DISINFECTION IN WATER DISTRIBUTION TO IMPROVE QUALITY AND REDUCE COSTS
Routh, J.D.,
Severn Trent Services Ltd
(free)
Disinfection at source works has now reached a stage where reliable and accurate dosing of disinfectant should be achieved with standard design and operation. The lower levels of disinfectant now commonly used in the water leaving the source works can lead to problems of low disinfectant levels further along the distribution network and increasingly there is a need for booster disinfection throughout the network to minimise these problems. An obvious place to treat water is at service reservoirs where losses of disinfectant levels can occur for reasons of long retention, stagnation, poor mixing and other reasons. Treatment has conventionally been at either inlet or outlet of the reservoirs with either gas or bulk sodium hypochlorite, all of these options have limitations.
Work has been carried out on methods of treating the bulk of water in the service reservoir by inducing mixing in the reservoir giving a system that removes problems with poor mixing and can cater for long retention times in reservoirs as well as wide variations in flows. These systems have shown good control of the bulk of water in the reservoir which offers further potential savings in maintenance as any requirement for fast response to problems is minimised.
Further savings have been demonstrated by using on site generated hypochlorite, as the raw material salt has an unlimited storage life and very low risk and can be stored in larger quantities cutting down on visits to sites that are remote and rarely visited.
KEY WORDS Disinfection, Distribution, Reservoir, RMS
