How do we optimize third-generation algal biofuels?

Algae can be a source of third-generation gaseous transport biofuel (either biomethane or biohydrogen). An optimal system is suggested which combines dark fermentation, anaerobic digestion, and carbon dioxide biofixation. Biogas upgrading through removal of carbon dioxide is required prior to utilization as a transport biofuel. Traditional upgrading systems are energy intensive and expensive. Carbon dioxide biofixation by microalgae, with a bicarbonate/carbonate cycle, offers energy and cost savings over traditional upgrading systems. The microalgae, which remove carbon dioxide, can be used as substrate for biogas, forming an energy efficient closed loop system. The proposed system has significant advantages in reducing parasitic energy demand in upgrading biogas, enhancing the energy yield three-fold, and minimizing carbon dioxide emission. (C) 2015 Society of Chemical Industry and John Wiley & Sons, Ltd