Biogas Plant Upgrade to CO2-Free Technology: A Techno-Economic Case Study

A techno-economic analysis was performed for a biogas plant with in-built algae production. Degradation in the fermenter occurs under mesophilic conditions, to produce 605 Nm³t⁻¹_TS of biogas and 343 Nm³t⁻¹_TS of methane after 50 days. The biogas was combusted in a combined heat-and-power unit to produce heat and electricity. Cultivation of Chlorella vulgaris was done in co-annular photo-bioreactors, with an annual productivity of 107.5 t. For cultivation, both autotrophic and mixotrophic growth were assumed. Detailed mass and energy balances were done. For both conditions of algae growth, the results are approximately the same after a 30-year payback period.