State-of-the-Art Algae PBRs

by Ron Kotrba (Biomass Magazine) Photobioreactor manufacturers detail their latest designs and performance metrics and provide project updates from around the globe. ... Whether through open ponds, raceways or closed photobioreactors (PBR), growing algae is both a science and an art.

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 tells Biomass Magazine. “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.

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.

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.”

“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.

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.

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.

“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.

Heliae Development manufactures a whole array of programmable PBRs of different sizes and capacities, depending on the purpose of a specific culture, 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.

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. READ MORE