Niko Schultz: Rethinking algae biomass production

[Global] Algae is a wonder of the natural world. It’s a highly adaptable organism, one that grows in both fresh and saltwater and can thrive in some of the harshest conditions. For that reason, hundreds of strains of algae exist across the globe.

If you find a place with water, sunlight and the right mix of nutrients, it’s very likely you’ll also find algae.

Algae isn’t only abundant, it’s also versatile. It can be transformed into fuel, food, nutraceuticals, cosmetics and even a water-purifying agent. However, maximizing commercial production to meet the growing demand, all while containing costs, is still a work in progress for many producers.

Today, dozens of algae strains can be industrially grown, and commercial algae producers are testing new technologies in their production facilities in an attempt to boost efficiency and increase yield. Closed photobioreactor (PBR) systems equipped with glass tubing, as opposed to open ponds, are known to provide an increased biomass yield, for example. an increase in dry biomass production through time, volume and improved process stability.

To keep pace with growing demand, algae producers increasingly rely on research partnerships to uncover new techniques that boost yield.

Boosting yield in closed PBRs

Algae has no problem growing in the natural environment, yet commercial algae producers are still searching for new ways to more effectively and profitably produce large amounts of algae biomass, especially given the struggles of open raceways or mixed ponds. Open ponds, which are shallow outdoor pools that rely on natural light to grow algae, are susceptible to environmental contaminants and other external factors, such as rainfall and sunlight.

Additional factors, such as temperature, pH, carbon dioxide addition and oxygen removal, can also impact algae yield. And since open ponds are exposed to the elements, they’re more susceptible to contamination by opportunistic organisms, such as competing algae strains, protozoa-like rotifers and bacteria and viruses. Also, due to the high rate of evaporation, there’s a risk of salinization.

 

Open ponds were long viewed as the least expensive method of commercial algae production. However, design enhancements in closed PBR systems—and the concomitant reduction in the ownership cost due to improved lifecycles—has encouraged more producers to employ enclosed PBRs. Recent research projects from SCHOTT and algae producers Heliae have tested new ways to make PBRs more effective. The studies found borosilicate glass tubing, specifically oval or thin-walled tubing, used in closed PBR systems increase the biomass yield for the more cost-efficient production of algae biomass with a small footprint.

Algae productivity is measured by produced dry mass per reactor volume and time, and algae grown in closed PBRs with glass tubing have at least twice the performance of open ponds. The algae concentrations in a large open-pond system might peak at 0.4 g/L dry biomass content and sustain a daily volumetric harvest rate of 20%, but an enclosed tubular system under the same conditions is capable of achieving dry biomass content of 2 g/L and a daily volumetric harvest rate near 40%.

Closed PBRs see performance gains due to greater photosynthetic efficiencies within the systems. For example, thin-walled glass tubes can increase light exposure to encourage photosynthesis and, in turn, increase yield. Additionally, PBRs offer producers greater control over the systems. For example, they can incorporate online monitoring and constant LED light dispersion.

Closed PBR systems hold a number of advantages over open pools or trenches, including smaller physical footprints (PBR tubes can be positioned vertically), decreased likelihood of contamination, increased biosecurity, reduced water consumption, tighter process control and added flexibility in terms of changing the species or strain of algae during production seasons. Commercial algae producers can scale these systems up, from seed reactors to full production systems, in order to increase profitability.

Glass’ long-term benefits in PBRs

While PBRs offer a controllable and scalable solution for algae production, the material used for the tubing plays a critical role in PBR success. While polymer tubing has long been an industry standard, it has a number of drawbacks that can significantly impact algae yield. Polymer tubing can degrade and grow opaque, resulting in reduced light transmission throughout its lifespan. This UV-induced darkening can decrease algae growth and biomass output. Scratches and chemical attack in cleaning processes can further reduce the transmission.

Borosilicate glass tubes, on the other hand, can be engineered to withstand scratches and abrasions, as well as chemical degradation, and therefore offer a longer lifespan within a PBR system than polymer tubes. Due to its reduced refractive index, the use of borosilicate glass tubes can result in about 1% more light transmission into the algae culture, and therefore encourage gains in growth and biomass output. Also, the stiffer glass tubes require less supports.

One important consideration is the glass tubing’s shape. Recent tests show algae grown in oval tubes increased yield over traditional, circular glass tubes. In artificially illuminated PBRs where oval tubes substitute round tubes, dry biomass output per day increased by more than 22%. The increased performance of the oval tubes is attributed to the larger cross-section that leads to more light absorption. The reduced inner volume of the oval tubes (round and oval tubes have equal circumferences) leads to an increased volumetric efficiency by more than 50%. The round-tube diameter in these tests was 65 mm. Tube design plays a crucial role in yield.

The future uses of algae

Algae was once seen as the heir apparent to gasoline or diesel, but today it’s viewed as more than just a potential environmentally friendly fuel source.

Throughout the world, key nutrients like protein and fatty acids are in limited supply, but algae offers an inexpensive way to boost undernourished diets. These nutrients can be derived from algae strains like Spirulina and others to supplement diets throughout the world. The substance astaxanthin, a natural dietary component, can be derived from the microalgae Haematococcus. The substance can be used as an immune-system-boosting antioxidant in humans, as well as an animal feed additive. Other strains of algae can also be used as feed in aqua farming in order to reduce pressures on wild fisheries.

Finally, algae is also used in wastewater recycling for the sequestration of nitrates, phosphates and contaminants, such as heavy metals. This process results in algae biomasses for use in industrial chemical production, including bioplastics and polylactic acid.

A focus on productive PBR systems

Humans have produced algae in open cultivation systems for many centuries. But new technologies have shifted algae production from large outdoor pools to closed PBRs equipped with glass tubes. This method of algae growth has proven more efficient and reliable, as well as far less expensive than previously anticipated. Plus, the long lifespan and efficiency of these units can increase biomass production and boost overall profitability. As the number of applications for algae continue to expand, so too will the methods of producing this wonder of the natural world.

 

Photo: Schott

View original article at: Rethinking Algae Biomass Production

 

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