Managing the Water Supply
Abstract
The treatment of water has recently undergone a great period of evolution driven by a greater understanding of the contaminants present in water and their health risks, as well as the need to develop cost effective processes.
Up until the early 1970’s, the basic treatment processes employed for municipal supplies were coagulation, settlement, sand filtration and disinfection by chlorine. Chlorine dosed in water and distributed in piped water supplies had been accepted as the single most important factor in preventing major outbreaks of water borne disease since early in the century.
In the 1970’s there have been a number of challenges to, and developments of, these traditional treatment steps including:
- identification of potentially carcinogenic disinfection by products (DBPs) of chlorine and other chemicals;
- need to address loss of chlorine residual in large distribution systems;
- use of chloramines or ozone and other disinfectants to minimise chlorine use and resultant DBPs;
- optimising filtration processes to minimise capital costs through use of direct filtration, multimedia filters and high rate filtration processes employing new coagulants and coagulant aids;
- development of low cost membrane technologies.
Water-borne disease had not been a major concern in developed countries, but re-emerged as a major public health issue. Since 1985, there have been some 12 documented water borne outbreaks of cryptosporidiosis in North America and eight in the UK. Typically, 1% of those contracting cryptosporidiosis require hospitalisation and the immuno compromised individuals may suffer a mortality rate of 50%. Currently, there is no known treatment for this disease, in contrast to giardiarsis which may be treated by antibiotics.