Application Note

Innovative pH Solution Protects Membranes In Reverse Osmosis Systems

Source: Emerson
Innovative pH Solution Protects Membranes

Reverse osmosis works by pressurizing water and forcing it through small, permeable membranes. The water passes through the membranes, but the dissolved solids are relatively impermeable and are rejected, producing high purity water.

pH measurement plays an important role in the membrane purification process for Beverage Producers. Most beverages are slightly acidic while raw pre-treated water tends to be slightly alkaline. In addition, the membrane fibers are cellulose based and degrade in alkaline conditions, which results in lower membrane efficiency from precipitation. Membranes can be regenerated through back-flushing techniques; however, long term exposure to alkaline conditions will eventually lead to membrane replacement at a significant expense.

Often, pH sensors are omitted from the Reverse Osmosis Systems to minimize initial investment expenditures. Integrating a pH measurement into the local RO control system requires significant programming efforts as well as hardware expansions to PLC’s and wiring personnel to bring the signals into the controllers.

Critical to the measurement is the pH sensor. The Model 399 General Purpose pH Sensor from Rosemount can accurately monitor the pH of raw water going into the RO Skid. The improved ACCUGLASS® glass formulation resists cracking, especially at elevated temperatures, which prolongs the sensor’s life. The sensor conveniently mounts via 1” MNPT process connection, and the water tight variopol cable connection allows for quick sensor replacement in the event of sensor failure.