Growing global demand for clean water and increasing environmental concerns make membrane filtration the technology of choice for several industries looking for efficient ways to treat their wastewater. In fact, wastewater reuse and recycling market is one of the highest growing markets in the water industry. Membrane filtration is one of the key applications for commercial and industrial wastewater recycling, as well as treating wastewater to increase plant efficiency, reducing operational cost and complying with stringent municipal discharge regulations.
Filtration is the process of removing particulate matter from water by forcing the water through a porous media, or a membrane. The media for filtration can be natural like sand, gravel and clay or it can be a membrane wall made of various materials. These membranes can be used for softening, disinfection, organic removal and desalination of wastewater. Depending on the size of materials that need to be removed from the water, there are different processes of filtration available to us.
We often get questions from clients about the level of filtration they require for their industry. We wanted to share a series of articles on the various levels of filtration processes with an in-depth look at particle filtration, ultrafiltration and reverse osmosis.
Filtration Processes
Water filtration systems and treatment methods differ because of the incoming water conditions and the output quality of the water needed for end use. Wastewater contains a range of contaminants and depending on the size of materials present in the water, different filters are required. Membranes provide a physical barrier that effectively removes suspended solids, bacteria, viruses, microorganisms, particulates and other natural organic material.
There are 5 levels of filtration that is available to you:
- Particle Filtration (Media filtration)
- Microfiltration (Fibre woven and spiral media filtration)
- Ultrafiltration (Membrane filtration)
- Nanofiltration (Membrane filtration)
- Reverse Osmosis (Membrane filtration)
Particle filtration is a process that separates solids from fluids, down to approximately 3 microns. The water quality is described in terms of total suspended solids (TSS) which determines the filtration technology to use. We will talk about it in detail in part 2 of this article series.
Microfiltration process removes bacteria. Micro filtration can be implemented in various water treatment processes when particles with a diameter greater than 0.1 mm need to be removed from the effluent. Even though we will not discuss microfiltration as a separate article, it is important to know that the application is often used in sterilization of beverages and pharmaceuticals, clarification of fruit juices and wines, separation of bacteria from water in biological wastewater treatment, separation of oil and water, and pre-treatment of water for more sensitive membranes.
Ultrafiltration can also be used as a pre-filtration for nanofiltration and Reverse Osmosis, and usually removes impurities down to a pore size around 0.01 micron. The major application of ultrafiltration involves clarification of suspended solids, removal of viruses and bacteria or high concentration of macromolecules. We will be covering ultrafiltration in Part 3 of this article series.
Nanofiltration functions similarly to Reverse Osmosis but is generally targeted to remove only divalent and larger ions. Divalent ions make the water hard, so nanofiltration is often used as a softener of hard water. The nanofiltration filter has a pore size of around 0.001 micron. We will not be covering nanofiltration as a separate article, however, look at the chart and see where nanofiltration can fit into your filtration process.
The membrane with the smallest pores is used in Reverse Osmosis. The pore size of RO filters is around 0.0001 micron. Reverse osmosis is used to remove all organic molecules and viruses. It also removes monovalent ions, which means that it desalinates the water. We will cover reverse osmosis in part 4 of our article series.
It is important to understand that you use products that require membrane technology everyday including your tap water, the juice in your cupboard and the milk in your fridge. Manufacturing facilities need to use different levels of membrane technologies for their water treatment processes. In parts 2, 3 and 4, we will dive into the amazing world of filtration and membrane technology and look at some of these processes in detail. If you have a question on membrane filtration, don’t hesitate to contact us.