activated sludge produced during waste water treatments

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Since domestic wastewater could be contained pathogenic enteric viruses released from infected persons the knowledge of the viral behavior in wastewater purifying process is important : it is, however, still poorly understood. In this study, we reported that the adhesion of Poliovirus (Sabin 1 strain) to activated sludge samples taken from wastewater purifying plants and the mechanism of the adhesion. More than 10^8 particles adhered to one gram (wet) of activated sludge, and the adhered viral particles maintained infectivity for longer period of time and showed higher thermo-resistant than the free viral particles. The adhered viral particles were released by increase of salt concentration or alkaline pH buffer as infectious particles. Although the Poliovirus particles have 2 isoelectric points, one at approx. pH 4.3(major population) and the other at approx. pH 7.2(minor population), the particles adsorbed much more strongly to a cation-exchange chromatography column than to an anion-exchange one at pH 7.2 and chelating agents interfered with the viral adsorption to activated-sludge samples, suggesting that activated sludge adsorbed the viral particles mainly through electrostatic interaction, acting as a cation-exchange adsorbent, and that multivalent cations play an important role in the viral adsorption. These data suggest that pathogenic viruses could adhere to the activated sludge by electrostatic interaction, be enriched, maintain the infectivity, and released to environments under certain conditions.