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Danish support to improved water quality in Central and Eastern Europe
1991-2001
General organic (oxygen consuming) pollution
The general organic pollution is usually measured and expressed as Biological Oxygen
Demand (BOD), which is the fraction, which consumes oxygen in the receiving water body
shortly after discharge (within a few days).
The oxygen demand caused directly by the wastewater is localised to the near downstream
part of a river, or to the near field in larger lakes and marine areas.
Microbiological pollution
Microbiological pollution refers to the spreading of pathogenic organisms (bacteria,
virus, protozoas and helminth eggs). Instead of measuring a multitude of organisms, the
microbiological pollution is usually characterised by the occurrence of a single
indicator, namely the number of E.coli bacteria.
Microbiological pollution causes health risk when humans are exposed to wastewater or
water influenced by wastewater. As pathogenic organisms survive only for short periods in
the natural environment, microbiological pollution, like oxygen demand, is in general a
relatively local phenomenon.
The nutrient elements N and P
The nutrient elements Nitrogen and Phosphorous are essential for plant growth,
including all sorts of water plants, notably phytoplankton. In the natural state, plant
growth in lakes, reservoirs and the Sea is limited by the amount of either or both of
these nutrient elements.
When the water bodies receive excessive amounts of the nutrient from e.g. discharge of
wastewater, the condition of the water body is changed into a state of
"overfertilisation" (eutrophication). This state is characterised by the water
being turbid (green) by an excessive growth of microscopic plankton organisms. In
particular, masses of blue-green algae (or cyanobacteria) are common in late summer, and
often cause problems for water treatment.
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