Report No DWI0232

TREATMENT AND DISINFECTION OF SMALL WATER SUPPLIES

First Annual Report to the Department of the Environment

September 1982 - October 1983

DWI0232

Oct 1983

SUMMARY

This contract runs from 1.9.82 to 31.8.84 and its objectives are as follows:

  1. To evaluate operational experience of equipment currently available for the disinfection of small water supplies.
  2. To test means of hypochlorite dosing and identify the factors that make for reliability and effectiveness.
  3. To develop processes and equipment specifications for treating water at small remote locations.

The contract is part of a programme concerned primarily with public water supplies of less than about 1 Ml/d, serving populations of up to about 5000. WRC has already reviewed methods of disinfection and made a detailed survey of about 200 small supplies.

Visits have been made to small supplies in Yorkshire, Wales and Scotland and sites have been identified for field evaluation of equipment. Experimental facilities have been offered at some disused supply sources.

Two hypochlorite dosing systems have been evaluated in the laboratory, both of the type which is powered and controlled by the flow of water to be treated. Both were found to perform to the makers' specifications and to levels of accuracy and repeatability considered to be satisfactory for small supplies.

Work aimed at the development of a battery operated chlorine residual monitor/contoller has continued. It has been noted that the signal from a commercial cell is sensitive not only to sample flow and pH, but also to incident light. The relationship of signal to pH has been investigated but is not yet clear.

WRC advised Thames WA on the design of inlet to a closed cylindrical contact tank. After construction the tank was tested and found to perform very efficiently.

A draft specification describing the requirements for that intended for use on small water supplies has been given limited circulation for comment. The amended text is included as an Appendix to this report.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.