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Hi

I am building up a comprehensive breakdown of the costs of a scalled up "photobioreactor" The design is very different to standard bioreactors and is aimed at incorporating the benefits of an open pond with those of a closed system, This system will still be closed but it looks at the cheapest meathod of achieving this. There are however input questions that still need to be calculated. Could anyone assist me with the following:

 What would the daily Co2 (Volume) say per metre cubed of growing medium be to ensure that algea growth is not limited by lack of CO2. In other words what volume of Co2 would need to be pumped into a Metre cubed volume (1000litres) to ensure that the algae obtains all CO2 requirements.

What would the daily usage of this disolved Co2 - to ensure that sufficient Co2 is continiuosly pumped into the growing medium to ensure that the CO2 saturation is maintained. This will need to incorporate a factor of what Co2 would not disolve into the medium and bubble through?

I hope that someone can assist?

R

Snori

Snori,

PBRs are not the way to go - raceway ponds are.  

The usage of CO2 is going to be a moving target.  To get maximum growth, we want to get the algae into, what in the natural world would be called a bloom.  Once we get it to that extreme productivity, we want to harvest enough to get it a lttle thinner and then let it grow back.  This could be a daily harvest or a continual harvest.  Most of the research that has been done has been focused on keeping the algae slowly growing to allow a strain to be easily preserved.  So we will need to figure out a much enhanced "feeding" schedule.  Only then will we be able to predict the usage of CO2.

Another way you might approach this is to design to your goal of production.  If you expect your pond to produce a kilogram of algae per day, you will have to feed it 3.7 kilograms of CO2 per day. (That is a very optimistic estimate - you may have to do more CO2.) 

If you have a raceway pond, some or all of the CO2 will come from Mother Nature.  If you have a PBR, you will have to pump in all of it. And remove the O2 the algae produces when it breaks down CO2. 

liberty1:

PBRs are not the way to go - raceway ponds are.  

This is the most practical discussion around building of a photobioreactor that I can think of.

Hi Liberty

This thread was not posted to debate which of the approaches (Open or PBR) are the best, as far as I can read none has been proved commercially scalable or viable. Having said this, after your post I think that it is important that if people are going to produce statements that PBR's are not viable, then they must either show that open ponds are or that algae to biofuels are not viable.

I am therefore in the process of having decided that open ponds are just not viable when scaled up. When I say this, its important that I expand on what I would preceive as "scale up". Open ponds on a 1 hectre basis might produce okay results, but the practicality of digging raceway ponds over say 400 hectres filling these with water and maintaining them on an ongoing basis I can not see as possible. Firstly your daily evapouration rate (Est it at 2.7 litres per M2 of surface area per day)(N1) - This is the rate of evaporation that effects our large Dam in Gauteng (Vaal Dam) South Africa - this is in a climate that would most likely produce the best growing yield. To replace this water is one aspect that would for me rule out this approach.

 Other's that would be a problem include; effect of wind on these, dust, birdlife, contamination not only by other algae speacies but other aquatic plants. Your ponds may become one massive reed bed in a few years (This is assuming unlined ponds)

I have no problem with critisism of any ideas put out in these forums, in fact this is the only way to ensure that you have looked at every possible problem that could go wrong and either adjust your approach or discarded your idea. What I do find rather unconstructive is to critisize an idea, put forward a suggestion but not substaciate why it is the approach to take.

I am not fully convinced that PBR are the way to go but I am convinced that open ponds when looked at from a practical point of view are not the way to go if there is a way to go at all.

I would find it interesting how you would overcome the daily water requirement of an open pond system and the potencial for contamination, etc?

Regards,

 SNORI 

N1 - Evaporation rate is calculated on an estimated 1000mm per year recorded for Vaal dam basin the calculation I did to convert this to litres is as follows: 1000*1m2 = 1 M3 of water evaporates per 1m2 surface area. 1 m3 water volume = 1000litres, 1000/365 = 2.7 litres per day per m2.

(On a 1 hectre setup est surface area at 90% so 10 000m2 per hectre of surface area = 9 000 m2 water surface. 9 000*2.7 = 24 300 litres per hectre per day!! that's a lot of water that has to get pumped from somewhere...)

 There is an interesting article about evaporation at  http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId=208.

 Your 2.7 liters per day from a lake surface is consistent with about 55 inches per year of pan evaporation  which appears to be roughly a median value for the US.  The map at the above link shows evaporation rates range from below 30 to over 140 in this country.  The text indicates lake surface evaporation is about the same as from heavy vegetation like tall grasses and alfalfa.

 That being the case the maintenance should not be a real problem in areas that support heavy vegetation, although some irrigation would be required since plants also pull moisture from the ground.  Of course this is all dealing with averages and any particular location would have it's own issues.

Thanks JustATrader,

Its good to validate my data. Its even slighly conservative as well. To get back to what this thread was intended for "Discussing the inputs required for PBR's I managed to locate the required info regarding daily flue gas requirements:

Links posted for those that may be interested:

http://www.ingentaconnect.com/content/klu/japh/2005/00000017/00000005/00008701

Snori

Snori:

Other's that would be a problem include; effect of wind on these, dust, birdlife, contamination not only by other algae speacies but other aquatic plants. Your ponds may become one massive reed bed in a few years (This is assuming unlined ponds)

 SNORI 

Not to forget about the effect a good old thunderstorm would have when it dumps 2inches of rain in less than an hour!!!!!!!

Snori,

Only a small part of my post was about raceway ponds vs PBRs.

Most of it was about the question you asked - how much CO2 - and a practical way to deal with that aspect of the design - whether you are building a raceway pond or a PBR.

More about the questions you raise later. 

Slippery:

Air carries .03% Co2

If you can bubble enough air through your tank you will not need to supplement with pure Co2. Most lab units only use air and I never found any specific research on any scaled up units so my use of Co2 will be by experimentation.

Only way you can really see how much Co2 is enough is by monitoring your Ph very closely - if your Ph rises the Co2 is not being absorbed by the algae and is converting to an alkali ( or is that an acid - can't recall now - will have to look up my notes) either way a rise in Ph is a Co2 overload.

There is more like 388ppm CO2 in the air...so ur #'s are off by almost a 1/3rd to the low.

Air has pathogen as well as other impurities in it. By bubbling more and more air...one will have to acct. for that in terms of sterility AND loading.

If too much CO2 is added...the pH will go down, your water will become acidic, not up as Slippery stated. In addition...CO2 is not the only thing that will raise/lower the pH in your system. I would think that one would need to do a multitude of optimization to the system before they can state 'Only way you can really see how much Co2 is enough is by monitoring your Ph very closely'. In addition to monitoring the CO2 is the formation of O2 which will cause many problems to a PBR.

Dear Snori,

Since you cite Doucha (Who has a more recent article in the same journal), I presume you have figured out that algae consume 1,5-2 (I used 1,83) kg CO2 per kg dry matter, but that the supply will not be used with 100% efficiency. Doucha mentions an optimum of 50%, Greenfuel 15% if memory serves. My point is that your design will have a big effect on the efficiency and since you mention a "different" design, only practice will give you precise answer. I would say you could consider yourself very lucky if you are able to reach 10% CO2 uptake efficiency, but that is more gut-feeling than experience. If it's an option, I would recommend to focus on a cheap, plentiful CO2 source. An average size 785 MWe coal-fired power plant produces 19 ktonne of CO₂ daily, applying this to your 400 hectare, and a high 70 tonne/ha/year, an efficiency of 0,8% would be enough to sustain your operation (well, not accounting for peak productions etc.).

In general, headspace pressure and concentration, bubble volume, residence time and turbulence and of course temperature all play a part in CO2 dissolution into water. Except for temperature in some cases, improving any of these factors requires more energy, so an optimum needs to be found. Maybe you can recruit a grad student with a background in physics and process engineering to get a handle on this.

BTW pH will go UP with CO2 consumption, dissolved CO2 forms an acid (HCO3-)

Are you at liberty to share some of your design concepts with us? 

Froggy,

Build up of O2 will only be a problem with fully enclosed PBR's. Snori says his design will be a combination of closed PBR and open pond so O2 should be able to escape when the medium is in the open pond area. 

Snori,

It was not my intention to reopen this debate.  I put in a note about raceways because new readers may not be aware there are several approachs and, if there is a long discussion of optimizing PBRs, may jump to the conclusion that PBRs are the only way.  As you point out, that is not settled.  Sorry if I ruffled your feathers - just trying to avoid sending newbies off in an unproven direction.

You are correct that there are no commercially succesful demonstrations of any system.  So we must all keep our minds open.  The following cause me to assume raceway ponds should be considered:  The ASP spent $100 million (in current dollars) over 15 years and came to the conclusion that raceway ponds are the way to go.  More recently, Navid compared the productivity of raceway ponds with several PBRs for several species.  The raceway ponds were more productive.  He kept a strain (CCMP647) growing for 13 months with little problem from contamination.  GreenFuels has spent millions on PBRs and has just had their PBR (a large pilot project) crash and had to lay off half their workforce. 

(I dislike the term biofuels because it has been polluted with political discussion.  So I will say "oil from algae".)

I believe oil from algae may be feasible.  While the factors in the second paragraph do not rise to the level of establishing a solid proof that raceway ponds are economically feasible, I feel that those factors give us cause to leave raceway ponds "in the running". 

There are sizable producers of algae products.  While they have high value products and can withstand higher costs than we can, we can learn a few things from them.  They do not try to build 400 H (almost 1000 acre) ponds.  I believe the largest anyone has done are 5 acres (2 + H).  I feel that we need to start with much more modest ponds until we are able to learn how to farm algae.  I believe the ASP, even though it was projecting enormous total acreage, was assuming each pond would only be 10 acres.  So I don't understand why you are assuming someone would build a 400 H pond.  Clearly, with our current knowledge, that is impractical.  The ASP discussed pumping in makeup water from the Sea of Cortez, so they had included allowance for evaporation in their calculations of the practicallity of raceway ponds. 

I assume you feel that PBRs will be at least 5 times as productive as reaceway ponds.  Does that mean that you intend to build a single PBR covering 80 H (160 + acre)?   

Most of the problems can be solved by using a marine species and siting the pond at least 10 km from the ocean.  Then the contaminates that fall in the pond will be freshwater adapted and will be killed by the culture medium.  Even reeds may have trouble with a marine culture medium flowing at 30 cm / sec.

I am sorry that you found my answer unconstructive - I devoted about 10 words to raceway ponds and the rest of the post to trying to provide a way for you to solve the question you asked.

Certainly, you should persue the solution that appeals most to you.  You may have recognized some facts that the rest of us have missed.  If you want to look at something other than raceway ponds, you should do so.  But that does not mean that there is no way they can be practical.  The only research comparision of raceway ponds and PBRs which I am aware of, concluded the raceways were more productive and were practical.

liberty1:

There are sizable producers of algae products.  While they have high value products and can withstand higher costs than we can, we can learn a few things from them.  They do not try to build 400 H (almost 1000 acre) ponds.  I believe the largest anyone has done are 5 acres (2 + H).

Just as an interesting fact: John Benemann mentions in his 1996 report that Earthrise (CA) has a 5 hectare (12.4 acres) and advises 10 ha (24.7 acres) for oil from algae.But this only confirms Bobby's point.

liberty1:

The only research comparision of raceway ponds and PBRs which I am aware of, concluded the raceways were more productive and were practical.

Not the right thread to discuss this, but some research comparing open and closed systems: Pulz, O. (2001). "Photobioreactors: Production Systems for Phototrophic Microorganisms." (any culture system is named a PBR), Borowitzka 1999 "Commercial production of microalgae: ponds, tanks, tubes and fermenters" and Amos Richmonds "Handbook of Microalgal Culture" (2004)

Hi Liberty1

 Thanks for the reply, I didn't take offence. I also do not for one minute profess to have all the answers. There are so many unknowns out there that only a fool would say he has the way and the only way. If you are looking at "oil from algae" as you put it, we have to eventually think big (Lets standardise it to 100 hectare’s - Not sure what acreage that is. I make use of this conversion site quite often for anyone’s interest:  http://www.onlineconversion.com/.)

I keep a very open mind to all idea's. But yes, if you are to start serious production it would have to be in the magnitude of 100 Hectare setup?

I think that we have established a conservative required Co2 input. My source would have to be flue gas (Approx 12% Co2?). To simulate this in a pilot project I will be burning Propane or any other natural gas and either pumping the flue gas (Un-scrubbed should be fine?) directly into the bioreactor or storing it (Probably inflated Tyre Tubes for input when required). I would also obviously assume that it would only be necessary to pump in Co2 during light hrs?

My setup is nothing revolutionary, when I stated that I have an alternate PBR I mean it would be different to what most would picture. Vis Greenfuels tubing on an angular metal frame. I agree 100% with you, their approach was never economical for algae oil. Having said that my approach has a pressure valve at the highest point to allow for O2 and un-dissolved Flue gas to exit. The reason I need to know the volume of gas getting pumped in is to ensure that I have adequate pressure valve/valves to allow this to happen. Additionally I would need to know the input pipe capacity to add this to my design for costing including a pump strong enough to get the gas in.

I don't mind sharing my assessments of the requirements once I’ve done some calculations.

Comments on your post:

"Most of the problems can be solved by using a marine species and sitting the pond at least 10 km from the ocean.  Then the contaminates that fall in the pond will be freshwater adapted and will be killed by the culture medium.  Even reeds may have trouble with a marine culture medium flowing at 30 cm / sec."

- Using a saline loving algae inland is one idea that I can agree with you might solve the problem of species invasion. However, I think we shouldn't underestimate nature in spreading life. Even 10km might be too close?

Thanks for your post, it was an interesting read.

Correction:

I implied that no one suggests building ponds larger than 10 acres (Sjorske said that should be 10 ha).

Tonight I find a photo of a 250 ha pond:

http://wwwscieng.murdoch.edu.au/centres/algae/BEAM-Net/BEAM-Appl4a.htm

Notice the upper left picture and its caption. 

It appears to be a pond that is not stirred.  I believe most species will require stirring.  So maybe I should have said, "No one suggests building stirred ponds larger than 10 ha".

This does suggest an interesting possibility.  If we can find a species that grows fast without stirring, we can greatly lower our capital and operating cost.  The species in the picture is Dunalriella salina .  GreenFuels was using two Dunaliellia species.  So this may be a possiblity. 

Sjorske,

Thanks for the references.  I was able to find the source for Pulz (Appl Microbiol Biotechnol) and of course the Pichmonds book, but I have been unable to find a more complete reference to Borowitzka.  Do you remember the source?

Snori,

I believe we had a semantic problem.  When you said 400 ha, I asumed you were talking about a single pond.  It has occured to me that you may have been talking about the total farm, made up of a few or many ponds.  So using 100 ha as a peg for the discussion is fine.  To supply even a small portion of national needs will require many more ponds or PBRs or whatever.

Greenhouses use propane burners to generate CO2 - helps their veggies grow.  That might be a good source for your pilot plant flue gas generator.  The tire tubes sound like a good idea for stabilizing flow.  You may find that you only need the supplemental CO2 to start one hour after sunrise and can curtail it one hour before sunset.  The early and late hours don't get many photons into your PBR. 

Pumping the CO2 will be a problem to design.  Another possibility - The PBR doesn't have to be under positive pressure.  What about building a solar chimney (paint it black)?  Then you can let the sun power your draft to move the CO2 from the flue gas generator into your PBR and move the unused flue gas and O2 out.  It will be more difficult to seal the PBR against negative pressures than positive, but the savings in buying pumps and supplying power to them may be worth it.  The inner tubes would no longer work.  If you need a buffer, you might try using tubeless tires and wheels from the wrecking yard.  If they will hold a slight vacumn, you might have a low cost buffer.

You are right to assume nature will try to add life to a pond.  We need to get some more details from Navid.  I was assuming that his research was done in Perth and that his lab would be close to the ocean. 

Slippery,

Your slogan was very appropiate for your last post.

I have seen nothing documenting it, but, from the photos, I believe Navid's ponds to be 1 meter square.  I feel we need to, as your slogan says, step up in small steps to 5 acre (2 ha) ponds.  After we get the 1 meter ponds working, maybe we step up to 4' by 16' (1 M by 4 M).

 (Note that I am rather loose about the size conversions - I don't feel there are any magic sizes, so make the ponds whatever is convinient for you.  It looks like Earthrise has standardized on lanes about 10 times as long as they are wide, so the pond is 5 times as long as wide - sounds like a good rule of thumb.)

This has drifted off the original topic - maybe PBR builders need to start with about a 150000 cc or 150 liter model and then step up to about 4 times as big in each new version.  Does that sound reasonable as a rule of thumb?