Please allow me to start another thread on this specific topic.
Growing algae, like any other production, takes feedstocks and turns them into something more valuable. In the case of algae, we have an autotroph inwhich turns sunlight, nutrients and other feedstocks into algae biomass. We all know that Sunlight is a feedstock. And so is Nutrients like NPK and micro's like Mg and Fe... Even water is a feedstock because H2 of the H2O is where all those precious H's come from. But specifically here, I would like to discuss the addition of CO2 to this list of important feedstocks. Its one of the 4 arrows into the autotroph system; Sunlight, nutrients, H2O, CO2.
I think this mega important feedstock is sorely missed when discussing algae, PBR's, deserts, ocean production... etc. One of the main reasons why pond efficiencies are so low is because of sub optimal CO2 conditions. One of the main reasons why lab results can show 10x pond yields, because of optimal CO2 conditions. CO2 is the essential building block of all of life. Carbon typically makes up ~ 50% of the weight of bone dry biomass and 90% C and O by weight. High lipid algae would be much larger % by weight C than lower, more oxygenated biomass.
CO2 in an aquatic condition adds a few twists and turns.
Bubbling air actually loses HCO3? pH issues? Concentrations? Coal exhaust? Can some plants extract C from organics? CO2 in the desert? ... lets hear it for CO2!
flectere si nequeo superos, Achaeronta movebo! -Virgil
According to the Chisti paper you posted a link to elsewhere on this forum, froggy, photosynthesis in a PBR splits oxygen out of water at rate of about 10g/M^3/min. That is a startling figure. Chisti also points out that too much oxygen in the water will, in simple language, burn the aglea. This situation becomes insupportable once the O2 level in the reactor broth reaches 4 times the O2 concentration in the atmosphere. The PH of the water rises as the concentration of O2 increases and this places more stress on the algae, limiting their ability to reproduce.
According to both Chisti and Kertz, the solution to this problem is heavy aeration of the broth. Chisti says that PBR tubing runs should not exceed 80M (~263 feet) without supplemental aeration. This is difficult to accomplish in a reactor made with hard tubes because it is necessary to vent them. Apparently water will absorb CO2 in favor of oxygen and and CO2 replaces oxygen in solution whenever the water is aerated.
This leaves a great many questions on how best to proceed when dealing with this issue. It is a condition that must be controlled. There is no way to avoid the necessity for it.
Is it necessary to pump pure CO2 into the system? Apparently not, although that would be a quick way to bring CO2 levels up. It is also a good way to overshoot the targeted saturation level. Too much CO2 in the broth will bring the PH down too far, and a PH that is too low will also inhibit reproduction.
I can see where having algae farms near heavy users of coal or hydrocarbons, steel mills, power plants, smelters and cement plants would make sense, but more because you could recover a lot of the energy you need to drive the algae could be obtained from the waste heat those kinds of operations produce. Using the CO2 from flue gasses will involve costs and control problems that are unnecessary. For one thing, the flue gasses need to be carefully scrubbed and then cooled pior to introducing them into the intense, barely balanced habitat of a PBR.
When you look at how the process works, it is just as effective from the standpoint of controlling CO2 emissions to pull the CO2 out of the atmosphere as it is to pull it out of the stack gasses directly. It is not as though the CO2 will run off and hide as it leaves the exhaust stack. It cannot leave the atmosphere.
Billy Greenacre: photosynthesis in a PBR splits oxygen out of water at rate of about 10g/M^3/min. That is a startling figure.
Billy Greenacre: too much oxygen in the water will, in simple language, burn the aglea.
But I think this points to the fact that to get optimal gas exchange and thus optimal plant growth... some real hard science and thought needs to go into air exchange in a PBR. This greatly increases the cost of production and infrastructure (and EROI).
froggy:But I think this points to the fact that to get optimal gas exchange and thus optimal plant growth... some real hard science and thought needs to go into air exchange in a PBR. This greatly increases the cost of production and infrastructure (and EROI).
Obviously you are correct on this point. In the PBR design I am working on I was planning on heavy aeration in the reservior where nutrient additions and harvesting would occur, but each bag consists of 68 tubes, each of which would be 4' 11" in height. That means that additional aeration is needed before the broth gets out of the first bag. Right now, the only thing I would know to do would be to intsall an aeration stone in three or four tubes of each bag. This would not be an intolerable increase in material cost per bag, but it does point to the need for an air compressor and air supply header. This is a significant increase in cost, not just for installation, but also for operation.
One possible fix would be to feed small quantities of supernatant from an anearobic digester into the system at strategic points. This would add needed nitrogen as well as carbon dioxide, but that is going to require some serious study because it brings up a number of control issues that would have to be dealt with, particularly with PH. Such a system might still require aeration and it would be necessary to see where the break-even point is on cost. One coudl also start with a supernatent rich mixture in the reservior. Again, quite a bit of experimentation and number crunching will be required.
Many moons ago I read about an article that talked about how the Navy was working on a membrane techology that would filter dissolved oxygen out water. They, of course, were hopeing to get rid of the electrolysis systems they use on nuclear subs. I don't think they ever decided to use that technology because I have read a recently published book by a submariner and he talked about the electrolylis system being called the "bomb". The sytem being a bomb is the reason the Navy was interested in the membrane technology. Anyway, that falls into the category of "shiny doohicky" unless you know about something I don't. It's likely that you do know something I don't. I am still trying to get a good grip on this stuff.
Another approach, ten years or so in the future, might be to engineer a C4 type algae. This would help matters a great deal, but I don't think it would eliminate the need for repeated aeration of the water. This is going to be one of those problems that doesn't have a silver bullet weakness.
Here is an interesting read on the HCO3- issue.
http://www.plantphysiol.org/cgi/reprint/65/6/1160
This may be nothing more than another futuristic shiny dookicky or it might be the real thing:
http://www.freepatentsonline.com/6235189.html
I'm going to check this one out, because it sounds like something that really could work.
As for the dark cycle, I am wondering, what constitutes "dark" in this context? It is an absence of light at the right wavelength, right?
I found the outfit that makes the submerged CO2 generator:
http://www.able-biott.co.jp/e-index.html
Judging from their product lines, they specialize in lab equipment. If demand went up for their CO2 doohicky, they probably would not have a problem with licensing their patent.
Billy Greenacre: As for the dark cycle, I am wondering, what constitutes "dark" in this context? It is an absence of light at the right wavelength, right?
The dark cycle happens removed in time and place from the light cycle. I think the simple answer is that the light cycle produces O2 and the dark cycle is poisoned by O2 and must be done in a different place. Im sure the dark cycle could be done in any light, just removed from the light cycle of the plant because of the O2.
froggy:The dark cycle happens removed in time and place from the light cycle. I think the simple answer is that the light cycle produces O2 and the dark cycle is poisoned by O2 and must be done in a different place. Im sure the dark cycle could be done in any light, just removed from the light cycle of the plant because of the O2.
None of the stuff you have been showing me jives with what I remember from my school days. Of course, I am almost old enough to think twice before buying green bananas, so what I am remembering is likely dated.
As I recall, ATP (adenosine tri-phosphate) is made from ADP (adenosine di-phosphate) whenever the chlorophyll catches a photon of the right frequency. There is then a place in most chloroplasts, the name of it escapes me, where the ATP then discharges by dropping one of its phospate radicals and becoming ADP once again. It is when the ATP becomes ADP that the energy released by that conversion to produce a sugar, a starch or a lipid.
None of this is mentioned in the Wikipedia or the article you linked. If it was left out for the purposes of simplifying the explanations offered by those articles, then I have to think that the limiting reagent when there is more than enough light is the ADP. In other words, the cell runs out of ADP to charge up into ATP. Once the entire store of ADP is converted to ATP, the cell cannot use any of the photons passing through it, even there are plenty of photons exciting the chlorophyll. What happens to the chlorophyll under these conditions? Does some of it break down? Does excess light prevent the ATP from reaching a place where it can safely discharge? What happens then? It can't be good, can it? It must be something akin to spiking gasoline with nitrous oxide--hard on the engine.
At any rate, before the cell can do anything with the energy it is recieving, it must recover some of the ADP it turned into ATP. At least, that it is what I think based on what I remember from my school days. I may well have it completely wrong end around given the age of my memories.
Billy Greenacre: There is then a place in most chloroplasts, the name of it escapes me, where the ATP then discharges by dropping one of its phospate radicals and becoming ADP once again. It is when the ATP becomes ADP that the energy released by that conversion to produce a sugar[.]
Billy Greenacre: Once the entire store of ADP is converted to ATP ... What happens then? It can't be good, can it?
Moral of the story is we need to keep the O2 down and the CO2 up. More CO2 and less O2 = less 'burning' like discribed and more fixing C.
I found a site that explained the modern discoveries in a way that was easier for me to follow here:
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html#Table%20of%20Contents
It turns out that there are two routes of of photosynthesis for C3 plants. One (the first discovered) uses the ADP to ATP route the other one uses the NADP to NADPH route. I had never heard of NADP/NADPH until you posted those links.
It still boils down to the same thing for the farmer and his algae. Lots of CO2 and lots of light, is tolerable. The algae will make more algae. Lots of light and lots of 02 is terrible. The algae bake themselves into itty-bitty green cookies.
I'm guessing that when CO2 concentrations are normal-to-high and the light levels are low, that the algae will decide that it is time to make spores and will, therefore, begin making more lipids than carbohydrates.
froggy:Moral of the story is we need to keep the O2 down and the CO2 up. More CO2 and less O2 = less 'burning' like discribed and more fixing C.
And I want to thank you for starting this thread. It has very likely helped me avoid a long drawn out head scratchin', wondering why my bugs are dying before they got to the end of the first bag in my reactor.
billy,
keep in mind that youll need to consider a means of agitation in your bag system. high light intensity with no agitation causes photolysis or photodestruction due to photoelectric effect ( electrons are boiled away) high light intensity with high agitation gives optimum growth all filaments or cells receive frequent light charges but are also shielded by other filaments or cells which protect against over exposure to light. low light with low agitation gives slow growth but pigmerntation is enhanced.
marc
Got it, Mark.
By the way, I think I can home brew a peristaltic pump. It won't be as efficient as the factory made pumps and it will not stand much head pressure, but it will move water--lots of water if you keep the head pressure down. I'm gonna use 2 x 4's, plywood, or thin plate and roller skate wheels. The tricky bit is finding the right driver/pulley combination.
Billy,
My guess is that this thing will use so much power making the CO2 that the algae oil will be too expensive. (Or it may cause a negative energy balance - if you prefer that view.)
liberty1:My guess is that this thing will use so much power making the CO2 that the algae oil will be too expensive. (Or it may cause a negative energy balance - if you prefer that view.)
We have a lot of room on the negative return on energy. Look at how many trillions of cubic feet of methane the Canadians burn to make gasoline and diesel for us. Then look at the return on coal-to-liquids. Also, I seriously doubt that any of these "alternative" fuels will do one bit of good for those who's goal is the reduction of CO2 emissions. You have to remember that ALL of the alternative energy schemes are differing methods to collect solar energy. Even though there is a great deal of solar energy available to us, it is very diffues and difficult to gather. In fact, all the energy we use now are differing forms of solar energy--stored solar energy. This, by the way, includes power derived from radioactive substances. Those substances were made by dying stars.
None of this bothers me over much, as I see liquid transport fuels as a way to answer a national security need. A negative energy return bothers me not at all so long as the process is profitable.
Some have expressed doubts or worries about mixing cyanobacteria with algae in a bioreactor. These two papers however, would suggest that there would be little harm in such a practices and it may be that genuine gains could be realized from it.
http://www.jcb.org/cgi/reprint/97/4/1266.pdf
http://www.biophysics.org/education/lavergne.pdf