Downsizing the microalgae hype

It has been some time since algae were the next fuel source. Given the substantial investment in research and development, I really wonder what happened to this technology, which had been so hyped 15 years ago. My PhD student Tong Wang at the Yale School of Engineering and Applied Sciences then got the opportunity to conduct a life cycle assessment and cost analysis of a specific technology for growing microalgae developed at the school by PostDoc Xiaoxiong Wang in Menachem Elimelech's lab.

The study shows that that the new technology can produce high-purity algae at lower cost and with lower impacts than alternative processes. The key of the new technology is that it uses heterotroph algea instead of phototrophic algea. The energy to grow the algea comes from straw rather than the sun directly. The costs are estimated to be close to $5 per kg algae, which can potentially be brought down closer to $3 per kg when various by-products are valorized. The production process causes just under 10 kg of CO2e per kg algae. Phototrophic algae production from sunlight in raceway ponds causes just over 10 kgCO2e, while the production in photobioreactors causes between 25 and 38 kgCO2e.

For me, these were indeed quite surprising findings. It is clear that algea cultiviation is miles away from being a process that produces energy, rather than consuming energy. It requires substantial infrastructure and inputs, and yields are modest. Producing algae using energy derived from straw is better than using sunlight directly. It also means that if you want to produce energy, do not use algae, use straw directly! Of course, growing biomass is a low-density way of energy harvesting to start out with, compared to wind turbines and photovoltaic cells. The commercial case for this technology is for cosmetics and other high-value specialty chemicals produced in small volumes only. An important clarification indeed!