Summary:

The article presents results of research carried out on four “DUOFILTER” type septic tanks. Analysed objects made first step of living sewage treatment in household sewage treatment plants. As a second step of treatment vertical flow sand filter was applied. Sewage flow through the tank in each case was less than 1,0 m³*d^-1. Septic tank consisted of three chambers: first – sedimental one and two flow ones, equipped with filter made of porous structures. The research was carried out during the period from October 2003 to May 2005. Concentrations of raw sewage pollutants were analysed – taken from the first chamber of the tank, and sewage primarily treated – taken on the outflow from the tank. Three indexes from the basic group: BOD₅, COD_Cr, total suspended solids were physicochemically analysed. On the basis of the carried out results’ analysis, mean effectiveness of BOD₅ was ascertained from 25,3 to 40,2%; COD_Cr from 32,4 to 43,5 %; total suspended solids from 35,9 to 56%.