Reverse Osmosis/Spot Free Rinse System

Reverse osmosis refers to a process of water purification that has been used primarily for the desalination of seawater. To understand reverse osmosis, it is first necessary to understand osmosis. Osmosis is the term for the phenomenon whereby if a semi-permeable membrane separates two salt solutions of different concentration, water will migrate from the weaker solution through the membrane to the stronger solution, until the solutions are of the same salt concentration. Reverse osmosis subverts this process. It involves applying pressure to reverse the natural flow of water, forcing the water to move from the more concentrated solution to the weaker. The semi-permeable membrane is porous, allowing water to pass through, but blocking the passage of the bulkier salt molecules (Binnie, Kimber, & Smethurst, 2002).

The semi-permeable membranes for reverse osmosis treatment are generally constructed from polyamide-based materials. These materials are resistant to biological degradations, but are subject to chemical attacks from chlorine.

Reverse osmosis has been used as a method of purification for ground and surface fresh water, in addition to its role as a desalinating agent. Working with such water sources creates some problems for the reverse osmosis system. Because of the very small pore sizes involved in the membrane, it is vital that ground and surface water is adequately pre-treated prior to the reverse osmosis process. Depending upon the hardness of the water involved, scaling of the membrane is likely to occur. If the concentration of the calcium or magnesium in the water (the chemicals that determine water’s hardness) is at a high enough level where the chemicals are insoluble, it will create a hard mineral on the inside of the membrane, rendering it impotent. (Vigneswaran & Visvanathan, 1995).

Accurate system design is critical to getting the most from your water treatment system. Dozens of factors can impact the productivity of a system. Reverse Osmosis System Design software is available from membrane manufacturers to allow application engineers to input data from a water analysis to offer the most precise design recommendations to optimize system performance. 

An entire RO / NF water treatment system consists of a pretreatment section, the membrane element system, and a post-treatment section. The membrane element system includes an inlet for feed water and outlets for permeate and concentrate.

RO / NF system performance is typically characterized by two parameters, permeate (or product) flow and salt rejection. These should always be referenced to a given feed water analysis, feed pressure, temperature, and recovery. The goal of the designer of an RO / NF system for a certain required permeate flow is to minimize feed pressure and membrane costs while optimizing permeate quality and recovery.

The steps to design such a membrane system are described below:

1.  Consider Feed Source, Feed Quality, Feed / Product Flow, and Required Product Quality 

2.  Select the Flow Configuration and Number of Passes

3.  Select Membrane and Element Type

4.  Select Average Membrane Flux (Design Flux)

5.  Calculate the Number of Elements Needed

6.  Calculate the Number of Pressure Vessels Needed

7.  Select the Number of Stages

8.  Select the Staging Ratio (Array Ratio)

9.  Balance the Permeate Flow Rate  (863) 644-6925" rel="">

Reverse Osmosis systems are used throughout the world the world to improve the quality of drinking water and the water that's critical to essential industrial processes like chemical processing, power generation, the manufacturing of food and pharmaceuticals, and Spot (mineral) Free Rinse Water. Reverse Osmosis technology is also vital to desalination and water reclamation efforts in communities with severe water shortages. See below for a brief list of categories and applications.