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measuring CO2 absorption
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emarden
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- Project Question: I want to see if algae is a phytoremediator of pesticides. I was thinking of atrazine, but the only way to measure if the algae helps remove atrazine from water is using test strips (I do not have lab equipment to run a sophisticated test using magnetic particles and a photometer). I'm not sure the test strips are sensitive enough or if there is another pesticide that might be easier to work with. Also, how much 4% atrazine solution I need to put in 100 ml water to get to 4 or 5 ppb. .
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measuring CO2 absorption
I want to find a way to measure the amount of CO2 taken up by a form of algae. Is it best to measure the amount of O2 produced in the water? The alternative would be to have a closed system and somehow measure CO2 decrease or O2 increase in the air in the flask; however, i'm not sure what device would be useful to do such a measurement. Any thoughts are welcome.
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SciB
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Re: measuring CO2 absorption
Hi,
I understand what you are trying to do and this is a challenging project. It can be done using electronic sensors for CO2 and O2, but unless you have already have these devices they are quite expensive to purchase. The simpler method is to measure a change in pressure of the gas in a closed system as you said.
Algae will use CO2 and sunlight to make carbohydrates by photosynthesis, but they also produce O2. Measuring one gas in the presence of the other is difficult. Metabolic processes like photosynthesis operate according to chemical rules called stoichiometry. That just means that for every molecule of CO2 absorbed, a certain number of molecules of O2 are produced.
I did a search to see if I could find how much O2 is produced for a given amount of CO2 and this source says that 6CO2 molecules used by a plant in photosynthesis will yield 6O2 molecules: http://tomatosphere.org/teachers/guide/ ... -and-light
I don’t know if that is correct and you should check other references to make sure. What I am getting at is that if you know the relative proportions of CO2 used to O2 produced then you can measure the total change in gas volume over a specific period and calculate what part is O2 and what part is CO2. Does this make sense?
I think the way you could do this would be to purge the algae container with CO2 from dry ice (some grocery stores sell it) then seal the top with an airtight stopper that has clear tubing connected to it. The other end of the tubing would be connected to a device called a manometer: http://classroom.synonym.com/manometer-2718.html https://www.youtube.com/watch?v=9SQ2FPHCZJk
As the pressure changed in the algae chamber you could read it from the manometer. You would want to do the pressure readings during daylight or if you have the algae under artificial lights, while the lights are on because plants utilize O2 by respiration during the dark.
There is one potential problem I see with this method and that is that CO2 dissolves in water to a certain amount and when it does so it forms carbonic acid that lowers the pH. If the pH of the algae solution drops below 4, it will retard photosynthesis and eventually kill them. If you can get some pH paper you can do some experiments to see how much CO2 you can introduce into the algae chamber without lowering the pH to a harmful level. The reason you want to increase the CO2 level is to increase the rate of photosynthesis and the O2 production.
I hope this is what you had in mind and that it answers your question. If you have a dissolved oxygen meter you might be able to measure O2 formation with that, but I did not think water could dissolve much O2 and wouldn’t the water already be saturated from O2 in the air?
If you have more questions, let us know.
Good luck,
Sybee
I understand what you are trying to do and this is a challenging project. It can be done using electronic sensors for CO2 and O2, but unless you have already have these devices they are quite expensive to purchase. The simpler method is to measure a change in pressure of the gas in a closed system as you said.
Algae will use CO2 and sunlight to make carbohydrates by photosynthesis, but they also produce O2. Measuring one gas in the presence of the other is difficult. Metabolic processes like photosynthesis operate according to chemical rules called stoichiometry. That just means that for every molecule of CO2 absorbed, a certain number of molecules of O2 are produced.
I did a search to see if I could find how much O2 is produced for a given amount of CO2 and this source says that 6CO2 molecules used by a plant in photosynthesis will yield 6O2 molecules: http://tomatosphere.org/teachers/guide/ ... -and-light
I don’t know if that is correct and you should check other references to make sure. What I am getting at is that if you know the relative proportions of CO2 used to O2 produced then you can measure the total change in gas volume over a specific period and calculate what part is O2 and what part is CO2. Does this make sense?
I think the way you could do this would be to purge the algae container with CO2 from dry ice (some grocery stores sell it) then seal the top with an airtight stopper that has clear tubing connected to it. The other end of the tubing would be connected to a device called a manometer: http://classroom.synonym.com/manometer-2718.html https://www.youtube.com/watch?v=9SQ2FPHCZJk
As the pressure changed in the algae chamber you could read it from the manometer. You would want to do the pressure readings during daylight or if you have the algae under artificial lights, while the lights are on because plants utilize O2 by respiration during the dark.
There is one potential problem I see with this method and that is that CO2 dissolves in water to a certain amount and when it does so it forms carbonic acid that lowers the pH. If the pH of the algae solution drops below 4, it will retard photosynthesis and eventually kill them. If you can get some pH paper you can do some experiments to see how much CO2 you can introduce into the algae chamber without lowering the pH to a harmful level. The reason you want to increase the CO2 level is to increase the rate of photosynthesis and the O2 production.
I hope this is what you had in mind and that it answers your question. If you have a dissolved oxygen meter you might be able to measure O2 formation with that, but I did not think water could dissolve much O2 and wouldn’t the water already be saturated from O2 in the air?
If you have more questions, let us know.
Good luck,
Sybee