Biofuels from algae: challenges and potential

Abstract

Algae biofuels may provide a viable alternative to fossil fuels; however, this technology must overcome a number of hurdles before it can compete in the fuel market and be broadly deployed. These challenges include strain identification and improvement, both in terms of oil productivity and crop protection, nutrient and resource allocation and use, and the production of co-products to improve the economics of the entire system. Although there is much excitement about the potential of algae biofuels, much work is still required in the field. In this article, we attempt to elucidate the major challenges to economic algal biofuels at scale, and improve the focus of the scientific community to address these challenges and move algal biofuels from promise to reality.

Figure 1. Previous and predicted global petroleum sources

(A) Global liquid fuel use in 2006 was predominantly (96.3%) conventional petroleum, with slightly less than 1% being biofuels. (B) In 2030, the International Energy Agency estimates that 29% of liquid fuels will originate from current conventional oil sources, 57% will be from undeveloped or unidentified conventional oil sources and 6% will be biofuels [4]. The large gray area of undeveloped or unidentified sources provides ample and possibly necessary expansion for nonconventional sources.

Figure 2. A combination of factors is expected to be required for algal fuels (red line) to become cost competitive with petroleum (green line: limited petroleum supply, resulting in increased costs; blue line: business as usual scenario)

These improvements will require years of research and cover (A) bioprospecting for high-oil-producing, low-input-requiring species; (B) engineering to improve growth, harvesting and nutrient recycling; (C) further strain improvement through breeding, selection and random mutagenesis; and (D) bioengineering to improve fuel traits, produce co-products and crop protection. Estimates given in this figure are for illustration purposes based on our best guesses. We believe that bioprospecting has high potential to identify a solid biofuel species in the next few years but subsequent improvement of that species, as well as solving engineering challenges to improve cost efficiency, will not occur as rapidly.

Figure 3. Algal biofuels production chain

Improved strains, as well as downstream efficiency, are integral aspects of the algae biofuel production strategy.

Figure 4. To maximize algae biofuel sustainability, nutrients must be recycled

This is a model of how we expect nutrient utilization to occur as the field matures. Algae will be harvested and the oil will be extracted, the remaining biomass (carbohydrates/proteins) will either be recycled for nutrients through anaerobic digestion or similar means, producing methane gas and a nutrient-rich slurry, which can then be fed back into the algal pond, rather than exogenously produced fertilizers, or used to for high-value co-products, ranging from industrial enzymes, nutraceuticals or animal feed stocks. Some of these nutrients can be recycled through waste water, while others will be lost due to runoff.

Figure 5. Additive effects of improvements on algal cost

In our model, our starting strain, with characteristics in brackets, has a break-even price of US$21.33. Significant improvements in all factors (blue) or exceptional improvements in all factors (pink) have break-even prices of US$4.23 or US$1.58 before co-products are considered. Our model consists of seven major factors: 1) annual maintenance costs: this includes personnel, land taxes, fertilizer costs, upkeep, water and power; 2) harvesting costs: this cost is incurred every time algae reaches harvesting stage which is a function of growth rate, and maximum growth density (it includes costs for water extraction, oil extraction and oil transport from harvest site to sales destination); 3) pond depth: this is how deep the ponds can be made while the algae still maintain optimal growth rates. The remaining four are characteristics of the algae; 4) lipid content; 5) growth rate; 6) maximum growth density; 7) marketable co-products produced by the algae. Based on our analysis, improvements in all seven factors are required for algae to come close to competitive with petroleum. Maximizing the last four characteristics require good crop protection, stressing the importance of developments in this field before the large capital investment required to build full scale algae biofuel farms. It is important to note this economic model does not include the initial capital costs to build the initial farms.