Scum
- Slovak term: Slovenský termín
- Layer of suspended solids less dense than water and floating on top of liquid waste from which they have separated by flotation (WHO 1992).
Explanation
Grease, oil, and other materials that are less dense than water float up to the liquid surface, forming a layer of scum which can become quite hard. Scums are less of a problem in marine water than in fresh water, as the frequency of occurrence of scums is higher in lakes than in coastal areas.
Biological organisms can form scums. Some species of cyanobacteria are capable of causing dense scums, which contain high concentrations of cells. Since most toxin is intracellular, scums caused by toxigenic strains of cyanobacteria may contain elevated concentrations of toxin. The existence of a cyanobacterial scum caused by a toxigenic species represents an increased human health hazard.
Blooms of non-toxic phytoplankton species and mass occurrences of macro-algae can affect the amenity value of recreational waters due to reduced transparency, discoloured water and scum formation (WHO 1992).
Example
“A septic tank is an underground watertight settling chamber into which raw sewage is delivered through a pipe from plumbing fixtures inside a house or other building. The sewage is partially treated in the tank by separation of solids to form sludge and scum.” (WHO 1992).
