Membrane Cleaning Article - Brent Stewart - Applications Engineer
The membrane separation process utilizes a high-pressure feed to force water through a semipermeable barrier. As the water passes through the membrane, contaminates are rejected and eventually flushed to the waste stream. The concentration of the contaminants is crucial to determine the design and operation of the membrane system. During normal operations, membranes can become fouled by colloidal material, inorganic oxides, biological matter, and scaling salts. Fouling involves the entrapment of material in the feed water or deposits on the membrane surface. Pure Aqua membrane chemical's products are formulated to treat a wide variety of commercial reverse osmosis (RO) systems, nanofiltration (NF), and ultrafiltration (UF) systems. To learn more about Pure Aqua's cleaning chemicals, please visit our website: http://www.pure-aqua.com/ro-chemicals.html
Reverse Osmosis membranes inevitably require periodic cleaning, the frequency is very dependent on the design, feed water quality and operations. Typical cleaning schedules vary from every 3 months to 1 year. While different types of fouling require specific cleaning techniques, I will discuss the basic methods. Firstly, when to clean, it is important to develop a normalized standard when the membranes are new to determine changes over time; membranes are typically cleaned when normalized variation is 10-15% of the following
parameters, permeate reduction, increased feed pressure, increased permeate conductivity and/or increased pressure drop across the membranes. It is important to normalize flows factoring in temperature as it dramatically impacts operating conditions/parameters.
In general there are two cleaning techniques, a high acid and low alkali clean. A low pH clean is used to remove organic fouling. Opening the pressure vessel end cap and running your hand on the inside of the vessel can indicate biofouling, a slime layer may have formed. A high pH or acid is clean is used to dissolve salts that have formed scale on the membranes.
Pure Aqua, Inc. has a standard line of CIP systems. The cleaning skid is designed for manual operation through a local control box located on the skid. A chemical storage tank is mounted on its own stand and connected to the skid with either hard PVC piping or quick disconnect fittings and flexible hoses. This gives the unit the ability to be mounted in a permanent location or totally portable if desired. The piping is schedule 80 PVC that is hydrostatically tested at the factory. The electrical enclosure is NEMA 4X. All skid wiring is completed and tested before shipment. Stainless steel or PVC cartridge filters are standard on all units, along with recirculation piping to allow for mixing (versus a mechanical mixer).
To view Pure Aqua's standard CIP skid line, please visit our website: http://www.pureaqua.com/membrane-cleaning-systems.html