Suspended solids

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Particulate matter or suspended matter are mineral or organic solids contained in water , air or another surrounding medium that do not go into solution and because of their small size and low weight (especially with a density similar to that of the surrounding medium) kept in suspension or can be redistributed even by slight movements of the medium.

In contrast, one speaks

  • in the case of substances that are transported on a river bed , from bed load and
  • in the case of substances that are transported on the surface of a body of water, floating matter .

Basic properties

Typical groups of suspended solids are:


Suspended solids are removed by means of settling basins (sedimentation), chemical precipitation , flotation , and filtering . If the distance is greater, HEPA filters are used for liquids , for example .


The suspended matter content can be determined directly by taking samples, separating them (e.g. electrostatically or by filtration ) and measuring residues.

Indirect methods by measuring the turbidity of the surrounding medium (optically by measuring scattered light or transmitted light) are also possible. Indirect acoustic measurement methods are also being developed.

Suspended solids in hydrology

Impressive examples of large amounts of suspended matter are rivers such as the Amazon , Nile and Mekong, or the former tributaries to the Jezero crater lake on Mars . Depending on their composition, the suspended solids produce a color typical of the river.

A delta can develop from the alluvial - often very fertile - suspended matter over the course of millennia , as the suspended matter is deposited depending on the flow velocity , its grain size and density (sedimentation). At high flow velocities, however, erosion of the sediments and thus further distribution of suspended matter can occur.

The terms of the

  • Suspended matter concentration or pollution (dry weight per volume)
  • Suspended solids management ( mass per period )
  • Suspended solids (mass per fixed period of time).

In general, suspended solids in aquatic ecosystems, along with water and sediment, are an important part of the ecosystem.

Suspended matter in rivers is mainly caused by erosion, weathering and decomposition of rock and the growth of slime-forming microorganisms .

In general, the limit particle diameter of suspended solids is 0.2 to 0.7 mm, depending on the conditions.

Individual evidence

  1. ^ Paul Profos, Tilo Pfeifer; Industrial Metrology Manual; ISBN 978-3-486-22592-1 .
  2. a b Wassernet: Suspended matter in flowing waters - guidelines for recording suspended matter transport .
  3. ^ Daniel Vischer, Andreas Huber; Hydraulic engineering: Hydrological principles, elements of hydraulic engineering, p. 56; ISBN 978-3-540-43713-0 .
  4. ^ Federal Environmental Specimen Bank : Suspended particles .