Tim,
This stuff gets complicated and confusing so no worries. We all make mistakes or come to incorrect conclusions at times. When I first got into pool water chemistry around 7 years ago, I initially used the molecular weight of hypochlorous acid (HOCl, 52.46 g/mole) for ppm FC & CC units and it took a year before I learned that the actual units used the molecular weight of chlorine gas (Cl
2, 70.91 g/mole).
TimS said:
So the problem is that the surfactants (hey, I spelled it right this time :-D) bind with the coagulants thus leaving fewer coagulants available to bind with bacteria and other gunk?
Yes, that is correct, at least when the surfactants are anionic (pool coagulants are almost always cationic). If the surfactants are cationic, then there probably isn't a problem.
TimS said:
Assuming that a pool doesn't have any coagulants in it, (as it normally wouldn't, right?) then the surfactants don't bind with the coagulants (since they're not there,) but instead get captured by the filter media itself, thus leaving less surface area for the filter to collect other gunk, thus resulting in the same basic outcome, (reduced filtering performance.)
A pool normally doesn't have coagulants in it unless you intentionally added some, such as a clarifier or even PolyQuat, or accidentally added some, as with swimsuits that have been washed but not thoroughly rinsed. Let's look at PolyQuat specifically since it is a cationic surfactant. The molecular structure of Poly{oxyethylene (Dimethyliminio) Ethylene (Dimethyliminio) Ethylene Dichloride} has each unit of the polymer as follows:
Code:
| |
-C- -C-
| | |+| | |+| |
-O-C-C-N-C-C-N-C-C-
| | | | | | | |
-C- -C-
| |
with each Nitrogen having a net (+) charge with a chloride ion (Cl-) attached (when in solid form; when dissolved in water the polymer and the chloride separate).
so its molecular weight is 253.17 for each "poly" unit which has two nitrogen. Each unit is roughly 1 nm in length and there are roughly 16 units in a PolyQuat molecule so that's 16 nm length which is 0.016 microns. So clearly the surfactant molecule isn't going to get caught in an uncharged filter. Sand and cartridge filters are typically uncharged, but DE and other silica-based filter material has a net cationic charge at typical pool pH so will tend to repel the "raw" surfactant. When surfactants combine with anionic (negatively charged) substances including cells in the water, they will tend to form larger clumps and it is these clumps that get caught in the filter. In the case of PolyQuat itself, it kills algae by binding to cell surfaces and interfering with ion transport essentially starving the algae of nutrients.
Surfactants in detergents tend to be longer polymers around 10 to even 300 times as long as PolyQuat. It's still too small (0.02 to 5 microns) to get directly caught in a filter, but is much better at clarifying the water and in fact specialized pool clarifiers tend to be more like detergent surfactants in size. Those that are based on ammonium compounds, such as PolyQuat, tend to get broken up into pieces since chlorine attacks the nitrogen sites though these pieces are still somewhat effective algaecides. Eventually, they get oxidized or caught and removed from the filter (if attached in clumps to dead algae, for example) which is why one needs to add PolyQuat weekly to replenish.
So the answer to your question about surfactants clogging the filter is no, not unless there are things to clarify in your pool in which case you want it to get caught in the filter so you can backwash such material.
Richard
)
The other dissolved minerals in ocean water make it hard.
[wanders off to enroll in a chemistry class to understand what the heck everybody's saying.]