Water and Wastewater.com Help Forum - Why foaming always comes along with rise of pH?

Water and Wastewater.com Help Forum - Why foaming always comes along with rise of pH?

Question
My SBR always have foaming along with a rise of pH within one cycle. I am wondering what substances responsible for this foaming and comes from the rise fo pH?

Answer
often foaming ability is related to pH values above neutral. This is the case for surface active materials like fatty acids and proteins. Alkalinity causes ionization of these substances.

your SBR-mix may contain fatty acids, proteins, biopolymers, biosurfactants and protein hydrolysates. Most of these contain anionic groups, mostly carboxyl groups. The latter are only ionized under alkaline conditions. Besides, the alkaline conditions will favor hydrolysis of biomaterials, this way increasing the concentration of foaming substances. This is related to the comment of judo.
So in summary, yes, under alkaline conditions the carboxyl groups will transform to carboxylate ions. In addition the alkalinity will cause hydrolysis.
What Grrun meant was foaming in hard water is often reduced compared to soft water. The reason behind this is that water "hardness" means the content of Calcium and Magnesium ions. These precipitate fatty acids, but also other anionic surfactants like sulfates and sulfonates. When shifting the pH of hard water to alkaline, hydrogencarbonates with limited solubility are transformed into carbonates with very low solubility thereby precipitating Magnesium and Calcium ions, softening the water. However, in presence of carboxylate ions this will precipitate the foaming substances. So this effect should not be the cause of foaming to occur.
To a more thorough description of the foaming one should also mention that foam stability is the highest at a distinct ratio of dissociated and undissociated carboxyl groups, with foam generation and stability will be influenced differently by this balance.

write comment - Why foaming always comes along with rise of pH?

comment by judo
Fatty acids and (soluble) proteins should be good substrates for bacteria. If there are these compounds remaining in the aeration tank enough to cause foaming, you would be in very serious trouble, far worse than just foaming.

What I meant to say on the earlier reply is foaming phenomenon at high pH is quite normal reaction for activated sludge process. I mean, just keep the pH neutral.


As a part of unknown foaming mechanisms, comformation change of biopolymers such as extracellular polysaccharides and glycoproteins due to pH change might be partly responsible for change in foaming property.

You should also remember that high pH has inhibitory effect on aerobic bacteria because proton-based active transport including oxidative phosphorylation gets difficult at basic environment. Many bacterial species are known to overcome this difficulty though, for example using sodium motive force. Those which do not have this ability have to "die" eventually.