DYNAMIC MODELING OF BACTERIAL-GROWTH IN DRINKING-WATER NETWORKS

Numerous biological and physicochemical reactions take place in drinki ng water distribution systems, and give rise to phenomena whereby the organoleptic or bacteriological characteristics of the distributed wat er are modified. Drinking water may contain residual biodegradable dis solved organic compounds which provide a primary source for the format ion of a trophic chain inside the pipes. Bacterial biomasses develop m ainly on the internal surface of the pipes, where they are relatively well protected from the action of chlorination agents. The detachment of these biomasses is responsible for most of the bacterial proliferat ion observed in water samples taken in distribution systems, and also contributes to the installation of undesirable metazoea such as Asellu s aquaticus. Combatting these biological developments calls for the ap plication of preventive and remedial treatments, and these can be stud ied more closely by the use of modelling. This article proposes a mode l for the study of the behaviour of bacterial biomasses in distributio n networks, taking into account the various major parameters which gov ern their structure, such as the ratio of biodegradable dissolved orga nic carbon (BDOC), temperature, residual chlorine, pH and the hydrauli c conditions of each pipe, The model makes use of the data supplied by the Piccolo hydraulic modelling software, which can provide predictiv e mapping of the situation of each section of the network. What is mor e, by taking into account the physiochemical and biological variations in the water at the intake to the network, this dynamic model forecas ts the evolution of the variables depending on residence time but also on time, thus enabling better visualisation of a disruption in the sy stem in real time. We discuss the influence of the expression of the d etachment of fixed bacteria on solutions of the system of differential equations. Use of the model reveals threshold values of temperature a nd BDOC which can enable a natural limitation of bacterial biomasses i n the network without the use of chlorine. Copyright (C) 1996 Elsevier Science Ltd