A mathematical model of a nitrifying expanded-bed reactor for the pretreatment of drinking water

Abstract

A kinetic model of a nitrifying expanded-bed reactor for the pretreatment of drinking water was developed to analyze its behavior under different concentrations of influent dissolved oxygen, ammonium, and organic substrate. In laboratory, an up-flow expanded-bed reactor (linear velocity: 15.5 m/h, space velocity: 7.8 h−1, specific surface area: 5587 m2/m3) was initially fed with synthetic water containing 1 mg NHx-N/L to stimulate nitrifiers growth, followed by varied NHx-N loadings (1–2 mg NHx-N/L with a fixed linear velocity). From tracer tests, the hydraulic regime of the expanded-bed reactor was simulated to be 11 tanks-in-series. To model the even distribution of media in the expended-bed height, a mathematical internal recycle flow with biofilm media was made. The performances were also studied on the pilot- and full-scale reactors receiving river water in two water treatment plants in Vietnam. A single set of biological kinetic and stoichiometric parameters was elaborated that successfully reproduced the five different datasets over the lab-, pilot- and full-scale reactors. The attachment/detachment specific rates of the biofilm were estimated during filtration cycles and backwash events. The graphical guidance and empirical equation were provided to obtain the reactor treatment efficiency under variable influent and temperature.