Reverse osmosis membrane conductivity issue
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A set of 90 t/h reverse osmosis system, using Hydranautics CPA3-LD membranes in a 10:6 arrangement. The process involves multi-media filters, security filters, and reverse osmosis; the conductivity of the inlet water is 530 μS, while that of the outlet water is less than 10 μS. The system has been operating normally throughout. The inlet pressure increased to 1.65 Mpa, and the conductivity also rose to 60 μS. Later, the customer tried cleaning with citric acid, but the results were not satisfactory. On-site measurements showed that the conductivity of the deionized water in each membrane housing in Section 1 and Section 2 is as shown in Figure 1, while the pressure values are shown in Figure 2: 1. The conductivity in Section 1 is around 23 μS, and that in Section 2 is around 100 μS. 2. Subsequently, one membrane from Section 1 and one from Section 2 were removed (see Images 3–6). White substances were found inside the membrane housings, and the outer surface of the membranes was dirty, with fine sediment present. The membranes were left in place for about ten minutes before being weighed; the weight of the wet membranes was 18 Kg, while the value stated in the available data was 16 Kg. This suggests a tendency toward scaling. 3. The equipment was cleaned, and after cleaning the pressure dropped significantly: the inlet pressure was 1.25 Mpa (I forgot the values for the other two pressures, but they were around 1.0 MPA). The conductivity was around 70 μs. Even after several days of operation, the pressure did not decrease. The conductivity of the fresh water passing through membrane stage 1 and stage 2 was measured, and it turned out to be significantly higher than before cleaning, as shown in Figure 7. Can the conductivity still not be reduced? ?
Could it be due to poor surface polishing quality? You can try comparing them to see
Has there been any change in water temperature? Water temperature has a significant impact on conductivity； What is the conductivity of reverse osmosis water? The concentration of the solution used during cleaning may cause damage to the membrane. It could also be due to water quality issues, leading to an increase in silt.
The pressure difference in stage 1 is 0.25 MPa, and that in stage 2 is also 0.2 MPa. The contamination of reverse osmosis systems can be primarily classified into three categories: first, organic matter contamination, which is manifested by an increase in the pressure difference in stage 1； II. Inorganic pollution, also known as scaling, is manifested by an increase in the 2nd pressure difference ； III. Microbial contamination, manifested by an increase in the operating pressure and pressure difference throughout the system ； Of course, in all the above cases, there is basically a decrease in water production ； In this case, it is certain that both scaling and organic contamination are present; moreover, the conductivity of the water produced by each pressure vessel in stage two is significantly higher. Has the O-ring been checked? What is raw water? Is there a water quality analysis report? Also, is the dosing of system scale inhibitors and biocides proper, and how long has the system been in operation? Suggestions: 1. First, clean the system; for scaling issues, use hydrochloric acid for cleaning, starting with acid followed by alkali, and then perform acid cleaning once more. 2. Check whether the chemical dosing in the system is operating normally.
I would like to ask how the concentrated water from reverse osmosis is treated – is it reused as reclaimed water?