Around the world, algae are being cultivated commercially for high value human nutritional products – mostly in small to medium-scale systems, each producing up to several hundreds of tons of biomass annually.
But despite the promise of this technology, the cultivation of microalgae for biofuels is not yet commercially viable. And the current technological and economic challenges faced by the algae industry mean we will have to wait a few more years before algae biofuel becomes a commercial reality. In this post, I want to take a closer look at those challenges.
Why are people so excited about algae? Algae represent the third generation bio-energy feedstock. As well as having much higher yields compared to earlier generation feedstock (e.g. corn for ethanol or soybeans for bio-diesel), they can grow in different environments and absorb carbon dioxide during the cultivation process. In addition, microalgae offer an efficient way to consume nutrients in wastewater and provide aerobic bacteria with the oxygen they need to break down organic components in wastes. It appears that the microalgae processing technology could provide us with a holistic approach to integrating waste and resources by producing biofuels as well as treating waste water.
However, this technology is not yet mature enough for full-scale commercialisation. Converting algae into fuel typically involves (1) strain selection, (2) cultivation and growth, (3) harvesting and drying, (4) extraction and (5) conversion to an energy product. Upstream processes such as strain selection and cultivation are unique to this industry and demand special attention. In contrast, converting the harvested algae into final fuel products is a relatively mature process similar to conventional technologies currently used in petrochemical plants.
For the upstream processes, researchers all over the world are desperate to find an indigenous strain of algae that has a high oil content with high productivity and can be easily harvested. Ideally, it would also be resistant to contamination, tolerate high oxygen levels, endure temperature extremes and adapt easily to the local water chemistry or other environmental perturbations.
Algae can be cultivated in either open or covered ponds or closed photobioreactors. Open ponds are cheaper to build, but can suffer from contamination and challenging hydraulic issues, especially if the pond is large. Closed photobioreactors have better processing control but are more expensive to build. In both these systems, it’s crucial to optimise the processing parameters and understand the effects of scaling up. Further research and development is needed to optimise the level of productivity, efficiency, stability, and harvesting techniques for producing biofuels effectively.
Cost is a major challenge, too. Based on the price of algal biomass for the nutritional market (although not for making oil), algal oil costs over 10 times more than crude oil. The capital and operation costs of the various production systems will ultimately dictate the adoption of this technology as a cost-effective alternative to fossil fuels.
This is why, at Arup, we prefer to work with locally available strains in construction projects. (We’re currently working with Tongji University in Shanghai to investigate the efficiency of four different algal strains for both open-pond and closed photobioreactor designs).
One algal strain is unlikely to have all characteristics required for biofuel production. So genetic engineering methods are also being explored to see if we could modify native strains to increase their oil content and make it easier to harvest and cultivate them.
I’m excited about algae’s potential as a biofuel but we need to be realistic about the amount of work there is to do before it becomes a reality on a commercial scale.