More Lightmanagement 4Hallo Oilgae friends,
just in another group "Algae to Growdiesel" the following question popped up:
How many photons does it take to make one gram of Nannochloropsis Oculata in an optimal concentration PBR setting?
A tricky question!? Yes indeed, and after the experience we made can this only be soled with practical experience.
The light used for the cultivation of phototrophic micro-organisms has to be in the spectral range of ~, 400 to 700 nm to activate the photosynthesis pigments [Heath, in 1972; Lawlor, in 1992]. An optimum irradiation strength (number of photons per surface needed and time [μE m-2 s-1], the photo synthetic photon flux density (PPFD) is different from specie to specie and can be derived from the light saturation curve.
Below minimum irradiation strength a photosynthetic driven micro-organism will use more energy for his (preservation) metabolism than it could get from the irradiated light (measurable photosynthesis rate and total oxygen balance negative).
The minimum necessary irradiation strength for a measurable positive photosynthesis rate will show in the light saturation curve and be market as light compensation point [Goldmann, in 1979; Kohl and Nicklisch, in 1988]. A growing PPFD rate will result in the production of oxygen until it reaches a constant maximum level of oxygen saturation. In the linear area of the light saturation curve every photon will be photo-chemical absorbed by photosynthesis pigments thus enabling the photosynthesis process. The photon exploitation at this level is at its maximum (maximum quantum yield); however, the growth rate of photosynthesis-active organisms is limited due to low a light intensity. We are now in the transition area of the light saturation curve when the photosynthesis rate is at its highest level but the amount of photons used for the photosynthesis are at a minimum. The light saturation is based on the limited reaction rate of plastoquinone or the oxidation of NADPH (Nicotinamide adenine dinucleotide phosphate) molecules in the Calvin cycle [Matthijs et al., 1996]. A part of the electrons animated in the PS II (photo synthesis system II/Calvin curve) can not be used, but this energy is being converted into warmth and fluorescence. Raising the light intensity may now result in a photo inhibition (reducing the photosynthesis rate) and may destroy photosynthesis receptors, light-absorbent pigments and the thylakoid membran [Hopkin
and H?ner, in 2004].
The density of cells during cultivation will lead to an increasing shading effect which will have to be compensated by an adjustment of light entry. As a result this limitation of light during the growths will not leave enough protons available for an optimal supply. Contradictory too much light entry in the beginning of cell cultivation would cause cell damage (photo inhibition). Another parameter which influences the light entry is the upper surfaces /
Volume (A/V) - relation of the photo bioreactor.
A homogeneous irradiation of all cells combined with an ideal A/V-relation, this in connection with a sufficient mixing would prevent a continuous change of light conditions from the unlit centre of the reactor to the illuminated surface.
If light is so vitally important for algae, - as much as too much light is
damaging, - just how much light do we need for algae breeding in a PBR system?
And what can we learn from all this?
They need light, off course, but are shy of direct solar radiation. How can we measure how much light? We use a patented Model-Reactor (Pat.Nr. 202007013 401.1) with an LED light source to find out the optimum growth level of algae species. Here we can simulate the light conditions of Germany, Spain, Australia or even India. Also different nutrition requirements can be tested. It has shown for us that here in Central Europe only 10% of solar radiation is necessary to achieve an optimum growth rate. Thus algae cells are converting 5% of the given light into bio energy (something that i.e. the sugar cane can only do with 1% effectiveness). We are able to boost the productivity of algae up to 100 gram per m? per day with this method of finding the right specie. But we even learned more. In a compact algae culture which is mixed up by streaming water, some algae will come into the (light) surface, some will return into the dark. From the view of an algae cell it might appear as if the light is flickering. This Disco-light effect was researched as well. Surprisingly the algae liked it very much! They are able to store the captured light and will use it later, in the dark, for their growth.
So how could you measure your light intensity compared to what you have as equipment (type of reactor), and to find out with the help of a light saturation curve just how much light you may need (that you will be able to find out just how much photons you may need per cell I may have the freedom not to believe?.. this was a joke, wasn?t it?) for optimum growth.
You would need a good photo meter (Quantum Sensor to measure photo synthetically active radiation (PAR ? LI-COR Biosiences) and at least 6 til 12 month time to go through all possible light conditions with your PBR. Good Luck!
You may see the ?Specification ?bio reactor? which you will find on my profile. You may notice that we are working with a continuous harvesting system that gives an excellent control over the cell density in our reactor model. Thus we can keep productivity high do not have to stress with light limitation factors through shading. And we work with greenhouses, - not only because of our northern Europe climate! ? no, we even shade our cultures up here in the north.. Andreas-Algae NovaNB. Just one little question I have, - if you have an optimal PBR setting, why do you want to count photons?
It`s a waste of time than.......