Clean In Place – Membrane Cleaning CIP System
A Clean in place CIP system is a very effective method widely used by RO Systems manufacturers and operators to preserve and also clean fouled or scaled reverse osmosis system RO membranes. Using certain chemicals and following procedures guided by each RO Membrane manufacturers. With few exceptions, all reverse osmosis systems and other membrane systems are subject to fouling by one or more source water components and therefore require periodic cleaning. Clean In Place CIP Membrane cleaning is usually performed without removing membranes from the pressure vessels or the system. A Clean In Place CIP system is designed to prepare and recirculate chemical solutions through some of or all membrane modules at low pressure.
The CIP system can also be used to feed special membrane post treatment chemicals. Not to be confused with membrane system post treatment. Membrane performance require post-treatment equipment in some cases. The clean in place CIP system also serves to prepare and transfer membrane storage solutions, or preservatives. Membrane “pickling” solutions prevent microbial growth and in some cases prevent freezing when the membrane system is shut down for extended periods, typically more than a week. The clean in place system for a Reverse Osmosis System or Nano-Filtration system should be designed to accommodate all cleaning and membrane storage solutions expected to be used at the plant.
Inadequate clean in place CIP System procedures will result in ineffective cleaning results. We will discuss the major parameters of membrane cleaning followed by cleaning instructions from RO membrane manufacturers and step-by-step procedure. The major parameters are:
- Chemicals
- Temperature
- Flow rate
- Time
Clean In Place Chemicals
We won’t remove a carbonate scale with caustic or remove a biofilm with low pH. We must use the right chemical(s) to dissolve as much of the foulant / scalant as possible. Things that dissolve will leave the Reverse Osmosis System easily. It is the things that don’t dissolve which give us the problems. Please contact BQUA for more information about choosing the right chemical for your cleaning.
Clean In Place Temperature
Temperature affects chemical reactions. In general, the rate of most chemical reactions will double with every 10°C increase in temperature. In other words, we can get the job done quicker if the cleaning solution is warmer. If the cleaning solution temperature is less than 16°C (60°F), then cleaning will have no effect since the water is too cold. The cleaning solution temperature should be at least 21°C (70°F). Even better, get the temperature above 27°C (80°F).
Clean In Place Flow Rate
Flow rate is critical for removing fouling particles. It is unlikely that we will be able to dissolve particles completely. We, therefore, must physically remove them. We do this with turbulence. The higher the flow rate, the higher the turbulence. The higher the turbulence, the more particles removed.
Clean In Place Time
Frequently RO membrane manufacturers and chemical cleaning vendors recommend a one-hour cleaning. If the scalant/foulant is stubborn, some soaking time prior to, or after, we recommend circulating the solution. This is fine for lightly fouled/scaled elements. This may work if cleaning is initiated when the Normalized Permeate Flow NPF has dropped no more than 10-15%Â and/or the Differential Pressure DP across a stage has increased no more than 15-25%. And will not work if fouling/scaling has been allowed to progress. It is not unusual to have to clean severely fouled RO Membrane elements for 72 continuous hours. Use clean in place CIP monitoring sheets during a cleaning, and trending graphs following a cleaning, to determine when cleaning completes. Much more time than usually recommended may be required.
BQUA Clean In Place CIP System design
Clean In Place CIP System Procedure
RO membrane manufacturers provide the following clean in place CIP System procedures. This is followed by an illustrated, procedure which contains the most important points of a good clean in place membrane cleaning.
RO Membrane Element Cleaning and Flushing
The RO membrane elements in place in the pressure tubes are cleaned by recirculating the cleaning solution across the high-pressure side of the membrane at low pressure and relatively high flow. That’s when we use a CIP system. A general procedure for cleaning the Reverse Osmosis membrane elements is as follows:
- Flush the pressure tubes by pumping clean, chlorine-free product water from the cleaning tank (or equivalent source) through the pressure tubes to drain for several minutes.
- Mix a fresh batch of the selected cleaning solution in the cleaning tank, using clean product water. Circulate the cleaning solution through the pressure tubes for approximately one hour or the desired period of time. At a flow rate of 35 to 40 gpm (133 to 151 L/min.) per pressure tube for 8.0(20.3 cm) and 8.5(21.6 cm) inch pressure tubes, 15 to 20 gpm (57 to 76 L/min.) for 6.0(15.2 cm) pressure tubes, or 9 to 10 gpm (34 to 38 L/min.) for 4.0 inch pressure tubes.
- After completion of cleaning, drain and flush the cleaning tank; then fill the cleaning tank with clean product water for rinsing.
- Rinse the pressure tubes by pumping clean, chlorine-free product water from the cleaning tank (or equivalent source) through the pressure tubes to drain for several minutes.
- After rinsing the Reverse Osmosis system, operate it with the product dump. Open valves until the product water flows clean and is free of any foam or residues of cleaning agents (usually 15 – 30 minutes).
If the system shuts down for more than 24 hours, the best procedure for storage is soaking the element in an aqueous solution. With 20 percent, by weight, glycerine or propylene glycol and 1.0 percent, by weight, sodium bisulfite or SMBS Sodium Metabisulfite.
Example on Before and After CIP Chemical Membrane Cleaning in a Brackish Reverse Osmosis System
CIP System in Multi-Array Systems
For multi-array (tapered) systems the flushing and soaking operations can happen simultaneously in all arrays. You should carry out separately high flow re-circulation, however, for each array. So the flow rate is not too low in the first or too high in the last. This can be accomplished either by using one cleaning pump and operating one array at a time, or using a separate cleaning pump for each array.
RO membrane clean in place cip system overall procedure
