Scaling Up. 6
This is part of an upcoming series of blogs titled ‘Bottlenecks, Trafficbocks and Deadends’ intended to address Algae Commercialization barriers.
Please check out for my introductory post at: http://www.oilgae.com/club/users/Gopinelli/blogs/1207
For an algae system, scaling up is the most important and complex commercialization barrier. There are lot of issues to be addressed for successful scale up of a bioreactor system.
In nature, open ponds are capable to provide proper light exposure to dense algae colonies at 10-15 cm depth. Such a culture usually yield 2-3 g/liter dry biomass. Thus, an open pond can contain upto 600 m3 media per acre. In raceway ponds, media volume is usually around 400 M3/acre. A bioreactor should considerably improve media holding capacity in order to justify high equipment cost. But, media capacity per acre of those bioreactors available today are not known.
Simply put, scaling up of a bioreactor means impropving both reactor volume and light penetration. Improving volume is no big deal. But, the problem lies in light exposure. Improving surface of light exposure by modifying shape of the container is one means to improve light exposure. Trying this usually take you to the dead ends.
You may consider a vertical tubular bioreactor because of the structural strength of the shape and that it allows light penetration from all around. But immediately you find that diameter of the tube can’t be increased beyond a limit for self shading of alge cells develop an internal dark region where the cells are unable to perform photosynthesis.
Vertivcal bioreactors deployed closely to one another shade each other. So you are forced to deploy the bioreactors spaced far apart from one another. You may consider increading height of the bireactors, But you find shading also inceasing in rproportion to increasing height, increasing the spacing of deployment. Further more, you need structural elements to support the tubes, inviting additional elements that shade the field. Finalky you end up with heavy imvestment, but no volume advantage.
You may consider modifying the shape in different ways. But, to your disappointment, the final outcome turns around to be the same. Now you understand the conservative nature of THE NATURE. And your only option is going back to open ponds and blogging on scaling up issues. Your fellow bloggers hail your language skills and that’s the desperate end of a “research”.
Let us look at the scenario in a different perspecive.
Light and shade are complementary to each other as night and day are. Shade occurs because there is light. Light causes earth shade, like any opaque object. Sun continuously illuminates one side of the earth causing the earth shade itself on the other side. Axial revolution causes alternation of light and shade in defenite pattern with reference to a particular pint on earth’s surface, causing the day-night transition. In nature, day and night are in perfect equilibrium in an ecosystem perspective. Life on the planet is adapted to this natural day-night transition.
Man has already manipulated natural phenomina, environmental elements, and even genetic sequences of organisms to make certain organisms work the way he wants.
Algae cells do shade under light, And closely deployed bioreactors shade each other too. And we know, algae need light to perform photosynthesis, while they do not need light for cell division..
Now, lets look at a large volume photo bioreactor, A part of a dense algae colony contained within the reactor should be receiving enough light to perform active photosynthesis while light penetration gradually declines until formation of a totally dark intedrnal region.
Here are my questions:
Can’t we isolate the outer illuminated region from the inner dark region?
Cant we expose a fully grown mature colony to the dark region so that the cells will divide in dark, while simultaneously allowing a young colony to perform photosynthesis and grow in the illuminated region?
A large volume bioreactor means more media volume per bioreactor. Isolating the inner shaded region from an outer dark region provides more flexibility to bioreactor size and thereby volume of the illuminated region.
But how can you effectively expose a part of a colony to light and another part of the colony to dark in the same bioreactor at the same time?
Like large plants, an algae colony comprises cells in various growth phases. But the colony can be synchronized to maintain cells in the colony in same metabolic state. Entire volume of the bioreactor can be effectively utilixed by exposing a young synchronized colony to the light region of the bioreactor and a mature synchronized colony to the dark period. Efficiency can further be improved by exposing the same colony alternatively to dark and light at a media flow rate regulated to match durations of dark period and light period of the cell cycle of the species.
Now, you are certain to encounter with the next issue. You need to deploy bioreactors spaced far apart from one another in the field to overcome mutual shading. This again lower media volume per acre.
What is the solution?
Like all green plants, algae can utilize only a very small fraction of insident light. The unused solar energy can be reflected to shaded areas using solar trackers. ***More on this at another time.
My patent pending bioreactor system has a much higher media volume per acre. A synchronized algae colony is exposed to alternate light and dark regimens. These large volume bioreactors are deployed closely to one another and sun light tracked to shaded areas using proprietary solar trackers. Depending on the cell cycle duration of the species, a daily harvest of 2,500 cubic meter to 10,000 cubic meter media per acre per day.
** Look out for my next blog post on 'Cell Cycle Management'