[Sunshine Cleaning]

Why if you have 2  or more membranes does the waste from one go to the input of the other?

[freshwater]

All depends on who buit it.

Reason:-

If you take the waste from one membrane say at 500ppm and put it through another membrane you will get reasonably clean water out the other end (say 25ppm), plus you will be saving on the waste water. However the final product water will always have a higher TDS than if you put the feed water through each membrane and let both drains go to waste.

We find it better to waste a bit more water than to use more resin cleaning up the higher TDS.

As an example our RO systems, 100, 200, 300 or 400 will take water at 280ppm and get it down to 8ppm (at 4bar pressure) this means the DI resin last a long time.

steve@freshwatersystems.co.uk

[matt]

if your on a meter though, surely its better to have little waste water ?? ?? ??

[P®oPole™]

We find it better to waste a bit more water than to use more resin cleaning up the higher TDS.

steve@freshwatersystems.co.uk

Are you a shiner then Steve?

ProPole

[freshwater]

No I am a water treatment equipment manufacturer, I only use RO to clean my car which is black.

There are a couple other technical reason for not re-circulating the waste. One being that the pressure of the waste is lower than the original water pressure, which in turn reduces water quality.

Its an idea that has filtered down from larger commercial system, but they use high pressure pumps 200psi upwards and the re-circulation is normally before the pump so there’s no loss and if they are re-circulating all the waste than a second pump is used. It makes sense on 200,000 GPD unit, but I think its less critical on the small low pressure systems used by window cleaners. The best way is the double pass RO where the pure(ish) from the first membrane is passed through a second membrane making very pure water, the waste from the second membrane (only a few ppm) is then mixed with water going into the first.

steve@freshwatersystems.co.uk

 

[P®oPole™]

Steve,

What exactly is an R.O membraine because it just looked like a bit of rolled up paper to me?

ProPole

[freshwater]

RO membranes are special plastic sheets that allow water to permeate through, but leave behind all the unwanted elements.

steve@freshwatersystems.co.uk

[Sunshine Cleaning]

Interesting.

My waste is about 80ppm and was wondering about adding another membrane, so it's the first time i've really looked at the setup. I guess with such a low waste there would be no benefit for me in your suggestion.

[stuart howes]

water is only about 90 pence for 1000 ltrs so if you take waste in to it as well you are prob only spending £1 -£2 a day on water  for an average days work
 stu

[freshwater]

Bear,

With such low waste TDS its worth re-cicing it. BUT check your tds meter reads TDS a lot fo lem divide by 10 your waste could be 800 ppm.

steve@freshwatersystems.co.uk

[Sunshine Cleaning]

I have 2 TDS a handheld and one reading in and out on the RO.

Our water reads 37-45 on both meters.

i got the RO from 24/7 his water which was still in the RO unit read 280 ish (Southern water)

How would I 're-cic it'?

[freshwater]

Bear,

You need to remove the drain restrictor, the fit a needle valave in its place. Fit a tee before the needle valve and run this back the the RO inlet, fit a check valve, a needle valve and then tee it in to RO inlet. You then need to adjust the two needle valves so you get the right percentage going back in the RO and the right percentage going to drain.

steve@freshwatersystems.co.uk

[freshwater]

A specialist RO component supplier.

steve@freshwatersystems.co.uk

[matt]

steve, whilst on the subject of RO's

i have a flow tap connected to my waste (it was the only connection i had to extend the waste pipe to the drain)

anyways, ive shut this tap slightly, thus the flow of waste is less thus the flow of pure is ALOT better

whats the score with this

[freshwater]

matt,

ROs work on pressure and the speed of flow, the way pressure is built up accross the membrane is by restricting the drain. You have restricted the drain and incresed the pressure accross the membrane and therefor are producing more water, but you can only go so far or your TDS will increase as the water flow slows and the back pressure increases. If you are happy with the out put TDS then all is OK.

steve@freshwatersystems.co.uk