Report No DWI0283


Final Report to Department of the Environment


Jul 1992


Granular Activated Carbon (GAC) is being increasingly used as a treatment process in the production of drinking water. However during operation of the filtration system microbial growth occurs over the surface of the carbon and the potential exists for the release of microorganisms into the distribution system.

A review of the current literature was conducted before the experimental programme was undertaken. The initial emphasis of our study examined suitable techniques for the recovery of bacteria from colonised carbon. The constraints imposed by the nature of the experimental programme necessitated the development of two procedures. A published technique in which homogenisation was used to desorb bacteria was found to disintegrate the carbon to produce fines which would interfere with the disinfection experiments. A procedure was developed to desorb bacteria which involved gentle agitation of the carbon. No improvement in desorbtion efficacy was achieved by incorporating a range of surfactants.

The pathogen survival studies found that E. coli was capable of surviving for several weeks on GAC in the presence of a heterotrophic bacterial population even when inoculated on to carbon taken from an in-service filtration system. The disinfection studies indicated that resistance to the action of the chlorine was afforded by protection from the action of the biocide as opposed to acquired natural resistance of the adherent bacterial population.

This study was funded by the Department of the Environment and carried out under the supervision of the Drinking Water Inspectorate.

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