We have a commercial grade 35 litre CO2 cylinder without a flow meter. Now, we want to infuse CO2 from the cylinder into 4 litre of algal broth culture (chlorella sp.). We are planning to pass CO2 into our culture on a daily basis. Can anyone suggest the duration for which we should pass CO2 into our algal culture of 4 litres volume each day?.
Should be 3% CO2 Volume/volume for optimal growth. you can only estimate time and concentration of CO2 without flow meter.
I agree 3% CO2 volume is a good number and probably will improve growth but it may not be the optimum. Actually I believe that the optimum growth rate for CO2 should be tested at different CO2 concentrations since rate varies by species and probable by strain. For example, many microalge species have been tested at CO2 concentrations of over 15% v/v. For example, Chlorococcum littorale was found to be able to grow at 60% CO2 (Kodama et al., 1994). Another high CO2 species is Euglena gracilis. Growth of Euglena gracilis was enhanced under 5-45 % concentration of CO2, although the best growth was observed with 5% CO2. Maeda et al (1995) found a strain of Chlorella sp. T-1 which could grow under 100% CO2, nevertheless the maximum growth rate was found under 10%.
If you have no way of metering it in, perhaps you should measure the pH. Depending on the media and salinity, the CO2 will push the pH down as you add it. So, the most you could add in a single shot would be that amount that lowers the culture pH within a tolerable range. Then let the CO2 be consumed and the pH will increase. If you have a pH buffer in the medium, you will only see the pH change when the buffer is saturated. And remember that if N or P is limiting, the cells wont use as much CO2 so the ratios are important. Most people add enough ingredients to get the biomass they want and don't do much to optimize production.
The 2-3% CO2 volume is a good level and may take a good growth and could be a optimum concentration.
Different concentrations of NaOH needs to be added to the growth medium, followed by gaseous CO2 directly from cylinders (99.9% CO2 gas) until the
pH came down to pH 6.0±0.1. Thus,incorporation of hydroxide could be the solution to the problem of low CO2 uptake in suspension cultures .
If you have the expertise, setting up a pH-stat is the most CO2-efficient approach for Chlorella growth. Bubble in standard air at ~0.2 VVM (volume air/volume culture/min) and set the pH-stat to trigger a solenoid valve at ~pH 7.8-8.0 to mix in 0.5-2% final [CO2] using your CO2 cylinder. Set the solenoid to close at ~pH 7.4. You can estimate the CO2 consumption by recording the time the valve is open and knowing the pure CO2 flow rate.
Organisms like Chlorella that take up bicarbonate will produce one mole of hydroxide per bicarbonate ion via the carbonic anhydrase-catalyzed dehydration reaction as follows: HCO3 -> CO2 + OH-. CO2 (not bicarbonate) is the substrate for RuBisco; the hydroxide ion is excreted to the medium so the pH will drift upwards. Adding carbon dioxide brings it back down due via these simple reactions: CO2 + H20 -> H2CO3 -> HCO3- + H+
You do NOT need to add NaOH.
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