As the human population continues to grow at an unprecedented rate, climate change and depletion of fossil fuel reserves have caused governments all over the world to shift priorities from unchecked economic growth to investment in sustainable technologies. As a result, the clean energy sector has seen explosive growth in the past decade both here in the United States and in economies all over the world; and this growth rate shows no signs of slowing down anytime soon. The International Energy Outlook 2013 (IEO2013) projects that world energy consumption will grow by 56 percent between 2010 and 2040. Although fossil fuels such as coal, crude oil, and natural gas continue to supply almost 80 percent of global energy use, these global energy demands cannot be met without the growth and expansion of renewable energy sources (International Energy Outlook, 2013). Replacing fossil fuels with renewable energy requires a massive overhaul of the world’s current energy infrastructure, a process that could take decades to complete. While governments continue to funnel money into the development of viable systems to support renewable energy, the world needs an intermediary fuel source to satisfy a portion of our global energy demand while we transition away from fossil fuels. The answer lies in an ancient photosynthetic microorganism that can be found in almost any aquatic environment today: algae. These modern descendants of cyanobacteria represent a robust and diverse group of organisms that have adapted to survive in some of the most extreme habitats on Earth. As our global energy demand increases, we now have a critical opportunity to harness the adaptive potential of algae blooms as a highly productive and sustainable fuel source.
Algae, like other plants, use photosynthesis to convert solar energy into chemical energy. They store this energy in the form of lipid oils, carbohydrates, and proteins. The plant oil can be converted to biodiesel. The more efficient a particular plant is at converting that solar energy into chemical energy, the better it is from a biodiesel perspective. As one of the most photosynthetically active plants in the world, algae grows at extremely fast rates with high lipid content, from which oil can be easily extracted with minimal resource input.
Compared to other forms of renewable energy and biofuels, algae can be cultivated on a large scale relatively easily with very high efficiency. Algal blooms require only sunlight, water, and a rich nutritional medium in which to float in order to proliferate. Since they grow in aqueous suspension with efficient access to water, CO2, and dissolved nutrients, algae are capable of fixing CO2 from the atmosphere and producing biomass much more rapidly and efficiently than terrestrial plants. Algae can produce up to 300 times more oil per unit area than conventional crops such as rapeseed, palms, soybeans, or jatropha. Since algae do not have to produce structural components such as cellulose for leaves, stems, or roots, they have a harvesting cycle of 1–10 days and can grow up to 20-30 times faster than food crops such as corn (McDill, 2009). Therefore, their cultivation permits several harvests in a short time frame, a strategy different from that associated with traditional oil crops with yearly schedules (Chisti, 2007). Unlike terrestrial crops, whose failure costs an entire growing cycle, an algal pond can also be reinoculated to resume production in a matter of days (Pienkos, 2009), a factor that can greatly extend the lifecycle and productivity of algae feedstocks for biofuels.
Algal biofuels also have many positive externalities in terms of environmental sustainability. Unlike traditional feedstocks for biofuel such as corn and soy crops, algae are not a primary food source for humans, meaning that it can be used solely for fuel with little to no impact on the food industry. As well, it acts as a much cheaper alternative to the traditional corn or grain-based feeds (Demirbas, 2008). At the end of the algal life cycle, after oil is extracted, the leftover biomass residue can be used as an animal feedstock or as soil fertilizer. This is a sustainable way to minimize waste while fulfilling the growing demand for animal feed. Algae can also help solve the problem of terrestrial biofuel feedstocks such as corn competing with agricultural resource priorities in land usage. Because algae can be grown without taking up arable land that would otherwise be used for growing food crops, it results in a much smaller land usage footprint. Thanks to recent advances in biotechnology, large-scale cultivation of algae now takes place in closed systems such as raceway ponds and photobioreactors. These systems provide great productivity and control, and produce more output with less light and land area. As a result, algaculture can be feasibly developed on marginal lands deemed useless for the cultivation of agricultural crops, such as arid land, land with excessively saline soil, and drought-stricken land (Schenk et al., 2008). This minimizes the issue of taking away pieces of land from the cultivation of crops. To further decrease its footprint and minimize its usage of natural resource inputs, algae can be grown using water from salt aquifers that is unusable drinking or agriculture (Bullis, 2007). It can even grow in ocean water, the most renewable and plentiful resource on Earth.
In terms of biodiversity, with careful planning, large-scale algaculture can develop with minimal impact on local ecosystems. Since algae can inhabit many “wastewater niches” with low habitability for species such as drought-stricken land and salt aquifers, its growth will not take away significantly from existing natural habitats. Compared to terrestrial biofuel agriculture, cultivation of algae also uses much less land, thus preserving more natural habitat for local biodiversity.
Besides requiring very few resource inputs, growing algae can also help clean up waste by processing ammonia, phosphates, and nitrates from wastewater. Wastewater contaminated with fertilizers, human sewage, and animal waste as well as CO2 emissions from industrial processes, all major pollutants and human health risks, can all be used as nutrients in algaculture. Nitrogen is one of the essential elements required for the growth of algae. Urea and ammonia happen to be a readily available source of nitrogen for algae. Therefore, algae actually thrive on saline, brackish and wastewater from the treatment of sewage, agricultural, or flood plain run-off because they are rich sources of nutrients for the algae (Demirbas, 2011). Because of this, the large-scale growth of algae for biofuel production actually helps to protect our fresh water resources by preventing contaminated water from mixing with the lakes and rivers that supply our drinking water. With just a simple cleaning and sterilizing process through anaerobic digestion, contaminated wastewater becomes suitable for algae growth.
The current global energy crisis and growing environmental concerns, such as imminent climate change and pollution of water resources, have sparked a surge in the clean energy sector. Advanced biofuels in particular have received a great deal of attention given the limitations of first and second-generation corn and cellulosic biofuels. Algae oil presents itself as a very promising source for biofuels given the extremely high renewability and sustainability of algae. As one of the most photosynthetically active plants in the world, algae grows at extremely fast rates with high lipid content, from which oil can be easily extracted with minimal resource input. Large-scale algae growth also provides environmental benefits such as wastewater diversion and atmospheric carbon capture. It can also help alleviate the food supply and land use issues associated with corn-based ethanol. The life cycle of algae can be further sustained by the production of valuable secondary products such as livestock feed. Recent advances in biotechnology to create cheaper production techniques have shown great promise. Algal blooms hold huge potential as an intermediary fuel source given their many environmental benefits. As the world awaits a solution to the global energy crisis, we should all keep algal biofuel on the radar, as it is certain to play an important role in the future of the world’s energy supply.
Lillian Wang is a senior at Tufts University majoring in Environmental Studies & Biopsychology.