Recovery of cooling tower blow down water

[MedicineEng]

Hi all:

Recently I had an out of the box idea to recover blow down water of our cooling towers (which in Summer can be in the range of 80-110m3/day) and would like to pass it through like minded individuals as the ones that visit this forum before I take it up on the corporate chain.

Our property is a resort with a significant number of rooms (>1500) that before Covid stroke was being run at 75-100% occupancy rate, year round.
We have separate networks for potable water and flushing water on the room towers and the cooling tower make up and the tower flushing water tanks are shared.
The cooling tower blow down is based on water conductivity.

My idea is to recirculate the blow down back to the make up cooling tower/tower flushing water tank.

Like this, the diluted blow down would be used on the tower toilet flushing as well.

So, I came up with the following Pros/Cons of this idea:

Pros:
1- Relatively inexpensive retrofitting solution
2- Thousands of m3 of water/year saved

Cons:
1-Cooling tower number of concentration cycles reduced due rising of the initial conductivity on the make up water;
2-Residual cooling tower chemical treatment being flushed on room toilets
3-During low occupancy periods, recovered blowdown will be a higher percentage of total water in the tank, exacerbating points 1 and 2 above. This would be addressed with a bypass to reestablish the system like it is currently used

What do you think of this idea and is there anything else that I'm missing?

Thanks a lot

 

[goutam_freelance]

Using blowdown water for toilet flush may be possible depending on treatment chemicals used and local environmental laws regarding allowing chemicals in sewage water.
Regarding recycling of blowdown for CT make-up it will defeat the purpose of blowdown itself, in the sense that with lower quality make up water you need to increase the blowdown rate to maintain the CT water quality keeping system corrosion and deposits etc. in view.
However basically the idea of conserving water is worthwhile. For this purpose various waste water treatment schemes are available. You may contact a Waste Water Treatment company or expert for this.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[nglty]

with this kind of water use and blow-down, you should look into chemical free Dolphin water treatment system. With Dolphin, you will increase of cycles to 6 to 8 (from 3 to 6) and no chemicals in your system.
AND, you can recover and re-use blow-down for other uses such as irrigation.
However, before you use blowdown for toilets, understand that blow-down comes from cooling tower sumps where water is stagnant and may be carrying legionnaires disease. Why bring potentially contaminated water inside the building? Why would you supply contaminated water into the fills for evaporation?
Anything contaminated should be disposed of.

 

[MedicineEng]

Thank you all for your input.

I understand that the overall water quality on the tank will be slightly worse, but given that the tank is currently used for cooling tower make up water+toilet flushing, the blowdown will be a very low percentage of total tank volume. If we assume a rule of thumb that the blowdown is around 5% of the total cooling tower water consumption and that on top of that we also have the toilet consumption, I estimate that the cooling tower blowdown will make between 1-3% of the total volume of the tank at any given time, so this blowdown will be very diluted when used as flushing water.
Regarding Legionella, we conduct monthly samples in the cooling tower basins and the system is well under control in regards to that point.
Furthermore, the level of chlorination of our make up water tank is pretty high, courtesy of the city water company, so any potential bacteriological contamination would be addressed by the tank chlorination.

Regarding Dolphin type systems, I'm not sold on those.
They seem to work very well on paper, but the people that I know that have tried it, have mixed feelings or are flat out not convinced.
They still use some biocide to address bacteriological contamination and still have to blow down time to time tp get rid of the solids.

 

[nglty]

Have you looked into the zero blow-down technology? different than Dolphin

https://www.prochemtech.com/engineered-systems-division