Hydrodynamic Cavitation-assisted Advanced Oxidation Technology For The Treatment Of Pharmaceutical Wastewater

The construction of ecological civilisation is related to people’s well-being.In the process of fighting the battle against pollution,the prevention and control of water pollution is a global concern.In order to effectively slow down the process of water pollution and solve problems such as water safety,the development of clean and efficient wastewater treatment processes and technologies is one of the effective ways to ensure the healthy development of the water environment.Advanced oxidation process（AOPs）is capable of producing reactive radicals with strong oxidising properties,which can decompose and mineralise organic pollutants,and has a very promising application in the treatment of organic wastewater.However,the single conventional advanced oxidation process has some drawbacks,such as easy agglomeration of catalysts,low efficiency and small treatment capacity.Hydrodynamic cavitation（HC）has attracted much attention in recent years due to its advantages such as easy operation,green and high treatment capacity.To further enhance the degradation efficiency and treatment capacity of advanced oxidation technology for pharmaceutical wastewater,HC technology can be organically combined with traditional advanced oxidation technology to construct a combined technology of HC-enhanced advanced oxidation.Based on the cavitation mechanism,this work combine photocatalysis,persulfate-based AOPs and peroxyacetic acid（PAA）-based AOPs and design three synergistic AOPs,namely HC assited photocatalysis,HC assited persulfate activation and HC assited PAA activation,and constructs an experimental HC reaction device with the characteristics of the combined technologies.By systematically investigating the operating parameters of hydrodynamic cavitation,including inlet pressure,initial concentration of pollutants,p H,material composition and structure of catalyst,type and addition of activator and other technical parameters,the final optimisation of the degradation effect of the pharmaceutical wastewater was achieved and the possible degradation mechanism of the pharmaceutical under different synergistic technology was further speculated.The details of the research in this work are shown as follows:（1）Based on the combination of HC and advanced oxidation processes（AOPs）,a hybrid method with enhanced oxidation capacity has been proposed to remove organic pollutants.In this study,we used a synergistic effect between the photocatalytic process and hydrodynamic cavitation to enhance the degradation of ciprofloxacin（CIP）by P-doped Ti O₂ catalysts.Compared to the degradation rates of 20.37%and 55.7%of HC and P-Ti O₂ photocatalytic processes alone,the CIP degradation rate of HC-assisted photocatalytic processes was as high as 90.63%under the optimal experimental parameters.By using SEM and BET analysis,it was found that the surface area of P-Ti O₂ nano-photocatalyst was significantly increased,the particle size was smaller,the surface was cleaner,and the dispersion was improved.The possible degradation mechanism and reaction pathway of CIP in mixed HC+photocatalysis were investigated by free radical capture experiments and liquid chromatography-mass spectrometry.Meanwhile,the impact of inorganic anions(H₂PO₄^-,Cl^-,SO₄^2-,CO₃^2-,and NO₃^-)present in real environmental conditions on the degradation efficiency was examined.The results indicate that the presence of Cl^-and SO₄^2-enhances the degradation efficiency.This is attributed to the formation of new radicals or more strongly oxidizing radicals in the system.However,the ions SO₄^2-,CO₃^2-,and NO₃^-all have a negative impact on the degradation efficiency.Additionally,an energy efficiency calculation was performed.The energy efficiency of hydrodynamic cavitation-assisted photocatalysis technology is 3.57×10^-6 mg/J.This hybrid HC+photocatalysis technology has potential applications in the treatment of antibiotic wastewater at the industrial level.（2）Magnetic Ce O₂-Mn Fe₂O₄ catalysts were prepared by constructing a new hydrodynamic cavitation assisted activated persulfate system.The degradation performance of this technique was evaluated by simulating the removal of Enrofloxacin（ENR）from real wastewater.In this work,a variety of characterization methods were used to investigate the crystalline characteristics,physical characteristics and the presence of chemical elements on the surface of Ce O₂-Mn Fe₂O₄.In order to achieve the best degradation,we investigated the influencing factors（such as molar ratio of Ce O₂ and Mn Fe₂O₄,dosage of persulfate and catalyst,initial solution concentration,etc.）for persulfate degradation of Enrofloxacin（ENR）by Ce O₂ and Mn Fe₂O₄.The inlet pressure using hydraulic cavitation technology alone is also explored to ensure the maximum effect of hydrodynamic cavitation.In addition,the mechanism of Ce O₂ and Mn Fe₂O₄ in the activation of persulfate was determined by first principles calculations.Finally,the active free radicals involved in the degradation of Enrofloxacin（ENR）were identified,and a possible mechanism of the HC-assisted activation of persulfate in the presence of a magnetic Ce O₂ and Mn Fe₂O₄ catalyst was proposed.The experimental results showed that in the presence of the catalyst,the degradation rate of Enrofloxacin（ENR）reached 98.9%by HC-assisted activated persulfate.The influence of inorganic anions is similar to that of HC+P-doped Ti O₂+photocatalysis,but with different degrees of impact.The energy efficiency of hydrodynamic cavitation-assisted persulfate activation technology is 1.567×10^-5 mg/J.（3）HC-assisted activated peracetic acid（PAA）degradation system was constructed.In this study,hydrodynamic cavitation-assisted activation of persulfate was used to degrade paracetamol（PA）in aqueous solutions.Among the transition metals tested(Fe²⁺,Fe³⁺,Co²⁺,Cu²⁺,Mn²⁺),Fe²⁺had the highest efficiency.The effects of p H,PAA dosage,initial concentration of PA,and Fe²⁺concentration on PA removal were studied.Using p H=6,4 m M of PAA and 0.4 m M of Fe²⁺,the removal efficiency was more than 95.63%within 30 minutes.The contribution of free radicals centered on oxygen was determined by adding a free radical trapping agent.Through the identification of free radicals in the reaction,it was found that the hydroxyl radical was the main oxidant,and the oxygen center radical（·R-O）had little effect on the degradation of PA.Seven intermediates of PA oxidation and the degradation pathway of PA in the presence of Fe²⁺was determined.In conclusion,this study shows that HC assisted activation of peracetic acid in the presence of Fe²⁺opens up a new perspective for advanced oxidative degradation of organic pollutants.The addition of SO₄^2-slightly increased the degradation rate;the impact of Cl^-on degradation is minimal,almost negligible;H₂PO₄^-,CO₃^2-,and NO₃^-ions all have negative effects,with NO₃^-having a greater impact at low concentrations.Upon calculation,the energy efficiency of hydrodynamic cavitation-assisted persulfate activation technology is 8.86×10^-6 mg/J.