Technical assistance: Reverse osmosis and mixed-bed regeneration issues

The key is what is the conductivity of the reverse osmosis feed water? What is the hardness? In addition, parameters of the mixed-bed such as diameter, resin height, and flow rate also affect its operating cycle. 2 days of regeneration shouldn’t be considered too short.

Check whether the conductivity of the water produced by RO is above the limit; it is necessary to improve the operation procedures to ensure effective resin regeneration

This post was last edited by hesonchang214 on 2013-11-27 07:41; secondary reverse osmosis will do!

Our plant uses two-stage reverse osmosis followed by a mixed-bed resin system; the conductivity is generally between 20 and 30, and the outlet water temperature is between 20 and 25 degrees. The mixed-bed resin system could previously operate for up to 70 hours, but now it only lasts for about a day. . Under the guidance of that expert. .

This post was last edited by hesonchang214 on 2013-11-27 07:41. You need to replace the resin!

This post was last edited by hesonchang214 on 2013-11-27 07:41: Incomplete resin regeneration or the resin needs to be replaced!

The last edit to this post was made by hesonchang214 on 2013-11-27 at 07:42. It’s not so much about the operating time of the resin, but rather about the amount of water produced per cycle – the resin needs to be regenerated whenever that amount of water has been produced； Determine whether it’s due to poor water quality or the resin is worn out and needs to be replaced

Could poor resin stratification be causing poor regeneration, thereby affecting the effluent quality and regeneration time? This post was last edited by li*ch on 2009-3-24 10:00]

1　 What is the conductivity of the water produced by your RO system? What was the conductivity of the water produced by it at the beginning? 2 How much water can your mixed-bed system produce? How much water can it produce at the beginning? 3 Has your mixed-bed been fully regenerated? How effective is the regeneration? Once these issues are clarified, it will be possible to determine where exactly the problem lies in your system. The main direction. This post was last edited by chuan800 on 2009-3-24 14:42.]

Is it poor regeneration of the mixed-bed that results in a short operating cycle?

This post was last edited by hesonchang214 on 2013-11-27 07:43. It’s mainly a problem with the resin, right?

There could be many reasons: poor stratification of the resins in the mixed-bed system, incomplete regeneration, low quality of the regenerating agents, or contamination of the resins leading to a decrease in their exchange capacity. A thorough inspection is necessary.

Precautions for regenerating water treatment mixed-bed resins: When the sodium content in the effluent from the mixed bed exceeds 5 ug/l, or the conductivity is greater than 0.2 us/cm, or the silica content is above 20 ug/l, it indicates that the mixed-bed equipment has failed and needs to be shut down for regeneration.
1. Check and close the manual valves for acid and alkali supply to the other two mixed beds, as well as the manual valve for the effluent from the faulty mixed bed; also close the manual valves of all instruments.
2. Alkali immersion: First, drain water from the mixed bed, then use air to loosen the resin. After draining all the water, add half a tank of alkali and let it soak for 4–8 hours (to prevent water from flowing back into the metering tank, close the manual valve for alkali discharge from that tank first). After that, start flushing until the alkalinity drops to ≤0.5 mmol/L.
3. Backwashing for stratification: Open the manual valve for water inlet to the mixed bed. Start backwashing with a high flow rate; once the resin has reached a certain height, reduce the flow rate and continue backwashing at this lower rate. Maintain this condition for 5 minutes through the observation hole. Then quickly close the manual valve and check whether the boundary between the different layers is clear. If not, continue backwashing at a low flow rate until the boundary becomes clear. This step is crucial.
4. Static settling: Allow the resin to settle statically for 10 minutes so that the layers can separate.
5. Water drainage: Open valves M10 and M11 to drain water, continuing until no water more comes out of M11. At this point, there will be about 100 mm of water layer on top of the resin layer; then close M11.
6. Regeneration of the anion resin: Open the middle drainage valve M6 and the alkali supply valve M7 of the mixed bed. Start the regeneration pump, open the outlet valve (Z1 or Z1) and the water inlet valve J6 of the alkali injection device. Adjust the regeneration flow rate to around 5 M/H. Slowly open the valve J5 for discharging alkali from the metering tank, and adjust the concentration of the sodium hydroxide solution used for regeneration to 4%. (If the temperature is low, use a heating device to warm the alkali solution.) Regenerate the anion resin for 40 minutes.
7. Replacement of the anion resin: Keep the conditions from the previous step unchanged, close valve J5, and perform a forward wash to replace the anion resin. This process takes about 40 minutes. After completion, close valves M7 and J6.
8. Forward wash of the anion resin: Open valves M1 and M10 of the mixed bed, and perform a forward wash with a high flow rate of 86 T/H. When water starts overflowing from M10, close it. The forward wash should last about 5 minutes, until the effluent no longer contains any alkalinity. Once the forward wash is complete, close valve M1.
9. Regeneration of the cation resin: Open the acid supply valve M8 and the water inlet valve S6 of the mixed bed. Adjust the regeneration flow rate to around 5 M/H. Slowly open the valve S5 for discharging acid from the metering tank, and adjust the concentration of the hydrochloric acid solution used for regeneration to 5%. Regenerate the cation resin for 30 minutes.
10. Replacement of the cation resin: Keep the conditions from the previous step unchanged, close valve S5, and perform a reverse wash to replace the cation resin. This process takes about 30 minutes. After completion, stop the regeneration pump, close valves Z1 or Z2, as well as M8, S6, and M6.
11. Forward wash of the cation resin: Open valves M1 and M5 of the mixed bed, and perform a mixed forward wash with a high flow rate of 86 T/H for both the cation and anion resins. Open valve M10; when water starts overflowing from it, close it. The forward wash should last about 5 minutes, until the conductivity of the effluent is less than 5.0 us/cm. Once this condition is met, close valves M1 and M5.
12. Water drainage: Open valves M10 and M11 to drain water, continuing until no water more comes out of M11. At this point, there will be about 100 mm of water layer on top of the resin layer; then close M11.
13. Mixing of the resins: Open the valve M9 for supplying compressed air to mix the resins. This process takes 0.5–1 minute; then close valve M9.
14. Forward wash: Open valves M1, M5, and M10 of the mixed bed to perform another forward wash. When water starts flowing out of M10, close it. After 5 minutes of forward washing, check the conductivity and silica levels. The forward wash is successful when the conductivity of the effluent is ≤0.2 us/cm, the sodium content is ≤5 ug/l, and the silica content is ≤20 ug/l. If these conditions are not met, repeat the processes of draining water, mixing, and flushing until they are satisfied.
15. Standby mode: Close the manual valves for water inlet, as well as valves M1 and M5. Once the regeneration is complete, the mixed bed can be put into standby mode.
16. During the regeneration process, stop the water production equipment and increase inspections to ensure safety.

Regeneration operation procedures for mixed-bed resins: 1. Backwashing and stratification: Open the inlet valve of the mixed-bed regeneration pump, start the regeneration pump, then open the outlet valve of the mixed-bed regeneration pump, as well as the backwashing drain valve, the air release valve, and the backwashing water inlet valve. After water flows out from the drain valve, close the drain valve. The flow rate for starting the backwash should be low; once the resin becomes loose, the flow rate is gradually increased until the entire bed is loosened, at which point the flow rate is approximately 10 m/h. The expansion rate of the anionic resin is over 70%, while that of the cationic resin is around 30%; as a result, the anionic and cationic resins separate after 10–15 minutes. (The water from the mixed-bed outlet manifold can be used, passing through the outlet valve, to increase the backwashing stratification flow rate.) ) 2 Close the water inlet valve for backwashing of the mixed-bed. After stopping, if the resin has not been properly stratified, repeat the backwashing process according to step 1. 3 Release water ； Once the cation and anion resins have fully separated, open the drain valve for normal washing to release the water from the mixed-bed, allowing the water level to drop to about 10 cm above the surface of the resin layer. 4. Regeneration liquid feed: Open the inlet valve of the mixed-bed regeneration pump, start the pump to operate; open the outlet valve of the regeneration pump as well as the water inlet valve of the acid-base injector and the intermediate drain valve. Maintain the water level in the exchanger at 10 cm above the surface of the resin, and keep this level stable for 2 minutes, after which open the outlet valve of the acid-base metering tank. Adjust the acid concentration to between 4-5%, and the alkali concentration to between 3-4%. 5 Permutation ； Once the acid and alkali have been added, close the outlet door of the acid and alkali metering tank, and continue to use the acid and alkali sprayer to maintain the original water volume for displacement until the water discharged from the middle becomes neutral. Close the acid and alkali inlet valves of the mixed-bed, the intermediate drain valve, the ejector outlet valve, and the regeneration pump outlet valve. Shut down the regeneration pump and close its inlet valve. 6 Mixing of cation-anion resins: Before mixing, open the middle drain valve to bring the water in the mixed bed to a level 100–150 mm above the surface of the resin layer, then close the middle drain valve. Open the air inlet valve at the bottom of the mixed-bed and the outlet valve of the main pipe. Compressed air is introduced from the bottom to mix the resin. The compressed air pressure used is 0.1–0.15 MPa, and the time required is about 5 minutes. After supplying compressed air, water should be drained quickly to force the resin to settle rapidly, preventing it from separating into layers again as it settles. Open the mixed-bed forward wash drain valve during drainage. 7 Normal washing: Open the inlet valve of the intermediate water pump, start the intermediate water pump, open its outlet valve as well as the inlet and outlet valves of the anion exchange resin bed. Then open the inlet valve of the mixed-bed resin tank and the drainage valve for normal washing, and carry out the washing at a flow rate of 10–20 m/h. It can be set aside for use or put into operation only after the water output meets the required standards. During regeneration, it is essential that the cation and anion resins be completely separated; otherwise, the precautions are the same as those for cation and anion beds.

Hello, CDPulin moderator. I have a question: how is the time required for adding acid and alkali determined? Since the diameter of the mixed-bed is fixed, the amount of acid and alkali needed for one regeneration cycle is also fixed; therefore, it’s sufficient to add a predetermined quantity into the metering tank. By then calculating based on the regeneration flow rate, the regeneration flow volume can be determined. Once the total flow volume is known, the time required to add acid and alkali can be calculated. However, this time differs significantly from 40 minutes. Please advise! If you are an expert in this field, could you be contacted? I work in water treatment equipment, and I often encounter issues related to the regeneration of mixed-bed filters when writing operation instructions.

16# Hanqiudong naturally starts timing from when the valves for acids and bases are opened.

This post was last edited by hesonchang214 on 2013-11-27 07:44. Resins have a limited lifespan, and improper handling will shorten it!

5# wolflotus: It seems your processing methods need to be improved. Either the quality of the raw water is too poor, or what’s the effectiveness of ultrafiltration, sand filtration, and softening? Check it out

A conductivity level of 20–30 for the water coming from the second-stage reverse osmosis process plus the water from the mixed-bed system is quite indicative of a problem. The conductivity of the water from the second-stage reverse osmosis process is usually below 10; with an inlet water conductivity of around 2500, the conductivity of the water from the first-stage reverse osmosis process is about 50, while that of the water from the second stage is around 1. The conductivity of the water from the mixed-bed system is below 0.1. Moreover, the regeneration cycle time is also very long. In your case, there is likely a problem with the reverse osmosis membranes; it’s necessary to check whether the resins are contaminated, whether their quality is satisfactory, and whether there is enough resin available.

There must be a problem with the resin regeneration