Using treated effluent for Cooling Tower makeup 3

[marcoh]

A client has asked advice on using treated effluent from a municipal wastewater treatment plant as makeup water for the cooling towers. Economically it makes a lot of sense as the water is much cheaper (WWTP is next door).

What effects will this have on the cooling tower water treatment requirement and what will the effect be?

 

[bimr]

"Economically it makes a lot of sense" ????

Not so fast, my friend. You have not spelled out the extent of treatment at the existing wastewater treatment plant.

Generally, you will need additional treatment to remove the phosphorous and ammonia, and then you will need to filter, and disinfect if you want to recycle the water for cooling tower use. That type of treatment is labeled as advanced treatment.

Advanced treatment is a significant cost and something most have walked away from. Everyone thinks that water is water until they look into the details.

Here some water guidelines for you.

Table 7 – Typical Quality Guidelines for Chemically Treated Circulating Water
Property of Water Recommended Level
pH 6.5 to 9.0*
Hardness as CaCO3 30 to 750 ppm2
Alkalinity as CaCO3 500 ppm maximum2
Total Dissolved Solids 1500 ppm maximum
Conductivity 2400 micromhos3
Chlorides 250 ppm maximum as Cl 410 ppm maximum as NaCl
Sulfates 250 ppm maximum
Silica 150 ppm maximum

http://www3.baltimoreaircoil.com/en...HBii2007_N10_Maint_Cross_Tower_rev_200612.pdf

 

[JedClampett]

Palo Verde Nuclear Generating Station near Phoenix does just this. But as bimr says it's not to be taken lightly. They have a huge water treatment facility treating the WWTP effluent.
Get some literature on this plant or give them a call.

 

[marcoh]

That is what my initial thoughts were. I am awaiting information of the predicted water quality but the effluent is treated with RO and UV and is claimed to be nearly as good as potable water.

http://www.westerncorridor.com.au/media/fact_sheets/water_recycling_fact_sheet.pdf

 

[gerhardl]

Quote:.............'but the effluent is treated with RO and UV and is claimed to be nearly as good as potable water.'

Question : Also regarding potential bacterial growth and legionella ? ( Possibly I'm way out here? This is not my field.)

 

[BigInch]

Wow. I'm having visions of the Hanging Gardens of Babylon.

http://virtualpipeline.spaces.msn.com

 

[bimr]

The water from the WRCW Project will definitely produce water with a quality that is suitable for a cooling tower. It should be somewhat obvious that the project is probably more concerned with removing endocrine-disrupting chemicals so that the water is suitable for human consumption. Treatment to remove endocrines will be a huge undertaking in the field of wastewater treatment in the future.

Reuse water for cooling towers does not require treatment to the same extent as that for the WRCW project. Water that is obtained after the membrane filtration treatment process will be suitable (along with disinfection) for cooling tower use.

If the water supply is so limited that you must resort to reuse, then what you should be thinking about is allocating water use by quality. For example, if the existing water supply to the cooling tower is potable water, then that water should be reserved for potable uses and reuse wastewater should then be designated for lesser quality applications like the cooling tower.

 

[bob1engineer]

Regarding Effluent Reuse, I am performing a study to see how WWTP's handle the returned cooling water blow-down (return to WWTP after use). Does anyone have examples of special agreements used to 1) Sell or permit cooling tower reuse of effluent? Cost associated? 2) Return to WWTP - any special user classification (Industrial user, Effluent Reuse Class, Institutional of special eg Utility/Electrical generation rate class)? and 3) Where in treatment train could the blow-down be returned (headworks? after primary treatment? at head to final disinfection?)
Thanks for your input.

 

[bimr]

It depends on what is in the water.

The typical cooling tower blowdown has suspended solids so you probably want to add the blowdown prior to the final clarifier or effleunt filter if you have one.

The probably will be some phosphorus in the cooling tower blowdown, so that is something else to think about.

 

[CCK54]

aluminum ion is also in the effluent. Does it effect the quality of cooling tower?

 

[bimr]

Would assume that you are talking about a trace concentration of aluminum. Aluminum is an amphoteric metal and tends to dissolve in either acid or alkaline waters. It precipitates best in a narrow range of pH values, 5.5 to 6.5. Aluminum should not be a problem for cooling tower makeup water.

 

[CCK54]

Thanks bimr.
But the criteria of recirculation cooling water mention the AL. ion must below 0.1 mg/l by EPA of USA.
Our effluent of municipal wastewater treatment is listed below:
1.Conduc.--406~468 us/cm
2.TDS---190~220 mg/l
3.TH---150~180 mg/l as CaCO3
4.Chloride--20~30 mg/l
5.Sulfide---50~70 mg/l
6.Alkality--70~100 mg/l
7.Suspended Solid--3~10 mg/l
8.Total Nitrogen --8~15 mg/l
9.Total Phosphate--1 mg/l
10.AL ion --- 0.72 mg/l
11. Fe ion---0.35 mg/l

Our consultant tell us the pre-treatment for the makeup of cooling tower is only sand-filter and UV-disinfection.
Can anyone tell me the risk?

 

[cub3bead]

With that much NH3 and PO4 (both nutrients)present there is a pretty good chance you will have a biofouling problem.

The ammonia will also attack any Cu bearing materials.

The high Fe will also cause deposition problems.

Other than that the water looks like a reasonable water quality for CT makeup.

 

[bimr]

CCK54,

Any FE or AL will be removed by the "sand filter" since these elements are insoluble in typical aerated wastewater. That is also why these elements are not found in surface waters in any great concentration. So I don't understand why you are focused on aluminum.

However, I have to agree with cub3bead 100% regarding the bigger problems of NH4 and PO4. After the typical 6 concentration cycles in the cooling tower, you will have 90 mg/l NH4 and 6 mg/l Phosphorus. That represents big problems for the cooling tower system. The ammonia will turn the cooling tower into a giant trickling filter.

You will have also have permitting problems should you desire to blow down your cooling tower to the sanitary sewer.

That is why the current approach to treating municipal secondary effluent is advanced treatment consisting of a membrane bioreactor, phosphorus precipitation, and UV disinfection. Removal of ammonia, phosphorus, suspended solids, organics, and disinfection. Equipment to handle the sludge will also add to the cost.

I have personally been down this road before. Everyone "thinks" it is such a great idea to recycle secondary effluent. Water is water, right?

Well, not so fast. After evaluating the cost of advanced treatment to clean up the water, most drop the idea as it is too costly. You should think about using a consultant that has experience in the power business.

 

[CCK54]

Thanks bimr.
We will discuss with our consultant carefully.