AWWA WQTC65982

Filtration processes efficiently remove most organisms but the accumulation and potential development of some of these organisms within the filter media can potentially lead to water quality problems, such as microbial non-compliance or aesthetic problems of the distributed water. Despite the fact that the risks related to filter colonization are usually managed by water professionals, little information is available concerning the level of contamination of typical filter media used for potable water production. In that context, the objectives of this project were to characterize the state of media contamination of a number of filtration plants and to optimize the procedures applied for media cleaning, in case of abundant colonization. The preliminary results obtained among 14 filtration units indicate that all the filter media, regardless of the type of media, are colonized by various organisms (amoebae, aerobic spores, E. coli, nematodes, etc.), and that the level of contamination generally depends on the influent water quality. The effectiveness of chlorinated backwash is not proven, whereas a higher backwash flow rate tends to improve the removal of organisms. Site investigations are still in progress and pilot scale trials will be undertaken to define decontamination procedures. Includes 12 references, tables, figures.