DI RO stage question

So my bro in law is a chemical engineer for a major plastics manufacturer here! I showed him my RODI unit and he wondered why the DI cartridge was last! On their systems they run the DI ahead of the RO! He said the DI cleared the water to save the RO membrane and that the RO membrane if good enough, will take more out of the water than the DI! He wasn't sure of the dynamics of water necessity for reef tanks though!

Just kinda curious why they would run it prior to the RO and we run if afterwards! BTW they use river water and filter it to the point that its acceptable to use for medical grade uses!

 

I know a lot of industry uses di, and only di. The reason we run it second is cause it doesn't last as long as a ro membrane. The ro pulls out around 98 percent of things and the di just picks up the left over. I believe for di to pull out as much as the ro it would have to have a much much longer contact time meaning slow water production.

 

yeah, he says his RO membranes will clear 100% or damn near as he said! Just curious! THX

 

NO RO membrane is 100% effective, none.
Industrial, commercial and municipal membranes are around 85-90% efficient in most cases and rely on chemical descaling agents, backwashing and cleaning in place with acids and chemicals. Our homeowner type units are more efficient at 96-98% rejection rate but do not have things like backwashing and chemical cleaning.

Large units such as he is talking about use many cubic feet of DI resins and can either regenerate it or it is replaced on a regular basis where we depend on the RO membrane to remove the 96-98% of the contaminants it does and the DI acts as a final polishing filter. You have it correct.

 

maybe he said it was near 100% after the RO not just the RO! i'll let him read this and answer! God bless ya, this stuff makes my brain hurt!