Enhanced light transmission leads to higher productivity in photobioreactors
Tubes for photobioreactors can be made of plastic or glass. If they are manufactured from plastic, this is usually PMMA or UV-PVC. Algae growth development is directly proportional to the light intensity that the algae are exposed to. This raises the question, whether glass, PMMA and UV-PVC all allow the same amount of light into the interior of the tubing.
The graph below shows the results of the comparison of the transmission values (air-material-air) of the three materials:
In order to make the comparisons of the calculations more conclusive for algae production, the average transmission in the wavelength range 420 to 720 nm was calculated, i.e. beyond the UV-PVC cut-off at about 400 nm. The results are shown below:
One can deduce that glass and PMMA feature low light loss, whereas UV-PVC allows less light to reach the interior of the tubing. How is this explained?
The transmission loss has two causes. The first is the light reflection on the surface boundaries, of which tubing has two, one on the outside and one on the inside. The reflection of glass is always in the range of 4%. This results in 92% light transmission. PMMA is very similar to glass, exhibiting a light transmission of around 91%. UV-PVC however loses approximately 1/3 of the light.
This is where the second root cause comes into play: PVC not only causes light loss due to reflection, but also due to absorption. UV-PVC is bluish in colour and appears far less clear than glass or PMMA. Accordingly, the calculations show that light in the blue spectrum hardly reaches the interior of a PVC tube.
This leads to the undesired effect of significantly reduced algae production in UV-PVC tubes: at least 25% less algae growth than in tubular glass systems.
Which additional differences can be found when using glass, PMMA or UV-PVC as container material for a photobioreactor?
Find out more in our e-book and download it here for free: “How to choose the correct tubing material for photobioreactors. A systematic comparison of glass versus polymer tubing.”