Citric Acid dosing as a carbon source?

[Randy Holmes-Farley]

I cannot find my copy of Chemical Oceanography (Millero) to find the most up to date values, but this reference cites two works showing the second pKa of phosphoric acid in seawater is 6.0 or 6.1:

Phosphate association with Na+, Ca2+ and Mg2+ in seawater

Association constants of orthophosphate ion with Na+, Ca2+, and Mg2+ were measured at μ = 0.68 and 20°C. The results were used to calculate phosphate …

www.sciencedirect.com

 

[Courtney Aldrich]

That would be the case, but in seawater the pKa shifts up. It is much easier to stabilize ions in seawater than in low ionic strength solutions. So all acid/base equilibria generally shift toward the higher charge form. I'll post the published pKa a bit later when I find it.

Thanks, this makes a lot of sense now. The pKa of H2PO4- is nearly same as bicarbonate in seawater, so now I see why phosphate can contribute to alkalinity. For those following the post, Randy has shown that production of polyphosphate will not increase alkalinity as I had suggested/misinterpreted from the posted paper.

It does appear that citric is a viable carbon source and may have the potential to help consume phosphate if there are polyphosphate-accumulating bacteria available, but it will not increase alkalinity.

Also thanks to arking_mark for the initial post that stimulated this constructive discussion.

 

[Randy Holmes-Farley]

One way that phosphate removal will contribute to an alk decline is precipitation of calcium phosphate, since the removal is PO4---, but the forms left in solution are in various protonated states,

 

[DrEggroll]

Reading this makes me want to dust off my high-school chemistry books and really get into the subject.

I’m hoping they are chemists in their day job. Took me back to first year med school. I also have no use for this really in practice so it pained me to try to turn some gears

 

[Randy Holmes-Farley]

I’m hoping they are chemists in their day job.

We are.