A3.10.1.2 Physical Technology & Water Pollution


Skimming & Filtration

Solid matter may be removed from water or wastewater through the use of skimmers, which remove large items from the surface. Filters allow the water to pass through, but retain the large particles (like a sieve).

Skimmers may also be used to remove oil from the surface of water.

Oil Interceptor

An oil interceptor allows the separation of water and oil. It is usually buried underground and comprises of a site’s drainage system. They are simple devices, based on the principle that oil floats on water. The water will be released from the tank through an outlet near the bottom, whilst the oil will remain on the surface of the water where it can be removed with a skimmer.

Please Note:   In the UK Interceptor are categorised a Class I (suitable for final discharge to controlled water) or Class II (suitable for final discharge to foul sewer).

Trickling Filter

A trickling filter consists of a fixed bed (made of rocks, gravel, slag, polyurethane foam, sphagnum peat moss, or plastic media) over which sewage or other wastewater flows. The wastewater or sewage flows downward causing a layer of microbial slime to grow, covering the bed of media.

Trickling filter systems are made up of the following components:

  • A septic tank for fermentation and primary settling of solids.
  • A filter medium upon which beneficial microbes are promoted and developed.
  • A container which houses the filter medium.
  • A distribution system for applying wastewater to be treated to the filter medium.
  • A distribution system for disposal of the treated effluent or percolation ponds.


The process mechanism involves both absorption and adsorption of organic compounds within the sewage by the layer of microbial slime.