Dosing CO2 for phyto production?

[MarkS]

I'm currently building a 10' x 10' green house and the majority of it will be to grow phyto. I believe I've read that most commercial growers inject CO2 instead of air to get denser growth, but how do you counteract the pH drop?

Any thoughts or advice?

TIA,
Mark

 

[MarkS]

Anyone at all?

 

[simonh]

I used to grow Nannochloropis with CO2 injection. IIRC I had the pH controller set around 7.0 - 7.5 without any problems for that species. Density increased much quicker leading to shorter harversting times.

Without CO2 you will find the pH rises due to photosynthesis (dependent on amount of CO2 you are able to supply in the air injected). When you inject CO2 it is been used for photosynthesis so doesn't cause the pH keep dropping once you have it matched up to the consumption by the algae.

 

[MarkS]

Thanks for the info.

One point I'm trying to figure out is how to control CO2 buildup in the green house. I have a 1600 CFM exhaust fan in a 800 cubic foot green house, but it's temperature controlled. Is there any device that monitors atmospheric CO2 levels and will turn on an exhaust fan when the levels get above a certain set point?

 

[MarkS]

Can someone move this to the marine plants forum. I completely forgot it was there.

 

[kmk2307]

Simon,
What kind of container / setup did you grow your phyto on?

Mark,
If you are growing phytoplankton in your greenhouse wouldn't your plants like the CO2? I don't think the excess CO2 that gets past your phytoplankton will be able to accumulate if plants are around.

Kevin

 

[MarkS]

Actually, the green house is being built for propagation purposes. There wont be any other plants unless I choose to grow mangroves in the future.

 

[MarkS]

OK, any ideas? I really don't like the idea of relying on a temperature controlled fan to remove the CO2. I imagine the levels will build up quite fast.

 

[kmk2307]

Hey Mark,

I really don't think that much CO2 will get past the phytoplankton. If you have the room in your greenhouse, I think a couple live plants would be a nice addition and would certainly use available CO2 for photosynthesis. How often do you think the fan that will control the temperature of the greenhouse come on? How long do you think it will stay on / how much air do you think it will circulate while it is on? I don't think you need to worry about the CO2 levels being dangerously high. Hypercapnia or extremely high concentration of CO2 in the blood doesn't seem to take place in humans until CO2 is more than 40 times the normal atmospheric concentration. I think CO2 is heavier than air so if the air in the room is very still when the ventilation fans aren't on it might be a good idea to have a fan circulating air in the greenhouse. I did a quick websearch and most CO2 meters that I saw were around $500.

Kevin

 

[MarkS]

Thanks for the info. I am going to set the thermostat at 75Ã"šÃ‚º. I don't know for sure how long the fan will stay on or how often it will come on, but with south Texas temps, I'm certain that it will stay on most of the day. As I've stated, it's a 1600 CFM fan in a 800 cubic foot green house, so I am looking at a 100% air exchange every 30 seconds.

My concern about the CO2 buildup stems from the fact that large bubbles are dosed. I'm not sure how much of that CO2 will be used before it reaches the surface of the container. I would imagine that most of the CO2 will excape. Not sure how this works though? Since the bubbles do not disperse, is the CO2 in them being replaced with O2 due to photosynthsis?

 

[kmk2307]

Mark, I don't think you want to have large bubbles. I believe the aim in CO2 dosing when culturing phytolankton is to have very small, fine bubbles. Do you have any pcitures of your culturing set up?

Kevin

 

[MarkS]

Mark, I don't think you want to have large bubbles. I believe the aim in CO2 dosing when culturing phytolankton is to have very small, fine bubbles.

I was under the impression that fine bubbles were a bad thing. Everything I've read about plankton production stated that you want bubbles big enough so that it does not create a foam. Small bubbles are supposed to trap the plankton. However, I may be confusing Rotifer and brine shrimp production with phyto.

Do you have any pcitures of your culturing set up?

No, I'm still working on that. Part of the reason for me posting here is to clear up some points. Once I'm satisfied that I fully understand all points, I'll start building the set up. I understand the majority of what is necessary, but there just seems to be some sticking points.

 

[rsman]

small fine bubbles only when the algae is in the light, or just before it goes into the light, small bubbles will become traped in most cultured zooplankton (rotifer/brine ...) this isnt a problem for algae you want the small bubbles so that they do not race up to the top and pop, if they do you are just wasting your co2. if you have a recirculation pump or 4 in your phyto dose the co2 into the input of the pump, use a bubble counter though so you can visually monitor the feed rate.

you wont have any extra co2 unless you have the airstone too high in your container or the cp2 flow up to high.

you welcome the ph drop otherwise it goes way high.

 

[rsman]

uugh forgot to add, if you create a closed loop with a long fall and rise, pump into the loop from inside the tank, and add co2 to the bottom of the input you will get good results also but do use clear tubing for the input side of the loop.

 

[MarkS]

What I am planning to do is create a PVC manifold that will hang from the roof of the green house. A CO2 tank with a solenoid will be connected to this manifold and each of the culture tanks will be connected to the mainfod and get the CO2 through CO2 safe airline. I plan on putting miniture ball valves between the manifold and the culture tanks to control CO2 dosing. It would look something like this, but longer and with more outlets.

 

[rsman]

how many gallons of phyto do you plan on growing??
how high a demand do you have ???
batch or continous??

seems way overkill for batch, so guessing continous and guessing lotsa algae with a high demand like maybee 50 gallons total with 25% collection per day or higher??