Industrial Bleach in Cooling Towers? 2

[TheDude75]

Trying to come up with a better system of killing the "bugs" in our cooling tower. A number of vendors all tout their chemicals - some are oxidizers, some not.

I mentioned just pumping industrial bleach, which is significantly cheaper than any of the other options, and have never gotten a straight answer from a vendor as to why it would NOT work to control biological growth safely inside our cooling tower.

Can anyone give me a "yea" or "nay" as to whether pumping industrial bleach straight into a cooling tower is a viable and safe alternative to the more expensive biocides available?

 

[aspearin1]

Well, from my microbiology experience, bleach usually doesn't cut it. It's actually a poor way to control bacterial growth. It's used to kill many of the pathogenic types for drinking water, but certainly doesn't stop all growth. The problem with most antibacterial agents is that they kill some and allow others to grow. One must pick and choose which bacteria he or she can tolerate in the system. UV light is also a good antibacterial agent. Perhaps a lamp could be installed somewhere in the syste.

 

[gkandy]

TD2K, Do you have any comments on this issue.I have been using biocides for so many years in cooling towers. It has never struck me why a simple bleach cannot be used.I hope somebody can answer this.( may be somebody working with the manufacturers of the biocides )

 

[TD2K]

I have never worked in this area.

I do know we used to use chlorine (chlorine gas, not a bleach solution) for continuous treatment (and shock treatment as needed) of the cooling water system/tower to kill bugs at the plant I worked in. There were concerns being expressed as to the trade-off of the benefical effect of the chlorine in killing bugs versus damage to the wooden members in the cooling tower but I don't recall if we were changing our cooling water treatment program when I left there.

Would industrial bleach throw off your cooling water pH too much by the time you got enough chlorine into the water?

 

[TheDude75]

Not sure about the pH - but I don't think it would take too much bleach, especially industrial grade, to get the required chlorine into the system.

A bit more background - the lab supervisor here and myself decided to experiment with the cooling tower and actually use commercial bleach in it for a period of time. We literally poured commercial bleach into the cooling tower. There was some foaming, which we expected, but not very much.

Anyway, about a week after that, we had a bio-test run on the tower - and scored between the good/excellent range. Previous to this we were in the fair/poor range.

What bothers me about this is that we've been working with a certain company for years - long before I came here - and the bug problem in the tower has never been fully addressed. I brought in another company to look at it - and asked them about using industrial bleach. They were all for it - and told me of a few companies that actually did just what I was mentioning.

Later follow-ups with both companies, however, have led to conversations where they want me to move away from the bleach idea and go with one of their proprietary chemicals. They've each used excuses such as "Bleach is good, but...." and mentioned corrosion of the pipes, rise in pH, etc. - but they were supporting it in the very near past.

It's very confusing - and I know I'm not going to get a straight answer from a company that's trying to sell me their biocide - which is why I came here. Both companies seem to support using industrial bleach until I decide not to buy theirs - and then they are against it.

I'm looking for unbiased answers on this. I thank all that have replied thus far.

 

[aliansari]

My experience on cooling tower operation suggests that selection of biocide depends on,

Inlet make up water micro biology.
Nature of process fluid contamination (Heat Exch. Leaks)

Most of the time, (in PVC and PTA plants) I found that injection of neat sodium hypochlorite (12-15% active chlorine) alone was efective to control bugs population below the maximum acceptable limit of 10^4/ml. This we achieved by maintaining 0.5 - 0.7 ppm free chlorine on a continuous basis.

However in a petroleum refinery, chlorine treatment alone was not found potent enough. Supplementary non oxidizing biocide was essential. We used s-triazine and tetra alkyl phosphonium chloride quite successfully.

A new and rather simple substitute is Cl-Br combination, which generates even more effectivee HOBr. Solution of NaBr and Sodium Hypochlorite is mixed prior to injection into cooling tower basin. Nalco Acti Brom is an example. However can be prepared in house using base ingridients. I found this combination extremely powerful.

I am not clear what hypo you mean by liquid bleach. Is is sodium based or calcuim based (we call bleaching powder). Using solution of calcium based bleach carried potential risk of cooling water scaling due to addition of calcium.

Best of Luck.

Mohammad Ali Ansari

 

[DeltaCascade]

You must have a small neglected system? Small cause you are considering buying a commodity, bleach, from a specialty chemical supplier .. neglected cause this hasnt been figured out before .. good thing you are on it now!

Of course you can use bleach .. it is just an expensie form of chlorine gas (chlorine gas in dilute caustic ... NaOCl) ... and it is not expected to cause foaming.
Regarding cooling tower pH control .. you feed acid anyhow, dont you, with a pH controller, etc?
You may also want to consider feeding of a non-toxic biosurfactant (eg: Betz has one), to loosen slime deposits so that chlorine can get at them to kill them.
Chlorinating make-up water as far upstream of the cooling tower as possible is also good, if it isnt already.
Take care when comparing chlorine's effectiveness in cooling towers compared to potable water .. in cooling towers, the chlorine contact time is essentially "infinite".
When monitoring micriological activity, consider monitoring for aerobic and sulphate reducers, both in bulk water (colonies/ml) and for cessile bacteria (coloines/cm2), too.
Consult Betz Handbook, etc, for info on chorination ... lower pH increases HOCl % (HOCl is a better biocide than NaOCl) ... HOBr is even better, at higher pH of alkaline cooling water treatment programs too .. you do not need expensive solid bromine donors, just NaBr solution freshly blended with high chlorine charge water ... bleach (or chlorine gas), however, and good control, should be fine.
What chlorine residual do you maintain ... 0.1 to 0.3 ppm FREE Chlorine is typically good. If it gets too high it will tend to increase yellow metal (copper alloy) corrosion.
Your water treatment vendors may need to smarten up, or, management of your relationship with them needs to be improved (two way street).'
Microbiological activity may never be "fully addressed" .. it is an ongoing quality control management issue...
Good luck

 

[smile1]

TheDude75

1) Bleach is possibly the most cost effective biocide in the market today. Chlorine gas is better, due to the pH depression, but the regulations required make it more expensive.

2) pH control is extemely important when using bleach. pH above 8 makes bleach as reported by DeltaCascade, mostly ineffective. The added problem with NaOH in the bleach raising the pH is another problem. If you use bleach, add acid.

3) Vendors time isn't free. Unless you are willing to sign a service contract with them, expect them to try to get paid by selling proprietary materials.

4) The foaming indicates a bio problem, mentioned by DeltaCascade.

5) Refineries, corn starch, breweries, anywhere where high organics are expected in the cooling water, it may be cheaper to use a non-oxidizing biocide. If you use bleach in these application to reach break, you will also need a lot of acid.

6) You need to make a decision whether you want to treat this system yourself, hire someone and pay them, ie consultant, or contract with a vendor and pay them through chemical purchase. Weigh the cost of your education into the equation.

Keith

 

[BarryMartin]

You don't mention the capacity required for your system.

As others have stated, bleach will kill most of the bugs and is commonly used as a biocide in many forms. Chlorine gas, sodium hypochlorite (bleach) in a liquid form, and onsite electrolysis of salt water solutions to generate bleach onsite are all means to provide the chlorination requiements you might need. Stored bleach can degrade (i.e., decompose with time because the hypochlorite converts back to salt and ozygen, especially if exposed to sunlight and/or heavy metals). Onsite systems can provide the bleach requirements on demand or with far less stroage and decomposition. Chlorine is good, but some people are concerned about safety issues.

 

[johngerhart]

We replaced chlorine cylinders on our cooling towers with bleach about 4 years ago . You must watch the materials of construction , but overall it is quite trouble free . Our supplier helped us spec the tank and pumps . Contact the Chlorine Inst pamphlet # 96 for handling instructions

 

[EMKWR]

Hypochlorite is used quite often here in the Netherlands to prevent the growth of micro and macro organisms (mussels) in cooling systems. It is however not necessary to chlorinate continuously. A lot of chemical costs can be saved by using monitoring systems to optimize this. Nice results can be achieved by the use of pulse-chlorination.

You can find more info on this subject on:

http://www.kema-kps.com/water/industrial_water/tools/index_e.htm

(use the menu on the left, the other links do not work).

Please excuse me for referring to my own website, but it's the only please I know to find the info. Edwin Muller
KEMA Power Generation & Sustainables
Arnhem, The Netherlands
E-mail e.f.muller@kema.nl
Internet:

http://www.kema-water.nl

 

[smile1]

So, TheDude75, what did you do?

 

[25362]

Excuse me, when you speak of bugs are you also referring to the pneumonia bacterium Legionella Pneumophilla ?

 

[DeltaCascade]

Sure. All sorts of critters, including legionella. The long exposure times (essentially "infinite", unlike potable water systems) to chlorine in the recirc water of a cooling tower's water will even help minimize growth of larger organisms ... you'd be surprised what you can find ... bugs that you can see with the naked eye, evan. (bugs may hide under slime matts where chlorine cant ge to .. that's where "corrosive" anaerobic sulfate reducing bacteria hide and live (and you dont detect them in bulk water samples)... good to use biosurfactant to help loosen slime deposits so chlorine can to its job on them, too.
cheers//

 

[TheDude75]

Smile1,

Actually, the point is moot now - since our plant is shutting down due to an acquisition.

But, just to answer the question - it was more cost effective for us to use commercial bleach and simply clean the cooling tower with steam every 3 months. While I would never recommend this in a larger facility, ours is (was) small enough to where this was the most viable option.

Alas - I'm searching for work now, and the cooling tower is now nothing but metal and ice. The good news, though, is that our biological growth is < 0.1 ppm due to the ice .

Thanks to all who replied, though. You've all really helped me out.

 

[smile1]

Dude,

sorry to hear about the &quot;job&quot; situation. Been there a number of times, so I finally started my own material handling business. The hours are bad, the anxiety is high, the pay fluctuates wildly, but I enjoy it. I was in water treatment for a decade, and can't seem to get out of it though. We are introducing a concept that I worked on when I was with Betz to pretreat cooling water better, and chemically treat less. The system we are starting next week, because of the unique well water, will have zero blowdown, only drift. I guess what I'm saying is that this job situation could be a good thing in the long run.

Great luck to you.

Keith

 

[DeltaCascade]

All the est Dude75.
Hay, Smile1.. I was with etz for 10 good years in Western
Canda (efore the last set of &quot;re-orgs&quot; aout 5 years ago...) Am an &quot;independant&quot; now, too. The water experience sure comes in handy. Where are you located? All the est. (sorry, ut my &quot;&quot; key is uggered).

 

[smile1]

Hey Delta, common history. I had a territory in Ohio with the industrial group, focused on breweries and food, with a minor in steel. Ever know Don Manlove, Dick Dudley, Stu Klatskin? I left in one of the earlier re-orgs, 6 months after the Dearborn thing. Seem to think I had made a few bad relationships with some of the higher ups when they were the competition. Such is life.
We are in Paducah, KY, and material handling (typically nano particles) is what I am trying to develop. The problem is I can't seem to leave water alone. My company's name is MidSouth Material Handling. Great to hear from you.

kfeather@midsouthmaterial.com

 

[paxondoug]

We have successfully used a Bromide biocide for many years. Tried sodiumhypochlorite, but too expensive, too volatile, too many safety issues, too hard to control.

 

[DeltaCascade]

I guess your bromide is the bromohydantoin solid halogen donors (pucks or pellets)... most expensive option, but ok for small systems due to their convenience (especially if simple bleach is too hard to handle), I guess.. larger installations that use bromine chemistry use chlorine gas or bleach combined with NaBr salt solution (cheaper than bromine donating solid hydantoins) to produce HOBr and NaOBr (and then combined bromines in the treated water just like HOCl does) ... jury is still out on effluent toxicity of bromine treated waters, although redox potential is lower than with chlorine...
You guys may want to read up on the basics of cooling tower chlorination cause this discussion looks pretty much beat up? Good luck!