Lately, I have been debating with several clients about the difference between membrane separation processes and conventional chemical treatment for water and wastewater treatment.

There are several advantages and disadvantages to both concepts. However, I believe that membrane technology is a much superior option to conventional chemical treatment.

To illustrate my point, I’ll use the example of a Drinking Water Treatment Plant.

In a conventional drinking water plant, the most common process unit used are pH adjustment, flocculation (or clarification), sedimentation, filtration and disinfection.

All of these units (except for filtration and disinfection) require large infrastructure and chemical injection to allow for enough residence time in the tank and therefore, efficient processing of the water. If the capacity is large, say for a large city, then the footprint of the plant is also large. The amount of chemicals being used is also large.

Should the composition of the feed water alternate, the operator must be able to adjust the chemical dosage accordingly to ensure proper purification.

When we introduce membranes in the picture, it’s a different story. I won’t go into specific about which membranes to use in which particular case, this will be a topic for a different article. However, membranes offer many benefits that most people do not consider.

• They offer a large surface area for processing in a small footprint.
• They do not usually require pre-filtration, although some membrane processes can be used as pre-treatment.
• They offer a barrier against micro-organisms

The key aspect of membrane processes is the fact that they use tangential flow. What does that mean? Simply that the flow is parallel to the membrane, allowing the barrier to act as a physical barrier between the clean processed water and the contaminants. This is not seen in conventional chemical processes, where a proper residence and contact time must be in place to ensure proper treatment.

Since membranes can usually handle pretty much anything you can throw at them, we are eliminating several steps in the process and hence, reducing the total footprint of the plant as well as the consumption of chemicals.

The main disadvantage is the capital cost of a membrane process, generally higher than conventional systems, but has a very low maintenance and operating cost, which conventional systems do not.