Membrane and Biological Filtration: Drinking Water Treatment Technologies

Water filtration systems

For most of the twentieth century, water utility companies used chlorination, granular media filtration and chemical clarification to treat drinking water. Starting from the last two decades of the twentieth century, however, these companies have been increasingly adopting newer water treatment technologies to cut operational costs, achieve even better water quality and lower waste production. Let us take a quick look at two of these technologies: membrane and biological filtration.

Membrane Filtration

Membrane filtration rids water of microorganisms, particulate matter and other contaminants using specialized membranes. These membranes come in two forms: low pressure, which include micro-filtration and ultra-filtration membranes, and high pressure, which include nanofiltration and reverse osmosis membranes. Low pressure filtration, which is particularly effective at particulate removal, is gradually displacing traditional filtration for surface water treatment at an increasing number of utilities. On the other hand, high-pressure membrane filtration is effective at removing organic and inorganic dissolved matter and is mainly used for softening and total dissolved solid (TDS) reduction. Both types of membranes are used together for enhanced effectiveness in certain two-stage membrane filtration applications.

Biological Filtration

As the name implies, biological filtration relies on biological rather than chemical or biological processes, as virtually every other water treatment technology does, to rid water of contaminants. The Environmental Protection Agency mandates this form of filtration for removal of biodegradable organic matter (BOM), a task for which the technology is particularly well suited, if ozone has been used during the treatment process (ozonating natural water increases BOM levels and may lead to biological regrowth if water is released into the distribution system without further treatment). Biological filtration utilizes granular materials, such as anthracite or granular activated carbon, as an attachment medium for the biological matter that does the actual work of removing biological matter. This technology can be used to remove organic and inorganic contaminants, including arsenic, calcium, bromate, chlorate and selenate.

As alternative water sources become harder to find and traditional water treatment methods hit their limits, water utility firms are increasingly looking beyond the established chlorination and filtration technologies to achieve their water treatment goals. Using innovative technologies such as membrane and biological filtration, utilities are now able to achieve excellent results even in situations where standard methods prove ineffective. Other technologies that utility firms are either considering or actively adopting include ultraviolet irradiation, ion exchange and advanced oxidation.