Modelling studies of water chlorination efficiency in municipal water supply network

Chlorination of water belongs to the basic methods of its disinfection and is commonly used, permanently or periodically, as the final stage of water treatment in many water treatment stations in Poland. Although, the chlorination process is a well-known phenomenon, the selection of an appropriate dose of disinfectant is still a difficult task. The lack of chlorine in the water or its excessively low content (below 0.2 mg × dm–3) may result in the lack of microbiological protection of water flowing through the pipes. A reverse situation is also unfavourable. The use of too high doses of chlorine at the entrance to the network, on the one hand, ensures adequate disinfectant concentration even in the fittings of the network, on the other hand, it can lead to dangerous for health disinfection by-products (DBPs) including trihalomethanes (THMs). The selection of the proper dose of chlorine should take into account factors affecting its consumption, chemical parameters of water as well as hydraulic parameters of water transport. Such possibilities are available due to application of numerical modelling to study the transport of chlorine in water. The aim of the presented research is to analyse the effectiveness of chlorination of water in a selected water supply network. Simulation tests were carried out for the various doses of disinfectant supplied to the network for the assumed duration of the simulation – 168 hours. The qualitative model was developed in the Epanet 2.0 software using a hydraulic model of the tested network. The first order chlorine decay reaction was assumed to modelling studies, with applied literature values of decay rate of chlorine in water. The results of simulation tests of chlorine transport in the network revealed difficulties in choosing the right dose of chlorine necessary to ensure microbiological protection of water in the network. The forced flow allowed effective disinfection of water.