An Introduction to Algae Biofuels
Algae are emerging as a promising feedstock for renewable biofuels. Algae can produce oil and biomass that can be converted into biodiesel, jet fuel, ethanol, and other energy products. The potential benefits of algae biofuels include:
- High yields - Algae can produce over 5,000 gallons of biofuel per acre per year, much more than traditional biofuel crops like corn or soybeans.
- Grow quickly - Certain algae species can double their mass several times per day. Their growth rate far exceeds conventional crops.
- Use marginal land and water - Algae cultivation systems can utilize non-arable land and non-potable water sources. This avoids competition with food crops for prime agricultural land and freshwater.
- Recycle CO2 - Algae growth can utilize flue gas CO2 emissions, potentially reducing greenhouse gas emissions from power plants and other industries.
However, several challenges must be addressed to scale up algae biofuel production. One key issue is the energy return on investment (EROI). Producing, harvesting, and processing algae into fuel requires energy inputs. If the EROI is too low, then little net energy is gained, reducing the sustainability of algae biofuels.
Improving Algae Biofuel EROI
The EROI of current algae to fuel processes ranges from 1.5 to 5 [1]. Values under 3 are generally not considered viable. However, there are several ways to potentially improve the EROI of algae biofuels:
Use Natural Algae Growth
Most algae production utilizes artificial growth systems like closed photobioreactors or open raceway ponds. These require energy inputs for pumping, mixing, CO2 supply, and infrastructure construction. A more sustainable approach is using natural algae growth in the ocean or other water bodies. This avoids the need for artificial growth systems. Companies like Bio Fuel Systems are pursuing harvesting wild algae from seawater and wastewater sources [2]. Challenges include managing inconsistent natural algae productivity and concentrations.
Combine with Wastewater Treatment
Siting algae systems at municipal or agricultural wastewater treatment plants can provide nutrients like nitrogen and phosphorus. This avoids the need for synthetic fertilizers, reducing energy inputs. The algae also benefit the wastewater plant by reducing nutrient pollution in discharge waters. New Zealand's Living Light is co-locating algae plants with dairy farm effluent ponds to mutual benefit [3].
Utilize Waste CO2 Sources
Flue gas from power plants, cement factories, and other industries can provide concentrated CO2 to accelerate algae growth. This both improves algae productivity and reduces CO2 emissions. Companies like Algenol are situating algae facilities next to ethanol plants and using the fermenters' CO2 off-gasses to grow algae [4].
Combine Algae Production with Other Revenue Streams
Developing integrated biorefineries that produce fuels along with other higher-value algae products can improve economics. Algae can yield nutritional products, pigments, and compounds used in cosmetics, nutraceuticals, and medicines. Solazyme is commercializing an algae-based platform that produces tailored algal oils for many non-fuel markets [5].
Optimize Harvesting Techniques
Separating and collecting algae cells from water requires significant energy. Novel separation methods like ultrasonic harvesting, electrical harvesting, and bio-flocculation may require less energy than traditional centrifuge or filter pressing approaches [6]. More efficient harvesting improves EROI.
Utilize Energy-Efficient Processing Technologies
Converting algae oils and biomass into finished fuels consumes energy for extraction, reactions, separations, and upgrading. Emerging processing methods like hydrothermal liquefaction, catalytic hydrothermolysis, and supercritical fuel conversion can produce higher fuel yields with lower energy inputs compared to conventional approaches [7].
Conclusion
While algae biofuels currently face economic hurdles like low EROI values, this promising renewable fuel can be sustainable and scalable in the future. By tapping into natural algae productivity, combining facilities with wastewater treatment and CO2 supply, producing co-products, and employing advanced harvesting and processing technologies, the net energy balance of algae biofuel systems can be significantly improved. With targeted research, development, and commercialization efforts, algae's vast potential as a renewable fuel source can be realized.
References
[1] J. Ryckebosch, M. Drouillon, and H. Vervaeren, “Techniques for transformation of biogas to biomethane,” Biomass and Bioenergy, vol. 35, no. 5, pp. 1633–1645, May 2011.
[2] Bio Fuel Systems, "Our Technology", https://biofuelsystems.com/our-technology/, Accessed Jan 2022.
[3] Living Light, "Dairy Farm Effluent", https://livinglightalgae.com/dairy-farm-effluent/, Accessed Jan 2022.
[4] Algenol, “Direct-to-Ethanol®”, http://algenol.com/direct-to-ethanol/, Accessed Jan 2022.
[5] Solazyme, “ fuels and chemicals”, http://solazyme.com/fuels-and-chemicals/, Accessed Jan 2022.
[6]B.S. Naveen, M. Azharuddin, and H.S. Kamath, “A review on technological options of biomass to liquid transportation fuels,” Renewable and Sustainable Energy Reviews, vol. 40, pp. 365-374, Dec. 2014.
[7] A.A. Peterson et al., “Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies,” Energy Environ. Sci., vol. 1, no. 1, pp. 32-65, 2008.