Biocontrol in open recirculating cooling water

[ammabua]

Pls can someone help with this.
I am struggling to conrol the biology of our cooling system. We alternate between oxidizing and non oxidizing biocides weekly as follows
week 1 - oxidising biocide
wee 2 -non oxidising
week 3 - oxidising
week 4 - non oxisiding.
And we alternate between 2 diffrent non oxidising biocide so that the bugs will not develop resistance to one.
our spec for 48hr count is 10000 and I managed to with the above schedule hit the count down to 200 which is excellent. But to my surprise, the count today suddenly jumped to over 10000 again. We have 3 towers and the behavoir is exactly the same on all. We have not changed anything in the process. I also know that the predominant bugs on tower and 1 and 2 are similar but tower 3 is different type. We also had slime build up in the system which could be re-introducing the bugs. What baffles me however is why suddenly??
Pls if you have experience to share with me I'd appreciate.
many thanks

 

[cub3bead]

A couple of questions on the application of the biocides.

1. Shock or continuous application of oxidizer?
2. Dosage
3. If shock, duration and frequency of dosing.

Are you going through a seasonal change at the moment?
Is the CT makeup water a surface water or well water?

 

[bimr]

You might want to check your records. Perhaps the operators are not following procedures.

 

[abcmex]

Typically you need to do two things:
a) kill the bugs
b) reduce the solids in the water which may help the biological growth.

To kill the bugs you are alreay in a good direction when you alternate the kind of biocides to avoid resistance.

How is your treatment? typically you need a continious one because the doing slug dosing once a week probably will not do the trick.

The second point is to use a bypass filter if you have solids. This will enhace the heat transfer coeficient but also helps to reduce the bio problem.

a third point is your make up water. If your water is not properly treated your system will be contaminated again and again.

 

[ammabua]

Thank you very much for all the contribution.

Cub3bead questions
1. We perform shockdosing as our electrochlorinators cannot produce enough strength to maintain the required background concentration
3. We perform the shockdose weekly and aim for a peak Cl2 5ppm which we attain, but all the residual Cl2 is usually gone within less than an hour probably bacause the Cl2 demand of the H2O is high and the open nature of the system.

bimr
I have checked over and over with our operations group and they appear to be following the schedule

abcmex
we do already have a side stream filteration to control the turbidity, the aim for <2NTU which we easily attain. Although I have recently seen a jump in one of the trains but not bad bad. Just 4NTU which is already back to normal.

Maybe we have to invest to upgrade out electrochlorinators but before I make that decision I want to be sure that is the reason.

Thanks again for all the contribution. And I will appreciate more thoughts

 

[cub3bead]

I suggest you try shocking 2 or 3 times a week until you get the problem controlled.