Mobile and emergency multi-media filtration solutions with three or more different types of media above the gravel bed.
Mobile and emergency multi-media filtration solutions with three or more different types of media above the gravel bed.
Influent water that is high in suspended solids can harm or reduce the effectiveness of downstream equipment such as reverse osmosis membranes and ion exchange beds. Pressure vessels with sand or other loose media are widely used to reduce the level of suspended solids (turbidity) in incoming water. Usually, sand filters are an economical choice.
A typical sand filter is considered a single media filter (the gravel is a non-filtering layer). In a single media filter, over several backwash cycles, the smallest particles, being lighter, move to the top of the media bed while the larger, heavier particles settle to the bottom of the filter. Most of the filterable particles in the source water are trapped in the top 1-2 inches, where the smaller media particles have the smallest spaces between them.
This is an inefficient use of the media depth. The filter runs a relatively short time before it needs to be backwashed. A multi-media filter addresses this inefficiency.
A multi-media filter is a pressure filter vessel with three or more different media above the gravel bed. The three media are ordered in decreasing porosity. Anthracite, sand, and garnet are often chosen due to their size and density differences. Anthracite is the lightest, then sand, and then garnet.
The larger (but lighter) anthracite stays on top and the denser (but smaller) garnet stays on the bottom. The largest particles are removed near the top of the media bed, in the large spaces between the anthracite. As particles, get smaller, they are captured deeper and deeper in the media. In this way, the entire depth of the bed acts as a filter. This gives more efficient particulate removal. Multi-layer filters trap and retain many more particles than sand filters before backwashing is needed. Because of how deep the particles extend into the media bed, multi-media filters are sometimes referred to as “deep bed filters.”
While crushed anthracite coal, sand, and garnet are the most common media used, other materials may be used. Activated carbon, and ion exchange resins have been tried. In these cases, the media are chosen to serve more uses than just removing particles. For example, ion exchange resins adsorb various substances.
Evoqua has numerous vessels in various configurations that can be used as multi-media systems. We have over 20 years of experience in designing remediation systems for a wide range of project sizes, contaminants, and geographic locations.
Groundwater Remediation
