Insight into the Mechanism of Ultrasonic Activation of Persulfate for Enhancing the Removal of Tetracycline Hydrochloride

Abstract

Tetracycline is often used in treating various diseases or infections, which also leads to severe environmental threats due to its toxicity, durability, and low biodegradation. Meanwhile, although ultrasound (US)-assisted activation of persulfate (PS) is a promising technology for water and wastewater treatment, its reaction mechanism is still not well-defined. Herein, we explored the effect of the enhanced mechanism of ultrasonic activation of peroxymonosulfate (PMS) on the degradation of tetracycline hydrochloride (TCH). The findings revealed that the US/PMS system was highly effective in degrading TCH, achieving an 83.2% degradation efficiency for a TCH concentration of 10 mg/L within 3 h. Moreover, the combination of radical quenching experiments and electron paramagnetic resonance (EPR) analysis confirmed the generation of different types of reactive radicals (such as sulfate radical (SO₄^•−), hydroxyl radical (•OH), superoxide anions (•O₂⁻), and singlet oxygen (¹O₂)) upon PMS activation under ultrasonic cavitation. Thus, US-assisted activation of persulfate is a more promising strategy for efficient removal of refractory organic contaminants in wastewater.

1. Introduction

In recent years, the excessive reliance on antibiotics, coupled with an unrelenting pursuit of economic gains and a disregard for the environmental pollution engendered by these pharmaceuticals, has resulted in the widespread dissemination and accumulation of antibiotics in various ecosystems [1]. It is noteworthy that the issue of antibiotic pollution has only recently begun to garner significant public attention within China. Presently, a diverse array of antibiotics has been detected in surface water, groundwater, sediment, and soil throughout China, indicating a critical situation regarding antibiotic contamination [2]. Tetracycline antibiotics, known for their broad-spectrum antimicrobial properties, minimal side effects, ease of use, and affordability, have been extensively utilized in various sectors. These antibiotics are engineered to be stable and resistant to biological degradation, rendering conventional water treatment methods ineffective for their removal [3].

Advanced oxidation processes (AOPs) have emerged as a promising alternative to traditional treatment methodologies, which are often characterized by low efficiency and inadequate stability when addressing antibiotic pollutants. AOPs have demonstrated superior treatment efficiency, low selectivity, and the capability to manage high concentrations of organic wastewater, particularly in the degradation of emerging pollutants such as tetracycline antibiotics [4]. Among these, the activation of persulfate (PS) is regarded as one of the most effective AOPs for enhancing the removal and degradation of organic pollutants in environmental remediation [5]. Generally, the stability of PS at room temperature and its ability to be activated for contaminant degradation make it a preferred choice over peroxide-based hydroxyl radical (•OH) oxidation processes. Sulfate radical (SO₄^•−) based AOPs rely on the generation of highly reactive free radicals like •OH, SO₄^•−, and superoxide anions (•O₂⁻) through the activation of PS via oxidation and reduction reactions [6]. So far, many methods have been used to activate PS to generate the highly reactive SO₄^•−, which is characterized by its nonselectivity and high oxidation potential of 2.60 V [7]. The activation of PS can be facilitated by a multitude of approaches, encompassing the employment of catalysts, thermal activation, exposure to ultraviolet or visible light, and application of ultrasound (US) [8,9,10,11,12]. Among them, US operates through a combination of cavitation, thermal and mechanical effects, and radical generation to enhance chemical reactions and pollutant degradation [13]. Ultrasonic cavitation involves the formation, growth, and implosive collapse of microbubbles within a liquid medium under the influence of ultrasonic waves, resulting in the generation of localized high temperatures (up to 5000 K) and pressures (up to 1000 atm) [14]. Importantly, ultrasonic cavitation can enhance the mass transfer of chemical reactions in the solution, accelerating the reaction processes, through the collapse of microbubbles generating highly reactive radicals, such as •OH [15,16,17]. These mechanisms render US a versatile tool in AOPs, particularly in the activation of PS for environmental remediation. However, despite its potential, a comprehensive understanding of the degradation mechanisms, especially at the molecular level, is still lacking. This knowledge gap may impede the development of more efficient treatment strategies.

In this study, we explored the synergistic effect of US cavitation and activation of peroxymonosulfate (PMS) on the degradation of tetracycline hydrochloride (TCH). We investigated the influence of oxidant species, PMS dosage, initial TCH concentration, initial solution pH, ultrasonic power and frequency to determine the optimal experimental conditions for the system. Additionally, we evaluated the anti-ion interference capability of the US/PMS system. Radical quenching and trapping experiments were conducted to elucidate the presence of reactive oxygen species (ROS) within the system and their roles in TCH degradation. The results indicate that ultrasonic cavitation facilitates the generation of •OH and singlet oxygen (¹O₂), which are highly reactive and can oxidize TCH in a wide range of pH. Furthermore, the effects of ultrasonic power and frequency on TCH removal in the US/PMS process were found to be more significant than those of the initial solution pH. The objective of this study is to elucidate the degradation mechanisms of pollutants within the US/PMS system and to provide insights for the advancement of more efficient wastewater treatment technologies.

2. Results and Discussions

2.1. Degradation of TCH by Oxidants and US/Oxidants System

Initially, a comprehensive investigation was conducted to assess the degradation of TCH in the presence of oxidants alone, as well as in combination with US and oxidants. As shown in Figure 1a,b, the degradation of TCH by oxidants is not pronounced, except under conditions involving PMS. The degradation efficiency of TCH when treated with hydrogen peroxide (H₂O₂), peroxydisulfate (PDS), and PMS alone are 3%, 5%, and 59%, respectively. Notably, PMS demonstrates a greater propensity for breakdown compared to H₂O₂ and PDS [18]. Consequently, PMS alone is capable of generating a higher concentration of reactive species for the degradation of TCH. Furthermore, the energy generated from cavitation facilitates the production of •OH through the decomposition of water [19], resulting in a TCH degradation efficiency of approximately 36% when subjected to US alone (as represented in Equation (1)). In comparison to systems utilizing single oxidants, the US/oxidants system exhibits superior degradation efficiency. As depicted in Figure 1c,d, the introduction of US significantly enhances the degradation efficiency of TCH. This enhancement can be attributed to the activation of H₂O₂ and PDS by US, which leads to the generation of additional reactive species (as shown in Equations (2) and (3)) [20]. In the US/PMS system, the degradation efficiency of TCH reached 83%. This substantial increase is due to the energy released during cavitation, which has the potential to accelerate the decomposition of PMS into SO₄^•− (as indicated in Equation (4)) [20]. In conclusion, the US/PMS system demonstrates a markedly more effective degradation of TCH compared to systems utilizing oxidants alone, as well as US/H₂O₂ and US/PDS. In addition to the chemical effects, US contributes to the desired turbulence within the system, thereby enhancing mass transfer and intensifying the degradation process [21]. These results indicate that the US/oxidants systems effectively facilitated the degradation of TCH. And the effect of US cavitation is obviously enhancing the removal efficiency of TCH in US/PMS system with a high kinetic constant of 0.01034 min⁻¹, which is twice as high as that of only PMS (0.00569 min⁻¹).

$${\mathrm{H}}_2\mathrm{O}+\mathrm{US}\to •\mathrm{OH}+•\mathrm{H}$$

(1)

$${\mathrm{H}}_2{\mathrm{O}}_2+\mathrm{US}\to 2•\mathrm{OH}$$

(2)

$${\mathrm{S}}_2{{\mathrm{O}}_8}^{2-}+\mathrm{US}\to 2\mathrm{S}{{\mathrm{O}}_4}^{•-}$$

(3)

$$\mathrm{HS}{{\mathrm{O}}_5}^{-}+\mathrm{US}\to \mathrm{S}{{\mathrm{O}}_4}^{•-}+•\mathrm{OH}$$

(4)

2.2. Influence of Various Experimental Parameters

2.2.1. Effects of PMS Dosage

To evaluate the impact of PMS dosage on the degradation of TCH in the US/PMS system, a series of experiments were conducted utilizing various concentrations of PMS, ranging from 0.5 mM to 4.0 mM. As shown in Figure 2a, when the PMS concentration was increased from 0.5 mM to 2.0 mM, the degradation efficiency of TCH rose from 67% to 84%, accompanied by an increase in the kinetic constant from 0.00574 min⁻¹ to 0.01041 min⁻¹. This enhancement can be attributed to the capacity of US to act as an effective activator for PMS, thereby facilitating the generation of reactive species. While it is noteworthy that when the PMS concentration exceeded 2.0 mM, the degradation efficiency of TCH did not exhibit a corresponding increase. This phenomenon may be ascribed to self-quenching and recombination reactions involving reactive oxygen species [22]. Furthermore, Yu et al. [23] have reported that the degradation efficiency of pollutants does not consistently increase with higher PMS dosages. The produced SO₄^•− can be recombined into S₂O₈²⁻, and it can also be quenched by excess S₂O₈²⁻ (Equations (5) and (6)) [11]. Additionally, an excessive concentration of •OH can adversely affect the utilization of free radicals, as less reactive hydroperoxyl radicals (HO₂^•) may be generated through the reaction between H₂O₂ and •OH, thereby diminishing the overall oxidative capacity of the system (Equations (7)–(9)) [24]. Thus, taking into account both raw material conservation and the degradation efficiency of TCH, the optimal PMS concentration has been identified as 2.0 mM.

$$\mathrm{S}{{\mathrm{O}}_4}^{•-}+\mathrm{S}{{\mathrm{O}}_4}^{•-}\to {\mathrm{S}}_2{{\mathrm{O}}_8}^{2-}$$

(5)

$$\mathrm{S}{{\mathrm{O}}_4}^{•-}+{\mathrm{S}}_2{{\mathrm{O}}_8}^{2-}\to \mathrm{S}{{\mathrm{O}}_4}^{2-}+{\mathrm{S}}_2{{\mathrm{O}}_8}^{•-}$$

(6)

$$•\mathrm{OH}+•\mathrm{OH}\to {\mathrm{H}}_2{\mathrm{O}}_2$$

(7)

$$•\mathrm{OH}+{\mathrm{H}}_2{\mathrm{O}}_2\to \mathrm{H}{{\mathrm{O}}_2}^{•}+{\mathrm{H}}_2\mathrm{O}$$

(8)

$$•\mathrm{OH}+{\mathrm{H}{\mathrm{O}}_2}^{•}\to {\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}$$

(9)

2.2.2. Effects of Initial Solution pH and TCH Concentration

Generally, one of the notable advantages of PMS-AOPs is their adaptability to varying pH conditions. In this study, we conducted experiments to evaluate the treatment efficiency under different initial pH levels, specifically focusing on pH values of 3, 4, 7, and 9, while maintaining a fixed PMS concentration of 2.0 mM. As illustrated in Figure 3a, the degradation rates of TCH at pH levels of 3, 4, 7, and 9 were recorded at 82%, 85%, 81%, and 82%, respectively. Although alkaline environments are more favorable for catalyzing the activation of PMS to yield SO₄^•−, US cavitation provides a wide pH range for the activation of PMS to enhance the removal of TCH degradation [25]. Figure 3b shows the effect of TCH concentration on the removal of TCH. The concentration of TCH with 10.0 mg/L resulted in a high removal of 85% with a maximum kinetic constant of 0.0125 min⁻¹ at pH 5. Under fixed reaction conditions, the amount of active species produced per unit time is constant. Consequently, the limited active substances were insufficient to degrade all TCH molecules. The low degradation efficiency of TCH may be ascribed to the insufficient ROS. Furthermore, some intermediates generated during the TCH degradation may compete with TCH for these active substances, thus lowering the degradation efficiency as a whole [26].

2.2.3. Effects of US Power and US Frequency

The efficacy and cost-effectiveness of the US/PMS system for the degradation of TCH are influenced, to a certain extent, by the US power and US frequency. As illustrated in Figure 3c,d, when the US frequency was maintained at 45 kHz, the removal efficiency of TCH increased from 83% to 90% with an increase in US power from 200 W to 500 W over a reaction period of 180 min. When the US power was held constant at 300 W, varying the US frequency to 20, 40, 45, and 80 kHz resulted in a degradation efficiency of TCH of 75%, 84%, 86%, and 90%, respectively. This enhancement in degradation efficiency can be attributed to the fact that higher frequencies and power levels generate a greater number of cavitation bubbles [27,28]. These cavitation bubbles produce reactive species, which further facilitate the activation of PMS, thereby promoting the degradation of TCH. Furthermore, Yao et al. [29] reported that the degradation efficiency of pollutants increases with elevated ultrasonic power. Moreover, previous studies have shown that sonication can exert a remarkable mechanical effect and speed up the mass transfer process in a homogenous process [21].

2.2.4. Effect of Inorganic Anions

Wastewater frequently contains a diverse array of cations and anions, among which various inorganic anions may significantly influence the performance of the US/PMS system. Meanwhile, chloride ions (Cl⁻) and sulfate ions (SO₄²⁻) are the most common anions in water treatment. Many studies have shown that Cl⁻ and SO₄²⁻ are commonly found in the real organic wastewater with concentrations of 50–300 mg/L [30]. And the existence of Cl⁻ and SO₄²⁻ in wastewater will have an inevitable influence on the removal of organic pollutants during their advanced oxidation process in different degrees [31]. Therefore, we chose to set the ion concentration range from 0 to 300 mg/L to investigate its influence on the activation of PMS under US irradiation for removal of TCH. The effects of Cl⁻ and SO₄²⁻ on TCH degradation are illustrated in Figure 4. As the concentration of Cl⁻ increased from 0 to 300 mg/L, the degradation efficiency of TCH exhibited a gradual decline from 80.6% to 74.4%. In the presence of Cl⁻, free radicals may react with chloride ions to generate reactive chlorine species. The observed reduction in TCH degradation efficiency can be attributed to the comparatively weaker oxidative capacity of the resultant reactive chlorine species (as indicated in Equations (10)–(12)) [26]. Furthermore, as depicted in Figure 4, SO₄²⁻ did not exert any significant effect on the degradation of TCH. It is noteworthy that SO₄²⁻ is a byproduct of the persulfate process, and its concentration gradually increases throughout the reaction. These findings suggest that the US/PMS system demonstrates considerable resilience to the interference of Cl⁻ and SO₄²⁻, thereby indicating its potential for practical applications in wastewater treatment.

$$\mathrm{S}{{\mathrm{O}}_4}^{•-}+{\mathrm{Cl}}^{-}\to \mathrm{S}{{\mathrm{O}}_4}^{2-}+\mathrm{Cl}•$$

(10)

$$\mathrm{C}{\mathrm{l}}^{-}+\mathrm{Cl}•\to \mathrm{C}{{\mathrm{l}}_2}^{•-}$$

(11)

$$\mathrm{Cl}•+{\mathrm{H}}_2\mathrm{O}\to \mathrm{ClH}{\mathrm{O}}^{•- }+{\mathrm{H}}^{+}$$

(12)

2.3. Identification of Active Species

In the US/PMS system, the degradation of TCH primarily involves the generation of reactive species. During this degradation process, scavenging agents can concurrently consume the corresponding reactive species, thereby inhibiting TCH degradation. Consequently, quenching experiments were conducted to identify the predominant active species involved in this process. In the quenching experiments, MeOH, TBA, PBQ and FA were, respectively, used as scavenger agents to quench the generated •OH, SO₄^•−, •O₂⁻, and ¹O₂. According to the references [32,33,34], 1~100 mM of MeOH, PBQ and FA were used as the optimal concentration of scavenger. Therefore, to better determine the generation mechanism of ROS during the process of PMS activation, we determined the scavenger’s concentrations as follows: (MeOH: 50 mmol/L; TBA: 100 mmol/L; FA, PBQ: 4 mmol/L). As shown in Figure 5a, the degradation efficiency of TCH decreased by 16%, 11%, 27%, and 46% following the addition of MeOH, TBA, PBQ, and FA, respectively. These results indicate that ¹O₂ is the principal active species responsible for TCH removal within the US/PMS system. Furthermore, Figure 5b demonstrates that FA exerts the most significant inhibitory effect on TCH degradation in this system. Electron spin resonance (EPR) spectroscopy provided additional corroboration for the findings of the quenching experiments, allowing for a comparative analysis of active species in both the US and US/PMS systems. As depicted in Figure 5c,d, TEMP-¹O₂ signal peak of 1:1:1 and the DMPO-•OH signal peak of 1:2:2:1 were clearly observed in US and US/PMS systems. By comparing with only US, there were significant enhanced signal peaks of ¹O₂ and •OH signal in US/PMS. This enhancement can be attributed to the cavitation effect, which enhanced the production efficiency of •OH, ¹O₂, and ^•O₂⁻ (as represented in Equations (1), (13)–(17)) [35]. The introduction of PMS further amplifies the production of active species (as indicated in Equations (18)–(21)) [11]. The EPR analysis revealed a minimal DMPO-SO₄^•− signal, which may be due to the greater scavenging capacity of DMPO for •OH compared to SO₄^•− [11,36]. These findings suggest that ¹O₂ plays a critical role in the degradation of TCH within the US/PMS system. Notably, since ¹O₂ possesses lower oxidation potentials than •OH [37,38], it is generally regarded as having selective reactivity towards pollutants. According to the previously reported study [37], TCH has a large amount of strong electron-donor groups, including -OH and -NH₂ and -NR₂; in addition, ¹O₂ has good selectivity for pollutants with electron-donating groups, which contributes to the excellent TCH removal efficiency [34]. Since TCH is a kind of electron-rich organic pollutant, ¹O₂ had excellent selectivity for electron-rich pollutants [39]; this selectivity contributes to the pH adaptability and resistance to anion interference exhibited by the US/PMS system.

$$•\mathrm{H}+{\mathrm{O}}_2\to \mathrm{H}{{\mathrm{O}}_2}^{•}$$

(13)

$$\mathrm{H}{{\mathrm{O}}_2}^{•}\to •{{\mathrm{O}}_2}^{-}+{\mathrm{H}}^{+}$$

(14)

$$•{{\mathrm{O}}_2}^{-}+•\mathrm{OH}\to {}^1\mathrm{O}_2+\mathrm{O}{\mathrm{H}}^{-}$$

(15)

$$•{{\mathrm{O}}_2}^{-}\to {}^1\mathrm{O}_2+{\mathrm{e}}^{-}$$

(16)

$$\mathrm{HS}{{\mathrm{O}}_5}^{-}+\mathrm{US}\to \mathrm{S}{{\mathrm{O}}_5}^{•-}+{\mathrm{H}}^{+}+{\mathrm{e}}^{-}$$

(17)

$$\mathrm{S}{{\mathrm{O}}_5}^{•-}+\mathrm{S}{{\mathrm{O}}_5}^{•-}\to {\mathrm{S}}_2{{\mathrm{O}}_8}^{2-}+{}^1\mathrm{O}_2$$

(18)

$$\mathrm{S}{{\mathrm{O}}_5}^{•-}+\mathrm{S}{{\mathrm{O}}_5}^{• }\to 2\mathrm{S}{{\mathrm{O}}_4}^{2-}+{}^1\mathrm{O}_2$$

(19)

$${\mathrm{S}}_2{{\mathrm{O}}_8}^{2-}+\mathrm{H}{{\mathrm{O}}_2}^{•-}\to \mathrm{S}{{\mathrm{O}}_4}^{•-}+\mathrm{S}{{\mathrm{O}}_4}^{2-}+•{{\mathrm{O}}_2}^{-}+{\mathrm{H}}^{+}$$

(20)

$${\mathrm{S}}_2{{\mathrm{O}}_8}^{2-}+•\mathrm{OH}\to 2\mathrm{S}{{\mathrm{O}}_4}^{2-}+•{{\mathrm{O}}_2}^{-}+{\mathrm{H}}^{+}$$

(21)

2.4. Mechanism for Degradation of TCH by US/PMS System

The proposed mechanism for the removal of TCH via the US/PMS system is illustrated in Figure 6. Under US irradiation, cavitation bubbles are continuously generated and subsequently collapsed. This process facilitates the ongoing production of •OH, ¹O₂, and SO₄^•−, while the high temperatures and pressures resulting from the collapse of the cavitation bubbles further enhance the activation of PMS. Consequently, the generation of reactive species within the system is attributed to both the cavitation effect and the activation of PMS. Subsequently, these reactive species contribute to converting the TCH to by-products, which finally completes its mineralization into H₂O and CO₂. The US/PMS system not only generates a substantial quantity of reactive species but also enhances selectivity towards organic pollutants. It could be attributed to the electron-rich feature of TCH, and ¹O₂ has excellent selectivity for electron-rich pollutants. Therefore, the significant production of ¹O₂ within the US/PMS system serves as a critical factor in its robust resistance to ionic interference due to its selectivity. These findings underscore the efficacy of the US/PMS technology for the treatment of TCH-contaminated wastewater.

3. Materials and Methods

3.1. Chemicals

All the chemicals used in the experiments were analytical reagent grade. Tetracycline hydrochloride (TCH, C₂₂H₂₄N₂O₈·HCl, purity of 96%), sodium persulfate (Na₂S₂O₈, purity of 99%), 2,2,6,6-tetramethylpiperidine (TEMP, C₉H₁₈NO, purity of 99%), 5,5-dimethyl-1-pyridine-N-oxide (DMPO, C₂H₇OP, purity of 99%), and persulfate (PMS, KHSO₅·0.5KHSO₄·0.5K₂SO₄, purity of 42% to 46%) were all purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Hydrogen peroxide (H₂O₂, purity of 30%) and ammonium persulfate (PDS, (NH₄)₂S₂O₈, purity of 99%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Methanol (MeOH, CH₃OH, purity of 99%), 1,4-benzoquinone (PBQ, C₆H₄O₂, purity of 99%), furfuryl alcohol (FA, CH₂O₂, purity of 99%) and tert-butylalcohol (TBA, C₄H₁₀O, purity of 99%) were purchased from Maklin Reagant Company (Shanghai, China). The pH was adjusted using HCl and NaOH. All solutions were prepared with ultrapure water.

3.2. Activation of PMS for Degradation of TCH

Degradation runs were performed in an experimental setup as shown in Figure 7. The experimental setup includes an ultrasonic reactor (KQ-500VDV, Chaoyi, Kunshan, China), a cantilever electric mixer (SN-OES-60SH, Beidi, Nanjing, China) and a cooling-water machine (CW, 5300ANSW, Beidi, Nanjing, China). The ultrasonic frequency was fixed at 45 kHz, the ultrasonic power was fixed at 300 W, the stirring speed was fixed at 400 rpm, and the water temperature was controlled at 25 °C. A solution with a volume of 200 mL was configured. After adding PMS to the solution, TCH degradation experiments were performed in a 500 mL reaction flask under the ultrasound. Samples (3 mL) were quickly collected at regular time intervals (0, 15, 30, 60, 120, 180 min), and 10 mM of Na₂S₂O₃ (3 mL) was used as the quencher to terminate the reaction In the experiments on the effect of free radical scavenging and water matrix on the degradation of organic pollutants, Cl⁻ (0, 50, 100, 200, 300 mg/L), SO₄²⁻ (0, 50, 100, 200, 300 mg/L) or free radical scavengers (MeOH: 50 mmol/L; TBA: 100 mmol/L; FA, pBQ: 4 mmol/L) were added to the reaction solution before adding organic pollutants [32]. All experiments were performed in duplicate twice, and the error bars in the figure represent the standard deviation.

3.3. Analysis Methods

Samples were withdrawn at designated times and filtered through Millipore 0.45 μm filters prior (Lingrui, Nantong, China) to analysis. The absorbance spectra of the untreated and treated samples were scanned using a UV/Vis spectrophotometer (N4S, Yidian, Shanghai, China). The degradation efficiency of TCH was calculated according to Equation (22):

$$\eta ={\displaystyle \frac{{\mathrm{C}}_0-{\mathrm{C}}_{\mathrm{t}}}{{\mathrm{C}}_0}}$$

(22)

where $\eta$ is the TCH degradation efficiency (%). C₀ is the initial concentration of TCH in mg/L. C_t is the concentration of TCH at t min of treatment in mg/L.

$$\ln {\displaystyle \frac{{\mathrm{C}}_0}{{\mathrm{C}}_{\mathrm{t}}}} =k\mathrm{t}$$

(23)

where C₀ and C_t are defined as in Equation (23). k is the reaction rate constant in min⁻¹. t is the reaction time in min.

The electron paramagnetic resonance (EPR) spectra of the active substances were measured on a Bruker-A200 nano-spectrometer (Bruker, Karlsruhe, Germany) using DMPO and TEMP as trapping agents. The generation of •OH, SO₄^•− and ¹O₂ in the US/PMS system was detected by the EPR technique.

4. Conclusions

In conclusion, the synergistic effects of US cavitation and activation of PMS on the degradation of TCH were systematically investigated. The results indicate that US effectively promotes the activation of PMS, thereby significantly enhancing the degradation efficiency of TCH, in the US/PMS system. The degradation efficiency of TCH achieved a maximum of 83% when the PMS concentration was 2 mM. Additionally, the degradation efficiency of TCH was observed to increase with higher US power and frequency. Notably, the interference of pH and anionic species on the US/PMS system was found to be minimal, suggesting that the system possesses a broad applicability. Moreover, •OH and ¹O₂ were demonstrated as the predominant reactive species for removal of TCH within the system. This work provides a more comprehensive understanding of PMS-based AOPs for the treatment of water and wastewater.