Biofuel production utilizing a dual-phase cultivation system with filamentous cyanobacteria

Biomass yields and biofuel production were examined in a dual (solid and liquid)-phase cultivation system (DuPHA) with the unique filamentous cyanobacteria, Pseudanabaena sp. ABRG 5-3 and Limnothrix sp. SK1-2-1. Continuous circular cultivation was driven under the indoor closed (IC) or indoor opened (IO) conditions and provided biomass yields of approximately 8–27 g dry cell weight (DCW) floor m−2 d−1. Alkanes of heptadecane (C17H36) or pentadecane (C15H32) as liquid biofuels were also recovered from the lower liquid-phase, in which cyanobacteria were dropped from the upper solid-phase and continuously cultivated with a small amount of medium. After the main cultivation in DuPHA, the upper solid-phase of a cotton cloth on which cyanobacteria grew was dried and directly subjected to a combustion test. This resulted in the thermal power (kJ s−1) of the cloth with microalgae increasing approximately 20–50% higher than that of the cloth only, suggesting a possibility of using the solid phase with microalgae as solid biofuel.