cooling tower make up water - ammonia presence 3

[keochu]

We are thinking in reusing of tertiary municipal wastewater as make up water for a cooling tower.

The problem is that there is no nitrificaction denitrification process in the treatmente plant, so values of 45ppm of NH4+ are expected in the make up.
Foreseen concentration factor is 2.

Has anyone experience in this isue?

Thanks in advance for your help

 

[Muggle]

Are you sure it's NH4? Ammonium is hard process for biological processes to convert to NH3 (ammonia) - then to nitrate. Depending on the volume per day of make-up water, NH4 could require a very large aerobic biological filtration system. If NH3 - that's much easier -

However, you need to figure out if it's NH4 or NH3, then - I suspect you want to limit the TKN - total nitrogen from the system to reduce bacterial growth. Aerobic filtration will convert the NH3 to nitrate NO3. So will ozone and/or simple aertion - but you have the nitrate present now. So electrolytic oxidation is better then ozone because it breaks the nitrate to NO gas and can do it faster and without the rsultant health and safety issues.

Any oxidation process will result in oxidation of heavy metals - so you will have to use mechanical filtration to remove the precipitate. Simple DE filtration is best where electrolytic oxidation is used as the polarity changes increase the DE filtration level down to about 2-micron of the precipitate. There also cheap and easy to use - this will remove a lot of precipitate prior to any Ultrafine or R/O - increasing the R/O or Ultrafine filter operational life substantially.

We looked at this for several major manufacturers in Florida a few years back - using Reclaim to reduce freshwater usage from the municipal plant to cut operational costs. When utilized - we figured a 75% increase in R/O membrane life and corresponding reduction in reject water.
Hope that helps -
Dave/Aquatic Technologies

http://www.eoh2o.com

 

[keochu]

Thanks Muggle.
I confirm it´s NH4+.
We are not thinking in reducing TKN, we are thinking in controlling bacterial growth with a combination of biocides. Chlorine dioxide is the biocide we foresee to use.
The make up water flow is 720 m3/h.
I am looking for someone experience with this level of NH4+ in draft cooling towers make up water.

 

[bimr]

Sure, and it will not work. By the way, the ammonia should have already been removed if it is truly a "tertiary" treated municipal wastewater

Other problems that you will encounter:

If you want to reuse municipal wastewater, you will probably need to remove the phosphorus as well and then disinfect the wastewater. You have to disinfect because you do not want to have a toxic aerosol coming off your cooling tower. To properly disinfect, you are also going to have to do a good job of filtration (prior to disinfection).

Reuse of municipal wastewater sounds like a simple solution, but it often turns out to be an expensive proposition.

In the ammonia removal process commonly used in municipal wastewater treatment, microorganisms (nitrosomonas & nitrobacter) oxidize ammonia to nitrate per this reaction:

NH4 + 2O2 >>> NO3 + 2H + H2O

Ask yourself the question:

Is it possible to control organics in the cooling tower, while at the same time one is encouraging organic growth of the nitrification organisms in the cooling tower?

The foreseen concentration factor of 2 is also not economical either as the excessive cost of treatment chemicals will quickly render the concentration factor obsolete.

In summary:

1. You need to remove the ammonia.
2. You need to remove the phosphorus.
3. You need to filter.
4. You need to disinfect.

.....if you want to reuse treated municipal wastewater.
3

 

[bimr]

"Tertiary treatment is used at municipal wastewater treatment plants when receiving water conditions or other uses require higher quality effluent than that produced by secondary wastewater treatment. Disinfection for control of pathogenic microorganisms and viruses is the most common type of tertiary treatment. The concentrations of suspended solids and associated BOD in treated effluent can be reduced by filtration, sometimes with the aid of a coagulant. Adsorption, ordinarily on activated carbon, can be used to remove some persistent organic compounds and trace elements. The concentration of ammonia in secondary effluent can be reduced by nitrification. Tertiary treatment to remove nitrogen and phosphorus, so as to mini-mize nutrient enrichment of surface waters, is common; nitrogen is usually removed by nitrification followed by denitrification, and phosphorus is removed by microbial uptake or chemical precipitation. "

http://www.epa.gov/owm/pipes/sludmis/mstr-ch3.pdf

 

[keochu]

Thanks Bimr for your help and interest. I´ll try to explain the global picture in order to give you a better understanding.

1- We take the water from a secondary wastewater treatment step that already exits without nitrification denitrification process.
2 - We plan to built a tertiary treatment to reduce colloidal, suspended solids, BOD, pathogenic microorganisms based on coagulation, floculation, filtration, desinfection and phosphorus elimination by chemical precipitation process. So no action on NH4. This will be the make up water for our cooling water.
3 - We plan to control biological growth and biofouling in the cooling tower by means of Chlorine dioxide. So no nitrosomonas & nitrobacter will be alow.

4 - We are trying to avoid a biological treatment of NH4 as is very space consuming and because we need a very reliable system, bacterias are quite capricious

5 - 2750 ?S/cm is the conductivity of this water, this is the reason of concentration factor selected

 

[cub3bead]

No yellow metals should be allowed in the system with that much NH4+ prresent.

 

[bimr]

Ammonia is detrimental in several ways. Ammonia attacks copper alloys as cub3beads stated and consumes biological control chemicals. Ammonia serves as a nutrient increasing biological growth. It is doubtful that the elevated ammonia will be acceptable.

For what it is worth, we did a study recently that showed that a process consisting of aearation, chemical precipitation, membrane filtration followed by uv disinfection was the most cost effective treatment scheme.

 

[keochu]

Thanks cub3bead no cupper alloys foreseen in our system, noted.

Bimr, no 100% agree with regard that ammonia consumes biological control chemicals,if the chemical is sodium hipoclhorite 100% agree but we foresee chlorine dioxide that does not react with ammonia.

We will study the scheme you propose, not so sure about membrane filtration with the quality we have.

I will continue looking for someneone with experience in ammonia content in make up water.

Thanks to all

 

[bimr]

I realize now that you are thinking that because ammonia doesn't consume chlorine dioxide, that it may be possible to operate with the ammonia. Don't know if you are aware that chlorine dioxide costs 5 to 10 times more than chlorine. Add that to your low concentration factor and you will have a very expensive operating cost.

Other considerations are the air emissions of ammonia and the wastewater discharge problems. Ammonia is considered to be an air toxic in some states. A wastewater discharge with 90 mg/l is also difficult to permit.

Ammonia is be a source of nitrogen--a necessary nutrient for the microbial population. When ammonia used as a refrigerant has leaked from refrigeration systems, nitrifying bacteria in the open recirculating cooling system convert ammonia to nitrate and acid that decreases system pH with corrosive results.

 

[bimr]

The membrane filtration that was refereneced replaces the clarifier in the process scheme.

 

[keochu]

you are right chlorine dioxide costs much more, but on the other hand we do not built a nitrification denitrification system that is really expensive, furthermore because of the "low" organic materia in the water the nitri-denitri system should be feed with ethanol, also expensive.

There is no regulation about air emmissions of ammonia where this plant will be erected and regarding discharge with 90 mg/l we will handle it with the authorities if possible.

My only fear is a clear stament of someone who has a similar experience thath for sure this won´t work.

 

[bimr]

My recent experience in the power business indicates that it is not a feasible proposition.

Suggest you contact one of the suppliers of the chemical conditioning programs for cooling systems. Someone like Puckorius & Associates, Inc. or Betz. One of them has probably seen some misinformed person with good intentions try it.

Puckorius actually authored this report:

http://www.sanjoseca.gov/esd/PDFs/cooling.pdf

 

[cub3bead]

keochu,

When you get the system built, despite some excellent advice from bimr trying to dissuade you from a very bad design, would you please post pictures of it. It could turn into one of the largest trickling filters ever built. I can envision the massive amount of slime hanging from the fill even now. WOW!