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Fate and removal of Cryptosporidium in a dissolved air flotation water plant with and without recycle of waste filter backwash water

TitleFate and removal of Cryptosporidium in a dissolved air flotation water plant with and without recycle of waste filter backwash water
Publication TypeJournal Article
Year of Publication2002
AuthorsEdzwald JK, Tobiason JE
JournalWater Science and Technology: Water Supply
Volume2
Issue2
Start Page85
Pagination85-90
Date Published04/2002
KeywordsCryptosporidium, dissolved air flotation, filter backwash recycle, filtration, Particles
Abstract

Pilot plant research focused on the removal of Cryptosporidium oocysts by dissolved air flotation (DAF) clarification and by dual media filtration and on the impacts of the recycle of waste filter backwash water containing oocysts. No impacts from recycle of filter backwash (10% rate) were found for turbidity, particle counts (2-15 μm), and UV254 on DAF and filtration performance. DAF achieved Cryptosporidium log removals of 1.6 to 2.2 without or with recycle of filter backwash. No impacts of recycle were found on filtration, and cumulative (DAF plus filtration) log oocyst removals exceeded 4 log. Model predictions show that the fate of Cryptosporidium and the build-up of oocysts in the plant influent depend on: DAF performance, the percent of filtered water production used for backwashing, and the percent of filter backwash recycle flow. A DAF plant using 2.5% of filtered water production for backwashing and achieving 1.6 log removal or greater of oocysts by DAF clarification will not have a build-up of oocysts in the plant influent regardless of the recycle rate.