We come across bisphenols (BP) daily by using polycarbonate plastics (food containers, drink bottles, toys, sports and medical equipment), epoxy resins (internal water pipe coating and protective coatings for the interiors and exteriors of food and beverage cans) and thermal paper (invoices, public transport tickets, parking tickets). The most commonly used BP is bisphenol A (BPA), but it is often replaced by other BPs due to its adverse effects on human health and the associated regulatory restrictions in the industry. The widespread use of BP is reflected in their greater occurrence in our environment. BPA, BPAF, BPF, BPS, BPAP, BPB, BPP and BPZ have been detected in the environment so far. The main source of these compounds in the environment is wastewater. BPs have been detected in both the infleunt as well as the effluent from treatment plants, which indicates that the currently wastewater treatment is not sufficient.
Cavitation is a physical phenomenon in liquids, where the formation, growth and collapse of bubbles occurs. Hydrodynamic cavitation causes the bubbles to form in the fluid stream due to an increase in fluid velocity, which occurs due to the geometry of the flow system or rather the reduced flow. Consequently, the pressure is reduced (e.g. Venturi restriction, multiple hole orifice plates, rotation generators). Once the flow is increased again, the pressure normalizes which leads to the collapse of the bubble. When the bubbles break down, it leads to a localized release of large amounts of energy. Areas similar to hot spots start to form, with temperatures rising up to 1000–10000 K and the pressure up to 100–5000 bars. Extreme conditions lead to the dissociation of aqueous molecules into OH˙ in H˙ radicals. Strong oxidation conditions are created which enable the oxidative decomposition of substances present in the liquid.
In the master’s thesis, we studied the removal or degradation of the following bisphenols with hydrodynamic cavitation: BPA, BPB, BPC, BPC2, BPE, 22BPF, 24BPF, 44BPF, BPAF, BPS, BPAP in BPZ. A rotation generator of hydrodynamic cavitation was used for the research. The efficiency of hydrodynamic cavitation in the waste water from laboratory bioreactors was evaluated under various experimental conditions (time, power and temperature of cavitation).
The results showed that HC does not remove the selected BP from the waste water in its entirety, but rather requires assistance from other methods of purification. It is important to note that the efficiency of HC for degradation of organic pollutants depends not only on the experimental conditions of cavitation, but also on the complexity of the matrix, the composition of the HC reactor, and the physicochemical properties of the compounds studied. Optimal experimental conditions for the degradation of the studied BP with HC in terms of results are 10 minutes at 9500 rpm and uncontrolled temperature. Under these experimental conditions, the following degradation rates are achieved: 54 %–63 % for BPB, BPC, BPZ and BPF, 38 %–49 % for 24BPF, BPE, BPAF, BPA BPC2 and BPAP, 15 %–24 % for 22BPF and BPS.
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