Process for physically and biologically purifying sewage

A process for the purification of sewage by means of a filter-percolating filter filled with a non-abrasive granular filter material, comprising the steps of:

• first distributing preliminarily clarified sewage equally over the surface of the filter material, so that the sewage trickles through the filter material;
• then simultaneously ventilating the filter material by means of passing air therethrough;
• then allowing the sewage to trickle through the filter material until sludge and microorganisms of the sewage have covered the surface of the filter material in increasing bulk and the passage of air through the filter material has increasingly been reduced as a result of the incrustations formed by the covering in the gaps of the filter material;
• after such gaps have been covered following the above steps, the process further comprises filling the filter-percolating filter with rinsing water for the purpose of agitating and washing of the filter material;
• blowing air under pressure into the filter so as to mix the filter material and rinsing water therein;
• drawing in the largest portion of the sludge resulting during the preceeding steps from the mixture of retained rinsing water, filter material and sludge through suction pipes extending into the filter material,
• draining off the rinsing water,
• the mixing of the rinsing water and filter material and the drawing in of the sludge being carried out progressively in a horizontal direction by the passing of a rotation device and a sludge removal device including said suction pipes through the contents of the filter-percolator filter.