Optimisation of complex water supply systems with water quality, hydraulic and treatment plant aspects

A model for optimal operation of a complex water supply system for drinking water and with water quality, hydraulic and desalination treatment plants developed by Cohen and others has been applied to a realistic regional network, in which water quality is defined by salinity, magnesium and sulphur. The model considers the hydraulics of the network, including pump stations, boosters and control valves. Solute transport in the model assumes conservative water quality parameters. Changes in water quality within the network are achieved by changing the removal ratio of reverse osmosis in desalination treatment plans and by control of mixing (dilution) at junction nodes. The decision variables in the model are the operation of treatment plants, pumps and control valves. The model minimises the sum of the costs of water at sources, treatment, energy and loss of agricultural yield due to irrigation with low quality water. Three case studies are presented: (1) a network without treatment plants and water salinity as the only water quality parameter; (2) as for (1), but with treatment plants included; and (3), as for (2), but with the addition of magnesium and sulphur quality parameters. The results demonstrate the ability of the model to handle a regional water supply system having water quality problems, with optimal solutions being found in cases where there is a conflict between hydraulic and water quality requirements.