Design of a floating photobioreactor for microalgae cultivation on Bonaire

Background

As populations continue to grow and increasing pressure is exerted on the availability of resources to meet rising demands, considerable efforts are being devoted to creating more sustainable practices around the world. Among the emerging ideas is the Biobased Economy, which encourages a transition from a fossil-based economy towards an economy in which biomass is processed into a range of products, including food, feed, chemicals, and energy. Microalgae have been recognized as a promising feedstock for biobased products. They are characterized by high growth rates and photosynthetic efficiencies compared to traditional agricultural crops, and contain valuable compounds such as oils, proteins, and carbohydrates. In addition, their cultivation potentially requires little space, avoids competition for arable land and freshwater, and allows for reuse of nutrients and CO₂ from waste streams.

Geographical locations in the tropics, such as the island Bonaire, are considered to be ideal for commercial cultivation of microalgae due to the high solar irradiance, stable climate, and availability of seawater. These conditions can facilitate high biomass productivities throughout the entire year, in contrast to many other places in the world. A major challenge for outdoor cultivation is temperature control. Culture temperatures in photobioreactors are known to increase due to the absorption of sunlight. To maintain optimal growth conditions for microalgae, cooling is often required, which can be expensive. In this research, we consider a floating cultivation system, in which the surrounding water acts as a heat sink and provides passive temperature buffering of the culture. Submerging part of the reactor in seawater presents a more cost-effective approach for temperature control compared to conventional cooling strategies used for land-based cultivation systems. Besides temperature, light is often the dominant limiting factor for the growth of microalgae. In this research, we look into a reactor geometry that enables dilution of sunlight to suitable intensities for microalgae. This allows for higher biomass yields on available light and higher areal productivities.

Aim

In this research, we design, test, and evaluate a novel floating photobioreactor for microalgae cultivation on Bonaire. Our objectives are:

• To define a reactor geometry that enables sufficient interception and dilution of sunlight;
• To investigate passive temperature control of the culture by submerging part of the reactor in water;
• And to evaluate the performance of the floating cultivation system on Bonaire.

The research results can provide insights for further development of floating photobioreactors. These emerging systems create new opportunities for offshore cultivation of microalgae, which can be especially attractive for islands or coastal areas around the world.

Approach

Design phase

Based on mathematical modelling of incident sunlight onto the reactor and temperature developments within the culture, the shape, orientation, and configuration of the photobioreactor will be determined.

Testing phase

The prototype will be placed in a water basin and tested under outdoor conditions at the AlgaePARC facilities in Wageningen.

Finally, the performance of the floating cultivation system will be assessed on Bonaire, starting with a marine reference strain, followed by a native Bonairean strain.

Evaluation phase

A techno-economic analysis will be conducted for floating cultivation systems, including an overview of their current status, major opportunities and remaining challenges, and future potentials.

Acknowledgements

This research is funded through the Caribbean Research Program from the Netherlands Organisation for Scientific Research NWO (ALWCA.2016.029).

Thesis project

There are different topics available for BSc or MSc thesis within the project. If you are interested, please feel free to Rocca Chin-on!