Constraints of Algal Biofuel Production

Peak oil is approaching, climate change is intensifying, and global reliance on fossil fuels is shifting. This is all occurring, at least in part, due to the nearly exclusive use of fossil fuels as an energy source. The detrimental effects of pillaging the earth for use of fuel that both degrades our land during extraction and pollutes our air during combustion have become a hot topic among concerned citizens around the world. Many geoscientists are pushing for alternative fuel, and algae may be just the answer they are looking for. With the characteristics of algae considered, it is an obvious choice as a primary biofuel producer.

Algae is a third generation biofuel, which means that it does not compete as a food source. Even though algae is used as a health food, that industry can remain largely undisturbed, because the algae used to produce fuel can then be sold to pharmaceutical companies and used as food. Algae has the potential to generate a lot more energy than corn and soybeans, costs less, uses less land, uses less water, and can utilize the CO2 from power plants to proliferate (Benemann). In addition, algae can be grown using wastewater that is rich in nitrates and phosphates. There have even been preliminary studies regarding the use of algae to treat wastewater in an ecologically safe manner. With all of these benefits, it's no wonder why algae have been chosen to lead the way in the sector of third generation biofuels. However, there are many constraints associated with this undertaking. These constraints can be separated into general constraints that deal with the management of the crop (light, mixing, temperature, gas exchange, and nutrients), and overall system constraints that deal with the technology used for outdoor pond systems. Although there are a wide range of indoor systems, it is harder to utilize natural resources, so an outdoor system is more resource efficient.

The general constraints of algae biofuel production allow for algae to be mass produced and therefore feasible for a growing biofuel economy. Light is needed for the algae's photosynthetic processes to take place. At low light intensity, the algae does not grow at any considerable rate, this is called the compensation point (Alabi). As more light is delivered to the algae, the productivity increases until it reaches a point of maximum growth, called the light saturation point. This is the point that algae farmers would attempt to maintain, because if excess light is delivered beyond this point, photo-oxidation could occur, which is harmful to the productivity of the algae. To ensure that the right amount of light is delivered, control of light intensity is imperative.

Mixing can also help to ensure that all of the algal cells receive equal amounts of light. When there are high concentrations of algae in a system, most of the light will be absorbed by the outermost layer of algal cells. This leads to an uneven distribution of light delivery, so to combat this, cells should be kept in suspension so all cells receive equal light.

Another factor that must be considered when farming algae is temperature. Since algae are grown in water and water has a lag in temperature response time, it is crucial to make sure that fluctuations are not too extreme. According to the Microalgae Technologies & Processes presentation by the Food and Agriculture Organization of the United Nations, " -- Because large water bodies have long response times to air temperatures, even when the air temperature is optimal, the algae culture temperature can be 10-15 degrees Celsius below optimal, therefore optimal culture temps are only achieved for part of the day." Furthermore, if the temperature of the water body gets too hot during a dark period, this can increase the algae losses overall.

As with any aquatic system, gas exchange is an important part of a healthy system. Since CO2 is constantly being depleted, additional CO2 must be added to maintain a constant concentration. There are many methods of CO2 delivery, which include air stone bubbling, plastic dome exchangers, injection into deep sumps, and CO2 trapping under floating gas exchangers (Alabi). As with all other growth factors, the levels of CO2 must be controlled to keep the biomass healthy and productive. If there is too much CO2 in the aquatic environment, photo-oxidation could result.
The general constraints of biofuel production are applicable across the board when it comes to algae. They are considered within every grow system, and they set the standard for how algae is cultivated. However, there is still a lot of variation when it comes to algal growth. The systems range from land based systems to sea based systems. Land based systems are by far the most popular and efficient for the current time, while sea based systems tend to be considered prototypes for a system of wastewater treatment and algae production. The land based production systems include two general types '" open systems and closed systems '" but within these two types there are many production systems. Outdoor ponds, bioreactors, wells, and plastic bag systems are all documented ways of growing algae for biofuel or wastewater treatment purposes. However, many of these technologies have not been fully developed for large scale production.

Outdoor ponds are the most widely used means of algae production. They can come in the form of an open system or a closed system. According to Originoil, "Currently, 98% of commercial algae is produced in open systems." This system allows for full utilization of sunlight. However, there is also a high water evaporation rate, so a renewable water source is essential. Also, locally occurring species of algae should be used, so if there is an overflow, invasive species will not be harmed. In addition, a renewable nutrient source must be used to make this an ecologically sound system.

There are four main types of outdoor ponds- the unmixed open pond, the raceway, the circular pond, and the thin layer/ inclined pond. Engineering is a must for all of these designs. Each of these systems must be covered, at least partially, to limit the amount of CO2 that escapes into the atmosphere (Gao). Also, constant agitation is a must, which rules out the efficiency of the unmixed open pond. Constant agitation must take place to keep the algal cells suspended. This scatters nutrients throughout the biomass and averts thermal stratification. The algae biomass can be kept in suspension through use of a paddlewheel, waterjet, or air pump system. According to the Intergovernmental Institution for the Use of Microalgae Spirulina against Malnutrition, the materials needed for these types of systems include the agitator (which can be a paddlewheel), isolation material, starter chemicals, culture, pH meter, conductivity meter, algae counter, algae filter, and solar panels to provide an energy source to the system.

These systems are attractive to algae farmers because they require low investment costs, they are easy to manage, and they utilize sunlight to grow the algae. However, there are still many areas that require additional technologies to make this system efficient on an industrial scale. One limitation of outdoor ponds lies in the choice to make it a closed system. Originoil states that, "Due to gas exchange limitations, closed systems cannot be scaled up, so far, beyond about a hundred square metres for an individual growth unit. A large-scale closed production system would therefore require thousands of repeating units." This seems to be a deterrent for algae farmers looking for the most beneficial system, but open outdoor ponds have their fair share of problems also. Carbonation appears to be a small factor when considering the overall costs of a system, but it can actually be one of the most expensive inputs (Gao). When an algae farmer chooses to have an open system, he must also choose to supply a constant amount of carbonation to the aquatic system. There are also costs associated with possible contamination of the biomass, unwanted precipitation, and variations in light and ambient temperature. Some of these limitations can be overcome, such as the problem with CO2 concentrations, which can be curbed by setting up a carbon recycling system. According to the humanities department of the University of Chicago:

The Weissman report estimates that in an open pond 60% of the algal biomass will be lipid, and only 90% of this biomass will be harvested. The remainder of the carbon-products will degrade either into gaseous products in the form of methane or CO2, or settle to become sludge or dissolve in the lagoon water. The gaseous products can be recollected and combusted to create a 35% CO2 mixture that can then be reinjected into the ponds.

Methods that use recycling to feed CO2 back into the system are becoming more feasible as technologies are developed, thereby maximizing the efficiency of algal biofuel production.

It is no surprise that there are many limitations when it comes to algal biofuel production. This sector is still new when compared to the standard fossil fuel production line. However, many of these constraints can be overcome with careful planning and consideration of the needs of the algal cell. There is no doubt that the outdoor pond system is the most ecologically sound system of algae growth at the moment. With time, this system can become the leading method of biofuel production.

Works Cited

Alabi, Abayomi O. "Microalgae Technologies and Processes for Biofuels and Bioenergy." FAO. 14 Jan. 2009. 25 Apr. 2010. http://www.fao.org/uploads/media/0901_Seed_Science_-_Microalgae_technologies_and_processes_for_biofuelsbioenergy_production_in_British_Columbia.pdf.

Benemann, John. "Open Ponds and Closed Photobioreactors." Bio.org. http://www.bio.org/ind/wc/08/breakout_pdfs/20080430/Track1_ContinentalA/Session9_230p400pm/Benemann_Continental_A_Wed.pdf.

Gao, Yihe. "Algae Biodiesel." University of Chicago. 7 Dec. 2009. 25 Apr. 2010. http://humanities.uchicago.edu/orgs/institute/bigproblems/Team1-1209.pdf.

Kane, Sam. "The Choice of Next-Generation." Originoil. Mar. 2009. 25 Apr. 2010. http://www.originoil.com/pdf/Scotia_Capital_Algae_Excerpt.pdf.

Kizililsoley, Mustafa. "Microalgae Growth Technology Systems." Intergovernmental Institution for the use of Micro-algae Spirulina against Malnutrition (IIMSAM). 25 Apr. 2010. http://www.iimsam.org/images/growthtech.pdf.