Filter Media

Filter media is anything placed in a filter that changes the quality of water flowing through it. With the variety of media available, specific types can be chosen to create the optimum environment for your application.

The three types of filter media are:

  • Biological
  • Mechanical
  • Chemical

All three types are recommended, but an effluent treatment plant needs to have biological and mechanical filters at minimum. Components of these media types can be incorporated in the same filter. The three types of filtration utilize three different types of media to perform their functions.

The efficiency of biological filtration media is determined by its surface area. The more surface area it has, the better it is able to house bacteria. Thus the general rule of thumb to compare media is by its surface area.

Biological Media

Biological media is anything inert that provides housing for beneficial bacteria that break down dissolved solids to a less toxic form. This is a media that should not be replaced unless it has become too clogged to function.

Biological filter media houses the natural bacteria involved in the nitrogen cycle. It provides a larger surface area for beneficial bacteria to colonize, allowing water to pass over the colonies, bringing nutrients and oxygen required for the nitrogen cycle.

To understand this media, first we must understand what the bacteria used for biological filtration need to thrive:

  • Environment above 55°F
  • Ammonia or nitrite as food source
  • Oxygen

Bacteria extract food and oxygen from the water passing over them. When particulate matter gets into the media, decreasing water flow, it "starves" that area of oxygen and food, causing bacteria in that area to die.

Once the bacteria have become established in the biological media, they are difficult to destroy, except by over-cleaning, using chlorinated water, or using certain chemicals.

A bacterial culture's activity will specifically depend on its exchange surface area (substrate and oxygen). In activated sludge, this surface area will be limited because of flocculated micro-organisms. In trickling filters, the developed area of the support medium per m3 of reactor remains low and achieving the ideal distribution of water to be treated over the entire biofilm can be problematic on an industrial scale.

Conventional granular media filters at both drinking and wastewater treatment plants have a challenging job. They need to handle the higher solids loadings common to today's plants, the customary use of coagulants aids, and the all too frequent occurrence of biological growths. The result is an increased potential for media fouling, especially when lower performance backwashing procedures are employed. When fouling occurs, as it often does, filtration performance and run length capabilities are reduced significantly.

Plastic filter media do not have the extensive surface area, but they are unlikely to clog and rarely need replacing. The introduction of plastic media such as plastic rings and saddles as media is largely responsible for the success of the modern trickling filter. This advancement allows construction of modules of superior compressive strength and higher void-volumes necessary for stacking to heights not achievable with rock filters. Greater specific surface area makes higher organic loadings possible.

Plastic filter media is essential for biological wastewater treatment, it is developed to serve as a house for attached growth bacteria. The retention time and biomass in digesting organic matter are increased to ensure very high biological degrading performance. Besides, the media serve to distribute thoroughly the whole surface area and prevent bacteria from being washed off with the effluent.

Mechanical Media

The components of mechanical media are inert - this means they will do nothing to interfere with your water chemistry. This media mechanically or physically strains solids from water passing through it, which is vital for the efficiency of your biological media. Mechanical filtration removes unsightly particles including fish excrement, sludge, uneaten food, or dust. To prevent build-up, the filter media must be cleaned regularly. Replacement is only required when the media can no longer release all the dirt that it holds.

Chemical Media

Chemical media is not used as often as biological or mechanical media, but can be effective for an assortment of filtering purposes. This media is available in a variety of materials that can remove one impurity or many.

The chemical method of filtration removes dissolved particulates via activated carbons, resins, and other adsorbents. Chemical filtration media helps to maintain water quality as unwanted dissolved matter adheres to it. The two most popular forms of chemical media are activated carbon and resins. Protein foam skimming or oxidation with ozone are two other forms of chemical filtration.