To profile a system, all individual pressure vessels are tested for their concentration of dissolved solids with a TDS or conductivity meter. Well designed systems normally have a test port in the permeate line of each individual vessel for this purpose. The permeate samples of all pressure vessels in the same stage should give readings in the same range. From one stage to the next the average permeate TDS or conductivity usually increases, because the second stage is fed with the concentrate from the first stage.
A vessel with a faulty membrane or damaged o ring will normally have a somewhat higher permeate conductivity than the others in the same stage.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
Thanks ashtree and bimr for the informative answer. Is it normal to RO plant to make it online conductivity profiling? Will it cost a lot to have this smart technology? Is it useful?
Most plants would at least have some basic conductivity monitoring on the permeate side so that in the event of significant failure it may trigger an alarm, or at least change the trend.
Whilst you could install a conductivity monitor on every pressure vessel, it would be quite expensive, and you would get lots of very slow trend data over a long period of time. In a large plant you might want to put a conductivity monitor in each group of vessels in a stage , but as you increase the number of vessels served by a single monitor the less likely that you will pick up a defect.
What i would suggest if your plant is reasonably large or the quality of the water is very important, to at least have a conductivity monitor on the plant, preferably one on each stage or one on a cluster of vessels. How many you can group together will depend on the layout of the permeate pipework. Then i would manually sample each individual pressure vessel regularly , perhaps weekly and record the results. This will allow a trend to be determined, and any unusual variations between vessels checked.
If there is a problem such as a leaking o ring or failed membrane you are likely to see the relationship between vessels in the same stage change.
But unless you are really pushing the membranes in terms of throughput, flux rates, operating pressures, and recovery , it is very likely that you will go many years between failures large enough to detect by profiling. Nonetheless it is a useful tool for monitoring the health of the system.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
Unless your plant is very large, conductivity profiling is not something that will be economical.
Conductivity profiling is a maintenance activity to pinpoint problems.
Each pH probe will cost a minimum of $500 just for the instrument. Add the piping connection and wiring, plc cost and programming will result in a large cost. The pH probes are also a consumable cost as they don't last forever.
