Land CultivationFrom Phyco.orgFarming algae involves cultivating and harvesting. This article discusses land cultivation, which is better suited to a small scale operation. Also, most research for growing algae has been done on land, though the knowledge is applicable to both land and sea.
[edit] PhotobioreactorsA photobioreactor is the name given to the device that houses and cultivates the algae culture(s). They are environments for growing algae, and include raceways, annuli, clear plastic bags, aquariums, and pop bottles. See: Photobioreactors [edit] NutrientsNutrients are a major determining factor in how fast algae grows and what composition it develops. [edit] LightPlant cells use only a small fraction of the sunlight that hits them, in two ways. Algae use only some colors of light. Moreover, sunlight is more intense, at all colors, than necessary for optimal algal growth. The effect of alternating light and dark is not well understood. Algae has been grown using no dark period, up to eighteen hours dark. Bright light may damage algae, which may extend required dark periods to effect repair. Long dark periods result in biomass loss and slower growth rates as algae consume carbohydrates and oxygen during photorespiration. There is no consensus about light and dark durations. Sunlight is bright enough to promote growth in about 10 times as much algae as that required to totally cover the surface of an algal culture. Thus, gently stirring a culture, to assure algae get 1/10 sunlight and 9/10 shaded by a dense-thick algal culture, will promote additional growth in sunlight, all other factors being the same. Moreover, an algal monoculture cannot use all light colors. For example, blue-green algae reflect blue-green light without using it and use red light. On the other hand, red algae use blue-green light but reflect red light. However, maximum algae growth only requires 1/32 of sunlight. Blue-green light penetrates deeper into water than other colors. Thus, red algae can grow at greater water depths than blue-green algae. These facts suggest that a mixed culture of blue-green and red algae may produce more biomass per m3 of culture than either one in a monoculture--needs research. Some algae grow faster in spring and autumn when days are shorter, and some grow faster in summer, when days are longer. For example, cyanobacteria tend be light limited in spring and autumn, allowing other algae, such as diatoms, to grow faster in spring and autumn than cyanobacteria. See: Light Requirements. [edit] TemperatureAlgae live in water from the equator to the Arctic and Antarctic. Consequently, there is no single temperature is best for all algae. One theory is that an algae species will tolerate a few degrees above the maximum summer temperature of its natural environment. Thus, the temperature range that a given algae species will tolerate may estimated by knowing its environmental range. However, to know the temperature at which an algae species grows best must be determined by experiment, except for those already known from prior experiment. Various algae species grow better at different temperatures and light conditions. Consequently, to optimize algal oil production of an outdoor pond or raceway may require growing several species of algae, one for each season--if such species exist. [edit] Site SelectionCalculation Site selection requires one know its purpose. Let's assume the purpose is to provide fuel for a diesel car that gets 50 mpg, which is driven 15,000 miles per year. The amount of fuel used per year is the following:
Let's assume that your car runs on straight algae oil (SAO). Thus, you need 300 gallons per year, which weighs about 7.5 pounds per gallon. Consequently, you need the following weight of SAO:
Moreover, the algae you will grow is 50% oil and you can press 80% of the oil from it. Consequently, you need the following amount of dry algae per year:
Further assume that your algae culture doubles its mass daily. Thus, you will need to grow the following amount of algae per day:
Lets round that up to 20 lbs of dry algae per day, because there are days when you will grow no algae. In other words, your garden needs to be able to grow 20 pounds of algae per day. Let's assume that you can harvest 0.1% = 0.001 dried algae per unit of culture--water in the culture is very heavy compared to algae dry weight. Consequently, to harvest 20 pounds of dry algae daily will require the following amount of culture:
Water weighs about 8 lbs per gal. Thus, you need the following amount of water:
One cubic foot holds about 7.5 gallons of liquid. Thus, twenty five hundred gallons needs about 335 cubic feet of space, which is a pond about 18' x 18' one foot deep. Now that you know the size of photobioreactor you need, it is possible to think about where in your yard to put it. Check Note: NREL estimates that "Two hundred thousand hectares (less than 0.1% of climatically suitable land in the U.S.) could produce one quad of fuel." Within this context, "fuel" refers to biodiesel. Consequently, NREL estimates that one acre of algae can produce 15,000 gallons of biodiesel. An acre is about 43,560 square feet. 0.2 = 300 gal / 15,000 gal 871 ft2= 43,560 ft2 * 0.2 29 ft = <math> \sqrt 871 ft2</math> In other words, the pond needs to be 29 feet on a side to collect enough sunlight to grow enough algae to produce 300 gallons per year of biodiesel. Differences We made an assumption of the algae doubling daily, which is optimistic. Doubling every other day is more realistic, which would require us to double the size of the 18'x18' pond to 25'x25'. Moreover, algae grows more slowly in months with shorter days, unless artificial light is used. Thus, NREL may have used figures with a seasonal bias. The NREL figures (the "Check") is based on area of sunlight needed to grow the algae. However, the site selection "Calculation" is based on volume of algae required when doubling occurs daily. Both of these figures are estimates of unknown quality, as experience with algae farms is very limited. Disclaimer These calculations illustrate a method that one can use to determine the size requirement of an algae garden. The following figures can be reused, because their values will change little from site to site:
All other figures are hypothetical. One should not infer they can get 300 gallons (1136 liters) per year, from an 18'x18' (6m x 6m) algae pond. Many factors influence the amount of algae that can be produced from a given photobioreactor, including climate, algae species, equipment and grower capability. [edit] ExamplesThere are thousands of varieties of algae, many bioreactor concepts, nutrient selections, lighting options, and temperature management strategies. Consequently, there will be many variations of an algae farm. We will examine a successful health food algae farm, and we will plan a small algae garden. See: Links to Existing Algae Farms, Theoretical_Algae_Solutions [edit] See also |
