a relationship (Rousseau et al., 2004; Kadlec and Knight, 1996) and the rate of
removal is then calculated assuming first-order plug-flow system. However, it has
been reported that a modified first-order model (Eq. (4)) can be used to describe the
relationship between P removal and hydraulic retention time (HRT) (Kadlec and
Knight, 1996; Tang et al., 2008).