30569952 Open Ponds Versus Closed Bioreactors

7/29/2019 30569952 Open Ponds Versus Closed Bioreactors

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Open Ponds Versus Closed BioreactorsThere are pros and cons associated with the economic commercial production of algae using

closed bioreactors and open ponds. Is one method superior, or is there room for both?By Anna Austin

The U.S. DOEs National Renewable Energy Laboratory concluded in 1990 in its Aquatic SpeciesProgram close-out report that open raceway ponds were the most viable solution for the massproduction of algae for conversion into biofuels, but that it was much too early to determinewhether open, closed or hybrid designs of growing algae would ultimately prevail.

Generally, open ponds have been associated with contamination issues, excessive spacerequirements and limited location possibilities due to climate. At the same time, closed bioreactorshave mainly been considered too expensive. There wasnt much room for doubting the accuracy ofNRELs report, but have technological advancements in the past two decades leveled the playingfield? Perhaps, but companies today pursuing either route still face the same hurdles theirpredecessors did. Whether it takes five, 10 or 20 years, the key to economic algae-based biofuelproduction is developing the most cost-effective growth model possible.

If light limitation is the main problem in achieving the commercial potential of algae in scaledcommercial cultivation operations, Massachusetts-based Bodega Algae may have the solution,according to CEO Joseph Dahmen. In January, Bodega Algae and Bigelow Laboratory for OceanSciences in West Boothbay Harbor, Maine, received a six-month, $150,000 Small BusinessInnovation Research grant from the National Science Foundation to develop and test a prototypefor growing high concentrations of algae for use as biofuel. More specifically, Bodega will use thefunds to develop advanced photobioreactors, and is making big advancements, Dahmen says.

Case Closed

One of the major issues in the cultivation of microalgae is light limitation, Dahmen says. This limits

the effective photosynthetic volume to basically the area within five centimeters of the surface of a

pond, he says. Everything below that tends to be light prohibited because the top layer limits the

light from getting in. The same is true for photobioreactors, he adds. So some people have tried

various solutions like flat plates or hanging bags, and in effect, what theyve done is limit the

cultivation volumes in an attempt to drive up the surface area to volume ratio.

These small volumes allow light to penetrate better, according to Dahmen, but the problem is that it

may lead to biofouling (the attachment of organisms to a surface in contact with water for a period

of time) and the cost of pumping the algae around through the small volumes increases. Were

bringing the light to the algae with some proprietary optics that are internal within the reactor,

Dahmen says. We have cultivation volumes that are lit within, so that allows us to cultivate very

efficientlyin effect, like three dimensions.

The bioreactors Bodega is currently experimenting with are bench units made of acrylic. In the long


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term, however, the company is looking at shipping containers and possibly petroleum dissolute

storage tanks.

Dahmen describes open ponds as a first-generation solution to growing algae. Theyre very land

intensive because the effective cultivation area is limited to a very thin slice of growth medium, so

the ponds have to expand, becoming very land hungry, he says. Also, if you look at the areas

receiving high amounts of natural sunlight or insulation where ponds make the most sense, you run

into tremendous problems with evaporation as well as cross-contamination of cultures. When you

start talking about acres and acres of ponds 16 inches deep, youve increased the surface area to the

point where land consumption is a huge problem.

Open ponds are relatively cheap to build compared with bioreactors, though, Dahmen says. But

what were seeing is a real need for cost-effective photobioreactors that can address the capital

expense issues while offering efficient cultivation in large volumes.

Numerous other companies share Dahmens perspectives, but have approached bioreactors in

different ways. Solix Biofuels, recently named a part of the U.S. DOEs $44 million National Alliance

for Advanced Biofuels and Bioproducts consortium, has attracted much attention in the past few

years. Along with Colorado State University, Solix has developed specialized photobioreactor

systems composed of long, closed plastic bags containing algae, which float in large water-filled

metal tanks to control temperature and are injected with CO2 through tubing to optimize growth.

California-based OriginOil, another bioreactor contender, has a cooperative agreement with the U.S.

DOEs Idaho National Laboratory for a multiphase algae research program. The company describes

its Helix BioReactor as an advanced algae growth system that features a rotating vertical shaft with

low-energy lights arranged in a helix/spiral pattern, resulting in a theoretically unlimited number

of growth layers.

While these particular companies have focused on bioreactor development, some such as

Washington-based Bioalgene Inc. have pursued both methods.

Open to Possibilities

A few years ago, aircraft manufacturer Boeing hired Bioalgene to survey indigenous strains of

algaeregional strains that grow fast and produce many lipidsin the Northwest U.S., according to

Bioalgene CEO Stan Barnes. The company has leased a decommissioned wastewater plant where it

is now testing selected strains. These are natural strains that already have defense mechanisms

against predators and disease and can thrive in this region, Barnes says. Now entering phase two

of its research project, Bioalgene will grow algae in larger, 220,000-gallon ponds on a five-acre tract

at Boardman, Ore., to test variances in growing and harvesting methods.


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Barnes says early on, the company built three bioreactors at Seattle University, and though being

able to grow pure strains was an advantage, capital costs to build, maintain and clean transparent

systems didnt seem to be an economic pathway to high-volume algae production. Using NRELs

research as a basis for the companys decision to move forward with natural strains in open ponds,

Barnes says Bioalgene utilized the already developed capabilities of algae to yield a simple system,

rather than a complex system. Evaporation is one of the things were concerned about though, he

tells Biomass Magazine. The whole question of water management is a challenge, and I think youll

have it anywhere. One big advantage a closed system has is no evaporation loss.

Adequate temperature and sunlight are only available in certain regions for limited periods of time,

but Barnes says one of the benefits Bioalgene will reap by growing algae at a coal-fired power plant

(besides using flu gas emissions to accelerate growth) is that the process heat allows growth into

December by warming water that is fed to the algae. As long as the water is warm, there is plentyof light energy to keep the algae growing, he says.

Although Bioalgene believes open ponds are the ultimate solution, it will utilize closed reactors as

nurseries to grow inoculation strains in pure forms before introducing them to ponds. Overall, the

potential for volume, we see, is more economical (in open ponds) than in large closed systems, he

says. Bioalgene expects its systems to be able to deliver more than 100,000 tons of algae per year.

But what if the algae are being produced for something other than oil? Jim Oyler, CEO of Utah-based

Genifuel Corp., says the method of growing algae is relative to the intended use. Algae oil

developers are looking to achieve the highest yields of oil possible using specific strains, but oil

yields arent important to Genifuel, as it is directly converting the algal biomass to natural gas via a

gasification process developed by the DOEs Pacific Northwest National Laboratory.

Room for Both

Though Genifuel is focused on mass rather than oil yields, growing the material as cheap and

quickly as possible is imperative. The company has open raceway ponds in Utah, which are

currently shut down for the winter months, but produced algae last year. In our case, were

interested in growing the most biomass possible per unit of area in our ponds, so our goal is

different than the goal of algae oil producers, Oyler says. We like fast-growing species and in

many cases these are tough, aggressive types of algae. Many of the oil producers, especially when

they are genetically modified, can be somewhat delicate or vulnerable, and are easily taken over by

weeds.

Most oil producers will make the case that they can get faster growth in bioreactors, while at the

same time avoid problems that arise from outdoor production, including susceptibility to parasites

and the potential for aggressive species to take over. The key question is, can you get enough


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additional productivity in bioreactors to offset the additional cost? Oyler says. There are some

very clever designs being developed. Solix Biofuels has a design thats not too expensivemore

expensive than open pondsbut it reduces capital costs in a productive way.

Open ponds have not always been consistent, however, as they have peak productivities that arent

maintainable or achievable in most climates over extended periods of time. There are also some

very clever designs that overcome some of those problems, Oyler says. But in order for

bioreactors to pay off, theyre going to have to achieve something in the order of double or triple

the productivity of an outdoor open pond. Its yet to be proven that it can be done. Theoretically it

might be possible, but no ones actually demonstrated it at a commercial scale.

Another advantage of closed systems is that they open up sunny, dry areas such as the Southwest to

biofuel production. Open ponds are unlikely to work in the Southwest because the water loss is

going to be enormous, Oyler says. Photobioreactors keep water enclosed, but thermal management

is still needed, because if you put an enclosed system out in the desert its going to get really, really

hot in there.

Open Ponds Versus Closed Bioreactors

Although the problems of predators and weeds have been solved with bioreactors, such closedsystems used to grow algae for other purposes have experienced problems with virus susceptibilityand/or bacteria attacks, which can take the whole system down in a matter of hours. There areways to deal with that, but I dont believe that it has ever been fully solved for long periods of time,

Oyler says. Both ponds and bioreactors have advantages and disadvantages right now. Theresmore experience with outdoor systems, but the closed systems have the promise of highersustained productivity, but only if they can overcome associated problems, especially thermalmanagement or diseases.

Al Darzins, principal group manager of NRELs National Bioenergy Center, shares Oylers sentiment.During the past couple of years, algae research has enjoyed a resurgence at NREL, includingprojects with Chevron Corp. and the Colorado Center for Biofuels and Biorefining, and Darzins saysin the extended future, both ways of producing algae will continue.

Back at It

NREL is currently experimenting with two algae production systemsin 270-liter ponds in a

greenhouse, and small bioreactors that hold media to grow algae in artificial light with CO2. When

we start scaling both up to the commercial realm, though, thats where the debate lies, Darzins

says. Its an argument that has been heated for the past several years.

When generating large amounts of algae outside in closed photobioreactors, conventional wisdom

is that the materials that go into making them are going to be cost-prohibitive unless the fuel

produced is cheap, according to Darzins. If youre making a value-added product that is worth a lot

of money, then it might make sense to grow the algae in a closed photobioreactor, he says. Right


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now, most people think the cost-effective way will be open raceway ponds, but there are some

companies such as Solix that are growing their organisms in kind of a hybrid cultivation technology.

Solazyme is growing algae not with sunlight, but within closed fermentation tanks with sugar.

Under those conditions you can get very high cell densities and very high amounts of oil produced,

but the main questions are, will that be cost effective and can you scale it up to be meaningful

enough to displace the 40 billion-odd gallons of diesel we use here in the U.S.? Where are you going

to get your cheap sugars to let your algae grow?

Some believe once lignocellulosic ethanol technology is mature, the sugars extracted from corn

stover and energy crops could be fed to bioreactors to reduce the cost of algae production. That

technology isnt quite there yet either, Darzins says. There are a lot of different technologies that

people are exploring but overall, the predominant method right now is open ponds.

Darzins believes if someone can develop truly novel bioreactors that are inexpensive to make and

maintain while isolating organisms that are very productive, then it might make sense to grow

algae that way, especially in more northern latitudes. On whether genetically modified organisms

are productive or not, Darzins isnt sold. We think Mother Nature has been engineering biology for

millions and millions of years and there are some very interesting organisms that we just need to

discover, he says. Over the past four years, algal biofuels have captured the public and scientific

communities attention and [its viability] really depends on whether we can produce it cost

effectively and sustainably, from the aspects of land usage, water usage and nutrient usage; we just

have to make sure all that can be done without competing with agriculture. We havent heard the

last of this debate, thats for sure.

30569952 Open Ponds Versus Closed Bioreactors

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