significantly increased biogas yield, because the solvent can be used as an additional substrate for methane production by archaebacteria.