Biological Purification of Sewage

A method for the purification of Sewage, in which organic impurities (e.g. faeces) are trandformed with the help of micro-organisms (bacteria, fungi, etc.) utilizing the oxygen present in inorganic compounds (e.g. Carbon Dioxide, water). The biological purification of Sewage takes place either in activated sludge tanks in so-called percolating filters, in which the Sewage is irrigated over elements with a large surface area (stones, slag, plastic honeycomb). The Sewage and the bacterial mass are separated from one another in secondary settlers or sedimentation tanks. The excess sludge is removed, and any remaining bacterial sludge is reused for Sewage Purification. The purification process operates without interruption provided that no bacterial toxins are introduced. The biological purification of Sewage removes about 80–90 % of the contaminants and Harmful Substances. The quality of the resulting Sewage frequently does not correspond to the stipulated requirements, so that a further Third Purification Stage must be used.