[Comparative study on methods to recover indigenous viruses from samples of activated sewage sludge]

Samples of activated sewage sludge were investigated for their contents of indigenous enteric viruses. Therefore sewage sludge solids were collected by centrifugation and the embedded viruses eluted by blending (Waring blendor), glycine buffer (0.05 M) treatment at pH 11.5 or Freon1 treatment. Eluted viruses were concentrated on microfiberglass filters ("Balston" filters) at pH 3.5 or by flocculation with beef extract (3%, pH 3.5). Simple blending of the activated sludge was found being not very efficient, while the other two methods gave better results in freeing the viruses from the sewage flocs. Usually highest virus titers were obtained after glycine treatment and concentration with Balston filters. Freon treatment of activated sewage sludge produces aqueous supernatants containing much denaturated floc material which seems to cause a certain number of viruses to remain in the supernatant after flocculation.