A combined hydrothermal gasification - solid oxide fuel cell system for sustainable production of algal biomass and energy

Hydrothermal gasification (HTG) is a promising technology that allows the recovery of nutrients from wet biomass with simultaneous production of an energy-rich gas. In this work, wastewater effluent (leachate) obtained from a composter sanitary system operating without external connection to sewer pipes was used as a feedstock for HTG process. The leachate effluent was characterized by its high moisture and inorganic content. Mainly H2 rich gas was obtained from the HTG of the leachate at 600 °C, 28 MPa with almost full recovery of nitrogen and phosphorus; up to 74.4% and 92% respectively. For an efficient power-generation system with low emissions, experimental results combining solid oxide fuel cells (SOFC) with the obtained gas from the HTG were performed. Thermodynamic calculations were performed on the gas compositions to evaluate the performance and the risk of solid carbon formation at a typical SOFC operation temperature 750 °C. Furthermore, for nutrient recycling purposes, the obtained nutrient rich effluent from the gasification was used as a growth medium for microalgae Chlorella vulgaris. Finally, a complete valorization chain based on both experimental study and model prediction that combine, energy conversion and microalgae valorization was investigated.