Environmental Science

An aquaculture device called ‘kelp elevator’ tested as a foremost biofuel source

An aquaculture device called ‘kelp elevator’ tested as a foremost biofuel source

The ‘kelp elevator,’ which was tested on the Southern California coast, grows the energy-rich algae four times faster than nature, demonstrating the potential for mass-produced seaweed to power vehicles with biofuel harvested from the ocean. For many years, the biofuels that power automobiles, jet airplanes, ships, and large trucks have been derived primarily from corn and other mass-produced farm crops. USC researchers, on the other hand, have turned to the sea for what could be an even better biofuel crop: seaweed.

Working with private industry, scientists at the USC Wrigley Institute for Environmental Studies on Santa Catalina Island report that a new aquaculture technique on the California coast dramatically increases kelp growth, yielding four times more biomass than natural processes. The technique makes use of a device known as a “kelp elevator,” which raises and lowers the bronze-colored floating algae to different depths to optimize growth.

The team’s newly published findings suggest that it may be possible to grow kelp crops for low-carbon biofuel in the open ocean, similar to how land is used to harvest fuel feedstocks such as corn and sugarcane – but with potentially fewer negative environmental consequences.

Scientists report that a new aquaculture technique on the California coast dramatically increases kelp growth, yielding four times more biomass than natural processes. The technique employs a contraption called the “kelp elevator” that optimizes growth for the bronze-colored floating algae by raising and lowering it to different depths.

According to the National Research Council, producing biofuels from feedstocks such as corn and soybeans can lead to increased water pollution. Farmers apply pesticides and fertilizers to their crops, which can pollute streams, rivers, and lakes. Despite these well-documented drawbacks, major food crops still provide 7% of the nation’s transportation fuel. And nearly all of it is ethanol made from corn.

“Creating new biofuel pathways necessitates proving that new methods and feedstocks work. This experiment on the coast of Southern California is significant because it demonstrates that kelp can be managed to maximize growth “Diane Young Kim, the study’s corresponding author and associate director of special projects at the USC Wrigley Institute as well as a professor of environmental studies at the USC Dornsife College of Letters, Arts, and Sciences.

The research was published in the journal Renewable and Sustainable Energy Reviews on February 19th. Researchers from USC Dornsife, which houses the Wrigley Institute, and the La Caada, California-based company Marine BioEnergy, Inc., which designed and built the experimental system for the study and is currently developing technology for open-ocean kelp farms, are among the authors.

Unlocking kelp’s potential as a major biofuel source

Though not without obstacles, kelp shows serious promise as biofuel crop

A new generation of climate-friendly biofuels holds promise for reducing net carbon dioxide emissions and reliance on foreign oil, according to government and industry. New biofuels have the potential to supplement or replace gasoline, diesel, jet fuel, and natural gas.

Kelp, if it lives up to its potential, is a more appealing option than the traditional biofuel crops (corn, canola, soybeans, and switchgrass) for two important reasons. For one thing, ocean crops do not compete for freshwater, agricultural land, or synthetic fertilizers. Second, when marginal land is converted to farming, ocean farming does not endanger important habitats.

The researchers concentrated on giant kelp, Macrocystis pyrifera, a seaweed that forms magnificent underwater forests along the California coast and elsewhere and washes up on beaches in dense mats. Kelp is one of nature’s fastest-growing plants, with a well-understood life cycle that makes it suitable for cultivation.

However, farming kelp entails overcoming a few challenges. Kelp must be anchored to a substrate in order to thrive, and it can only grow in sun-soaked waters up to 60 feet deep. In open oceans, however, the sunlit surface layer lacks nutrients found in deeper water.

To maximize growth in this ecosystem, scientists had to figure out how to give kelp a foothold to hang onto, as well as plenty of sunlight and nutrients. They also needed to see if kelp could survive deeper beneath the surface. So, Marine BioEnergy developed the concept of depth-cycling kelp, and USC Wrigley scientists carried out the biological and oceanographic trial.

The kelp elevator is made up of fiberglass tubes and stainless-steel cables that hold the kelp in place in the open ocean. A horizontal beam is attached to juvenile kelp, and the entire structure is raised and lowered in the water column by an automated winch.

Beginning in 2019, research divers collected kelp from the wild, attached it to the kelp elevator, and then deployed it near Wrigley’s marine field station on Catalina Island’s northwest coast. For about 100 days, the elevator would raise the kelp to near the surface during the day to soak up sunlight, then lower it to about 260 feet at night to absorb nitrate and phosphate in deeper water. Meanwhile, the researchers monitored water temperature and conditions while comparing their kelp to control groups raised in natural conditions.

“We found that depth-cycled kelp grew much faster than the control group of kelp, producing four times the biomass production,” Kim said.

The push to develop a new generation of biofuels

Prior to the experiment, it was unknown whether kelp could absorb nutrients effectively in the deep, cold, and dark environment. Nitrate is a major limiting factor for plants and algae, but the study suggests that when the kelp was lowered into deep water at night, it found everything it needed to thrive. Moreover, the kelp was able to withstand the increased underwater pressure.

Marine BioEnergy co-founder and chief engineer Brian Wilcox stated: “The good news is that the farm system can be built using off-the-shelf components and does not require any new technology. Depth-cycling farms, if implemented, could pave the way for a new year-round source of affordable, carbon-neutral fuel.”

According to Cindy Wilcox, co-founder and president of Marine BioEnergy, it would take a Utah-sized patch of ocean to produce enough kelp biofuel to replace 10% of the liquid petroleum consumed in the United States each year. Only 0.13 percent of the Pacific Ocean is occupied by Utah.

California and the federal government have made developing a new generation of biofuels a priority. The Advanced Research Projects Agency-Energy of the United States Department of Energy invested $22 million in efforts to increase marine feedstocks for biofuel production, including $2 million for the kelp elevator study. The Department of Energy is conducting research to find a billion tons of feedstock per year for biofuels; Cindy Wilcox of Marine BioEnergy believes the ocean between California, Hawaii, and Alaska could contribute to that goal, helping the United States become a leader in this new energy technology.