AN INVESTIGATION OF THE INFLUENCE OF BACTERIOPHAGES ON THE BACTERIAL FLORA AND PURIFICATION POWERS OF ACTIVATED SLUDGE

Abstract

This report describes the isolation of bacteriophages (phages) infectious for dominant bacteria in the activated sludge of a public sewage disposal plant, and the influence of the phages on the bacterial flora and the purification powers (biological oxygen demand [BOD], chemical oxygen demand [COD] and sludge volume index [SVI]) of the sludge. The activated sludge used contained two groups of dominant bacteria, M1-W and M1-P. Their phages were easily found in spring and autumn in the sludge or in the environment around the plant. Eight phages attacking M1-W strains and two phages attacking M1-P strains were isolated during 30 months' investigation. At the time of the isolation of these phages, a disturbance in the normal bacterial flora possibly due to phage infection was observed, as well as a change in dominant strains (for example, when the phage attack on M1-W strains occurred, M1-P strains became dominant). Such disturbance was considered to cause a decrease in the purification powers of the activated sludge.