Factors which control bulk chlorine decay rates

Several computer programs for modelling water distribution networks have be en developed which incorporate a facility for modelling chlorine decay. Pro blems have been experienced with the calibration and durability of these mo dels due to both temporal and spatial variability in the decay constants. C hlorine will decay either due to reactions at the pipe wall or due to react ions in the bulk water. The aim of the work presented in this paper is to i nvestigate the factors which influence bulk decay. Over 200 determinations of bulk chlorine decay against time were performed on waters taken from 32 sampling locations within the Severn Trent region, U.K. The bulk decay cons tant was observed to show significant variation with temperature, the initi al chlorine concentration and the organic content of the water. An equation was derived relating these parameters which could be used to update the de cay constants in network models and improve their durability. (C) 1999 Else vier Science Ltd. All rights reserved.