Overall, there are four main membrane types: Microfiltration, Ultrafiltration, Nanofiltration, and Reverse osmosis. The choice of membrane, and thus the pore size, depends on the filtration purpose, which can be disinfection, desalination, organic removal, or softening of water and wastewater. The membrane types can be divided into two subcategories:
1. Low pressure operations: Microfiltration (0,1µm pores) and Ultrafiltration (0,01µm pores)
2. High pressure operations: Nanofiltration (0,001µm pores) and Reverse osmosis (<0,001µm)
Membrane technology is widely used in many industries, from the food industry to pharmaceutical industry and the metal finishing industry.
Membranes are very flexible and can be used as both a pre-treatment or as the main source of treatment. Furthermore, both the permeate and the retentate can be re-used for process purposes.
As an example membrane filtration is used as a pretreatment for perkolat in one of Aquardens projects, as showed in the. In this example the nanofiltration is used to remove particles from the stream before the stream is treated with ion exchange and SCWO. Reverse osmosis is used to create soft water, or in combination with ion exchange to get demineralised water.
Size exclusion is the dominant filtration mechanism in membrane filtration. Particles larger than the retention rating of the membrane collect at the surface, while water, a smaller particle passes through. Therefore, it is necessary to choose the right filtration for the task at hand:
Eden Aquatech AB Copyright © 2020
Biological water treatment