Stability of viruses in waste water sludge eluates

Abstract

The survival of indigenous enteric viruses in samples of unconcentrated and concentrated waste water sludge eluates, which had been prepared using a combination beef extract elution – organic flocculation concentration procedure, was studied at 2, 23, and −70 °C. Changes of virus titer occurring in the samples were followed during an 84-day observation period, with rates of change then calculated by least-squares regression. Virus survival in both types of eluates was statistically dependent (p ≤ 0.05) upon storage temperature. Based upon the observed rates of inactivation the average times which would be required for a 90% decrease (one log₁₀ unit) in virus titer for unconcentrated eluates are 27 days at 23 °C, 198 days at 2 °C, and 375 days at −70 °C. The calculated average times required for a 90% decrease in virus titer for concentrated eluates are 22 days at 23 °C, 132 days at 2 °C, and 246 days at −70 °C. In both types of eluates the rates of virus inactivation at 2 °C were statistically different from those observed at 23 °C, but not different from those observed at −70 °C. The three study temperatures were selected to approximate holding of samples in an air-conditioned room, fluid on wet ice (H₂O), and frozen on dry ice (CO₂).