DI water across RO Membranes question

[PurewaterGuy]

I recently was experiencing high TDS readings on the permeate side of some RO membranes. The TDS readings were high on six RO units. The original setup was as follows.

Two carbon units prior to each RO. (that's all)

The new setup I installed was as follows.

One 5 micron prefilter, two carbon tanks, one deionizer tank, one .35 micron postfilter.

Since installing the additional equipment the TDS readings have dropped down to <1

However, I received email stating the rejection rates are dropping on the membranes.

Any ideas on whether the DI is having a negative impact on the RO membranes? Even if the PH factor is being altered it should be in the range of tolerance for the membranes.

 

[bimr]

Where are you getting the water? Sometimes municipal water quailty changes when the City puts a different well in service.

 

[PurewaterGuy]

The water is coming from the Massachusetts MWRA. After some phone calls to them it has been revealed they are working and have been working on a certain stretch that would or could be causing problems where the equipment is located.

Once the new equipment goes in I'm confident we will stop this problem. The equipment slated to go in as a central system will consist of the following pieces of equipment to feed 6 dialysis stations.

1- 12"x52" Multimedia Filter (backwashable) with a Fleck 2750 Head

2- 14"x65" 3.6cft Acid washed carbon units (backwashable) with Fleck 2750 heads

1- 20" 5 micron prefiter

1- 5 GPM Reverse osmosis unit with recycle option 4- 4"x25" TFC Membranes

1- 200 Gallon Poly storage tank

Dual distribution pump station, 1- 20" big blue filter housing with a .35 micron filter, 1- ultraviolet unit all feeding the pipe loop consisting of GF pigmented socket fusion pipe, NO DI required, the system will run 24/7/365 recirculating back to the storage tank, over and over and over ,,,,,
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As for the DI regeneration. All the cell quality lights I use for tap water are 5 meg cutoff lights. Once the light is out the resin iin the first tank is exhausted. It is then warehoused in drums and regenerated in 30 cft lots. In a normal operation naturally I would use DI beds in tandem and once the quality light indicates the first tank is exhausted the second tank (the polisher) should pick up the slack as usual until such time as the tank is rotated and a new tank is placed in the polisher position.