The Impact of Pesticides - Academy Publish

As seen in Table 4, as the concentration increases, the length of the mass transferzone (MTZ) increases and the fractional bed utilization (FBU) decreases. Therefore,in general terms, as the initial concentration increases, the driving force or masstransfer increases, and results in a decrease in the mass transfer zone (MTZ). Inlaboratory experiments, the fixed beds are not used long enough to ensure a fullydeveloped profile (a constant pattern behaviour); where the same operatingconditions, the value of MTZ remains constant. In this case, when working withvery short columns, the mass transfer zone moves to non-constant velocity, since theconstant pattern is not fully developed. In this case, an approximate expression forestimate MTZ parameter has been used (constant velocity supposed), so results thatmay not match those expected can be obtained (Wankat, 1990).Mass transfer zone increased with increasing flow rate, leading to faster saturation ata higher value of the volumetric flow rate. In this case, as the volumetric flow rateincreases, the mass transfer zone (MTZ) and the fractional bed utilization increases.If the concentration profile, C/Co versus length, is studied, an increase of thevolumetric flow rate leads to an increase of the mass transfer zone and worsens theuse of the bed.BREAKTHROUGH MODELLINGThe estimation of error between the experimental and predicted values of C/Co wasdone by using modified form of the Marquardt’s percent standard deviation (MPSD)represented by Eq. (5) in Table 1. Therefore, adsorption capacity obtained byThomas and Wolborska model and value obtained by Yoon-Nelson model werecompared with experimental parameters using standard error of estimate (SE)method: Eq (6) and (7), in Table 1.The Thomas ModelThomas model parameters, k T and q 0, were determined by not linearized expressionof Eq (1). K T and q 0 values are shown in Table 5. It can be observed from Table 4that the values of q 0 increased with an increase in the value of C 0 and with adecrease in the value of the volumetric flow rate.Table 5. Predicted parameters for Thomas model and model deviations forisoproturon adsorption on activated carbon.C 0(g.L -1 )Q(mL.min -1 )Z(cm)K T(L.h -1 .mg -1 )q 0 exp(mg.g -1 )q 0 cal(mg.g -1 )MPSD SE50 1.0 2.0 0.10 16.51 15.57 62.16 0.13150 1.0 2.0 0.06 16.75 18.86 21.46 0.42100 2.0 2.0 0.11 19.97 25.31 203.13 0.75100 3.0 2.0 0.09 13.69 20.75 40.87 1.21Fig. 3 (a-b) show the experimental and theoretical breakthrough curves obtained atdifferent operating conditions using Thomas model.AcademyPublish.org - The Impact of Pesticides346