AWWA QTC97134

Utilities often grapple with the problems of unsteady-state conditions in the hydrodynamics of the distribution system. Large excursions can occur over a matter of hours and even minutes. It is expected that these excursions affect the detachment of biofilm organisms in the distribution system in response to changes in shear stress, etc. However, little is known about the specific effects of changing water quality on the phenomenon of regrowth. This study examined the effects of changes in loading of organic material, temperature and disinfectant residual in laboratory and pilot-scale distribution systems. The resulting changes in coliform and heterotrophic plate count (HPC) numbers should provide qualitative and quantitative information about the relative importance of these phenomena and the time scales over which the effects of transients can be expected to be felt. Coliform-containing biofilms were established and, once a relatively stable population had formed, the system was subjected to one of three changes: an increase in substrate (assimilable organic carbon) loading; a decrease or increase in disinfectant residual; and/or a change in temperature. While changes in temperature were deliberately gradual (simulating, for example, turnover in a lake), changes in organic loading and disinfectant residual were more abrupt. Laboratory systems utilized rotating annular reactors with either polycarbonate or mild steel slides, while pilot system studies used recirculating pipe loops or annular reactors with mild steel surfaces. These systems were examined for attached and suspended microorganisms (both HPC and coliforms) during the application of these transients.

Product Details

Published:

01/01/1997

ISBN(s):

0898679583

Number of Pages:

21

File Size:

1 file , 150 KB