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We have a serious water shortage in South Africa, my question is can the waste water that has been discarded during the reverse osmosis process be recycled through the RO system as this can saves a lot of wastage

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Sintesi
We have a serious water shortage in South Africa, my question is can the waste water that has been discarded during the reverse osmosis process be recycled through the RO system as this can saves a lot of wastage

Good question.I'm not really familiar with the R.O. system but I know it can be very wasteful.I use rainwater harvesting which leaves very little left to do with the water as it's so pure already.Best of luck


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HollasSpecialistCleaningSystems

I don’t think harvesting rainwater is currently an option in s.a


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AGlassAct

The simple answer is yes, just bear in mind the waste has all the rubbish that was removed during the purification process so when you use it as your source water again the TDS will be a lot higher. I think the difficultly would be storing the waste water then boosting it enough to go through the RO again. Take your tap TDS and waste TDS and you’ll see quite a difference so every time you re-use the waste water it will have a much higher TDS.


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Part Timer
1 hour ago, We Wash Windows said:

We have a serious water shortage in South Africa, my question is can the waste water that has been discarded during the reverse osmosis process be recycled through the RO system as this can saves a lot of wastage

What is your TDS, in the short term is it not possible to double DI? Whilst this is very expensive if your TDS is circa 300 there is no waste 

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We Wash Windows

Thanks for your replies , I understand that the RO membrane will have a shorter life span but when processing 500l pure water and wasting 1000l ,especially here when water is short , I have to try the recycling, 

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We Wash Windows

Hi Guru do you mean filtering the water only through DI, and not using the RO system, resin is expensive here , our municipal TDS is around 85.

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Part Timer
23 minutes ago, We Wash Windows said:

Hi Guru do you mean filtering the water only through DI, and not using the RO system, resin is expensive here , our municipal TDS is around 85.

Yes as you will get no waste. I don't know how expensive resin is over there but if you use the link below you can calculate the cost. 

 

https://www.windowcleaningwarehouse.co.uk/resin-calculator.html

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spruce
7 minutes ago, We Wash Windows said:

Hi Guru do you mean filtering the water only through DI, and not using the RO system, resin is expensive here , our municipal TDS is around 85.

 

What isn't expensive in SA at the moment?

 

I'm surprised your tds is only 85ppm considering where the water comes from. Where are you?

 

If you are looking at 85ppm then you can restrict your waste much more. You could even get away with 40% waste to 60% pure. At 85ppm you could even catch that waste water and pump it back through your r/o at a later date, but you would need a pressure pump to do that. I'm guessing but from 85 to the tds of your caught waste water might get to around 150 depending on the waste to pure ratio. Its been a long time since I measured input and both outputs at the same time so can't remember the figures. But I can remember being surprised at how low to tds of the waste water was because I was expecting it to be much higher.

 

There is a window cleaning business down the south area of London. He once but a video up of his operation and he quickly mentioned that he had a bit of equipment that he tried to use to 'infuse' some of his waste water back into the r/o. It sounded like Robak but I never did find any info on it. In fact I didn't bother too much as he said it was an expensive bit of junk that didn't work.

 

Its all down to 'economies of scale' and you need to find the sweet spot. Obviously restricting the waste will mean the r/o membrane will suffer quicker deterioration. You will also need a little more resin to polish the pure off as the r/o won't work quite as efficiently. So you will play those 2 factors off against the cost of water and the restrictions in place to save water.

 

 

 

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We Wash Windows

We have very good water in south africa, dont have to buy drinking water! 

I appreciate all your comments so have to balance the cost of water against extra resin or membranes

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Dave B

Tds of 85 isn't bad

Don't forget that if you used double di you would get a lot more life out of your resin if di only

If i had 85 not the 340 i have i would use double di and no ro

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We Wash Windows

thanks for that I will give it a try

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Sintesi
I don’t think harvesting rainwater is currently an option in s.a


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Though great as a free add on.If you have any commercial or industrial jobs that would allow you to store two or more 1000 litre I.B.C. tanks which would store almost pure rainwater with a Tds of around 4 to 20 then all you have to do is run through hose to single small 5 litre di vessel.I'd say you get some epic rains in S.A. That would fill these up in no time for free.Worth looking into as a cheap booster.


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HollasSpecialistCleaningSystems

I’m sure s.a are currently in a 4 year drought. Cape towns reservoirs are dry and they’ve limited the population to 50 litres pppd. They’re expecting the whole city to run dry by May. I thought this post was a wind up when I first read it.


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We Wash Windows

We have had good rains in other regions in SA , 

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