Industrial Reverse Osmosis: Fundamentals of Reverse Osmosis Design By Layne Christensen At Isnare.com Ezine Articles

Industrial Reverse Osmosis (RO) is frequently used in industrial and commercial environments as a reliable and cost effective means of producing high purity water. While water purification is the predominant application for Industrial Reverse Osmosis, in some applications, for example the Food and Beverage industry, the "reject" of the reverse osmosis process is the desired product. A classic example of this is a facility that opts for reverse osmosis to concentrate fruit juice instead of a more traditional evaporative process.

Still other facilities use Industrial Reverse Osmosis as a means of concentrating wastewater streams thus minimizing the amount of waste that must be treated by the local municipality.

It should be clear then that the end use of the reverse osmosis process whether it be the permeate or the reject will define the overall design of the Industrial Reverse Osmosis Equipment.

No matter what the intended use of your Industrial Reverse Osmosis system there are four main components or building blocks that you will be combining in order to most effectively meet your overall process goals.

The Four Industrial Reverse Osmosis Equipment Components:
Element – Array (Train) – Stage – Pass

The RO Element is the building block of any RO system. It is the individual component, where the Reverse Osmosis (RO) process occurs.
There are four main designs for the elements:
•Spiral Wound – Most common design for water purification
•Hollow Fiber – Very large membrane surface areas are possible in this design. Used in seawater desalination
•Large Tube – Similar to a shell-and tube heat exchange in appearance and design. Used in special wastewater treatment and food processing applications
•Flat Plate – Similar to a plate-and frame heat exchanger. Used in food processing applications

Regardless of the element design, high pressure and flow is needed to force pure water through the Reverse Osmosis (RO) membrane to become permeate. Because of the high pressures needed, each element must be designed so that the internal structures can withstand a feed water pressure of several hundred psig.

The number of elements needed will be determined by the amount of the final product needed daily.

The RO Array is simply the way in which the elements are grouped together, in series or parallel.

An RO Stage is a series of elements linked together so that the reject (concentrated) water from stage 1 becomes the feed water for stage 2. (To view the associated diagrams please download the white paper) The individual elements in stage one can be set up in series or parallel, but their reject is all collected and is fed to stage 2. The reason for the reprocessing of the reject from stage 1 in stage 2 is to reduce wastewater, and to increase total recovery from the RO array.

A Reverse Osmosis (RO) Pass is an arrangement of elements designed so that the permeate from pass 1 becomes the feed water of pass 2. In other words, the permeate is re-processed (polished), so that the final product is more pure than can be achieved using only one pass. To view a diagram of a multi-pass Reverse Osmosis system - click here.

An RO Array (Train) is illustrated in the figure referenced above. It is the total configuration of elements in series and parallel, and may consist of one or more stages, (generally up to a maximum of three), and one or more passes (generally, up to two, although three have been seen). There may be several RO arrays in one application.

The final Industrial Reverse Osmosis Equipment design for any Food and Beverage plant design will depend upon:
•Final water or product quality required
•Daily amount of water or product needed
•Inlet feed water (product) quality
•Cost to treat wastewater
•Type of upstream feed water (process) treatment equipment

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