Reverse osmosis stops at scaling, not at salt
RO concentrate treatment is where recovery is usually surrendered. CHEMRO removes the scale-forming species first, then recovers water at high pressure. What is left becomes salt instead of a tanker load.
What is RO concentrate treatment?
RO concentrate treatment is the stage that recovers water from the stream a reverse osmosis system rejects, instead of paying to dispose of it.
CHEMRO does it in two moves. Chemical pretreatment removes the components that scale. A high-pressure membrane system then keeps recovering water from what remains.
The permeate is blended with the product water from the main reverse osmosis system and reused. The final concentrate is either consumed on site or crystallized into product salt.
Why recovery gets surrendered
Most plants stop at 75% because of scale, and call it the design.
Reverse osmosis does not stop because the water is too salty. It stops because the sparingly soluble species left behind reach saturation. They then precipitate on the membrane surface.
So operators back the recovery off to protect the membranes. The plant settles well below what the salt balance would permit. The rejected 25% then leaves by tanker, every day, for the life of the plant. That is not a design decision. It is a limit nobody removed.
How CHEMRO works
CHEMRO stands for chemical treatment combined with reverse osmosis. The order is what matters: take the scale out first, then apply pressure.
Chemical pretreatment precipitates and removes the scale-forming species. Only then does the stream enter the high-pressure membrane system, which can now run at a concentration factor that would have wrecked a conventional rack. The principle behind our nanofiltration concentrate treatment is the same: remove what limits the process instead of pushing harder against it.
The main reverse osmosis system yields 75% product water. Its concentrate, a quarter of the flow, passes through CHEMRO and gives back a further 15%.
Total recovery reaches around 90%. What was a daily tanker movement becomes 10% of the flow going to a crystallizer.
Two things to do with what is left
The final concentrate does not have to leave the site as waste. Where the plant has a use for it, it is consumed internally. Where it does not, it goes to evaporation and crystallization and comes out as a solid.
On industrial projects that solid is frequently a saleable industrial salt rather than a landfill item. That is the difference between an operating cost and an operating credit. It is also where concentrate treatment stops being a water problem and becomes a resource recovery one.
Where it is applied
Landfill and waste-to-energy leachate
Paired with nanofiltration concentrate treatment, this is the stage that takes a leachate plant from around 75% recovery to around 90%.
High-hardness and high-silica industrial water
Mine water, coal chemical effluent and cooling blowdown are scaling-limited rather than salinity-limited. That is exactly the constraint CHEMRO removes.
Ahead of evaporation in a ZLD train
Every cubic meter recovered here never has to be evaporated. Evaporation is the largest energy cost in a zero liquid discharge plant.
Frequently asked questions
What is RO concentrate treatment?
It is the stage that recovers water from the stream a reverse osmosis system rejects. Left untreated, that concentrate is the plant's disposal cost. Treated, most of its water comes back and the residue becomes a solid.
Why does reverse osmosis stop where it does?
Scaling, not salinity. As water is removed, calcium, sulfate, silica and carbonate concentrate until they precipitate on the membrane. Operators back off the recovery to protect the membranes, so the plant settles well below what the salt balance would allow.
How does CHEMRO get past that limit?
By removing the scale-formers before the membrane rather than tolerating them. Chemical pretreatment drops the scaling species out of the concentrate. A high-pressure membrane system then recovers water from a stream that no longer scales, and the permeate is blended with the main RO product and reused.
What happens to the final concentrate?
Two routes. It can be consumed on site where the plant has a use for it. Or it can go to evaporation and crystallization and become product salt. On industrial projects that salt is often saleable, which turns a disposal line into a revenue line.
How much extra recovery does it give?
In the leachate configuration we run most often, the main RO system yields 75% and the concentrate stage returns a further 15%, for around 90% total recovery. The exact gain depends on the scaling potential of your specific water.
Is it patented?
Yes. The reverse osmosis concentrate treatment stage is covered by Chinese patent ZL 2014 2 0508999.6. The nanofiltration concentrate stage that often sits alongside it is covered by ZL 2013 2 0699919.5.
Tell us what your RO is rejecting
Start here
If your plant is capped at 75% recovery, the reason is usually visible in the concentrate analysis. Send it and we will tell you how much of that stream is recoverable.
Useful to include
- RO concentrate flow and current recovery
- Calcium, sulfate, silica and alkalinity
- TDS and conductivity
- Current disposal route and its cost
- Whether a crystallizer already exists on site
Contact us directly
- info@jing-yu.com
- Phone
- +86 21 6593 0816
- Office hours
- Monday to Friday, 9:00 to 18:00 Shanghai time (GMT+8)