Spatial distribution of microorganisms and measurements of oxygen uptake rate and ammonia uptake rate activity in a drinking water biofilter

The biofilm characteristics (population dynamics and biofilm composition) i n a biological filter for the removal of iron, manganese and ammonium were studied in a drinking water treatment plant. The objective was to examine t he spatial distribution and biological composition of active biomass that g rows in a biological filter and to verify the effect of the backwashing on the quantity of fixed biomass and on the density and activity of the biolog ical population. Heterotrophic microorganisms activity was higher in the up per layer of the filter. Nitrifying microorganisms colonized the biofilter in a stratified manner and their activity was higher in the second layer of the filter. A total of 14 species of ciliated protozoa and 7 species of fi lamentous microorganisms wee found in the biofilters. Ciliates were concent rated in the filterbed layer in which the heterotrophic activity was higher . The grazing activity of ciliates on heterotrophic bacteria reduced the co mpetition pressure on nitrifying microorganisms, supporting their growth an d thus raising the ammonium removal efficiency In general, filamentous micr oorganisms appeared to be indifferent to operating changes in the plant suc h as backwashing and filtering cycles. Crenothrix was the prevalent filamen tous microorganism in terms of both frequency and abundance; it was found p revalently in the first layer where the oxidisation of iron and manganese o ccurred.