reverse osmosis

Reverse Osmosis ("RO") is a process whereby water is forced through a membrane which prevents the passage of contaminants. The resulting pure product water, called "permeate," is then used in a wide variety of processes including:

In RO and other filtration applications, the Zeta Rod™ extends the life of filter media and membranes, greatly reduces downtime for cleaning, and stabilizes permeate production at a high level.

By preventing the attachment of particles including microbes, to wetted surfaces and membranes, the Zeta Rod™ stops membrane fouling.

Read our publication in AIChE's Environmental Progress, titled "Application of Electrotechnology for Removal and Prevention of Reverse Osmosis Biofouling."

Membrane fouling is the principal problem faced in reverse osmosis operations. Fouling has been labeled as unavoidable by many sources. The origin of fouling varies from one location to another. It can be of a mineral origin, biological origin or a combination of both.

The Zeta Rod™ system effect in preventing membrane fouling comes from the alteration of surface charge densities both on waterborne particle as well as wetted surfaces; membranes are included among these wetted surfaces.

Membrane fouling will manifest itself by one or several of the following signs:

• Increase in feed pressure to maintain permeate flow.
• Reduction in permeate flow at constant feed pressure.
• Increase in pressure differential.
• Increase in salt rejection rate and decrease in recovery rate.
• Reduction of permeate quality.
• Variations in the fouling matrix indicated by high fluctuations in pressure feed and pressure drop.

The fouling rate can be determined by establishing the time it takes for a clean set of membranes to drop their productivity by a given percent (usually at a 10% loss in permeate, membrane cleaning is performed).

A Zeta Rod™ application to a clean membrane system will produce:

• Significantly reduced fouling rate
• Stable permeate rate at constant feed pressure
• Low transmembrane pressure drop
• Stable salt rejection rate
• Stable recovery rate.

On a fouled system, application of the Zeta Rod™ will produce:

• Increase in normalized permeate flow rate at a constant pressure
• Significant decrease in pressure feed to maintain constant permeate flow rate
• Reduction in transmembrane pressure drop
• Increase in recovery rate

The conditions listed above represent effects that have been consistent in Zeta Rod™ RO applications. Specific results vary from system to system depending on the age of the membranes, membrane condition, water quality, and operating conditions. The performance of an RO system will improve in cases where the membranes are fouled, and the system will operate closer to the design parameters for much longer periods of time when the Zeta Rod™ is installed before significant fouling has occurred.