Tertiary Filtration of Wastewater

Tertiary wastewater filtration: methods and processes

Tertiary filtration of wastewater is a process for separating solid particles from wastewater through a filter medium. It is a mechanical process, meaning that it uses only physical means.Thus, no chemicals or biological processes are used.

Tertiary filtration is an increasingly common process, partly in light of increasingly stringent regulations regarding the quality of purified wastewater. It thus allows treated water to be discharged into surface water bodies, such as rivers and lakes, while complying with regulations and avoiding exorbitant fines. But that’s not all. After a finishing stage with final filtration, it is often possible to reuse the “blue resource” within the company’s internal processes.

Wastewater filtration methods can be distinguished according to the type of filter media used.

• Sand filtration. This method uses a layer of sand as a filter medium for particles larger than a certain threshold size. A simple and economical type of tertiary wastewater treatment.
• Cloth filtration. The cloth used as the filter media can be micro-net (and in this case we speak of surface filtration) or free-fiber (depth filtration, analogous to sand filtration): two low-energy methods, with better suspended solids removal efficiency to the advantage of the latter. With special free-fiber cloths, particles up to 5 microns in diameter can be removed without particular difficulty.
• Microfiltration and Ultrafiltration. The medium in this case is a membrane, with pore sizes as small as 0.1 micron for microfiltration and 0.001 micron for ultrafiltration. These technologies separate most of the suspended solids while preserving the salinity characteristics of the water.
• Nanofiltration and Reverse Osmosis. In this case, the filter medium is a semipermeable membrane, which allows the passage of water but not dissolved substances. These are technologies that require upstream water that has already been pre-treated with other filtration systems, and are dedicated to processes of softening, desalination, treatment of particularly resistant dissolved pollutants, and production of pure water for industry.