Oceans of Biomass
From animal manure to crop residue, all options are being explored to reduce global dependency on fossil fuels. In response to this quest, one Costa Rican scientist poses a novel question: What about the ocean? Seaweed is primarily grown in the Eastern Hemisphere to produce fertilizer and food, but what potential do these plants and our oceans hold for biomass applications?
In regard to the current biofuel battle, particularly over the use of cropland to produce fuel rather than food, Radulovich believes he has come up with a solution. "I went to the sea over 10 years ago looking for irrigation water and found a wonder that humanity has barely begun to unfold," he says. "The main potential player in this bioenergy race-biomass production at sea-is ignored. The oceans are the largest active carbon sink on the planet, and cover more than 70 percent of its surface area. In other words, the oceans are vast and grossly underutilized fields that are well provided with insulation and water."
After working for years with limited funding, the Sea Gardens Project received a $198,000 grant from the World Bank's development marketplace program. Those funds and a 50 percent match from the University of Costa Rica allowed the project to take off. "It's still not a lot of money," Radulovich says. "But it's enough so that we can develop and implement sea gardens with poor coastal inhabitants."
Radulovich compares sea gardens with home gardens. "Simply put, sea gardens are small-scale sea cultivation systems," he says. "They include mariculture and other production activities at sea including floating horticulture and fresh-water production through distillation and rainwater harvesting." Radulovich believes these gardens have the potential to be expanded. "On the issue of seaweed culture for bioenergy, where large areas of seaweed farming are needed to produce large quantities of energy, small sea gardens may not be the right option-medium- to large-scale operations may be far more efficient, though this remains to be tested."
Studies on cultivating micro-algae at sea are being conducted in Costa Rica through extensive farming in nutrient-rich gulf waters, Radulovich says. "These resemble true [land-based] plants in many ways, including in appearance and size, while they do not require soil or cultivation, and are already provided with all the water they need, which is a major advantage to using the ocean as water is the most limiting factor for the expansion and survival of agriculture."
Seaweeds are classified into three groups-brown, red and green-and consist of thousands of different species, although few are currently cultivated or harvested. "Red and brown seaweeds are the most commonly used because of their fast growth rates and their composition, which provides for a host of chemical products. We are just beginning to characterize and use them," Radulovich says. "Imagine the tremendous potential that will unfold when genetic manipulation techniques are applied to seaweeds, even if only for conventional breeding techniques. For example, increasing oil content for biodiesel is one of the expected results." Although there is the potential to harvest large amounts of the plant, Radulovich says precautions must be taken. "Harvesting massive amounts of naturally occurring seaweed populations may be equivalent to large-scale deforestation in terms of atmospheric CO2 (carbon dioxide) addition, habitat loss and fragmentation," he says.
A Salty Solution
Energy applications from seaweed biomass are similar to those from land vegetation, according to Radulovich. "The simplest option is direct burning for electrical and heat generation, such as is currently done with bagasse from sugarcane. Next is the production of biofuels such as ethanol, biodiesel and methane. Current biofuel production technologies may suffice in some cases, while next-generation technologies will come to improve seaweed biofuel yields."
As with nearly every agricultural production system, seaweed farming would require adequate nutrients and fertilizers. "Common fertilization, besides being costly and energy consuming, would add large amounts of nutrients to the oceans with unknown results," Radulovich says. "There is, nonetheless, a great and grossly misused nutritional resource: domestic wastewater." He says that millions of tons of wastewater are dumped into the sea daily, and applying it to large seaweed fields-an option already explored by the Woods Hole Oceanographic Institution and the Harbor Branch Oceanographic Institution-could be an economically sound use.
If the seaweed concept were further explored, where are the best areas to grow seaweed? "There are many places already identified where seaweeds can be properly farmed such as on the Pacific Coasts of North and South America, and in the Caribbean where there are currently several seaweed farms," Radulovich says. In those places, the seaweed is grown primarily for food and fertilizers. "Actually, any place where seaweeds grow naturally may be good for farming. In fact, since farming implies using ropes and other means for seaweed attachment, many seas where seaweeds don't grow naturally could also be good places for farming." Radulovich emphasizes that if the seaweed can be tied for floatation or drifting, farming could be an option. "I think even the Sargasso Sea, with its extensive calm waters, could be used for this," he says. In the future, he would like to explore the Sargasso Sea further, as it may provide a low-cost basis for large-scale seaweed cultivation.
An Ocean of Possibilities
Although Radulovich and other Costa Rican researchers have yet to produce their own micro-algae at sea, they have explored several possibilities. "Among these, we are learning to harvest using large cloths, and are preparing some low-cost floating enclosures where we will produce controlled eutrophication," he says. Eutrophication is a process where water bodies receive excess nutrients that stimulate plant growth. "One of the ideas behind this is to be able to harvest large amounts of micro-algae during naturally occurring algal blooms, which are oftentimes composed of toxic micro-algae," Radulovich says.
So what can be done with this biomass? "The least good use will be to burn it for carbon-neutral electricity generation after extracting compounds with high market value-a process that should include cold pressing the liquids out, and perhaps drying." Radulovich describes cold pressing as squeezing the juice out of the seaweeds by passing them through presses, leaving behind its intercellular contents and a much drier biomass. "The liquid could be further subjected to extraction and separation procedures while the biomass, which now weighs much less-though still has a substantial amount of water in it-can be more easily transported and subjected to digestion for alcohol or other biofuels, or even burned for electrical power generation."
As part of his research, Radulovich calculated the expected energy yield from a seaweed farm. He believes his projections can be improved, however. "I am using 45 [metric tons] (49 tons) of dry biomass produced per hectare (2.5 acres) per year. This is a number for good husbandry with current state-of-the-art technology," Radulovich says. "I am also
focusing on Sargassum, a brown seaweed with several positive characteristics-yet other species can behave in a similar manner."
Radulovich says his experiments involve obtaining 2 percent recoverable oil content on a dry-weight basis. "This produced about 1,000 liters (264 gallons) of oil per hectare per year," he says. The oil yield can be increased by selecting or developing seaweed strains that produce more oil.
After the oil is extracted, the seaweed biomass may be used for alcohol production. "Ethanol yield is expected at about 40 percent of the biomass yield on a dry weight basis," Radulovich says. "Thus more than 20,000 liters (52,843 gallons) of ethanol per hectare per year can be obtained."
After ethanol production, a considerable amount of residue is left, which can be burned to generate electricity.
Although current methods of seaweed harvesting are time-consuming and require a considerable investment, Radulovich insists his calculations indicate these costs could be lower
than the cost of growing crops on land. "Harvesting is normally done by hand," he says. "However, there are mechanical harvesters for aquatic plants that have been used successfully on seaweeds."
Another concern besides the over-harvesting of naturally occurring seaweeds is making sure the farms are not in the path of hurricanes and other bad weather. "After that, temperature is a consideration," he says. "Seaweeds grow well in low temperatures."
Large-scale seaweed cultivation has potential, Radulovich says. "The key point, of course, is to develop large-scale seaweed cultivation techniques," he says. He says if proper yields were met, the area needed to replace the world's fossil fuel use would require less than 3 percent of the world's oceans-approximately 20 percent of the land currently being farmed. "The surge of interest in biomass and biofuels has placed agriculture and photosynthesis back onto the main stage," he says. "If we want to get amounts of energy similar to fossil fuel consumption, we have plenty of room in the world's oceans."
Anna Austin is a Biomass Magazine staff writer. Reach her at firstname.lastname@example.org or (701) 738-4968.