Pokročilé oxidační procesy pro snižování obsahu zapáchajících látek v odpadním vzduchu

Abstract

This thesis is focused on the evaluation of the efficiency of selected advanced oxidation processes (AOPs) in the degradation of pollutants from waste air. The study was conducted in a continuous photochemical pilot-scale unit consisting of a photolytic/photooxidative reactor (air/VUV185/UV254) and a photochemical reactor (water/UV254/H2O2). As model contaminants were used volatile organic compounds (VOCs), namely styrene, xylene, and toluene; and then ammonia. Advanced analytical methods were used for the analysis of selected contaminants: gas chromatography with flame ionization detector (GC-FID) for VOCs and Fourier transformation infrared spectrophotometry (FTIR) for ammonia. Degradation products and intermediates in the liquid phase were identified using a gas chromatograph with a quadrupole mass selective detector (GC-MS), ion exchange chromatography (IEC), and a total carbon analyzer (TOC). The experimental results showed high efficiency of VOC degradation, with the highest conversion achieved for styrene (up to 74 % at an inlet concentration of 50 ppmv and a flow rate of 100 m³/h). The styrene and xylene mixture showed a total conversion of 54 %, and xylene alone 48 %. It was confirmed that the efficiency of VOC degradation significantly depends on the residence time in the reactors - higher air flows led to lower conversion. Analysis of the liquid phase confirmed the formation of simple organic compounds, mainly organic acids (acetic, formic, lactic, oxalic), as well as ethanol, methanol, acetone, and CO2. The conversion of ammonia in the first stage of the decontamination unit was low (max. 30 % at a flow rate of 150 m3/h and an inlet concentration of 20 ppmv); however, in the second stage, more than 90 % of it was absorbed into the peroxide solution. The rate of ammonia degradation from the liquid phase proved to be relatively low, with the best results achieved with a combination of UV254 and ozone. Two optimization modifications were tested to increase the efficiency of decontamination. The first consisted of the application of heterogeneous photocatalysis, where ceramic foam plates coated with a layer of nanostructured TiO2 were inserted between the lamps in the first stage of the degradation unit. Toluene was chosen as the model pollutant for these experiments (inlet concentrations of 50 and 100 ppmv and flow rate of 100 m3/h). This modification led to an increase in toluene conversion by almost a third. However, the total toluene conversion after passing through both stages remained at a similar level to that of the non-optimized system. The second modification involved a change in the geometry of the first stage of the unit. By switching from a horizontal to a vertical reactor arrangement, styrene conversion increased by 25 %. At a flow rate of 10 m3/h, styrene degradation of 97.2 % was achieved in the first stage of the unit. Mathematical modeling confirmed that changing the geometry extends the residence time of contaminants in the reactor, which leads to higher efficiency. It was also proposed to install a rigid cross-shaped partition in the center of the photolytic reactor, which, according to calculations, should extend the residence time of particles. Modeling showed that with this arrangement it would be possible to achieve complete removal of styrene (initial concentration 50 ppm, flow rate 100 m3/h) already in the first stage of the technology, while eliminating 80 % of organic carbon. A pilot-scale two-stage decontamination unit has proven its effectiveness in degrading contaminants from the air stream. In the proposed arrangement, the unit could be used for post-treatment of exhaust air in smaller industrial and agricultural applications.