Reverse Osmosis (RO) Membranes: How to clean them
The efficiency of the cleaning substances, their professional application, and the design and operation of the cleaning equipment all play a role in successful membrane cleaning. RO membrane cleaning should be done with both high and low pH cleaning solutions for the best results.
1. Cleaning RO Water Purifier with high pH
The high pH cleaning is done to get rid of biological or organic foulants that have carboxylic functional groups in them. At high pH, weak acids obtain an anionic charge, allowing them to spread. The calcium that connects foulants and biofilms to one other and to the membrane surface is chelated by high pH cleaning solutions because they can't remove the calcium bridging and commodities like NaOH are only marginally effective.
2. Cleaning RO Water Purifier with low pH
Prior to high pH cleaning, a low pH cleaning may be a better solution in some circumstances. Organic foulants, on the other hand, may lose their anionic charge if low pH cleaning is conducted first, and may become compacted in the membrane. Complete Water Solutions can assess your system and perform a foulant study to determine which solution is best for you.
3. Cleaning RO Membrane in stages
Cleaning outcomes are best achieved when each step is cleaned separately. Cleaning will allow for the highest possible flow velocity. When both stages of a 2:1 array system are cleaned at the same time, each pressure vessel in the second stage receives twice the flow velocity as the first. If the first stage parts are cleaned at ideal flow velocity, this will result in membrane telescoping in the second stage. Alternatively, basing the flow velocity on the second stage might result in insufficient surface scouring of the first stage membranes.
4. Cleaning RO Membranes with chemicals - A Step-by-Step Guide
- a) Examine the cleaning tank, hoses, and cartridge filters to ensure they are in good working order. If necessary, clean the tank and flush the hoses. Replace the cartridge filters with fresh ones.
- b) RO permeate or DI water should be used to fill the cleaning tank. Turn on the agitator or recirculation pump in the tank.
- c) Slowly pour the chosen RO cleaning product into the cleaning tank, based on the total volume of the CIP and the product strength required, and properly mix.
- d) Check the temperature of the solution. If the temperature of the solution is below the specified level, adjust the heating control to get the desired temperature. Contact Netsol’sComplete Water Solutions if the manufacturer's recommendation isn't accessible.
- e) The pH of the solution should be checked. The pH should be around 12 or whatever the membrane manufacturer recommends. Adjust the pH with sodium hydroxide (NaOH) or similar chemicals as indicated by the membrane manufacturer if the pH is too low. Adjust the pH using hydrochloric acid (H2O:HCl) if it's too high.
- f) For 30 minutes, circulate the solution through one stage at a time in the feed flow direction. Circulate at the membrane or system manufacturer's recommended flow rate. If the manufacturer's recommendation isn't available, contact the friendly team atNetsol’s Complete Water Solutions. Pressure should be kept low enough during cleaning to produce minimal permeate, but never exceed 60 psig [4.2kg/cm2].
- g) To avoid redeposition of removed materials, the first return flow (up to 15% of the cleaning tank volume) should be routed to drain in cases of high fouling. In a multistage system, each stage must be cleaned independently for best performance.
- h) Before continuing, dump the tank and create a new cleaning solution if the first stage cleaning solution becomes turbid or discolored. If the pH or temperature of the solution deviates from the prescribed range, a new solution should be made.
- i) Before putting the system back in service, give it a good rinse with RO permeate.
- j) Divert product water to drain until any remaining cleaning solution has been removed from the system before resuming service.