Sand filter

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Sand filters , a synonymous term for the gravel filters used in water technology , are filters that work with sand as the filter medium. They are used in several areas.


The sand filter is a special aquarium filter within the aquarium hobby . It is one of the external filters.

The sand filter is a multi-partitioned extra basin in which the water flows through different filter floss and layers of sand. The extra tank is located below the actual aquarium tank. The water gets through an overflow into this extra basin, which is usually located in the base cabinet. In the last chamber there is an electric submersible pump that pumps the water back into the basin.

The sand filter is suitable for both fresh and marine water aquariums.

Shelter technology

Sand prefilter in a shelter, on the left there are air blast protection valves

A sand filter is built into many protective structures. It is an important component of the protective ventilation system, which is responsible for supplying the shelter occupants with clean, chemical-free air. It basically consists of one or more concrete or steel pools that are filled with sand. The way it works is simple: the fresh air flows through the suction device (s) into the sand filter room and is then drawn through the sand. Three things happen:

1. The air is freed from (radioactive) particles and biological and chemical warfare agents.

2. If the air temperature is increased, for example due to fire outside the shelter, the sand absorbs the heat so that tolerable temperatures can still prevail in the shelter.

3. A possibly penetrating blast wave is dampened, unless it has already been stopped by the air blast protection valves upstream in some shelters.

There are two types, the sand prefilter and the main sand filter. The main sand filter is used independently and is intended to ensure complete filtration of the fresh air, while the sand prefilter is always used in conjunction with room filters and the air is only intended to pre-filter the air to protect the room filters from clogging too quickly or burning. The main difference between the main sand filter and the sand prefilter is the finer filter material and the resulting better filter effect.

Wastewater treatment in sewage treatment plants

A sand filter is usually used as the last cleaning stage in a sewage treatment plant. First of all, it is used to filter suspended particles in wastewater, but also for subsequent denitrification by adding easily degradable organic compounds.

Filtration of suspended particles in wastewater:

  1. The wastewater is fed into the sand filter via the inlet.
  2. It flows through three layers of sand (expanded shale, quartz sand, support and distribution layer made of quartz sand).
  3. Then it flows out again through a filter base.

With this process, the wastewater is freed from solids to 99%.

In rural areas, sand filters are also used to purify domestic sewage. In areas outside the catchment areas of a sewer system, the wastewater must be treated with a small wastewater treatment plant. Subsequent to a septic tank (mechanical cleaning), the pre-treated wastewater is sprayed in bursts on a sand filter. When it seeps through the filter, the water is biologically cleaned and can be released back into the environment in a clear state. Sand filter sewage treatment plants do not require pumps on slopes.

Other usage of the term

In aviation technology, special filters in front of the air inlets of turbines are called sand filters or foreign matter separators. These constructions keep the sand and other small parts away from the turbines and thus greatly increase the service life and reliability of the drives. They are mostly used in helicopters that fly in desert regions or often over unpaved ground.


  • 10.6 Sand Filters. In: Allen P. Davis, Richard H. McCuen: Stormwater Management for Smart Growth. Springer 2005, pages 192 to 197

Individual evidence

  1. Christoph 31 tests sand filter