Reducing Organics and its Water Quality Impact

Over the last five years United Utilities has undertaken major capital investment to further reduce the risk from Cryptosporidium and trihalomethanes in more than half the supplies in the northwest of England. The majority of the supplies in the region come from upland surface sources which historically have had minimal treatment and in consequence high organic concentrations. The factors influencing the integration of new treatment processes with existing, the choice of process and the challenges arising are discussed, as is their impact on the water quality. In particular, the benefit to the two measures which are driving the investment. The consequences extend beyond that achieved at the water treatment works. The reduced organic input into the distribution network has resulted in chlorine persisting a lot further into the distribution system. As a result of this, and the lower organic input, bacteriological activity has fallen substantially with consequent reduction in the presence of coliform bacteria. The lower concentration of organics has contributed to a substantial reduction in lead concentrations. This has been clearly illustrated by lead concentrations observed at lead pipe rigs situated within the distribution network.