Virus behaviour within a distribution system

If viruses are introduced into a drinking water distribution system they will be submitted to various phenomena, including inactivation, aggregation, adsorption but the actual inactivation rate is impossible to estimate. A pilot-scale study evaluated the behaviour of viruses sporadically introduced into a distribution system. In particular, phenomena such as virus adsorption onto clay particles or onto pilot surfaces covered by a biofilm, which could provide viruses with a protection against trace amounts of residual disinfectants were studied. Poliovirus 1, pre-adsorbed or not on particles of Na-montmorillonite, was pulse-injected into a pilot distribution system and traced both in the water flow and in the biofilm. The viral responses observed in the water flow at the pilot outlet can be described by a Gamma law or by an analytical model that includes both viral inactivation and adsorption to the biofilm. Pre-adsorption on 40mg/l Na-montmorillonite increases about 3-fold the residence time of the viruses within the pilot. In the presence of chlorine, pre-adsorption on clay does not prevent chlorine inactivation of viruses. In every case, a greater amount of viruses is recovered 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 into a distribution system and, in particular, allows for their accumulation within the biofilm.