Guidelines for service water disinfection via Chlorination

[MartinLe]

At a wastewater treatment plant, part of the discharge shall be used for sanitary purposes (toilets, hand washig etc).

The use is non-potable, so far I did not find a specific code that applies. The country is Germany. We are alternativly considering a UV disinfection, but I think the lower cost and the long-time effect of chlorination make it worth considering.

Because only a part stream of the water shall be disinfected, I want to chlorinate after pressuriizing the water to 4-6 bar.

IMO this rules out the use of gaseaus chlor.

The big question is retention time, chlorination needs 15-30 minutes it appears. So I would, for 20m³/h, need a 5m³ pressure vessel at least. This seems excessive (and expensive!) plus I still need to learn about gaseus chlorination products that may provide additional headaches.

My next steps are talking to suppliers, questioning the need for a service water tream without chlorination, getting information about how intermittent the service water use will be - it may be that the pipeline system on site provides some retention time.

What I need is feedback on retention time and its necessity and general advice how and where to integrate chlorination into a service water installation.

 

[ashtree]

I would suggest that hand washing is getting pretty close to a potable standard and so may some of the "etc" that you have not listed. Chlorination will be important but the amount of detention time etc is going to depend on a lot things including:

1) What type of wastewater the plant treats.Is it an industrial plant , domestic wastewater, livestock or something else.
2) The type of treatment processes used to produce the wastewater/recycled water. Producing water that is safe for recycling is more than just adding chlorine.If the water goes through membranes it is likely to be safer for recycling than if just clarified activated sludge for example.
3) The quality of the water produced.
4) What quality safeguards you have in place eg: online monitoring , regular la testing etc.

I would suggest that you really need to reconsider what you are actually trying to achieve, what are the actual uses and what are the quality requirements for those uses.Likewise is this actually worth doing?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[MartinLe]

You are right. Water for washing hands needs to be potable and this is not worth pursuing.

Other uses would be cooling, cleaning that don't need potable water. The general wisdom seems to be that recycled service water is not a major infection risk on wwtp (comnpared to the surfaces and equipment to be cleaned) but the client may still want desinfected service water.

 

[RSD90]

Hi MartinLe,

After having achieved the discharge norms, the effluent from the wastewater treatment plant can be considered fit for secondary use. After treatment the potential harm causing elements that remain in treated water are pathogens. Chlorination helps in making water pathogen free thus it can be deemed fit for washing hands.

However if you feel gas chlorination to be tough then there are other methods of chlorination too.

And true that in any case we should be using disinfected water, even if it is used for cleaning purposes so that the pathogens do not spread to the personnel working nearby.

 

[QualityTime]

Common sense should prevail here. Using effluent water for hand washing is nuts. Pathogens can kill or maim people for life. What happens when the chlorination system fails? Everything eventually breaks down

 

[MartinLe]

In case it wasnt clear enough, we completely moved away rom the idea of using effluent (in any form) for hand washing.