BOREHOLE WATER FOR IRRIGATION AND FLUSHING: PROBLEMS

[paduk]

I am designing a plant to re-use greywater, produced by a borehole cooling system, to irrigate gardens and flushing toilets.
In design this system I have come across several problems which I am trying to solve and I would like to ask you some advices.

The first problem concerns Legionella: the greywater I am going to use is at a temperature of 28 C which is in the range of Legionella growph.
The water is not going to produce any droplet or areosol as drip irrigation is to be used and flushing toilets should not be a big deal but I am not totally sure about these assumption I am making.
Would you say 28 degrees without droplet and aeresol should not be a problem as far as lEGIONELLA is concerned?

The second problem concerns the treatment of greywater: I was thinking to use chlorine dioxide in case the system requires anti-Legionella treatments but I have read that this chemical can harm plants and soil in long term usage.
Does this appear to you too? And which could be a solution to avoid this problem considering that all the others treatments have been rejected as too expensive or ineffective?

Last question is: does anybody know the concentration of chlorine dioxide allowed in UK for these purposes?

Thank you very much

 

[paduk]

Guys, nobody can help me?

 

[ch81pc]

Having just gone round doing legionella assessments for a number of sites, the HSE do state that toilets produce aerosols (interestingly more aearosol is produced with the lid down!). Therefore you would need to comply with their assessment by either:

chlorinate
ozonate
or keep you temperature below 20 degrees


Chlorine dioxide would work, but the reactor used to make it in situe can be an issue. Why not suoer chlorinate with NaClO up to say 2.5ppm and then dechlorinate with bisulphite? Although if using grey water your clorine demand would be high and you wouyld end up with higher organo-chlorines in your water which may be an issue for plants if used for food crops.
Ozone is another option that would give you both the disinfectant and oxidation associated with ClO2.

 

[bimr]

I agree with ch81pc comments, but would add that you need to filter the water in addition to disinfection.

Here is a reference that may help:

http://www.watereuse.org/ca/pdf/RecycledWaterUserManual.pdf

 

[paduk]

Thank you so much guys.
Unfortunatly the client wants UV treatment now so...