The growing amount of various wastes in the environment is one of the major problems facing humanity. One of the major sources of environmental pollution with various micropollutants are wastewater and waste activated sludge (WAS). Their treatment presents a big challenge for wastewater treatment plants. Sludge is the final product of wastewater treatment process and the proper disposal of sludge is crucial. Due to the presence of various micropollutants, it is necessary to properly process the WAS before disposal – stabilization, dehydration, thickening. Anaerobic decomposition is useful for reducing the amount of waste sludge. However, the process needs a major upgrade to reach its full potential. To improve anaerobic digestion, pre-treatments of waste sludge are often used. These processes improve the disintegration and solubilization of WAS. Mechanical pre-treatment processes such as cavitation are often used for this purpose. In my master’s thesis we focused on the pre-treatment of WAS with hydrodynamic cavitation. Cavitation causes a sudden drop in pressure in a liquid, which triggers the formation of vapour and gas bubbles within the liquid. The reduction of pressure in the liquid can be achieved with the help of the rotor and stator and the resulting cavitation is called hydrodynamic cavitation. The result of cavitation is the homolysis of water molecules, which results in hydroxyl radical (•OH) that drive chemical processes. The use of cavitation for sludge pre-treatment promotes anaerobic digestion, which helps to increase biogas production, reduces the amount of sludge, reduces the amount of pathogenic organisms and removes unpleasant odours. The advantage of hydrodynamic cavitation over other processes is lower operational costs and better scaling possibilities.
The purpose of the research work was to compare four different cavitation regimes and determine which one is the most effective for the disintegration of WAS. For the pre-treatment of WAS we used a rotational generator of hydrodynamic cavitation at the laboratory scale with pined and serrated disc. The effectiveness of the cavitation regimes was compared with respect to changes in chemical parameters (sCOD, soluble NH4-N and NO3-N) before and after cavitation using the spectroscopic method, disintegration degree and energy efficiency. The best disintegration of WAS was achieved with regime with pined disc.
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