Algal Fuels: Simple idea, complex problem
Today, many innovative companies seek to replace petroleum fuels using algae. But they use highly mechanized and costly processes to grow, collect and process algae. If we hope to make algae fuels cheap and sustainable, there are many fundamental biological, physical, and chemical challenges that must be simplified and solved.
Biological Challenges: Algae grow on their own terms
1. Land: Meeting the world’s fuel needs with renewable algal oils grown through farming will require large, mostly flat tracts of land near sustainable water resources located in favorable climate conditions. The cost of surveying and purchasing suitable plots of land for industrial-sized needs is significant.
2. Water: Even though algae can thrive in salt and waste water, as well as fresh water, using large amounts of water for growing algae may be at odds with water needs of population centers, agriculture, and wildlife habitat. Evaporation alone can consume millions of gallons a day from moderately sized operations.
3. Nutrients: The availability and balance of nutrients dramatically affect the types and productivity of algae populations. Managing sufficient resources of nitrogen, phosphorus, carbon, and some 57 other nutrients—many of which are in diminishing supply—contributes heavily to a project’s operating costs.
4. Strain Selection: Identifying and maintaining the ideal composition of species in large-scale production of algae is needed to generate a consistent high quality product. Oil content and productivity, as well as, resistance to contamination and adaptation to the local water chemistry, among several other factors, are essential in determining a viable strain that promises high yields.
5. Temperature: Specific temperatures must be maintained for specific algal strains to thrive. Weather is inherently unpredictable requiring constant monitoring and expensive heating and cooling equipment to maintain consistent temperatures.
6. Predators & Parasites: Algae ecosystems are extremely vulnerable to invasive species and bacteria. Closed systems lower the risk of exposure, but are too expensive to scale and maintain for commercial production. On the other hand, open ponds are less expensive to build and operate and can be more easily scaled, but it is nearly impossible to control the introduction of undesirable algae strains, algae predators or other microbes that impact the cultivation of algae.
7. Toxins: Maintaining a clean, unpolluted environment is crucial for algal growth. Similar to the risk posed by invasive species, contamination from outside sources puts the ecosystem at risk of dramatic productivity losses.
8. Salt: Using salt water for algae production eliminates direct competition with agricultural water use, but evaporation increases salinity in open ponds, and if salt concentration exceeds a certain level, the algae cannot survive.
Physical Challenges: Algae are small, but the volume of water isn’t
9. Pumping: The circulation of water and nutrients throughout the production system is crucial for maintaining algal growth and harvest rates, but it also requires enormous sums of energy and capital. Many of the current process require large investments in mechanical equipment, which is not a scalable solution and is exceptionally energy intensive. With current technologies, we would need to pump the equivalent of Lake Superior to produce 20 million gallons of algal oil. This is an engineering challenge of unprecedented proportion. No single water treatment facility has ever moved water at this rate, let alone simultaneously incorporated an advanced materials processing system with sensitive biological and technological components.
10. Harvesting: Removing algal biomass from the water culture in high concentrations is a difficult and costly process. Current technologies rely on energy intensive equipment, chemical flocculation, and other methods that can harm the algae and have extremely high operating costs. To economically harvest algae at scale, simpler and more efficient systems must be implemented.
11. Concentrating: Though algae-laden water looks quite green, it is deceptively dilute. By weight, algae are approximately one part in 3,000. Typical concentrating techniques (microstrainer, centrifuge, filtration, etc.) can only bring this ratio down by an order of magnitude, and these processes are not economical or scalable.
Chemical Challenges: Unlocking algae without a sledge hammer
12. Extraction: Removing the oil and nutrients from harvested algae is a complex process. Many companies are searching for a “lipid trigger,” or a way to easily turn algae into a single-cellular oil factories. But altering the metabolisms of microorganisms is extremely complex and is not a feasible approach to attaining the production levels of today's energy industry. Similarly, the use of powerful, expensive chemicals and physical processes is equally unrealistic for producing large volumes of low-cost fuels.