Occurrence of free-living amoebae in drinking water

Abstract

In the present study water samples were collected from 4 drinking water treatment plants (DWTPs) located in Fayoum governorate. Three DWTPs namely: New Azab, Old Azab and Old Kohafa are working with rapid sand filtration system, while the fourth DWTP namely New Kohafa was operated by slow sand filtration system. Three types of water were collected from the 4 mentioned DWTPs: raw (inlet) water, finished (outlet) water and tap water from the distribution system. Water samples were collected monthly from each water type along one year period from March 2010 to February 2011. Each water sample was filtered and the obtained sediments were cultured on non-nutrient agar (NNA) plate seeded with living Echerichia coli bacteria and incubated at 30°C and then microscopically examined. The morphologically identified free-living amoebae were subjected to molecular confirmation by simple PCR techniques using genus specific primers for Acanthamoeba and Naegleria as well as species specific primers for Balamuthia mandrillaris. In general, the occurrence of free-living amoebae in Nile water reached 72.9%. The highest occurrence of free-living amoebae (91.7 %) was recorded in the intake of Old Azab DWTP, while the occurrence of free-living amoebae in finished water reached 25%. The same occurrence of free-living amoebae (25%) was recorded in finished water of all DWTPs and the occurrence of free-living amoebae in distribution system of Fayoum governorate reached 22.9 %. The highest occurrence of free-living amoebae (91.7 %) was recorded in the distribution system of Old Azab DWTP. Concerning seasonal variations, the highest occurrence of free-living amoebae in the raw water of the examined DWTPs was recorded in summer (91.7%) while the highest occurrence of free-living amoebae in the finished water of the examined DWTPs was recorded in autumn (41.7%) also the highest occurrence of free-living amoebae in distribution systems was recorded in autumn (41.7%). Efficiency of DWTPs for the removal of FLAs, It was found that the removal percentage of free-living amoebae through different treatment processes reached its highest rate in Old Azab DWTP (70%), followed by New Azab DWTP (62.5%). On the other hand, the capability of Old Kohafa and New Kohafa DWTPs in removing free-living amoebae through drinking water treatment processes was equal as each of them could remove 57.1% of free-living amoebae present in their intake water.