Application note A109 - FP02

Controlled CO2 supply for algae growth

Radius, a strategic research group of the Belgian Thomas More University of Applied Sciences, investigates the conversion of CO2 with sunlight into specialty chemicals. Microalgae play a key role here, and their CO2 fixation rates and growth capacities are examined. 

This research falls within European efforts to build a low-carbon economy to guarantee a sustainable, reliable and affordable supply of energy (e.g. biofuel) and materials (e.g. chemicals and cosmetics). In this respect, the greenhouse gas carbon dioxide (CO2 ) is considered a valuable alternative source of carbon that is abundantly available, in applications for food, feed and biobased chemicals.

The researchers of Radius cultivate microalgae in photobioreactors. In order to investigate how much CO2 gas is captured and converted by their algae, they need an accurate method to control and measure the CO2 gas flow supplied to the algae during cultivation. To this end, the help of Bronkhorst's devices was requested.

Application Algae farming
(Source: Thomas More | Agro- and Biotechnology)

Application requirements

The amount of CO2 that is dosed to stimulate the growth of the microalgae also influences the pH in the cultivation system that - in turn - has a large influence on the microalgae growth conditions. Therefore, the accuracy of the CO2 supply according to the pH in the growth medium of the microalgae is important. Moreover, all parameters that are involved in the process need to be monitored.

Important topics

  • Automated process for accurate supply of CO2 based on current pH value
  • Monitoring of process parameters

Process solution

At Radius, experiments for microalgae cultivation on a pilot scale are conducted in closed, tubular photobioreactors with a total volume of 300 liters each, operating at atmospheric pressure in a climate-controlled greenhouse. Two IN-FLOW thermal mass flow controllers are used, each of them to supply CO2 to these pilot scale reactors, with a maximum dosed flow rate of 886 milliliters CO2 per minute for each reactor. There is a direct, automatic feedback between the current measured pH value and the supplied CO2 flow to optimize growth conditoins in this algae bioreactor application.

After a meeting with their supplier of CO2 gas, Radius was introduced to Gefran, which is a distributor of Bronkhorst products in Belgium. Radius and Gefran together looked for a system that could accurately dose CO2 based on the pH value in the growth medium of the microalgae. The combination of their requirements ultimately led to the purchase of  the IN-FLOW mass flow controllers from Bronkhorst.

Flow scheme
Flow scheme

In the past, the supply of CO2 gas as well as the control of the pH had to be done manually. With this new system, which utilises LabVIEW (instrument driver), they can perfectly monitor the CO2 dosage in their pilot plant, and keep the pH at the desired level without too much effort. The best conditions for the algae to grow are in the pH range between 6.5 and 9.5, preferably around 8. This pH is similar to the natural alkaline habitat of the cultivated algae. 

According to Radius, the accuracy of the mass flow controllers, the capabilities of the PID controller and the usability of LabVIEW makes Bronkhorst IN-FLOW mass flow controllers a solid and reliable gas dosing system. Currently they are looking for an extension of the system to monitor the outgoing CO2 flow, in order to be able to even more accurately monitor the CO2 uptake by their microalgae. This will provide enhanced insights in the algae growth conditions and an optimum between the CO2 gas flow supply and pH control in photobioreactors.

Moreover, in the future, two larger photobioreactors with a total volume of 1800 liters each will also be equipped with Bronkhorst mass flow controllers for the control of CO2 flow supply. 

Read our blog about Algae growth

Response Thomas More University

Joris Doumen: "With a balanced CO2 dosing system, the future of algae cultivation becomes even more sustainable and greener!"

Algae farming
(Source: Thomas More | Agro- and Biotechnology)
Algae farming
(Source: Thomas More | Agro- and Biotechnology)