Effect of water composition on organic micropollutant removal by ozonation Parti II : Simulation of micropollutant removal in ideal reactors
Micropollutant (P) oxidation in an ideal ozonation reactor uses the kinetic équation: (d[P]/dt)=(KD[O3]L+KID[OH∘])[P] kD and kID : kinetic rate constant of ozone and hydroxy radicals on the micro -pollutant P. In part 1, the theoritical équation shows that [OH°] is proportional to the ozone concentration ([OH°] = k'[O3]) and thus the following equation is obtained : (d[P]/dt)=KG[O3]L[P] with KG=KD+KIDK' In a completely stirred tank reactor, ozone concentration in liquid phase is constant and pesticide elimination is given by the equation : ([P]/[Po])=(1/1+KG[O3]L τ) with τ=(V/Q) In a plug flow reactor, ozone concentration in liquid phase varies along the column. To modelize them, we use the model of completely stirred tank reactors in series where the unit volume is ∆V. In our calculations, this volume is obtained by S (reactor cross section area) and ∆h equal to 0,01 m. In this volume ∆V, ozone and micropoliutant concentrations are considerad as a constant. Simulation calculations are based on the knowledge of global kinetic constant kG and ozone concentration. The value of the ozone concentration is obtain from mass balances on the oxklant (on a ∆V or V volume reactor) : ozone inlet + transferred ozone = consumed ozone + ozone outlet The quantifies of transferred ozone are calculated from the Henry law and a semi empirical kLa equation. The quantity of consumed ozone is calculated from the equation in part I (d[O3]L/dt)=w[O3]L Experimental results are obtained with parathion, an organo-phosphorus pesticide on a bubble column pilot plant: Parameters are contact time (300-600 s), pH (6,7-8-2) and ozone treatment rate (1 to 5 g/m3). A kG value of 500 or 600 M-l s-l shows a good correlation between predicted and simulated pesticide concentrations. However, there are noticable differences, especially at the bottom of the column. This shows the necessity to take into account the hydrodynamic properties of the reactor during next works. The use of the simulation program lets to calculate the elimination of pesticide versus the two main parameters : the factor kGteta and the value of w.