Peracetic acid as supplemental sanitiser/disinfectant for pool?

[fresh]

Hi folks,

I know everyone here says to 'just use chlorine', when it comes to sanitisers, but nonetheless, I wonder if anyone can weigh in on this.

Peracetic acid (PAA) - made from mixing concentrated hydrogen peroxide (h2o2) with acetic acid (vinegar), and using an acid catalyst to kickstart the reaction - is apparently a strong chlorine alternative for municipal water treatment. (Seems to be raved about in that industry.)

I wonder of its usefulness for pools?

It seems to be stronger than chlorine as a disinfectant in many cases, it can be used as a steriliser (unlike chlorine), and it doesn't form disinfection byproducts (DPBs) like chlorine can (at least if chlorine's not done properly).

AFAIK, PAA doesn't last very long - when added to regular water it breaks down in under an hour, or even in mere minutes. It does seem to leave residual h2o2 (and also PAA is always sold in solutions which have a certain degree of h2o2 in it alongside the PAA), but I know that h2o2 is more of an oxidiser rather than a good sanitiser (microbe killer), and h2o2 can eat away at chlorine, so the h2o2 isn't a benefit in most cases.

But could a PAA 'zap' of a pool - including swishing water around with the pool broom to make it react with the whole pool depth rather than just the top - help reduce chlorine usage overall, if it means less surviving microbes are needing to be handled by the chlorine?

(I like how borates can lessen the amount of chlorine needed by stabilising pH and also by acting as a mild algaestat. Could PAA similarly increase chlorine's effectiveness, because of how strong it is?)

As for algae, I have concerns / am confused. I see scientific discourse that seems to suggest that PAA can actually serve as useful fuel to help algae grow, not kill it. If true, it'd only be advisable when pool is already crystal clear and no nascent, cloudy / mature algae present. Perhaps dosage matters - higher PAA concentration harms algae and lower helps it.

About residuality, I'm confused as to why PAA is so useful in pre-treating city water, if it barely lasts for long in the water - is it a quick but extremely effective 'zap', as I'm suspecting? And does the residual acetic acid (the other byproduct) break down later in the stream? (If not, it would taste and smell a bit vinegary right?)

Lastly I wonder if PAA has usefulness for 'spot cleaning' or helping to rid biofilm from plumbing lines. I know chlorine shocking can do everything, but it's interesting to think of alternatives out there. Doing a supershock for days on end because of a small area seems exhausting and maybe not always the most economical choice.

What I do know is that peracetic acid is hazardous stuff to handle. PPE is needed (gloves, eye protection, clothes) - don't breathe in, preferably decanter it outside, don't spill on skin, and don't get in eyes.

Any benefits to it?

Thanks,

fresh

P.S. How's this for diving into the deep end?

 

[Bperry]

Hi folks,

I know everyone here says to 'just use chlorine', when it comes to sanitisers, but nonetheless, I wonder if anyone can weigh in on this.

Peracetic acid (PAA) - made from mixing concentrated hydrogen peroxide (h2o2) with acetic acid (vinegar), and using an acid catalyst to kickstart the reaction - is apparently a strong chlorine alternative for municipal water treatment. (Seems to be raved about in that industry.)

I wonder of its usefulness for pools?

It seems to be stronger than chlorine as a disinfectant in many cases, it can be used as a steriliser (unlike chlorine), and it doesn't form disinfection byproducts (DPBs) like chlorine can (at least if chlorine's not done properly).

AFAIK, PAA doesn't last very long - when added to regular water it breaks down in under an hour, or even in mere minutes. It does seem to leave residual h2o2 (and also PAA is always sold in solutions which have a certain degree of h2o2 in it alongside the PAA), but I know that h2o2 is more of an oxidiser rather than a good sanitiser (microbe killer), and h2o2 can eat away at chlorine, so the h2o2 isn't a benefit in most cases.

But could a PAA 'zap' of a pool - including swishing water around with the pool broom to make it react with the whole pool depth rather than just the top - help reduce chlorine usage overall, if it means less surviving microbes are needing to be handled by the chlorine?

(I like how borates can lessen the amount of chlorine needed by stabilising pH and also by acting as a mild algaestat. Could PAA similarly increase chlorine's effectiveness, because of how strong it is?)

As for algae, I have concerns / am confused. I see scientific discourse that seems to suggest that PAA can actually serve as useful fuel to help algae grow, not kill it. If true, it'd only be advisable when pool is already crystal clear and no nascent, cloudy / mature algae present. Perhaps dosage matters - higher PAA concentration harms algae and lower helps it.

About residuality, I'm confused as to why PAA is so useful in pre-treating city water, if it barely lasts for long in the water - is it a quick but extremely effective 'zap', as I'm suspecting? And does the residual acetic acid (the other byproduct) break down later in the stream? (If not, it would taste and smell a bit vinegary right?)

Lastly I wonder if PAA has usefulness for 'spot cleaning' or helping to rid biofilm from plumbing lines. I know chlorine shocking can do everything, but it's interesting to think of alternatives out there. Doing a supershock for days on end because of a small area seems exhausting and maybe not always the most economical choice.

What I do know is that peracetic acid is hazardous stuff to handle. PPE is needed (gloves, eye protection, clothes) - don't breathe in, preferably decanter it outside, don't spill on skin, and don't get in eyes.

Any benefits to it?

Thanks,

fresh

P.S. How's this for diving into the deep end?

Not a chemist, but sounds like similar issues as biguanide?

 

[ajw22]

What I do know is that peracetic acid is hazardous stuff to handle. PPE is needed (gloves, eye protection, clothes) - don't breathe in, preferably decanter it outside, don't spill on skin, and don't get in eyes.

I don't think you need to know more than that for why it is not a consumer product.

Any benefits to it?

Not with those cautions.

Chlorine is readily available, safe to handle, and inexpensive.

 

[JoyfulNoise]

It’s far too dangerous to use as a consumer product. Have you ever been around PAA? I have and it’s absolutely horrid smelling … like vinegar and acrid smoke only a thousand times more powerful. Only when it is used as a weak solution is it even bearable. In the lab, we could only open containers of it inside of a fume hood or else the vapors would be powerful enough to make a person gag. It’s just not a practical sanitizer and it’s much more of an oxidizer than a disinfectant. It will leave almost no residual sanitizer levels and it leaves acetate behind in solution which other halogen based sanitizers will convert into formaldehyde. Formaldehyde in water can make you very sick as it is a skin and respiratory absorption hazard.

Short answer - NO. Not worth it at all.

 

[fresh]

Thanks for weighing in - thought it strange to not see it discussed here yet, given its massive hype in the water treatment industry as a 'chlorine replacement' (or accompaniment).

But it sounds like it doesn't play well with chlorinated water - similar to h2o2 being chlorine incompatible (in that it cancels out with it - I know of this hilarious story).

@JoyfulNoise do you have a link or paper - I enjoy reading science - documenting how PAA does - or can 0 leave behind acetate? Is it only temporary (e.g. evaporates), so only a risk if enough chlorine is already in the water? I just checked and it seems formaldehyde itself also evaporates like chlorine does.

I know residuals are the whole point of good, whole-pool sanitation, so just wanting to know the chemistry. (I wonder about its usefulness for one-time treatments of white water moulds lurking in the pipes via a 10-min soak or closed-loop circulation like this idea, followed by letting any small amounts of acetate/formaldehyde residual evaporate from pool over 24h. Not sure if residual chlorine keeps formaldehyde trapped in the water. I know things can be complex.)

Also, I now suspect that the high amounts of acetic acid in PAA solutions are problematic in serving as food for algae and microbes in the pool. (I'm doing experimentation.) So for treating whole, large bodies of water like a pool, I currently think that PAA is not suitable, for that reason, even if chlorine isn't present in pool.

So indeed, I've handled PAA (in the manner I described - outside, some PPE and carefulness), so I agree it's not consumer friendly AT ALL. However, MA is also strong and not safe to breathe in/douse/splash on eyes. (As is high strength h2o2, like 50% solution, which I handle regularly.) I wonder if 32% Hcl is also bad idea to use indoors? How much worse is PAA than that?

Thanks for any further info.

 

[JoyfulNoise]

Doesn't really require scientific papers but since you asked, these two have all the data you need to see why it won't work well -

Xiu-wei Ao, Jussi Eloranta, Ching-Hua Huang, Domenico Santoro, Wen-jun Sun, Ze-dong Lu, Chen Li,
Peracetic acid-based advanced oxidation processes for decontamination and disinfection of water: A review,
Water Research, Volume 188, 2021, 116479, ISSN 0043-1354, Redirecting.
(https://www.sciencedirect.com/science/article/pii/S0043135420310149)

and

Xuebing Zhao, Ting Zhang, Yujie Zhou, Dehua Liu,
Preparation of peracetic acid from hydrogen peroxide: Part I: Kinetics for peracetic acid synthesis and hydrolysis,
Journal of Molecular Catalysis A: Chemical, Volume 271, Issues 1–2, 2007, Pages 246-252, ISSN 1381-1169, Redirecting.
(https://www.sciencedirect.com/science/article/pii/S1381116907001768)

The basic chemistry is pretty simple. PAA is created by a strong acid (sulfuric acid) catalyzed reaction of acetic acid with peroxide -

CH3COOH + H2O2 ←→ CH3COOOH + H2O
acetic acid + peroxide <---> PAA + water

The pKa for that reaction is approximately 8.2 and so the only way to drive the creation of PAA is to use a strong acid to drop the pH below that of acetic acid. The formation reaction for PAA is actually quite a bit more complicated as there are several intermediates but the above overall reaction tells you what you need to know - if you add PAA to pool water at typical pool water pH (7.2-8.0) then the PAA will be driven to dissociate back into acetic acid and peroxide. In fact, almost all of the PAA will get used up and this is exactly how and why PAA works so well - the formation of peroxide, and subsequent formation of hydroxyl radicals, creates a highly oxidizing and disinfecting solution. But it's not long lasting and within about an hour all of the peroxide will be gone. That leaves acetate behind because acetic acid is always in equilibrium with its conjugate base, acetate. And since the pKa of acetic acid/acetate is roughly 4.8, most of the remaining acetic acid will be acetate at pool water pH. Acetate isn't volatile, at least not at low concentrations, and so it will remain in the pool water. If one were to then add any kind of halogen based sanitizer, then halogenated oxidation by-products will be created. Not good stuff at all. Formaldehyde is simply one possible by-product (and it is not totally volatile either but will establish a very strong aqueous concentration as it has fairly high solubility in water).

Yes, PAA is used a lot in water treatment but there is a significant difference between a municipal water supplier attempting to create potable water for human consumption versus pool water. These things are not equal and so what might work in one context could be absolutely useless in the other context. Water treatment for potable water is a very complex process as you have to work hard at both treating the incoming source water stream to remove a lot of natural and man-made pollutants (both dissolved and suspended) without creating chemical by-products that are harmful. Then you have to also treat the out-going water supply so that it can be disinfected once it leaves the treatment plant and remains potable all through out the distribution network. These requirements necessitate very different filtration and disinfection processes. But, just because a process is used at some point along the treatment path doesn't mean one can take it out of context and use it in a completely different scenario. For example, water treatment often uses lots of coagulation and flocculation techniques to reduce suspended solid loads and they are very effective at doing that .... however, coagulation and flocculation is almost never needed for pool water and, in fact, can cause enormous problems with pool filter equipment when it is generally applied under the wrong circumstances.

 

[JamesW]

I think that it is mainly wastewater being treated vs. people's tap water.

How peracetic acid is changing wastewater treatment

How peracetic acid is changing wastewater treatment

cen.acs.org

 

[JoyfulNoise]

I think that it is mainly wastewater being treated vs. people's tap water.

How peracetic acid is changing wastewater treatment

How peracetic acid is changing wastewater treatment

cen.acs.org

There was a program by the City of Tucson water supplier to create potable water from runoff and waste water supplies. The created a pilot process at one of their facilities to demonstrate the feasibility and they marketed it to the public giving it the tag line - “From the toilet to the Tap!!” - and they wondered why it failed spectacularly with the public

 

[JamesW]

Sulfuric acid and hydrogen peroxide can create Piranha Solution.

The traditional piranha solution is a 3:1 mixture of sulfuric acid and 30% hydrogen peroxide.

Molecular models of the different molecules active in Piranha solution: peroxysulfuric acid (H2SO5) and hydrogen peroxide (H2O2).

 

[JamesW]

 

[JamesW]

Applications For PAA​

At present, the two most common applications for PAA are in healthcare and food sanitation, due to its ability to break down into predominantly neutral components (oxygen and water).

That being said, PAA has been finding increased usage in industrial wastewater treatment applications. Manufacturers that produce organic waste, such as food processors and breweries, are increasingly applying PAA as a pretreatment before further treating and discharging effluent.

A number of studies have also been conducted regarding the effectiveness of PAA in municipal wastewater treatment to reduce biofouling. So far, it is finding adoption among municipalities with high levels of industrial waste for which UV treatment has been ineffective. It is also popular in areas that are struggling to meet state or federal maximums for chlorine-derived DBPs.

In addition, PAA is beginning to make inroads in drinking water treatment. Its main use is to treat influents to remove bacteria and oxidize other microorganic matter. Used in this manner, it is not a substitute for chlorine, but rather a way of mitigating total organic matter that can react with chlorine to form DBPs downstream.

What You Need To Know About Peracetic Acid (PAA) For Water Treatment - Blue-White Industries

Peracetic Acid has a unique chemistry that is highly effective against bacteria and other contaminants. It does not form any known DBPs and has a less environmental impact. Before substituting chlorine with PAA, it is critical to understand the chemistry, its applications, and methods of...

www.blue-white.com

 

[JamesW]

Peracetic acid (PAA) has gained momentum in the United States as a primary wastewater disinfection technology and alternative to chlorine.

PAA has low residual toxicity, does not form harmful DBPs and has minimal impact on the environment.
While the lack of a stable residual reduces its environmental impact post wastewater treatment, this characteristic decreases its values as a terminal drinking water disinfection technology – PAA residual at the point of use would be impractical to maintain.

However, PAA may potentially be used in a disinfection treatment train approach as an early stage disinfection chemistry coupled with other methods such as membrane filtration, ozone and UV.

In this scenario, PAA may provide “log reduction” credits to an overall multi-barrier disinfection scheme.

This strong oxidizing potential indicates that PAA can oxidize a variety of organic species.

Thus, PAA may be utilized as a “pre-disinfection” agent in drinking water applications to reduce the amount of oxidizable organics in the raw water prior to final chlorination.

Therefore, PAA can be used to reduce the formation of trihalomethanes and haloacetic acids after chlorine disinfection of drinking water by reducing the level of precursors through oxidation.

https://active-oxygens.evonik.com/en/attachment/154105?rev=5f278a9f4488984d25efcddde8b78728

 

[JamesW]

"Unlike chlorine, PAA does not result in a consistent residual and therefore is only suitable for pre-oxidation, not as a final disinfectant".

Hazen and Sawyer | PAA as a Pretreatment Alternative to Free Chlorine…

The McKeesport WTP is a 10 MGD conventional WTP, owned by the Municipal Authority of Westmoreland County (MAWC) and located in McKeesport, PA. MAWC has…

www.hazenandsawyer.com

https://www.sciencedirect.com/science/article/abs/pii/S0043135423007972

 

[JamesW]

Adding acetic acid will result in HAAs.

Haloacetic acids (HAAs) are one of the most abundant types of DBPs in swimming pool water.

 

[JamesW]

Vinegar is a horrible idea. It will form haloacetic compounds. Definitely do not use vinegar.

Haloacetic acids (HAAs) including monochloroacetic acid, dichloroacetic acid and trichloroacetic acid are classified as disinfection by-products (DBPs) along with other disinfection by-products (DBPs) like trihalomethanes, and chloramines.

These are definitely something that you do not want to intentionally introduce to the pool water.

 

[JoyfulNoise]

Currently, the major drawback for the use of PAA in wastewater disinfection is its high cost, which is partly due to limited production capacity worldwide. The cost in Europe is about US$3 per gal (US$0.80 per liter) for 12% PAA solution, approximately four to five times the cost of sodium hypochlorite. As there is no mass production of PAA, especially in the United States, chemical manufacturers cannot quote prices comfortably for large demands such as for wastewater treatment plants.

From:

Disinfection of wastewater with peracetic acid: a review
Environ. Int., 30 (1) (2004), pp. 47-55, 10.1016/S0160-4120(03)00147-8


Ask any former Baquacil pool owner how much they enjoyed paying 3X more than chlorine pool owners for their chemicals which usually resulted in several algae-white mold blooms every season and water that would just never get cleared up enough. We used to have a sub-forum dedicated to pool owners that switched from Baquacil (where peroxide was one of the main chemicals used) to chlorine and 99.9% of them were happier with the results. Even if PAA could be provided as a pool sanitizer, I suspect it will earn the same fate - an overly expensive product that only sometimes gives outstanding results but generally isn’t any better than chlorine.

 

[fresh]

Hi again (and apologies for delay, email notifications aren't working for some reason),

Many thanks @JoyfulNoise for your reply and information. I'm going to chemistry school here, and I appreciate it.

(Fun fact: I loathed chemistry at school. It was my most hated subject of all. But these days I love all science, because I now actually have a reason to: to improve my health, to keep a pristine pool, etc.! I will learn ANYTHING I have to for goals that matter! Says something about standard school education systems. Those chemical equations were boring because they had no meaning for me. Now, they're precious/interesting chemicals - carbon! oxygen! hydrogen! - which actually have an impact on me. The design of the standard system clearly is very poor.)

So, TIL that acids produce a 'conjugate base' when diluted in water. Interesting. So it ain't just 'acetic acid breaks down to safe nothingness'! (How about diluted vinegar, like 8% stuff? Is it guaranteed 8% pure acetic acid with little to no acetate because the low ph of that acidic strength keeps it from breaking down?)

I read that further h2o2 could possibly oxidise generated formaldehyde from water (though it may need an alkali, whatever that means for applicability to a pool). In either case, I can see that I won't be experimenting with PAA anymore. Acetic acid is just a no-no for a pool.

Thank you so much for your info, and @JamesW too.

It seems that PAA is basically a sort of 'explosive' form of, 'it's about to be peroxide, baby!' - and thus a good oxidiser, but I'm not sure why it could be a stronger one. (Wouldn't straight h2o2 be better/more efficient? Isn't the acetic acid/acetate redundant in oxidising/sanitising? Or is the oxidation by-product of formaldehyde why it's so effective in wastewater treatment?)

Or is it that PAA creates more hydroxyl radicals than straight h2o2?

Google's AI gives these generated answers:

"PAA is more reactive with organic compounds than H2O2 because it has a lower o-OH bond energy and unoccupied molecular orbital energy."

"PAA has greater lipid solubility than H2O2."

So although this is tantalising:

"PAA is more biocidal than H2O2, even at lower concentrations. For example, 100–200 ppm of PAA is more biocidal than 10,000 ppm of H2O2."

Due to the acetic acid component, I'm just not interested in it now. I'm not a transient wastewater treatment plant. And I'm not a fan of DBPs (whether as a result of CC, PAA, or anything else).

Perhaps there could be a intense use-case if you used enough PAA all at once to clear a swamp (and then cleaned up DBPs with h2o2/FC or whatever), but there are other ways, including large amounts of h2o2 itself, and of course, superchlorination.

 

[JamesW]

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[ol_whistle_britches]

I’ve been thinking about this a lot and thought I’d share a real-life experience for anecdotal purposes. I was getting ready to SLAM earlier this month after new years and talking to a buddy of mine, and he mentioned he had once shocked his pool with PAA when it was nasty. He sells down-hole chem out in the oilfield and had been talking about his green pool to one of his chemists on staff, who promptly handed him a jug of PAA and told him it was his favorite way to do it and would clean him up lickety-split.

Eager to clear his pool and lacking further instruction in the finer points of chemistry, said son of the oil patch went out to his back yard and upended the jug into his pool. He tells me the reaction was immediate and “awesome” to watch. He said you could watch the algae die and fall out of solution right before your eyes. About this time I was thinking this was the solution for me. Indeed, it did work wonders for my buddy…

A few days later his brand new pentair intelliflo pump began leaking in an uncontrollable fashion. An oilfield autopsy was performed around the company water cooler the next day (that is to say, no physical inspection) by a mortician bearing similar resemblance to the staff chemist, who surmised that the do-gooder may have added too much PAA to the pool water and thus upset the pH in the pool water and “done ate the seals right up”.

In other news, I did SLAM my own pool… without PAA.

 

[JoyfulNoise]

I’ve been thinking about this a lot and thought I’d share a real-life experience for anecdotal purposes. I was getting ready to SLAM earlier this month after new years and talking to a buddy of mine, and he mentioned he had once shocked his pool with PAA when it was nasty. He sells down-hole chem out in the oilfield and had been talking about his green pool to one of his chemists on staff, who promptly handed him a jug of PAA and told him it was his favorite way to do it and would clean him up lickety-split.

Eager to clear his pool and lacking further instruction in the finer points of chemistry, said son of the oil patch went out to his back yard and upended the jug into his pool. He tells me the reaction was immediate and “awesome” to watch. He said you could watch the algae die and fall out of solution right before your eyes. About this time I was thinking this was the solution for me. Indeed, it did work wonders for my buddy…

A few days later his brand new pentair intelliflo pump began leaking in an uncontrollable fashion. An oilfield autopsy was performed around the company water cooler the next day (that is to say, no physical inspection) by a mortician bearing similar resemblance to the staff chemist, who surmised that the do-gooder may have added too much PAA to the pool water and thus upset the pH in the pool water and “done ate the seals right up”.

In other news, I did SLAM my own pool… without PAA.

Same thing can be done with chlorine - just drop an uncontrolled measure of muriatic acid into the pool to the get the pH below 5 and then dump in enough liquid chlorine to raise the FC up above 100ppm. You will instantly see a green pool go grey and then clear up as all the dead matter drops to the bottom. With the pH so low and FC so high, you'd basically create a solution of chlorine gas dissolved in water which will kill and oxidize just about anything ...

... and it will completely wreck the pool equipment and damage the pool surfaces ... so don't ever do that.