Mathematical modelling of biofilter effectiveness in pH regimes

Abstract

The efficiency of a biofilter filled with pine bark charge was modelled under conditions of interchanging pH. Hydrogen ion concentration is significance for the growth of microorganisms, therefore biological metabolism is strongly dependent on pH. Many microorganisms will only grow within a particular pH range. Since pH has a strong influence on kinetic parameters and governs the process into the biofilm, proton concentration (H+) was included as a state variable in the model. Different approaches to model pH variations in biological systems can be found in literature. The biofilter model was implemented in a home-made simulation environment developed in MATLAB. Model evaluation was performed by comparison of model predictions with experimental data obtained in the pine bark charge of biofilter. The model was able to predict qualitatively and quantitatively the behaviour of the system under dynamic conditions, particularly for pH. Modelling were performed with different pH regimes (4, 5, 6, 7, 8, 9 and 10) in the charge filled with pine bark. Moreover, the dependence of the filter efficiency on its charge height (0.15–0.75 m) with different initial pollutants (xylene, butanol and buyl acetate) concentrations and at different velocity of passing air (0.02–0.1 m/s) were modelled. Similar to experimental tests, the increase in the charge height from 0.15 to 0.75 m results in the increase in cleaning efficiency. For example, when the pH of 7 is maintained in the biocharge and the air is being cleaned of butyal acetate (with its initial concentration of 74 mg/m³) the efficiency of removal of butyl acetate starting with the height of the charge equal to 30 m is 70.1 %, starting with the height of 60 m is 77.6 %. Furthermore, modelled expression were similar to experimental data of the air flow rate results in the decreased efficiency of the biofilter. Respectively, when the pH of 7 is maintained in the charge and the air is beeing cleaned of xylene (with its initial concentration of 63 mg/m³), with the velocity of the passing air increased from 0.04 to 0.08 m/s, air cleaning efficiency significantly reduces from 76.8 to 68.3 mg/m³. Therefore, mathematical expression of environmental processes such us biofiltration lighten theoretical calculations and seek ultimate air cleaning efficiency.