VIRUS BEHAVIOR WITHIN A DISTRIBUTION-SYSTEM

If viruses are introduced into a drinking water distribution system th ey will be submitted to various phenomena, including inactivation, agg regation, adsorption but the actual inactivation rate is impossible to estimate. A pilot-scale study evaluated the behaviour of viruses spor adically introduced into a distribution system. In particular, phenome na such as virus adsorption onto clay particles or onto pilot surfaces covered by a biofilm, which could provide viruses with a protection a gainst trace amounts of residual disinfectants were studied. Polioviru s 1, pre-adsorbed or not on particles of Na montmorillonite, was pulse -injected into a pilot distribution system and traced both in the wate r flow and in the biofilm. The viral responses observed in the water f low at the pilot outlet can be described by a Gamma law or by an analy tical model that includes both viral inactivation and adsorption to th e biofilm. Pre-adsorption on 40mg/l Na-montmorillonite increases about 3-fold the residence time of the viruses within the pilot. In the pre sence of chlorine, pre-adsorption on clay does not prevent chlorine in activation of viruses. In every case, a greater amount of viruses is r ecovered from the biofilm than from the water flow, by a 2-fold or by a 10-fold factor in the absence or presence of chlorine, respectively. Viral adsorption to biofilm is thus a leading phenomenon that, along with viral inactivation, directs the fate of the viruses introduced in to a distribution system and, in particular, allows for their accumula tion within the biofilm. (C) 1997 IAWQ. Published by Elsevier Science Ltd.