Influence of phosphorus on biofilm accumulation in drinking water distribution systems

Abstract

Continuous reactor tests using rotating reactors with polyvinyl chloride (PVC) coupons were conducted. Laboratory tap waters with and without 50 μg P/L KH2PO4 (phosphorus water and non-phosphorus water) were supplied to the reactors in the absence of residual chlorine. Numbers of cells attached on the surface of the coupons (biofilm cells) and numbers of cells suspended in the influent and effluent waters (planktonic cells) were enumerated, and then specific growth rates of biofilm cells and planktonic cells were estimated. Concentrations of assimilable organic carbon (AOC) in both feed waters were comparable, whereas numbers of biofilm cells in phosphorus reactors were 1 order of magnitude larger than those in non-phosphorus reactors at the steady state of the continuous reactor test. Total planktonic cell concentrations in phosphorus reactors were also 1 order of magnitude higher than those in non-phosphorus reactors. Specific growth rate of biofilm cells estimated from heterotrophic plate count in non-phosphorus reactors was 1 order of magnitude higher than that in phosphorus reactors. This study concluded that phosphorus would increase amounts of biofilm cells on distribution pipe walls because phosphorus lengthened the generation time of biofilm cells. The concentration of AOC could not represent the potential of biofilm accumulation sufficiently.