Harvesting Algae for Biodiesel Research

The search for new forms of alternative, environmentally friendly fuel sources is an ongoing one. Alga (or, algae per its plural form) caught the eyes of scientists some years ago, and has been a popular host of biofuel research ever since. Algae don’t only grow naturally all over the world, but they also grow in abundance—presenting as a readily available potential resource to biofuel researchers. Under optimal conditions, algae can be grown in massive, almost limitless, amounts.

Since 2008, the San Diego Center for Algal Biotechnology (SD-CAB) has been conducting research into algal applications for biofuel. A joint collaboration between several departments of the University of California/San Diego faculty and students—including the University’s Scripps Institution of Oceanography, the Scripps Research Institute, as well as non-academic industrial corporate participants—SD-CAB moved beyond its campus-oriented research facility in San Diego in 2011, to a field laboratory in the Imperial Valley of California. About 100 miles east in the Sonoran Desert, one-acre algae ponds were made available for hands-on research testing.
 
The field location gave SD-CAB the opportunity to considerably expand its algae growing volume from simple, in-laboratory vats. The ponds used were massive in comparison, and provided the largest field laboratory of any academic institution in North America for the growing and research of algae for use as a biofuel.
 
Accumulating algae
Algae thrive in fresh water and seawater, including all types of water up to a salinity of about 0.5% (50% higher than seawater). They can grow in desert ponds, employing high-saline water from aquifers that cannot otherwise be used. Growth isn’t dependent on a particular season; algae can proliferate wherever there are nutrients and light.
 
Approximately half of algae’s composition, at least by weight, is lipid oil. It is this oil that researchers have been studying for its ability to convert to biodiesel. Algae biofuel burns cleaner and more efficiently than petroleum.

Having performed much prior in-lab research with the processing of smaller quantities of algae, the San Diego Center for Algae Biotechnology was well versed and outfitted with the necessary knowledge and equipment for properly:

•    Growing algae;
•    Handling the drying of the biomass on racks, so as to remove 90% of the water;
•    Extracting the oil with a screw press;
•    Purifying it in a centrifuge; and
•    Converting this oil to biodiesel, using the traditional open-processing reaction method. 

The algae were first tested to determine the levels of free fatty acids and moisture content, so as to establish the exact mixture of chemistry needed. Balancing the methanol and sodium hydroxide is required to effect the desired reaction. This process wasn’t a problem, but SD-CAB had little experience with how to actually harvest algae from the one-acre ponds—which posed a considerable obstacle for the group.
 
“We knew, starting off, that the biggest challenge would be the harvest,” says Kristian Gustavson, part of the UCSD student-led, algae-based biodiesel research study. “We could grow the algae all day long, and once we had the dry biomass, we could turn it into fuel…but, it was the matter of harvesting. We experimented with several methods that were not very successful.”
 
Algae harvesting
After some trial and error, and upon careful review, a unique, dissolved air-flotation system was eventually selected to help with the matter of harvesting. The Algae Harvesting Technology Optimized (AHTO) Dissolved Air-flotation System (DAF) is specifically equipped for the yielding of algae from water, and proved to be an efficient and compact treatment method.

AHTO involves pond water being pumped into the DAF, where suspended solids in the form of algae are separated from the water. This is accomplished by the process of dissolving air into the water under pressure, thanks to the addition of a polyacrylamide flocculent. Upon release of that pressure, micro-bubbles form. These micro-bubbles interact with the algae particles, attaching to the biomass surface and affecting the particle density so that they float to the surface of the DAF. They are then skimmed with a chain and flight mechanism to a sieved product, known as Thickening Beach.

Thickening Beach allows free water to be drained, thereby thickening the algae particles and achieving an efficient liquids and biomass separation. A patented, air dissolving technology is also utilized to create the robust whitewater in the AHTO system, which saturates the effluent pond water entering the DAF with atmospheric air.
 
As part of this process, heavy sand and grit particles settle to the bottom, where a timer function controls the removal. Clean water is continuously removed from the DAF and piped back into the ponds, allowing new pond water laden with algae to enter for separation.
 
“We got the chemistry set and were able to harvest continually from the ponds,” explains B. Greg Mitchell PhD, research biologist and senior lecturer at Scripps Institution of Oceanography, UC San Diego, and associate director of SD-CAB. “We added fertilizer to the ponds as it was being harvested to keep it at a steady state where it was still growing in a nutrient-rich environment, to help maximize the lipid content.”
 
The AHTO process proved to be a highly efficient system for separating algae from liquids. The technology can achieve biomass removal efficiencies exceeding traditional DAF performance. Up to 9,000 gallons of algae-laden water can be processed per minute, at a 95% capture rate, yielding up to 20% algae concentrations.
 
Algae biofuels
When processed properly, biodiesel runs cleaner and more efficiently than petroleum-based diesel, and provides needed lubricity to petroleum-based diesel. According to the Department of Energy, use of biodiesel in a conventional diesel engine results in a substantial reduction of unburned hydrocarbons, carbon monoxide, and carbon dioxide emissions, as well as particulate matter.
 
As the popularity of alternative fuels gain momentum, biodiesel—and, specifically, algal-based biofuel—continues to strengthen its position as an attractive option to offset petroleum-based diesel usage. The introduction of non-commodity feedstocks such as algae, along with attractive US Federal and State subsidies for both biodiesel production and consumption, are inciting equipment manufacturers to develop better processing systems that are faster, safer, and more efficient.

Compared to crops used to produce vegetable oil for biofuels, algae are far more productive, generating up to 50 times the yield of oil per acre. The San Diego Center for Algae Biotechnology scientists plan to make sustainable algae-based fuel production a reality within the next five to 10 years. Its goal is to create a facility that provides a national and global model for the commercialization of algae fuel.


The San Diego Center for Algae Biotechnology was established in 2008 as a consortium of researchers. The center collaborates with non-academic organizations to apply its algal laboratory discoveries to industry through research and development in biology, chemistry, and engineering.

World Water Works, Inc. specializes in developing and providing highly efficient wastewater treatment solutions. The company manufactures a complete array of products addressing various problems in the wastewater industry.
    
 
The San Diego Center for Algae Biotechnology, Division of Biological Sciences
www.algae.ucsd.edu

World Water Works, Inc.
www.worldwaterworks.com