One of the main sources of environmental pollution is waste sludge. Most sewage treatment plants first properly treat the sludge and then take it to incineration. Some wastewater treatment plants stabilize waste sludge in anaerobic reactors and produce biogas, thus at least slightly reducing the total cost of wastewater treatment. Various pre-treatment methods can be used to increase the amount of biogas.
One of the processes that can be used as a pre-treatment process is cavitation – a physical phenomenon where small vapor bubbles form in a liquid due to a local pressure drop. When bubbles collapse, huge amounts of energy are released. They are responsible for the mechanical (i.e. extreme shear forces, micro-jets, and extreme pressure pulsations) and chemical (formation of predominantly ● OH with homolytic cleavage of water molecules).
In the thesis, we evaluated the disintegration of waste sludge from the treatment plant using hydrodynamic cavitation. We used a laboratory version of a rotary hydrodynamic cavitation generator and studied its cavitation efficiency under different rotor-stator installations. We have determined cavitation performance by measuring relevant parameters, such as total and soluble COD (chemical oxygen demand), and soluble NH4-N (ammonium nitrogen) soluble total carbon before and after cavitation. Through degree of disintegration and specified energy consumption, we estimated the energy efficiency of the installations.
The results showed a low level of disintegration in all setups (<10%) suggesting that HC was not effective in degrading the cell wall of the microorganisms. It is worth noting that the efficiency of HC is influenced by many parameters due to which the overall impact is often unpredictable. The setup of the rotor with 8 cylindrical pins without a stator proved to be the most effective. The achieved degree of disintegration was 9.6%. The same setup also used the least amount of energy (852 kJ/kg TS), which, considering the increase in soluble COD, meant 37 kJ/g sCOD.
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