Membrane technology – an effective solution for purification, clarification and concentration

The micro-filtration (MF) method was developed in the early 1900 s when the first membrane emerged and has become very important in industries such as medicine, pharmaceutical manufacturing, microbiology and the food industry.

Reverse osmosis membranes were the next class of membranes invented in 1959 by Loeb and Sourirajan at the University of California, Los Angeles, with the original goal of producing drinking water from saltwater and seawater. They managed to create a functional synthetic RO membrane from cellulose acetate that worked similarly to a filter, allowing only water molecules to pass by rejecting NaCl and TDS (the total content of dissolved solids).

A little later, ultrafiltration (UF) emerged, fitting well between the salt-rejecting RO and the salt-permeable, particle-retaining MF. ROS and UF membranes worked well for many applications, but there was an increasing need for a membrane with performance characteristics between ROS and UF membranes.

Osmosis

Osmosis is a pure water pass through the membrane. See figure 1. A partially permeable membrane is inserted between two compartments in the solution tank; to the left, containing low-concentration water (low salt content) and to the right, containing high-concentration water (high salt content). Assuming the membrane is permeable only to water, not dissolved salts, the system will attempt to strike a balance, resulting in the same concentration of salts in both compartments. Clean water from either side of the diluted solution vessel moves through the membrane (which retains salts) to a concentrated solution.

Because water from a low-concentration solution passes through the membrane to a high-concentration solution, the fluid level changes. The low-concentration solution loses water, so the liquid level drops, while the compartment containing the concentrated solution gets water, allowing the level to rise. The high concentration solution continues to rise to sufficient pressure (due to the difference in levels between the two compartments) to stop the osmosis process. This pressure is called osmotic pressure and is equivalent to the force osmosis produces to align concentrations on both sides of the membrane.

Reverse osmosis

Reverse osmosis is when the pressure (greater than the osmotic pressure of the solution) is delivered to a high concentration solution which causes clean water to flow through the membrane in the opposite direction to the compartment of the low concentration solution.

Nanofiltration membrane

There are three types of flows in the cross- flow membrane system: incoming water, permeate and concentrate (Figure 3). Incoming water flow is water that enters the membrane system. Permeate flow contains “clean”, desalinated water with high concentrations. Sometimes permeate is also called “product” water. The concentrate stream contains the “rejected” water present in the system, it contains mostly contamination and dissolved salts that do not pass through the membrane.

We have implemented such and similar solutions for companies in different sectors. Contact us to learn how we can help your company.