Dear all
I have to desalinate a feed water with about 2000 ppm total dissolved solids (TDS) using reverse osmosis process and the product water TDS should be less than 10 ppm. According to Filmtec ROSA design software the mentioned product water can be achieved using following two design options:
1. Two passes RO plant with brackish water membranes, or
2. One pass RO plant with seawater RO membranes
Because salt rejection of seawater RO membranes are more than brackish water ones, they can reduce the feed TDS to the acceptable range in one pass with higher operating pressure.
Does anyone have any experience in this field and does the ROSA software simulation results are achievable in operating conditions?
Best regards.
Practically yes; however, two passes RO plant should be more economical and provide higher recovery. With this rawwater quality, even one pass RO with brackish water membrane could be enough to produce the quality required. You may add polishing unit such as one unit mixed bed (demineralizer) to ensure the quality of product.
Two passes RO plant is more desirable... As rightly pointed out by Mr Al-Khaldi, the process is more economical... Also, the membrane fouling is less in this case. Preferably use a primary filtration unit beforehand.
Dear Fahad and Sankha
Thank you for your reply.
As I found from your responses using RO process with seawater membrane is practically in this case.
The water you want to treat is 2000 ppm compared to 35000 ppm (NaCl) of seawater. That means the seawater membranes are designed to operate at high pressures which means more energy consumption. In this case you can use less "tight" membranes for reducing the TDS.
As for all RO membranes, you have to feed them with a SDI index lower than 5 (some manufactures require 3) which means there probably has to be a pretreatment stage.
In my opinion, long term economics dictates the use of a pretreatment stage for the two pass brackish water membranes. You will find that the lower energy consumption, less frequent cleaning, and more stable operation will provide a more desirable economic outcome.
You can use,but required high energy and also chances of membrane fouling increased.
We have an experience in designing a RO system to produce a demineralized water from well water with low TDS. In order to get a better quality, than we used a brackish water RO. Of course, it requires higher operating pressure than low pressure RO to achieve a desired product flowrate. This decision is based on a simulation using software program provided by manufacturer which is then applied for the plant. According to my opinion, the software provided by manufacturer is best suit to the characteristics of their products. However, we still have to consider or set a safety factor from the simulation data.
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