RO/DI Filter Stages - Particle Sizes

flinka · 05/04/2007, 06:21 AM

I have been reading up on and researching RO/DI units. Most articles from “reputable” information sources (e.g., reef central, wetwebmedia.com, etc.) recommend decreasing filter particle size as you progress from one stage to the next (e.g., 1st stage 10 microns, 2nd stage 5 microns, 3rd stage 1 micron, etc. or some similar stepped down approach) so that each filter stage helps out the next stage without trying to do too much at one stage resulting in clogging, pressure issues, etc. Yet, almost every RO/DI unit I have seen has a very low size (<5microns and sometimes 1 micron or less) for the 1st pre-filter (sediment) and larger sizes upstream. The only exception I have seen so far are the AirWaterIce units.

My two questions are:

1) Is there something flawed with the decreasing filter particle size theory?
2) Is AirWaterIce the only company following that approach?

Thanks!

bmk · 05/04/2007, 06:47 AM

Hi
Check out this site, it's where I got mine from "http://www.ro-man.com/?src=google&gclid=CJ3Hg9D-84sCFRGCGgodCmiibA"
I have the four stage unit (5 micron pre-filter, carbon block, membrane and DI unit). They state that if you are using more than one 'pre filter' use a 5 micron first and then a 1 micron after it as it will get clogged if using the 1 micron first.

AZDesertRat · 05/04/2007, 07:18 AM

AS a water treatment plant operator by trade I used to agree with the decreasing micron size method. I have since had my mind changed for me by Charles Mitsis the owner of Spectrapure.

The problem is if for example you use a 10 micron prefilter followed by a 5 micron carbon block any particles smaller than the prefilters rating are passed through to the carbon block causing it to plug prematurely. The carbon is going to trap things in the 5 to 10 micron range and cause head loss or a pressure drop at the RO membrane.

Now if we take a 0.5 micron prefilter it will trap things much smaller so it does not pass on to the carbon so the carbon continues to function as it was designed adsorbing VOCs and chlorine. Better yet they now have a 0.2 micron prefilter that is absolute rated meaning it is much more efficient plus it is a pleated material and has 10x the surface area so can trap much more before plugging. The 0.2 micron is also of sufficient size to filter out viruses and bacteria unlike any other filter so now you can run the carbons longer without fear of growing things inside the housings if you keep a a properly maintained system. I intend to run my carbon for its full 20,000 gallons instead of changing at 6 months like before. I use a low level chlorine test kit to monitor its condition, if I see chlorine breakthrough I know its exhausted.

05/04/2007, 06:21 AM	#1
flinka Registered Member Join Date: May 2006 Location: Indianapolis, IN Posts: 149	RO/DI Filter Stages - Particle Sizes I have been reading up on and researching RO/DI units. Most articles from “reputable” information sources (e.g., reef central, wetwebmedia.com, etc.) recommend decreasing filter particle size as you progress from one stage to the next (e.g., 1st stage 10 microns, 2nd stage 5 microns, 3rd stage 1 micron, etc. or some similar stepped down approach) so that each filter stage helps out the next stage without trying to do too much at one stage resulting in clogging, pressure issues, etc. Yet, almost every RO/DI unit I have seen has a very low size (<5microns and sometimes 1 micron or less) for the 1st pre-filter (sediment) and larger sizes upstream. The only exception I have seen so far are the AirWaterIce units. My two questions are: 1) Is there something flawed with the decreasing filter particle size theory? 2) Is AirWaterIce the only company following that approach? Thanks!

05/04/2007, 06:47 AM	#2
bmk Registered Member Join Date: Apr 2007 Location: England Posts: 278	Hi Check out this site, it's where I got mine from "http://www.ro-man.com/?src=google&gclid=CJ3Hg9D-84sCFRGCGgodCmiibA" I have the four stage unit (5 micron pre-filter, carbon block, membrane and DI unit). They state that if you are using more than one 'pre filter' use a 5 micron first and then a 1 micron after it as it will get clogged if using the 1 micron first.

05/04/2007, 07:18 AM	#3
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	AS a water treatment plant operator by trade I used to agree with the decreasing micron size method. I have since had my mind changed for me by Charles Mitsis the owner of Spectrapure. The problem is if for example you use a 10 micron prefilter followed by a 5 micron carbon block any particles smaller than the prefilters rating are passed through to the carbon block causing it to plug prematurely. The carbon is going to trap things in the 5 to 10 micron range and cause head loss or a pressure drop at the RO membrane. Now if we take a 0.5 micron prefilter it will trap things much smaller so it does not pass on to the carbon so the carbon continues to function as it was designed adsorbing VOCs and chlorine. Better yet they now have a 0.2 micron prefilter that is absolute rated meaning it is much more efficient plus it is a pleated material and has 10x the surface area so can trap much more before plugging. The 0.2 micron is also of sufficient size to filter out viruses and bacteria unlike any other filter so now you can run the carbons longer without fear of growing things inside the housings if you keep a a properly maintained system. I intend to run my carbon for its full 20,000 gallons instead of changing at 6 months like before. I use a low level chlorine test kit to monitor its condition, if I see chlorine breakthrough I know its exhausted.