AWWA PATH56553

The elimination of thermotolerant coliforms (Coli44) and spores of sulphite-reducing clostridia (SSRC) by full-scale water treatment was determined by large volume sampling. The objective was to determine the efficacy of full-scale treatment processes against microorganisms, both against relatively sensitive vegetative bacteria and resistant bacterial spores. In two short periods in winter and summer, much information was collected about the elimination of Coli44 and SSRC by the overall treatment, the contribution of the unit processes and the variability in elimination. Coli44 concentrations in the source waters were reduced by 3.2 to 6.3 log to an average concentration sufficiently low to achieve more than 99% compliance with the drinking water standard. The elimination of SSRC was lower (1.4 to 4.2) and SSRC were observed occasionally (>1%) in finished water by the routine weekly sampling of 100 ml samples. The study also yielded much information about the elimination efficacy of unit processes at the different locations. For instance low inactivation at one of the full-scale ozonation processes for both indicators, different efficacy of different floc-removal processes after coagulation, low elimination of SSRC by filtration processes with infrequent filter bed cleaning and Coli44 breakthrough through treatment in winter due to concurrent failure of coagulation and disinfection. This information enables process optimization and improved process control. Relating these breakthrough events to raw water quality or process conditions may lead to measures to prevent these risk-events. The quantitative information on efficacy of full scale treatment systems may also be used as input for quantitative risk assessment. SSRC data appear to be applicable in quantitative assessment of the risk of resistant pathogens, such as Cryptosporidium, for describing the efficacy of coagulation/filtration and disinfection processes, but not for slow sand filtration or granular activated carbon (GAC) filtration. Includes 15 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

09/22/2002

Number of Pages:

12

File Size:

1 file , 210 KB