Reduction of indicator microorganisms in agricultural and domestic sewage in perspective stages of three stage waste water treatment Lezany plant

The studies conducted in the three-stage waste-water treatment plant for agricultural and domestic sewage in Łężany showed that the greatest reduction of indicator microorganisms, between 70% and 100%, occured in biological ponds. Biofilters (rotating biological disks and multicage rotating contactor) reduced the occurence of the studied microorganisms by 40—70%, mechanical purification by 40—50%. The purified sewage flowing to Legińskie Lake possessed the features of unpolluted or only slightly polluted water.