I have a bioreactor for algae cultivation, and I sparge CO2 into the bioreactor, when I increase the CO2 flow, the pH value decrease. I record the pH, and want to use the pH to calculate the dissvoled CO2, but I tried lots of different equations, give me a reverse result, as below:
Method 1: I use the equation from this attached book chapter, file:///C:/Users/wangz/Downloads/ColeandPrairieCO2InlandWaters.pdf
According to it when pH increase Alkalinity (ANC) increase as well,
And [ANC]= [DIC]* (Ka1[H+]+2Ka1*Ka2)/([H+]2+Ka1 *[H+]+Ka1*Ka2)+Kw/[H+]-[H+]
[CO2]=[DIC]*[H+]2/(Ka1*Ka2+Ka1*[H+]+[H+]2)
so from the equation, when pH increase, ANC increase, DIC increase, dissovled CO2 increase?
But should dissovled CO2 increase, pH decrease???????
However, according to this equation, when pH=8 can have a 10 times higher dissovled CO2 than the situation when pH=7.
I also tried many other equations found in those papers, but the calculation results also is pH increase, dissovle CO2 increase? I'm confused.
Method 2:
http://www-naweb.iaea.org/napc/ih/documents/global_cycle/vol%20I/cht_i_09.pdf
http://www-users.med.cornell.edu/~spon/picu/calc/basecalc.htm
Ct=([H+]/K1+1+K2/[H+])[HCO3-]
based on the Henderson-Hasselbalch equation:
HCO3 = 0.03 * pCO2 * 10 (pH - 6.1)
This is also pH increase, Ct increase!!!
Method 3:
Article Growth CO2 Consumption, and H2 Production of Anabaena Variab...
Ctot=10-1.5 xCO2+ (10-7.8/10-pH)xCO2+(10-28.1/10-2pH)xCO2
This equation also has the same issue, when pH increase, Ctot increases.
Could anyone help me is there anything wrong I did? Why I want to use the pH to calculated the dissovle the CO2, when pH increase the dissolved CO2 also increase? Why?????
I think you have all the formulas you need. It is just to use them in the right order.
In your reactor pH is determined by alkalinity and PCO2. The alkalinity, or acid neutralise capacity (ANC), is in your system approximately: ANC ≈ [HCO3-] + 2[CO32-]. If pH is below 7.5 it simplifies to ANC ≈ [HCO3-].
If you determine the alkalinity from one point there you know PCO2 and measure the pH you can calculate PCO2 at any other pH.
Another approach is to calcualte the alkalinity of the media from the receipy adding the carbonate and other basic components up.
CO2 is an acid gas. When dissolved in solution, pH will normally decrease. Therefore; applying Lechatelier principle; higher pH will dissolve more CO2. This is my simple understanding. I hope it is correct .
- Badges
- Science topic