Phosphate removal

[amin36]

During studying
"Guidelines for Safe Recreational-water Environments Final Draft for Consultation
Vol. 2: Swimming Pools, Spas and Similar Recreational-water Environments" from W.H.O website i read highlighted text below:


7) Algicides
Algicides are used to control algal growths, especially in outdoor pools. Algal growth is possible
only if the nutrients phosphate, nitrogen and potassium are present in the pool water. Phosphate
can be removed from the pool water by an optimal flocculation and filtration step during water
treatment. Consequently, such growths are best controlled by ensuring effective
flocculation/filtration, disinfection and good hydraulic design. In such properly managed pools,
the use of algicidal chemicals for the control of algae is not necessary (Gansloser et al., 1999). If
problems persist, however, then proprietary algicides can be used. Quaternary ammonium and
polyoximino compounds and copper salts can be used, but any based on mercury — a toxic and
cumulative heavy metal — should not be added to swimming pools (PWTAG, 1999). All should
be used in strict accordance with the suppliers’ instructions and should be intended for
swimming pool use.

Here is the link:

https://www.who.int/water_sanitation_health/bathing/recreaII-ch5.pdf?ua=1

My question is that we discussed phosphate removal and for this purpose you said the solution for getting rid of phosphate is using phosphate remover but W.H.O is suggesting flocculation and filtration . can flocculation help it?

Thanks

 

[setsailsoon]

Amin,

Phosphates are water soluble so I don't see how they would be removed by flocculation which removes very fine particulates unless the WHO terminology categorizes lanthanum chloride as a flocculent. Let's see if one of our experts can help @JoyfulNoise.

Chris

PS Phosphates aren't something we worry about since proper FC/CYA disinfects even if phosphates are present. Use of phosphate remover usually causes more harm than good since the lanthanum chloride - phosphate precipitate clogs filters and potentially swg cells.

 

[ajw22]

Lanthanum chloride reacts with the free, dissolved phosphate compounds to form a salt (precipitate) of Lanthanum and phosphate (lanthanum phosphate) which is not soluble in water. The precipitate can then be filtered out.

Why that writer thinks floc may need to be used to capture the precipitate is not stated. But if you don’t have an effective filtration system then floc to have it settle to the bottom of a pool and vacuum out may be an alternative.

There is a lot not stated and assumed.

 

[JoyfulNoise]

I don't want to get into the detailed chemistry of it (mainly because I don't have the time to write out a lengthy post), but the traditional chemicals used for flocculation (ferric compounds, aluminum chloride and sulfates, etc) will react with and remove phosphates. Flocculation can also remove dissolved metal contaminants to a certain extent. Lanthanum chloride is simply a more efficient, but much more expensive, way of removing phosphates and lanthanum chloride is considered a flocculation chemical. Drinking water and waste water treatment facilities will almost always use traditional flocs to remove suspended solids and lower phosphate levels. Flocs used in a swimming pool require vacuuming the settled solids to waste (removal of water) which, for some pool plumbing setups, is not possible. Flocs vacuumed into the filtration system will cause clogging and, as the floc breaks down over time, it will re-release the particulates into the water.

 

[setsailsoon]

Thanks Matt!