PretTreatment micro high counts 3

[npomies]

Hi,

My site installed a Purified Water system some time ago.
We experienced some micro high trends in the Pre-Treatment plant (in softeners and 1micron pre-RO filters). Funnily enough, at the same time no high count was recorded from the Carbon Filters samples.
This does not affect the quality of the water downstream, but does submit the Generation plant (RO, DI, UV) to some level of stress I presume.
We use sodium hypochlorite as a sanitant and perform regular sanitisation of the PreTreatment plant (every few months).
The main organism present was identified as C. acidovorans.
Did anybody has had some experience dealing with this before?
Any thoughts would be appreciated.

Thanks

 

[EdStainless]

Do you have inspection access points in the system? You need to do some hunting.
It may be that you have some sections with little-to-no flow. (dead legs, branches and so on) These would not see adaquate sanitization and could be a hideout for the contamination.
Even improper slope of lines could make sanit difficult.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[MedicineEng]

Just to confirm:
Carbon filter is before the pre treatment? I am asking this because in my previous experience with PW systems I didn't work with carbon filters.
If yes, then I would look to the sampling point itself. Maybe you have a dead leag there or the sampling valve is not adequate for PW systems.
It is strange that you have contamination in those points because you still have chlorine in your system, that will be only be right removed before the RO (by sodium metabisulphise or any other way). Usually the problems appear here, between the chlorine reduction and the RO.
Were these contamination problems happening since the beginning?

 

[npomies]

Thanks EdStainless and PauloRibeiro for your replies.

This is the description of the system:
One pre-treatment plant treats raw water and feeds the generation plant. The pre-treatment plant consists of 20um pre-filter, raw water break tank, pump, activated carbon filter, softener (regenerated with salt/brine) and 1um cartridge filter.
Post Pre-Treatment, the generation plant feeds the distribution system and consists of a single pass RO unit, a DI unit and an UV unit.

As the purpose of Carbon Filters is mainly to remove Chlorine, the sanitisation with Sodium Hypochlorite is done by sanitising the Carbon filter part of the Pre-Treatment plant with high dose of Chlorine, and then perform the sanitisation of the softener part by by-passing the Carbon Filter... so that every part gets hit by enough chlorine.

What seems strange to me is that as far as I know the Carbon filters part should be more prone to microbial growth than the softener/1um filter part.
Other point: it seems that the "only" microorganism present in those high counts is Comamonas acidovorans... I went for a quick search on the web, and I found that this bug is known for its affinity with Chlorine... so it would be more happy to develop in bleach sanitised systems than other bugs...
Nothing (maintenance activities, etc.) seems to explain what's the cause of it... the only "pattern" in the maintenance log is a regular (average every 2 weeks) clog of the 1um cartridge filter... we change this filter every time we're aware is blocked... my main guess is that this clogging comes from fines from the Carbon Filter... but would that explain why we develop that growth??

To answer your question PauloRibeiro, this trend is showing for a couple of months now...

So you guys think this may be more related either to a "dead-leg" issue within the Pre-Treatment or a sample valve local contamination... am I correct?

Thanks for your help...

 

[quark]

Generally, chlorine can't do much with pseudomonos types and it is better if you try out formaline. The charcoal filter does absorb organic matter which is very critical for the microbes to grow upon(and chlorine as well).

It is better if you first find out the source. Once the microbes go into the membranes, they live and we are dead. Have you analyzed your regeneration chemical?

Regards,

 

[npomies]

Thanks quark,

Again, the growth can be seen from the softeners up to the RO break tank... The Carbon filter part is under control, and no TVAC count was recorded for sample points post-RO (and hopefully never will...)

when you talk about regeneration chemical, do you mean the brine solution? if so don't you think that the osmotic pressure is such that no bug would last very long?

regards,

 

[quark]

Yes, it is better if you check the brine solution. Dead legs may become a breeding ground but they are not the source. Low pH in softner(atleast during regeneration) favors the growth of these microbes. Also check for organic fouling of resins.

Pressure is not a criteria in my opinion. RO may trap the microbes but they foul faster and it may be a headache to frequently change the membranes.

Regards,

 

[Muggle]

Since your dealing with a form of psuedomonas - yo might try raising the dissolved oxygen level of the water prior to the carbon filter - psuedomonas, as a rule, does not like high dissolved oxygen. The other is pass the incoming water through and electrolytic system - this works well for inactivation of the various fungus/molds/yeasts/coiforms, etc. in the agriculture industry - single pass through the electrode chamber at sufficient voltage (amperage is immaterial here) will work.
Dave/Aquatic Technologies

 

[MedicineEng]

Why do you have the chlorine removal before the softener? You should minimize the path where you have water without chlorine and still with potential micro growth. In my plant we have the softener before the chlorine reduction (that is done with sodium metabisulphide). You already pointed out one of the problems of carbon filters, that is the fine releasing. This can also clog you RO membranes and reduce its life span.
If this doesn't improve, go for the heavy weapons, use formaldehyde. But this procedure has to be doen with extreme care since this is a hazardous product and then you need to purge the system for several hours (count with at least 12) and buy a detection kit to check if you still have formaldehyde in the system. Merck has that kit ( Formaldehyd-testy 1.08025.0001).
Go luck with your bug fight.
PR

 

[clearh2o]

Hello,
First of all. Is your pretreatment recirculating?
I suggest that during times of non RO operation that you maintain the entire pretreatment system in recirculation. You will have to set up an auto dump feature to introduce fresh water and keep your temperature under the 30degC mark. Alternately, you can install heat exchangers to cool this water. Installing UV can also help.
When it comes to sanitizing the pretreatment, if your system is capable of handling 85deg C then recirculating hot water is the best. If not, then 1% sodium hydroxide for 2 hours recirculated. You must do a double regen on the softener before this. Another problem area can be the 1micron filter. Pleated paper filters with rubberized ends are especially problematic. Good reading suggestion: William Collentro's book Pharmaceutical Water Systems
Good Luck