State-of-the-Art Algae Photobioreactors

By Ron Kotrba | July 22, 2015

Whether through open ponds, raceways or closed photobioreactors (PBR), growing algae is both a science and an art. Just as there are numerous ways to grow algae, its uses are exponentially varied: high-end nutraceuticals, cosmetics, pharma ingredients, fine chemicals, food ingredients, proteins for livestock and aquaculture, and biofuels. In the biofuels category alone, some companies focus on lipids to manufacture biodiesel and renewable diesel, others target sugars to ferment into ethanol, and still others concentrate on general biomass production to produce bio-oil or green crude. 

While open ponds may be right for some applications, Miguel Olaizola, director of production science with Heliae Development LLC, says PBRs have certain advantages over open systems. PBRs can, for example, offer some protection from contamination, but they can’t eliminate it completely. “This means that the costs associated with taking down a culture, cleaning the system and reinoculating can be lower since the frequency of culture crashes is expectedly lower,” Olaizola says. “PBRs can also be more efficient at utilizing the carbon dioxide provided to phototrophic cultures, again lowering costs.” He says PBRs can also save on water usage since evaporation is better controlled, noting that in warmer locales this may lead to higher cooling costs. “In places where windblown sand and dust persist, PBRs can keep the ash content of the crop low,” Olaizola adds. “Finally, cultures in PBRs can be more effective at harvesting sunlight while minimizing photo-inhibition, resulting in a higher photosynthetic efficiency.” 

The No. 1 reason closed PBRs may be better than open ponds for growing algae is light distribution, says Paul Woods, founder and CEO of Algenol LLC. “Getting a little light to the maximum number of cells is the key, and there is ample evidence now that vertical beats horizontal by at least two to one,” Woods says. “It’s also important to be able to manage passively or actively factors such as temperature, pH, salinity, oxygen, nutrient levels and contaminants.” Woods says the closed system allows for better passive, systematic and automated controls of the conditions necessary for optimum growth. “Our system also allows the entire culture to have sun exposure and doesn’t require expensive mixing,” he says.    

Ultimately, closed PBRs may be better than ponds for certain products but not for others, according to Olaizola. “Also, they may be better for some parts of the process, such as seed or inoculum production, but not for others, like very large-scale units,” he says, adding that in the end, one should judge a specific growth system on a very simple metric: money spent (capital expenses plus operating expenses) per ton of final product generated of a certain quality.

Algae Systems
Last August, Algae Systems LLC announced successful completion of a unique algae demonstration unit with Japan’s IHI Corp. located at a wastewater treatment plant in Daphne, Alabama. The PBRs take up about a half-acre of space but instead of using up precious land, they float in Mobile Bay. The setup is unique; not only is algae grown for biofuel conversion, but in doing so, Algae Systems provides a service to Daphne Utilities by treating 40,000 to 60,000 gallons of wastewater per day. “We’re connected to their sewer line, so we take dirty water from them and give clean water back to them,” says Eric Sundstrom, principal research engineer with Algae Systems. “The wastewater supplies all the nutrients the algae need, and a vast majority of the carbon.” The continuous batch system is totally enclosed, so nothing is taken from or dumped into the bay. Gravity feeds the wastewater into the PBRs and once algae blossom through photosynthesis while consuming nutrients and carbon, the raw, aqueous algae is pumped into the plant where it is dewatered. The treated water is then discharged through regular, permitted channels. 

Algae Systems grows entirely natural, ecological polycultured strains. “We don’t actively control what we grow,” Sundstrom says. “What happens is, different strains dominate at different times of the year due to environmental conditions and ecology predation. If one strain is taken out by a predator, many other strains are present to fill that need. It’s a stable system, and we need that because we cannot have crop failure. If we do, wastewater treatment goes down. We don’t have culture crash, just variation in the dominant strain.” 

Mobile Bay is home to 24 of these floating bags. They are made of flexible plastic and are 150 feet long by 6 feet wide. They are durable too. Mobile Bay has alligators, and on occasion they like to get atop the PBRs and soak up the sun. 

The company is on its second-generation of PBRs. “We did a complete redesign,” Sundstrom says. “We corrected everything we learned from the first generation.” 

For starters, the whole system is automated via PLC controls, so it can be easily run without anyone attending it. Durability was also improved. “We streamlined it and eliminated failure points,” Sundstrom says. Algae Systems works with famed shoe company Nike on the plastic material. “It’s a better UV-stabilized material,” he says. The second-gen units are also twice as big as their predecessors. 

“We try to keep costs low because you can’t get much cheaper than two layers of plastic, flexible film,” Sundstrom says, “so we’re trying to drive the cost of plastic down, for which we pay a small premium now.” Another unique design component is the cooling and mixing effects of the water on which the PBRs float. “We can make use of any body of water for cultivation requiring no infrastructure and no leveled land,” Sundstrom says. “Also, our design can run a system with no added carbon dioxide—the wastewater provides ample organic carbon, it’s a very nice gas exchange. The algae produce oxygen as they grow, and there’s enough carbon in most wastewater to get full wastewater treatment in our system with no added carbon dioxide.” He says while there are some benefits to adding carbon dioxide to the PBRs, it’s not necessary. 

Algae Systems’ conversion approach, in partnership with Auburn University, is a hydrothermal liquefaction process that utilizes wet algae, saving time and money on drying. Hydrothermal liquefaction can also extract oil from nonlipid portions of algae biomass. “That’s important because we’re not growing pure, high-lipid strains in our system,” Sundstrom says. The end result is bio-oil suitable as-is for bunker fuel or further hydrotreating into renewable diesel or biojet fuel. 

Sundstrom says Algae Systems will continue refining its PBR system. “At this stage, it’s no longer about proof of concept, but mechanical reliability, performance and scale-up,” he says.

Algenol’s Direct-to-Ethanol technology is a unique, two-step process that produces ethanol directly from the algae. Algenol then converts the spent algae biomass to biodiesel, green gasoline and biojet fuel. The company currently has two demonstration facilities, one in Ft. Myers, Florida, and another in India near Reliance Industries Ltd.’s oil refinery, the largest in the world. “We have approximately 7,000 [PBR] units in Florida at our demonstration facility, and a smaller unit in India,” says Woods. “We are currently planning for the same size unit in India as in Florida.” 

Algenol’s 100-liter PBRs are constructed of a flexible plastic film with a proprietary design that best facilitates ethanol production and biomass collection. “The plastic used for PBR construction has been specifically engineered and enhanced to optimize a variety of performance metrics,” Woods says. “Each individual PBR consists of ports for ethanol and biomass collection and the introduction of carbon dioxide.” He says Algenol’s PBRs are designed to maximize light exposure to all cells, to evenly dispense carbon dioxide throughout the culture, and to last many years in the field. “Once the PBRs are deployed, it’s important for everything to be automated to save time and money,” he says. “Nutrient and carbon dioxide levels are monitored and adjusted in an automated fashion to allow for the most optimal growth conditions. After a batch of algae is harvested, the bag is cleaned in place and reinoculated with the next batch.” 

Annually, Algenol’s PBRs produce 8,000 gallons of liquid fuels per acre. A majority of the liquid fuel is ethanol, with about 1,000 gallons of gasoline, jet, and diesel fuel refined from the green crude. “This compares favorably to corn at 420 gallons per acre per year,” Woods says. “We use 5 percent of the land that corn ethanol uses to make the same amount of fuel, so our land use is much more efficient than other biofuels. In addition, we don’t need farmland—we need marginal land. We also use saltwater, not freshwater, in our process.” 

Through the years, Algenol has experimented with several different plastics, orientations, sizes and spacing, and found that its current PBRs produce the best yields. “We’ve evolved from horizontal to vertical design, from smaller sizes to larger sizes,” Woods says. “Perhaps most significantly, we now manufacture our own PBRs, which allows us greater control over the product.” He says outdoor testing has proven Algenol PBRs are durable, lasting up to three years. “Weather-ometer testing simulates eight years,” Woods says. “So far, we target six years in the field.”   

Woods says the state of PBR art today is varied, and often changed to best suit the product being produced and its value. “We will always continue to do R&D to further drive yield and reduce cap-ex,” he says. “While we are happy with our ability now to produce fuel for $1.30 a gallon and to produce 8,000 gallons per acre per year, we are always seeking to do even better. Future improvements will come from enhancement to our PBRs and to our algae strain itself.” He adds that it’s important to emphasize PBRs’ ability to concentrate carbon dioxide uptake. “One metric ton of carbon dioxide fed into the Algenol process produces around 144 gallons of fuels,” he notes, adding that algae technologies such as Algenol’s are the only solution to mitigating climate change while monetizing carbon dioxide through utilization. “This drastically alters the current paradigm by turning an environmental and economic liability into a revenue-generating asset,” he says.

Heliae Development
Heliae Development manufactures a whole array of programmable PBRs of different sizes and capacities, depending on the purpose of a specific culture, Olaizola says. “Our PBRs are designed to provide optimal growth conditions for specific crops,” he says. “They’re designed to adjust, in real time, growth conditions such as pH, nutrient concentrations, temperature and more.” He explains that the effectiveness of control of growth parameters is, itself, dependent on a good understanding of turbulence within the reactor. “Depending on the unit, the PBRs may have a photic zone, a zone for gas exchange, a zone for temperature control, shade control,” he says. Different probes provide signals that are communicated to a PLC programmed to respond to those signals by adjusting, for example, valves that permit carbon dioxide to be bubbled into the culture or add nutrient components on demand. “This approach offers us the flexibility to use the same PBR for very different crops,” he says.

The smallest-scale PBRs Heliae uses are standard lab units—flasks and carboys—up to 20 liters. The next step in scaling up includes the use of proprietary plastic PBRs with capacities of up to 400 liters. “Depending on the crop, we also use glass tubular reactors up to 550 liters,” Olaizola says. The smaller units have two functions—product development and production of inoculum, or seed, for larger production units. The larger units consist of open-channel reactors protected by a greenhouse-type structure that provides the benefits of closed PBRs at a very large scale. “Our newest PBR has a capacity of 600,000 liters over a 4,000-square-meter footprint,” Olaizola says. “We use some of the smaller units in mixotrophic mode—the algae receive both sunlight and fixed carbon (e.g., acetate), which results in productivities of 1 to 1.5 grams per liter per day equivalent, in our system, to 1 to 1.5 kilograms per square meter per day.” 

Olaizola says what makes Heliae’s PBRs unique is harnessing not only phototrophic growth platforms, but also mixotrophic. “This is accomplished by combining the right vessel with the specific production mode,” he says. “We have PBRs from lab-scale to 130,000-liter capacity that can be used in mixotrophic mode. The ability to shift a culture between purely phototrophic and mixotrophic production modes sets us apart. It gives us the ability to modulate the production of certain cellular components, which results in a more valuable crop.” 

The company has two dozen PBRs of different designs and scale at its facilities in Gilbert, Arizona, along with one system at Arizona State University (also in Gilbert), and six systems in Japan. “We recently conducted a six-month demonstration test using some of our units colocated at an incinerator plant in the city of Saga in southwest Japan,” Olaizola says. The project in Japan [with Sincere Corp.] has now moved into the construction phase of a commercial facility using our proprietary technology and reactors.” Commissioning is expected early next year. 

Some of Heliae’s reactors have been in operation for several years, but proper preventive maintenance has maintained the systems, which Olaizola says have run nearly continuously. “Perhaps the most common repair needed every few months is a bad pH probe,” he says. “On occasion, high winds have produced tears in our large PBR greenhouse covers.” This happened twice in the past year.  

Two drivers guide Heliae’s PBR development efforts: increasing the flexibility of each system for different products and species, and lowering the cost of the unit itself and its operation. “In general, we have developed PBRs that permit better control of parameters such as pH, temperature, gas exchange and turbulence,” Olaizola says. The company is currently working on two aspects of PBR development, one of which is exploration of different construction materials that can lower the cost of larger units. “Some of these materials will be cheaper to purchase—think polymer versus glass tubes, for example—and also cheaper to maintain,” Olaizola says. This allows greater longevity and easier cleaning. “Second, we are pushing automation of functions so that manpower costs can also be reduced,” Olaizola says. “Heliae has always been big on automation. Now we are pushing that functionality even further.” 

Heliae is in collaboration with several partners to continually improve not only its PBRs, but also other aspects of the production cycle. It’s working with Evodos on downstream processing, specifically using its separation equipment. “And more specifically, pertaining to the PBRs themselves, we’ve been working with Schott, testing their new oval glass tubes in our Helix platform, a tubular PBR,” Olaizola says. 

Schott also collaborates with Algatechnologies Ltd. The two signed an R&D agreement following a successful one-year study of new glass tubes at Algatechnologies’ production facility in Israel. Schott’s thin-walled Duran glass tubes significantly improved cultivation efficiency in the yields of Algatech’s AstaPure natural astaxanthin, an antioxidant. The two firms partnered in 2013 to produce nearly 10 miles of thin-walled Duran glass tubes for testing in Algatech’s PBR systems in Israel. 

In addition to Evodos and Schott, Heliae is also working with Philips Lighting for indoor and outdoor work, using newly developed LED units to decrease the heat load in indoor PBRs, and to augment natural sunlight in outdoor systems, Olaizola says. “And considering that strain development is an intrinsic part of success in our field, we are working with Triton Health and Nutrition to scale up the indoor and outdoor cultivation of algae designed to produce high-value therapeutic proteins.” 

Olaizola says the algae industry is “far from where we need to be” regarding state of the art. He says algae can generate many products such as nutrition, energy and materials, along with services such as water reclamation, carbon capture and heavy metal remediation, but at a high cost. “A large part of the current cost relates to the cost of the growth units themselves,” he says. “We need to make those units a lot cheaper. Alternatively, we will limit ourselves to produce high-value products like astaxanthin or specialty proteins. But those markets are small.” He says to manufacture algae-derived products at a more competitive price, the emphasis should not only be on PBR designs, but also the protocols developed to optimize their operation, including ancillary support systems from the inoculum to downstream processing platforms.

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