RO Prefilters
RO Prefilters
(OP)
Any recommendations on what to install for filtering the water going to an RO unit?
Inlet water to the filter would be potable water that varies in quality since the source is a lake.
Throughput needs to be 4,000 - 6,000gpm.
I think sand filters are out of the question because of size constraints.
This plant has had many problems with their RO because they would run straight city water to it.
Inlet water to the filter would be potable water that varies in quality since the source is a lake.
Throughput needs to be 4,000 - 6,000gpm.
I think sand filters are out of the question because of size constraints.
This plant has had many problems with their RO because they would run straight city water to it.





RE: RO Prefilters
The .5 micron filtration is required due to the pore sizes of the membranes themselves. And the multi-media filtration is required to reduce the loading on the cartridge filters as these types of elements cannot be cleaned; rather when around a 5-8 psid is reached across the filter it is taken off-line and the elements manually changed. With proper upstream filtration, this procedure may only have to be performed every few months or so.
You said that they are currently running city water directly into the RO. I trust there are chemical feeds to reduce residual chlorine to 0 and the addition of anti-scalant chemicals to prevent scaling in the membranes?
RE: RO Prefilters
RE: RO Prefilters
RE: RO Prefilters
Regards,
Repetition is the foundation of technology
RE: RO Prefilters
Yes the anti-scalant was being added and sodium bisulfite treatment for chlorine was being done when the RO was online previously. They had UF filters before RO's. But the UF's plugged up (due to solids/silt in the city water) so they bypassed them (dumb) and went straight to the RO.
My concern with multi-media filters is that they would have to be too large for our flow-rate and we're somewhat limited on space. Does anyone have experience with the cartridge-type filters that can be backwashed?
RE: RO Prefilters
I had come across a filter type the other day we were condsidering for our own use. It's an autocleaning filter, generally used on machines with recycled fuel and oil. It can continually remove sediment above a certain size and cleans itself. Check out www.cuno.com
Contact the SASS group, if you are interested.
RE: RO Prefilters
You're probably using very small membranes. Our RO membranes are 8" x 40" long and rated capacity of 1 membrane is over 6gpm of permeate.
RE: RO Prefilters
What is the MWCO or NMWL of your membranes?
RE: RO Prefilters
I don't recognize those acronyms. The membranes are Dow Filmtec BW-365, so they've got 365ft2 total area each. With our high-pressure multi-stage pumps, our RO inlet pressure is 360 - 400psi.
RE: RO Prefilters
The acronyms are Molecular Weight Cut-off and Nominal Molecular Weight limit. It seems the difference between the systems we were looking at was to operate at a much lower pressure. More information on the autocleaning filters: the cleanest rating is nominal 40 microns, meaning it will catch most particles at and above 40 microns. I'm not sure how much help that is, but I thought I'd throw it out there.
RE: RO Prefilters
Congratulations , you made a great Panel.
Everybody share a little, to make a big total and in my opinion every body is right.
I designed a system after looking at the problems of other system and it has been running great, with waste paper mill water.
The Key issues for sucsesfull design were.
1.-Identify composition and sise of contaminants to be removed. Sorry there is not free lunch in technology, you have to analize.
2.- Do all the Chemical conditioning recomended
3.-Then do Do Prefiltration in stages, acording to the amount and sise of contaminants.
4.-Prefiltration is not one or the other, you need them all and probably an Ultrafiltration membrane before the RO membrane is required, I sugest you get into the clasification of membranes by the dimentions of the particle you try to separate
5.-If my gut feelins are right you will need first Coarse filtration,Multimedia with activated carbon will help If you have a lot of disolved organic material, as you will, if the water comes from a lake, then Ultrafiltration , and then the water will be conditioned for the High pressure membranes you have, they will will work beter
6.- aspearing 1 is in the BINGO trayectory I sugest very strongly you pursue this lead very intensively
7.- It looks like the membrane design was not the best some body did not made all the previous Homework and now you will have to do it.
Good Look.
RE: RO Prefilters
RE: RO Prefilters
I'm still working on getting a 12-month profile of the water here. The numbers I'm seeing in our inlet water reports are a bit puzzling because the water quality seems fairly good. Turbidities tend to stay below 2.0, alkalinity below 1.5, TDS below 400, and SDI below 7.0.
But the RO has never performed well. There may be some design issues. One thing that strikes me is that the RO is vertical. Any comments as to how detrimental this is?
I'll check up on our ultrafilters. Our water treatment service company has already suggested low-pressure membranes and we will eventually go that route. But I want to make sure our pre-filtration is set up right.
We ultimately need demin water for 1000psi+ boilers.
RE: RO Prefilters
RE: RO Prefilters
nic
RE: RO Prefilters
Note that it is common practice to filter potable water prior to RO. By the way, you can stack the filters on top of each other to save space.
IMHO, the older UF system should have had a multi-media filter pretreatment system. The older UF was probably installed in lieu of the multi-media filter pretreatment. Probably a bad decision.
If you install a multi-media filter and use a little cationic polymer, you will probably get a SDI of 1.
You should also consider replacing your DI unit with the newer CDI units as the same time.
The backwashable cartridge-type filters that I am familiar with have been used in condensate polishing systems in nuclear plants where the goal was to reduce radwaste. This filters are similar to the standard cartridge filters, but are backwashed to avoid having to change a hot filter. These are only used on water with extremely low solids. These filters are probably too expensive for your application.