Comparison of Elimination of Bacteriophages MS2 and φX-174 During Sewage Treatment by Natural Lagooning or Activated Sludges. A Study on Laboratory-Scale Pilot Plants

Using appropriate laboratory pilot plants we studied phage elimination during sewage treatment by lagooning and activated sludges. Sewage fed into two types of pilot plant was seeded with a somatic coliphage (φX-174) or an F-specific RNA phage (MS2). Samples were taken from inside the biological treatment tanks to follow phages disappearance. The kinetics of their elimination were compared with that of an inert tracer, rhodamine B. Other samples were taken at the outflow to evaluate the efficiencies of phage removal for the two treatment processes. The elimination of MS2 in the absence of any specific solid phase was also studied. Results show that rapid adsorption on solid particles was less marked for rhodamine than for the phages. The regression coefficients calculated for MS2 and φX-174 were, respectively, 0.46 day−1 and 0.37 day−1 for lagooning, and 0.13 h−1 and 0.128 h−1 for activated sludges, whereas those of rhodamine were 0.069 day−1 and 0.024 h−1. Thus elimination of the phages was faster than that of the tracer. This reflects the influence of factors acting exclusively on the viral particles. The phages do not therefore behave as inert molecules. The efficiencies of removal of the two types of phage were comparable for the two treatment processes. The extent of elimination was of the order of 2 log. The study of the elimination of MS2 in the absence of any specific solid phase showed that the floc of the activated sludges system favoured elimination more than the sediments in the lagooning system.