By Drew Casey
Recently, we have experienced increasing uncertainty about the threat of climate changes due to increased carbon emissions as well as volatility of global oil prices. Fossil fuels have been such a major part of modern society, but the recent problems that we have experienced are attributed to an over reliance of these finite resources. Biodiesel production from algae has recently received considerable attention in the race to bring sustainable fuels to market, and its future looks promising. In order to facilitate the production of algae biodiesel on a commercial scale, we need to use our ingenuity and take advantage of existing resources such as emissions from coal-burning power plants, agricultural runoff, wastewater effluent, and even leftover material from the algae biodiesel production facilities.
How can we take advantage of modern agricultural and industrial practices and resources in order to transition to large scale production of microalgae biodiesel? First, let’s look at the land requirements. Microalgal biofuel production is ultimately the most efficient biofuel, both in terms of land use and energy conversion (Chisti, 2007). One of the most promising aspects of cultivating algae for biodiesel, is that algae are not dependant on a particular landscape or soil type in order to grow. Many different types of land and climates, preferably those with moderate temperatures and sunlight, are ideal for successful growth of algae for the purposes of biodiesel production. In this regard, abandoned land or land not suitable for development or agriculture, which is plentiful in the western United States, are ideal locations for the thousands of acres that are required for large scale production of biodiesel from algae. This wide range of suitable locations for microalgae is a tremendous advantage over other potential biofuel feedstocks, such as corn, soy, or even palm, which must compete for limited acreage of fertile agricultural land which is primarily used for food and feedstock production. There is no need to disrupt the nation’s food supply by displacing fertile agricultural land. In addition, and perhaps even more intriguing, microalgae systems use far less water than traditional oilseed crops. Salt water is more economical than fresh water for growing algae, so southwestern states with saline aquifers could be an ideal location to grow them on a large scale. Solix Biofuels CEO Douglas Henston states, “We could replace all the diesel fuel that we use in the United States by harvesting algae on an area of land that’s about one-half of 1 percent of the current farm land that we use right now.” (Haag, 2007)
Algae farms could be strategically located around the country in places where waste streams (either human waste, animal waste, or agricultural runoff) are readily available as a food source. Algae rely heavily on high levels of nitrogen and phosphorus, which in certain locations, are found at high levels in wastewater effluent and stormwater drains. These waste streams, instead of draining into our precious waterways, could be diverted away from high population urban centers, out to rural areas that house the algae farms.
During the production of biodiesel from algae, after the lipid, or oil, component of the algae biomass is removed through mechanical processes, it is then combined with a small percentage of alcohol to make biodiesel. Even if 50% of the algae biomass is extracted as oil, this leaves a substantial amount of leftover material. Many modern industrial processes may discard waste material after the primary component is removed, or extracted, but the leftover biomass has tremendous value. By reusing this “waste” material, it can be a valuable source of energy and material inputs to make the production process more self-sustainable.
After the removal of the algal oil, extracting those same nutrients from leftover algal biomass after the oil is removed is a fantastic way to make fertilizer. This is certainly a more hygienic method than for adding these nutrients back into the fertile farmland than modern practices such as spreading manure or wastewater treatment plant solids. By using these waste streams as the nutrient source, these farms essentially also provide a means of recycling nutrients from fertilizer to food to waste and back to fertilizer (Briggs, 2004). Capturing agricultural runoff to feed algae factories could prevent considerable environmental impact. Modern agricultural practices used to grow corn, for example, have negative impacts to biodiversity and ecosystem services. Nitrogen inputs from agricultural land into the Mississippi River has been linked to massive hypoxic zone in the Gulf of Mexico (Nassauer, 2007).
The biomass can also be subject to a process called anaerobic digestion, which efficiently produces “biogas”, or methane, as a primary byproduct. Once this biogas is captured, it can serve as the primary source of energy for most of the production and processing of the algal biomass. The generation of surplus energy is expected and this could be sold to grid to further improve the economics of the integrated process (Chisti, 2007). The technology available today for anaerobic digestion and conversion of methane to electricity is highly advanced, and the byproducts of algal biomass being used to power the entire facility is not as far-fetched as one might think. It would require some considerable engineering and design expertise to make a large-scale facility as efficient as possible.
Another highly available resource, and in plentiful supply, to enhance growth of algae at production facilities is carbon dioxide (CO2). Approximately half of the dry weight of the microalgal biomass is carbon, which is typically derived from carbon dioxide. For every 100 tons of algal biomass, our little green friends have the capability to fix roughly 183 tons of carbon dioxide. This carbon dioxide must be fed continually during daylight hours. Microalgal biomass production can potentially make use of some of the carbon dioxide that is released in power plants by burning fossil fuels (Chisti, 2007). Algal biodiesel is one of the only avenues available for high-volume re-use of CO2 generated in power plants. Locating algae farms in the vicinity of power plants may present a challenge, but the need for carbon disposal from polluting facilities and clean-burning fuel alternatives makes algal biodiesel an exceptional solution. Electricity generation is the single largest source of CO2 emissions in the United States, representing 41 percent of all CO2 emissions (EPA, 2009). Although coal burning technology has made significant advancements to reduce the total amount of CO2 that enters our atmosphere, this method of producing electricity is cheap but still disastrous to our environment.
I believe we have the ingenuity and the resources to make biodiesel production process almost 100% carbon neutral. By capturing methane biogas from the leftover biomass and using a small portion of the biodiesel produced to produce enough electricity to power the algae production facilities, this system can easily be completely self-sufficient. Perhaps with advances in technology, and production of algae biomass on a commercial scale, these tiny organisms could also provide a substantial amount of carbon sequestration capability. It is possible to sequester as much as one billion tons of CO2 per year from algae farms in lands not useful for agriculture or development in the Southwestern United States (ENS, 2008). During the next few years, we need to capitalize on existing waste streams from agricultural runoff, wastewater effluent, and power plant carbon emissions. These processes provide essential nutrients (nitrogen and phosphorus) and carbon dioxide that algae require in order to thrive in their growth medium. If we continue on our present course, our seemingly harmless practices could lead us to environmental disaster. Algae has the potential to replace almost 140 billion gallons of gasoline and diesel for our automobile industry, and lead us on a global path towards environmental sustainability. In order to make these processes work in conjunction with each other, a significant effort must be initiated to reform our energy and fuel infrastructure, as well as design and build algae biodiesel production facilities in close proximity to coal-burning power plants, wastewater treatment plants, and agricultural areas. Logistically, this could make the production and transportation of algal biodiesel much more efficient than traditional fossil fuels.
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