Contribution information

Title IMPACT OF HYDRODYNAMIC CAVITATION ON BY-PRODUCTS FORMATION IN POST-CHLORINATED DRINKING WATER
Status Accepted
Final type Lecture
Final session Environmental engineering
Authors M., Čehovin1, A., Žgajnar Gotvajn2
1 MAK CMC Water Technology Ltd., Ljubljana, Slovenia
2 University of Ljubljana, Faculty of Chemistry and Chemical Technology, Ljubljana, Slovenia
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Brief content The objectives of the research work were to assess the effects of hydrodynamic cavitation on performance of O3, H2O2 and UV advanced oxidation processes (AOPs) on samples containing natural organic matter (humic acid) and synthetic organic matter (methylene blue dye, metaldehyde, iohexol, diatrizoic acid). Since the reactions can also follow radical pathway, typical of Advanced Oxidation Processes (AOPs), cavitation is being researched for oxidation effects either as a stand-alone process or in combination with ozone, hydrogen peroxide, UV and classic AOPs. Cavitation is the formation, cyclic growth and rarefaction with terminal implosive collapse of vapour bubbles in the liquid phase. The effects of the treatment by the applied AOPs alone and those coupled with hydrodynamic cavitation on the decolourization of methylene blue solution and the removal of metaldehyde, diatrizoic acid and iohexol as micropollutants were investigated as well. From the conducted research and under herein described conditions, the application of HC resulted in: (i) increased turbulence throughout much of the plug-flow UV reactor (cavitation zone), with much higher dispersion and diffusion in the form of increased radial and counter-current turbulent eddies, thus improving the exposure of the sample to the uneven UV fluence rate distribution at a given cross-section of the reactor in the cavitation zone; (ii) improved mass transfer of the oxidants and a higher yield of radical species (HO• and HOO•) that was expressed in the increased removal rate of the investigated organic pollutants. The results of the electric energy per order of removal show that the application of hybrid HC, as showed herein, can also be as efficient in terms of the electrical energy consuption as the applied AOPs alone. The potential benefits of the HC application as a hybrid process to the applied AOPs were emphasized in the conditions of relatively (i) high UV absorbance (at λ = 254 nm) and colourization of the matrix, i.e. unfavourable conditions for the efficient fluence rate distribution in the photolytic reactor; (ii) high pollutant concentrations; (iii) low dosages of oxidants and UV; (iv) low ratio of (photo-) oxidants dosages to pollutant concentration. When issues of additional energy consumption to drive the process and material wear of HC generators will be improved and optimised, the potentials of such technology are believed to increase significantly.
ID 55