Effectiveness of indicator bacteria removal in vertical flow filters filled with natural materials

The effectiveness of removing indicator bacteria from domestic sewage using a vertical flow filter filled with natural materials has been analysed. The count of Escherichia coli and coliform bacteria was measured in raw and treated sewage and effectiveness of their removal under variable conditions of hydraulic load and depending on the filter filling (type, size and filling proportions) was assessed. A single-layer sand or zeolite filter was the most effective in reducing bacterial contamination. The sand-filled filter allowed the removal of 99.993–99.997% of Escherichia coli and the one filled with fine zeolite of 99.995%. The principal component analysis was used to comprehensively evaluate the filter performance. Three principal components were identified and they were responsible for 81% of raw data variability. The effectiveness of indicator bacteria removal depended mainly on the filling grain size and did not on filling proportions or its type.