Floating floc - Discussion at the Waterandwastewater Help Forum

Question

We are using a new parts washer detergent (mainly Sodium hydroxide, tkpp, soda ash), and have started to have floating flocs.
Some white residue got past the sedimentation tanks, sand filters, 1 micron cartridges, and finaly clogged the RO membranes.

After cleaning the membranes we removed a white solution, that when floculent was aded produced white strings.

Any ideas what this could be?
Is there a chemical that can de-emulsify the oil from the detergent?

Answer

as you said, you have an alkaline cleaner without or with low content of surfactant. Probably part of the oil/grease (mineral oil?) is saponified and precipitated as unsoluble soaps by water hardness? Soaps will be also precipitated by cationic flocculants.

By neutralization or shifting the pH to slightly acidic conditions the emulsions should be demulsified.

Reply
It changed everything!

I reduced the PH to 7. The foam disapeared and small oil particles started to float, however flocculation ceased, I played arround with the qty of floc/coag.and could not fix this situaton.

I returned PH to 9 and continued to produce white floating flocs.

Answer
as your contamination is oil removal by flotation or an oil/water separator is much more efficient than sedimentation. Sedimenting flocs can only be achieved by heavy ballasting, maybe using bentonites or a high dosage of precipitated iron salts.

The situation with demulsification and flocculation is the following.

The emulsion droplets are stabilized by negativ surface charges at high pH. Adding cationic polyelectrolytes or iron/aluminum ions flocculation or coagulation is achieved.
At neutral pH emulsion droplets are destabilized and coalescence, but will not interact with cationic additives. (Question - is the coalescence efficient enough to remove the oil by an oil-water separator or oil skimmer?).
If destabilization is not efficient enough you might either readjust the pH to alkaline and add a low amount of cationic flocculant to enhance separation or adjust the pH to slightly acidic and add an anionic flocculant (low amount). In both cases the oil droplets will float.