The change of colors is likely due to a change in pigment composition of your algae that may reflect a change in physiological state (moving from exponential to stationnary growth phase). Many parameters may have induced that change.

Your culture may be sensitive to mechanical agitation due to bubles if your tube goes into the media ? Do the gaz come straight in the media, if so try to decrease the gas flux and agitation ?

You may also have bacterial contamination coming from your gas ?

Or from your initial culture (is it axenic)? You should check it under microscope for instance.

Hope it helps.

Marc Long

The change of colors is likely due to a change in pigment composition of your algae that may reflect a change in physiological state (moving from exponential to stationnary growth phase). Many parameters may have induced that change.

Your culture may be sensitive to mechanical agitation due to bubles if your tube goes into the media ? Do the gaz come straight in the media, if so try to decrease the gas flux and agitation ?

You may also have bacterial contamination coming from your gas ?

Or from your initial culture (is it axenic)? You should check it under microscope for instance.

Hope it helps.

Marc Long

Accumulation of pigments is common in micro algae, during stress/ adverse conditions micro algae accumulate different type of pigments ( yellow or red/pink). Euglena, Chlorella, Chalmydomonas and several other algal forms are good example for this phenomenon.

Do you get the same effect from pure CO2?

Dear Dr Paul thank you for your question, I have seen this phenomenon(change of the pigment) in local lakes and ponds. Then we collected the water samples for observation. In above experiment also may be co2 is responsible.

With regards

GMNRAO

Dear Mark Long,

Thanks for your thought.

We didn't see this effect when growing algae in BG11 bubbling with just air. Yes the culture is axenic. We did the microscopy for any contamination and there is few bacteria but not much which you can't avoid anyway.

Also we have been growing algae to 3 (OD680). Since our main objective is to mitigate the CO2 in flue gas therefore on direct injection of flue gas into the reactor, we observed the algae started losing the green color and a significant decrease in optical density (680nm). The flue gas is passed through prefilters. Since flue gas has also the NOx and SOx, literature says Algae can use the NOx as a nitrogen source. SOx is almost negligible in the flue gas we are using. The only thing left is then the Carbon monoxide (CO) which is around 600 ppm. May be CO is causing toxicity. We are using flue gas with CO2 around 10% which is really good for our strain when we did lab scale experiments as its a CO2 tolerant strain.

Some people suggest first reacting the CO2 with casutic soda and converting it into a sodium bicarbonate which the algae can easily take.

sudden changes in the growth condition always alters the growth and biochemical composition of algae due to the stress. is the species is really co2 tolerant. please double check and try to adapt the algae to the new treatment or condition. it always take some time for the adaptation process.

Dear GMNRAO

People stress algae to get some high valuable pigment but since our goal is to remove more CO2 therefore we would like to keep the algae in the exponential phase. What I fear is we didn't do much lab scale work about growing the algae in flue gas rather we used pure CO2 in the lab. Since flue gas has all other stuff there, may be it needs time to acclimatize to this newly hostile condition. Do you think we should we should do the strain optimization starting with a low conc. of flue gas and going higher and use that stain for the large scale production and mitigation?

Dear Paul,

We get a good healthy culture with pure CO2 as I said earlier we found this strain after a screening process for CO2 tolerance.

Dear Puganeswary

That is my fear too. May be we will have to start with a very low concentration of flue gas so that the algae get adapted to the newly environment.

yes. adaptation with flue gas would be better.

Did you observe any major shift in the pH of the culture while purging the PBR with flue gas? CO2 purging is known to acidify the culture which might be putting the alagl cells under stress.

As it disintegrates, its chlorophyll content decreases. Change in pigment in algae is very common.

Dear Neha,

The only once dropped to 7.2but mostly it was around 8.5 to 8.7. You are right CO2 acidifies the medium. But in our case it didn't drop significantly i mean below 7.

The fact is that the algae are stressed and are dying down, and possible causes have been highlighted above. However, I will like to emphasize the that the flue gas should have been introduced bit by bit in low concentrations to allow the organisms to acclimatize and balance out easily. Another concern should be the growth stage and life cycle of the algae. As they get older and towards the end of their life cycle they tend to respire more than they photosynthesize (decline in growth rate), plus the ''surprise'' introduction of the flue gas will slow down metabolic activities.

Dear Felix,

I strongly agreed with you. These were also my concern. Acclimatization of the algae to flue gas and the introduction time. We introduced the gas in late exponential phase. The flue gas introduced was chilled and mixed with ambient air with only 30% flue gas (around 4.5% CO2).