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Reverse Osmosis Rising TDS with Stable Feed Water TDS

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Reverse Osmosis Rising TDS with Stable Feed Water TDS

Date : 12/26/2015
From : joe

Question

I am seeing a rise in my RO product TDS which is lowering my percent rejection but Im not see an increase in my feed water TDS Any ideas

Answer

Raising TDS is normal for RO over time. As the membrane pores open you get both a rise in TDS and in production flow rate at the same water temperature and pump pressure.

The main cause is usually chlorine which nibble away at the edges of the pores.

There can be other reasons as well.

Higher levels of CO2 in the water can also raise the product TDS since CO2 it rejected completely at pH less than 8.5. To rule this out, take the sample and stir it and recheck the TDS with a hand meter if available.

If it is a sudden increase, it could be an o-ring failure, membrane glue failure or something similar.

Over time you can also see deposits on the surface that could effect product TDS. In that case you would see an increase in TDS with a lowering of flow rate at the same water temperature and pressure.

The most likely cause is membrane degradation cause by chlorine. You should routinely check the total chlorine levels on the reject water of the RO. That level should be less that 0.1 p.p.m. Any chlorine in the water will degrade the membrane over time. Chlorine is removed prior to reverse osmosis by activated carbon.


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