Evaluation of bacteriophages during the treatment of sludge.

The aim of this work was to determine the effect of liming and composting on the fate of three bacteriophages (somatic coliphages, F-RNA phages, Bacteroides fragilis phages) considered as potential indicators of viral contamination. It was shown that the three bacteriophages studied exhibited variable densities in sludge. Somatic coliphages were most abundant (10(4) to 10(5) x 10 g(-1) DM) then F-RNA bacteriophages (10(2) to 10(4) x 10 g(-1) DM) and Bacteroides fragilis phages (10(1) to 10(2) x 10 g(-1) DM). The efficacy of liming was found to be pH dependent but also sludge dependent. The pH allowing 99% elimination of somatic coliphage is close to 9 for solid sludges and close to 13.5 for liquid sludges. For composting, our findings clearly demonstrated that phage inactivation is very clearly temperature-dependent. For temperatures reaching 70 degrees, there is a 5 log reduction in somatic coliphages while for temperature in the 50-55 degrees C range, the drop off is only 2 log. Considering the efficacy of the treatment methods, it is clear that the well-established industrial procedures that reach temperatures in the 60-70 degrees C range totally inactivate all 3 phages tested and present in sludge before composting.