Occurrence and levels of phages proposed as surrogate indicators of enteric viruses in different types of sludges

A method based on the treatment of sludge with beef extract recovered, with similar efficiency, the three groups of bacteriophages studied from differ ent kinds of sludges, The three groups of bacteriophages were found in high numbers in the different sludge types, the highest value being that of som atic coliphages in primary sludge of a biological treatment plant (1.1 x 10 (5) pfu g(-1)) and the lowest being that of Bacteroides fragilis phages (11 0 pfu g(-1)) in de-watered, anaerobically, mesophilically-digested sludge. All phages studied accumulated in the sludges. In primary and activated slu dges, all three types accumulated similarly but in lime-treated sludge and de-watered, anaerobically, mesophilically-digested sludge, the relative pro portion of F-specific bacteriophages decreased significantly with respect t o somatic coliphages and bacteriophages infecting B, fragilis. All phages s urvived successfully in stored sludge, depending on the temperature, and ag ain, F-specific bacteriophages survived less successfully than the others.