What is really the point of cleaning the sewage, since
wastewater mostly is organic matter, which is returned to
nature?
A main problem is that the wastewater contains many nutrition
salts (especially phosphates and nitrates) which algae and other
micro-organisms use for their growth. Removal of the nutrition salts
prevents an unwanted growth of algae and bacteria in the recipient
of the wastewater, which otherwise can lead to a reduction of water
quality. In addition, the hygienic conditions are improved.
Another problem arise if industrial companies are connected to
the wastewater network. Then the sewage may contain different
types of toxic wastes. This must, of course, be
removed.
