Cultivation of Algae in Photobioreactor

Cultivation of Algae in Photobioreactor

Algae cultivation can be achieved in two ways: open ponds and photobioreactors (PBR). A photobioreactor is a closed equipment which provides a controlled environment and enables high productivity of algae. As it is a closed system, all growth requirements of algae are introduced into the system and controlled according to the requirements. PBRs facilitate better control of culture environment such as carbon dioxide supply, water supply, optimal temperature, efficient exposure to light, culture density, pH levels, gas supply rate, mixing regime, etc.,
Photobioreactor - How it works

Working of a photobioreactor:

Flow description:

1. From the feeding vessel, the flow progresses to the diaphragm pump which moderates the flow of the algae into the actual tube. Built into the pump is the CO2 inlet valve.

2. The photobioreactor itself is used to promote biological growth by controlling environmental parameters including light. The tubes are made of acrylic and are designed to have light and dark intervals to enhance the growth rate.

3. The photobioreactor has a built-in cleaning system that internally cleans the tubes without stopping the production.

4. After the algae have completed the flow through the photobioreactor, it passes back to the feeding vessel.  As it progresses through the hoses, the oxygen sensors determine how much oxygen has built up in the plant and this oxygen is released in the feeding vessel itself. It is also at this stage that the optical Cell Density sensor determines the harvesting rate.

5. When the algae are ready for harvesting, they pass through the connected filtering system. This filter collects the algae that are ready for processing, while the remaining algae passes back to the feeding vessel.

6. The flow continues.

Advantages of Photobioreactors

• Cultivation of algae is in controlled circumstances, hence potential for much higher productivity
• Large surface-to-volume ratio. PBRs offer maximum efficiency in using light and therefore greatly improve productivity. Typically the culture density of algae produced is 10 to 20 times greater than bag culture in which algaeculture is done in bags - and can be even greater.
• Better control of gas transfer.
• Reduction in evaporation of growth medium.
• More uniform temperature.
• Better protection from outside contamination.
• Space saving - Can be mounted vertically, horizontally or at an angle, indoors or outdoors.
• Reduced Fouling - Recently available tube self cleaning mechanisms can dramatically reduce fouling.

Covering ponds does offer some of the benefits that are offered by photobioreactors, but enclosed systems will still provide better control of temperature, light intensity, better control of gas transfer, and larger surface area-to-volume ratio. An enclosed PBR design will enhance commercial algal biomass production by keeping algae genetics pure and reducing the possibility of parasite infestation.

Source :
http://www.oilgae.com/algae/cult/pbr/pbr.html