Preparation of Zn-Doped Amino Functionalized Biochar from Hazardous Waste for Arsenic Removal.

The utilization of sludge from Far Eastern Memorial hospital (New Taipei city, Taiwan) wastewater treatment plants as biochar adsorbent was investigated. The sludge was carbonized using microwave carbonization and then chemically activated at high temperatures by using ZnCl2 to enhance porosity and surface area. A newly designed Zndoped amino-functionalized sludge biochar (Zn-SBC-DETA) presents effective As adsorption in water. The adsorbent was characterized by nitrogen adsorption-desorption, scanning electron microscopy (SEM) and thermogravimetric analysis. Results show that the surface area and average pore volume of Zn-SBC-DETA are 525 m² g-1 and 0.35 cm³ g-1, respectively. SEM results reveal that Zn-SBC-DETA has uniform pore size. The highest adsorption efficiency of As(III) is 79% at pH 3 with an adsorption capacity of 0.84 mg g-1. In addition, the adsorption efficiency of As(V) is 98% at pH 3 with an adsorption capacity of 1.43 mg g-1. The adsorption data can be described well by the Langmuir model rather than by the Freundlich model The data show good compliance with the pseudo second-order equation, and the correlation coefficient for the linear plots is higher than 0.97. Combined with the As species after reacting with Zn-SBC-DETA, the As transformation and adsorption mechanism are also discussed.

Exploring Nanosilver-Coated Hollow Fiber Microfiltration to Mitigate Biofouling for High Loading Membrane Bioreactor.

For the first time, a nanosilver-coated hollow fiber microfiltration (MF) was fabricated by a simple chemical reduction method, then tested for membrane biofouling mitigation study under extreme high mixed liquor suspended solid (MLSS) concentration for long term. This study presents a simple and novel technique to modify a commercially available MF membrane using silver nanoparticles (AgNPs) followed by an investigation of mitigating membrane biofouling potentials using this modified membrane to compare with an unmodified membrane for 60-day operation period. The modified membranes showed that AgNPs was attached to the MF-membrane successfully with a high density of 119.85 ± 5.42 mg/m2. After long-term testing of 60 days in membrane bioreactor with a MLSS concentration of 11,000 mg/L, specific flux of the AgNPs coated MF (AgNPs-MF) decreased 59.7%, while the specific flux of the unmodified membrane dropped 81.8%, resulted from the increase of transmembrane vacuum pressure for the AgNPs-MF was lower than that of the unmodified one. The resistance-in-series model was used to calculate the resistance coefficients of membrane modules, and the result showed that the cake layer resistance coefficient of the unmodified membrane was 2.7 times higher than that of the AgNPs-MF after the 60-day operation, confirming that AgNPs displayed great antimicrobial properties to mitigate membrane biofouling under such high MLSS.

Preparation and Photocatalytic Hydrogen Production of Pt-Graphene/TiO2 Composites from Water Splitting.

Hydrogen is considered as a promising energy source with its high energy yield, renewable, environment friendly properties. TiO2 modified with noble metal and nonmetal is widely used. In this study, Pt and graphene (GN) were used to modify TiO2 nanoparticles. GN/TiO2 (TG), Pt-TiO2 (PT), Pt-GN/TiO2 (PTG) was successfully synthesized by modified Hummers' method, alcohol thermal and photodeposition method, respectively. The characterizations of the synthesized catalysts by UV-vis/DRS, components analysis, XRD and TEM analysis were conducted. Results showed the maximum hydrogen production rate was approximately 4.71 mmol h-1 g-1 when the Pt content was 1.0 wt.%. Higher and lower than 1.0 wt.% of Pt loading content both result in low efficiency of hydrogen production. The situation of graphene is similar to Pt. The optimal ratio for grapheme is 10 wt.%. The highest hydrogen production rate is 6.58 mmol h-1 g-1 by 1.5 wt.% Pt-5 wt.% GN/TiO2 (1.5PTG5), which is about 1.4 and 2.2 times higher than that of Pt-TiO2 and GN/TiO2 binary composites, respectively. The utilization of low-cost graphene can reduce the use of noble metal Pt in photocatalytic hydrogen production. The mechanism of Pt-GN/TiO2 for the improved photocatalytic activity is proposed. 0.1 g L-1 is found to be the optimum catalyst concentration for optimal hydrogen production.

Effects of Different Sacrificial Agents and Hydrogen Production from Wastewater by Pt-Graphene/TiO2.

The Pt and graphene (GN) were used to modify TiO2 nanoparticles. GN/TiO2, Pt-TiO2, Pt-GN/TiO2 were successfully synthesized by modified Hummers' method, alcohol thermal and photodeposition method, respectively. The characterizations of the synthesized catalysts by different characterization techniques, including N2 adsorption-desorption isotherm, fourier transform infrared spectroscopy (FTIR), inductively coupled plasma (ICP) technique and element analyzer (EA), respectively. In addition, different sacrificial agents (methanol, ethanol, n-propanol, i-propanol, n-butanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol and glycerol) have been investigated. There is clearly a linear relationship between hydrogen production rate and the polarity of monohydric alcohols. According to the Langmuir-Hinshelwood results, the surface pseudo-first order rate constant k = 15.06 mmol h-1 g-1 and the adsorption coefficient k = 0.50 mol L-1 were obtained. The feasibility of hydrogen production from wastewater obtained from terephthalic acid industry was studied. After reusing the catalyst under the same experimental conditions, the hydrogen production rate has only slightly decreased for 3 more cycles, which indicated the stability of the synthesized catalysts.

Preparation of Zn-Doped Biochar from Sewage Sludge for Chromium Ion Removal.

Recycling and reuse waste can result in significant savings in materials and energy. In this study, the adsorption of Cr(VI) was analyzed using activated carbon (AC) and biochar (BSC) made from sewage sludge. BSC materials were synthesized using zinc chloride as an activator coupled with carbonized sewage sludge. Specific surface area, pore size distribution, and pore volume were determined by measuring nitrogen adsorption-desorption (BET). BSC morphology was measured using field-emission scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). Results showed that the surface area and average pore volume of the BSC were 490 m2 g-1 and 0.8 cm3 g-1, respectively. SEM results revealed that BSC had uniform pore size. Effects of varying the initial Cr(VI) concentrations, pH values, and dosages of BSC on adsorption performance were also determined. Results showed that the maximum removal efficiency of Cr(VI) was above 99%, and adsorption capacity of 50% ZnCl2-BSC was 677 mg g-1.

Exploration of polyelectrolyte incorporated with Triton-X 114 surfactant based osmotic agent for forward osmosis desalination.

Selection of a proper osmotic agent is important to make the forward osmosis (FO) feasible. The objective of this study was to enhance FO by lowering reverse solute flux and maintaining high water flux. Poly(propylene glycol) with molecular weight of 725 Da (PPG-725) was found to possess high osmolality, making it a strong candidate for using as a draw agent. In addition, to reduce the partial leakage of draw solute, a non-ionic surfactant (Triton X-114) has been incorporated. Typically, when the hydrophobic tails of Triton X-114 interacted with the membrane surface, a layer on the surface of membrane is produced to constrict the pores and thus minimize the reverse solute flux. In this study, different concentrations of PPG-725 incorporated with different concentrations of Triton X-114 (0.2-0.8 mM) were used to evaluate their osmotic potentials as draw solute. The specific reverse solute flux (Js/Jw) of 40% PPG-725 doped with Triton X-114 was found to be 0.01 g/L, considerably much lesser than the conventional inorganic draw agents. Finally, membrane distillation operation was utilized as the recovery system in which solute rejection of 97% was achieved for 40% PPG-725/Triton X-114. Therefore, the overall performance supported PPG-725/Triton X-114 as being an efficient draw agent for forward osmosis-membrane distillation hybrid process.

Hg removal and the effects of coexisting metals in forward osmosis and membrane distillation.

In this study, we investigate the rejection of Hg, Cd, and Pb and the effect of coexisting metals on Hg removal through forward osmosis (FO) and membrane distillation (MD) in order to establish a more effective water treatment process. The results of our laboratory experiment indicate that more than 97% of the rejection for each metal is achieved through the FO system, and this rejection is the highest among previous studies using membrane filtrations. Moreover, we examine the matrix effect of the coexisting Cd and Pb on the rejection of Hg in the FO system. Hg2+ rejection increases with increase in the concentration of the coexisting metals. Furthermore, we study the effect of the Hg concentration and the water temperature on rejection of Hg2+. Indeed, the rejection of Hg2+ is achieved above 95% under any condition. However, approximately 1-10 ppb Hg from the feed solution remains in the draw solution due to permeation. Therefore, we use a FO-MD hybrid system. Approximately 100% rejection of Hg2+ and a stable water flux are achieved. Thus, the FO-MD hybrid system is considered an important alternative to previous studies using membrane filtration for heavy metals removal.

Adsorption of Methyl Blue on Mesoporous Materials Using Rice Husk Ash as Silica Source.

It is recognized that recycling and reuse of waste can result in significant savings in materials and energy. In this research, the adsorption of methyl blue (MB) using waste rice husk ash (Rha) and mesoporous silica materials made from Rha (R-MCM) were analyzed. Mesoporous silica materials were synthesized using cetyltrimethyl ammonium bromide (CTAB) as a cationic surfactant and Rha as the silica source. The prepared samples were characterized by Brunnaur-Emmet-Teller (BET) adsorption isotherm analyzer and transmission electron microscope (TEM) analysis. The results showed the surface area of R-MCM materials was 1347 m2g-1 and the pore volume was 0.906 cm3g-1. TEM analysis showed that the mesoporous materials generally exhibited ordered hexagonal arrays of mesopores with a uniform pore size. The effects on adsorption performance under different initial dye concentrations, different pH values and different dosages of adsorbent were also studied. Both Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The results show that the maximum removal efficiency of MB more than 99%.

Influence of micelle properties on micellar-enhanced ultrafiltration for chromium recovery.

An investigation of micelle properties on the recovery of chromium for micellar enhanced ultrafiltration (MEUF) process was conducted using cationic surfactant of cetyltrimethylammonium bromide (CTAB). The relationship between degree of ionization, micellar sizes and chromium removal were determined in this study. The results showed that the complete ionization for CTA+ and Br- was observed for CTAB lower than 0.72 mM and aggregation initiated at concentration of CTAB higher than 0.72 mM to yield attraction of counterion. The micellar sizes increased with increase in concentration of CTAB (higher than 4.02 mM) to generate micron-sized micelles. The distribution of micellar sizes was used to estimate the molecular weight cutoff of membrane used in the MEUF process. As chromium was added into aqueous CTAB solution, the chromate was dominant and bound on the micellar surface instead of Br-. Moreover, the presence of micelle formed a gel-layer to slightly shrink the membrane pore, therefore, UF membrane of 30k Da molecular weight cutoff (pore size≈7.9 nm) was selected in the MEUF process to achieve the removal efficiency of Cr(VI) higher than 95%.

Recovery of Cu(II) by chemical reduction using sodium dithionite: effect of pH and ligands.

Wastewaters containing Cu(II) and ligands are ubiquitous in various industrial sectors, and efficacy of copper removal processes, especially precipitation, is greatly compromised by ligands. Chemical reduction, being commonly employed for production of metal nanoparticles, is also effective for metal removal. Adjustment of pH and addition of ligands are important to control the particle size in metallic nanoparticle production. Exploiting the fact that ligands and metals coexist in many wastewaters, chemical reduction was employed to treat ligand-containing wastewater in this study. The experimental result shows that depending on pH, type of ligands, and copper:ligand molar ratio, copper could be removed by either the reduction or precipitation mechanism. Almost complete copper removal could be achieved by the reduction mechanism under optimal condition for solutions containing either EDTA (ethylenediaminetetraacetic acid) or citrate ligands. For solutions containing ammonia, depending on pH and Cu:ammonia molar ratio, copper was removed by both precipitation and reduction mechanisms. At pH of 9.0, formation of nano-sized particles, which readily pass through a 0.45 µm filter used for sample pretreatment before residual copper analysis, results in the lowest copper removal efficiency. Both cuprous oxide and metallic copper are identified in the solids produced, and the possible explanations are provided.

Application of forward osmosis (FO) under ultrasonication on sludge thickening of waste activated sludge.

Forward osmosis (FO) is an emerging process for dewatering solid-liquid stream which has the potential to be innovative and sustainable. However, the applications have still been hindered by low water flux and membrane fouling when activated sludge is used as the feed solution due to bound water from microbial cells. Hence, a novel strategy was designed to increase sludge thickening and reduce membrane fouling in the FO process under ultrasonic condition. The results from the ultrasound/FO hybrid system showed that the sludge concentration reached up to 20,400 and 28,400 mg/L from initial sludge concentrations of 3000 and 8000 mg/L with frequency of 40 kHz after 22 hours, while the system without ultrasound had to spend 26 hours to achieve the same sludge concentration. This identifies that the presence of ultrasound strongly affected sludge structure as well as sludge thickening of the FO process. Furthermore, the ultrasound/FO hybrid system could achieve NH4+-N removal efficiency of 96%, PO4(3-)-P of 98% and dissolved organic carbon (DOC) of 99%. The overall performance demonstrates that the proposed ultrasound/FO system using seawater as a draw solution is promising for sludge thickening application.

Innovative hyper-thermophilic aerobic submerged membrane distillation bioreactor for wastewater reclamation.

For the first time, a hyper-thermophilic aerobic (>60 °C) bioreactor has been integrated with direct submerged membrane distillation (MD), highlighting its potential as an advanced wastewater treatment solution. The hyper-thermophilic aerobic bioreactor, operating up to 65 °C, is tailored for high organic removal, while MD efficiently produces clean water. Throughout the study, high removal rates of 99.5% for organic matter, 96.4% for ammonia, and 100% for phosphorus underscored the impressive adaptability of microorganisms to challenging hyper-thermophilic conditions and a successful combination with the MD process. Despite the extreme temperatures and substantial salinity accumulation reaching up to 12,532 µS/cm, the biomass of microorganisms increased by 1.6 times over a 92-day period, representing their remarkable resilience. The distillation flux ranged from 6.15 LMH to 8.25 LMH, benefiting from the temperature gradient in the hyper-thermophilic setting and the design of the tubular submerged MD membrane module. The system also excels in pH control, utilizing fewer alkali and nutritional resources than conventional systems. Meiothermus, Firmicutes, and Bacteroidetes, the three dominant species, played a crucial role, showcasing their significance in adapting to high salinity and decomposing organic matter.

Granulation of biological flocs under elevated pressure: characteristics of granules.

Aerobic granules (AG) have good settling ability and are relatively insensitive to the variation of organic loading rate. When sizes of granules become bigger, substrate and oxygen become limited in the granule core, leading to cell lysis and disintegration of granules. The higher the dissolved oxygen, the deeper the oxygen penetration inside AG. AG operated under elevated pressure might be a possible way to maintain long-term stability of granules. In this study, formation and characteristics of AG in the reactor operated under elevated high pressure (HP) and ambient pressure (AP) are investigated. Results show that both systems removed an average 95% of total organic carbon. Sludge volume index at 5 and 30 min settling times under HP are 35% smaller those under AP, indicating that HP granules have a better settling ability and a denser structure than AP granules. The granule size in the HP system is very uniform, while size distribution in the AP system is broader, indicating that the AP system contains flocculent sludge. Extracellular polymeric substances and polysaccharides (PS) are almost the same for HP and AP; however, exopolymeric protein (PN) is very different. PS/PN ratio for HP sludge is four times that of AP. The result is consistent with sludge settleability, which is improved with increasing PS/PN ratio.

Effect of biomass retention time on performance and fouling of a stirred membrane photobioreactor.

Co-culture of microalgae-activated sludge has the potential to purify wastewater while reduce energy demand from aeration. In this work, a mechanically stirred membrane photobioreactor (stirred-MPBR) was used to evaluate the impact of the biomass retention time (BRT) on the treatment performance and membrane fouling. Results showed that stirred-MPBR was affected by BRT during treating domestic wastewater at a flux of 16.5 L m-2 h-1. The highest productivity was attained at BRT 7d (102 mg L-1 d-1), followed by BRT 10d (86 mg L-1 d-1), BRT 5d (85 mg L-1 d-1), and BRT 3d (83 mg L-1 d-1). Statistical analysis results showed that BRT 7d had a higher COD removal rate than BRT 10d, however, there is no difference in total nitrogen removal rate. The highest TP removal occurred when the biomass operated at BRT as short as 3d. Reduced BRTs caused a change in the microalgae-activated sludge biomass fraction that encouraged nitrification activity while simultaneously contributing to a higher fouling rate. The bound protein concentrations dropped from 31.35 mg L-1 (BRT 10d) to 10.67 mg L-1 (BRT 3d), while soluble polysaccharides increased from 0.99 to 1.82 mg L-1, respectively. The concentrations of extracellular polymeric substance fractions were significantly altered, which decreased the mean floc size and contributed to the escalating fouling propensity. At the optimum BRT of 7d, the stirred-MPBR showed sufficient access to light and nutrients exchange for mutualistic interactions between the microalgae and activated sludge.

Intermittent high-pressure sequential bioreactor (IHPSB) with integration of sand filtration system for synthetic wastewater treatment.

A pressurized activated sludge reactor with a sand layer installed at the bottom of the reactor for filtration purposes was employed for treating synthetic organic wastewater. The intermittent high-pressure sequential bioreactor (IHPSB) was pressurized to facilitate efficient oxygen transfer under elevated biomass conditions with pressure released periodically, i.e. aeration, for mixing and exchanging air. The sand layer integrated in the bottom of reactor was employed to separate sludge from treated water during the effluent discharging period. The results show that the proposed system can achieve chemical oxygen demand (COD) removal of higher than 90% under COD loading ranging from 3.3 to 14.3 kg COD/m3/day. SS of the effluent is quite stable and is less than 30 mg/L when MLSS is less than 18,000 mg/L. Oxygen transfer in the IHPSB is quite effective. Dissolved oxygen (DO) ranging from 16 to 10 mg/L was achieved with aeration cycle varying from 3 to 15 min. Thus, IHPSB can be quite energy efficient compared with traditional aerobic activated biological systems and membrane biological reactor systems.

Enhanced understanding of osmotic membrane bioreactors through machine learning modeling of water flux and salinity.

Mathematical modeling can be helpful to understand and optimize osmotic membrane bioreactors (OMBR), a promising technology for sustainable wastewater treatment with simultaneous water recovery. Herein, seven machine learning (ML) algorithms were employed to model both water flux and salinity of a lab-scale OMBR. Through the optimum hyperparameters tuning and 5-fold cross-validation, the ML models have achieved more accurate results without obvious overfitting and bias. The median R2 scores of water flux modeling were all over the 0.95 and the most of median R2 scores from total dissolved solids (TDS) modeling were higher than 0.90. During model testing, random forest (RF) algorithm presented the highest R2 score of 0.987 with the lowest root mean square error (RMSE = 0.044) for the water flux modeling, and extreme gradient boosting (XGB) algorithm exhibited the best results (R2 = 0.97; RMSE = 0.234) in the TDS modeling. The Shapley Additive exPlanations (SHAP) analysis found that the phosphorus concentration was a critical input feature for both water flux and TDS modeling. Finally, the selected ML models were used to predict water flux and salinity affected by two input features and the predication results confirmed the importance of the phosphate concentration. The results of this study have demonstrated the promise of ML modeling for investigating OMBR systems.

Microplastics waste in environment: A perspective on recycling issues from PPE kits and face masks during the COVID-19 pandemic.

During the COVID-19 pandemic, the extensive use of face masks and protective personal equipment (PPE) kits has led to increasing degree of microplastic pollution (MP) because they are typically discarded into the seas, rivers, streets, and other parts of the environment. Currently, microplastic (MP) pollution has a negative impact on the environment because of high-level fragmentation. Typically, MP pollution can be detected by various techniques, such as microscopic analysis, density separation, and Fourier transform infrared spectrometry. However, there are limited studies on disposable face masks and PPE kits. A wide range of marine species ingest MPs in the form of fibers and fragments, which directly affect the environment and human health; thus, more research and development are needed on the effect of MP pollution on human health. This article provides a perspective on the origin and distribution of MP pollution in waterbodies (e.g., rivers, ponds, lakes, and seas) and wastewater treatment plants, and reviews the possible remediation of MP pollution related to the excessive disposal of face masks and PPE kits to aquatic environments.

Water reclamation and microbial community investigation: Treatment of tetramethylammonium hydroxide wastewater through an anaerobic osmotic membrane bioreactor hybrid system.

Tetramethylammonium hydroxide (TMAH) is a toxic photoresist developer used in the photolithography process in thin-film transistor liquid crystal display (TFT-LCD) production, and it can be removed through anaerobic treatment. TMAH cannot be released into the environment because of its higher toxicity. A tight membrane, such as a forward osmosis (FO) membrane, together with an anaerobic biological process can ensure that no TMAH is released into the environment. Thus, for the first time, an anaerobic osmotic membrane bioreactor (AnOMBR) hybrid system was developed in this study to treat a low-strength TMAH wastewater and to simultaneously investigate its microbial community. Microfiltration extraction was used to mitigate the salinity accumulation, and a periodically physical water cleaning was utilized to mitigate the FO membrane fouling. The diluted draw solute (MgSO4) was reconcentrated and reused by a membrane distillation (MD) process in the AnOMBR to achieve 99.99% TMAH removal in this AnOMBR-MD hybrid system, thereby ensuring that no TMAH is released into the natural environment. Moreover, the membrane fouling in the feed and draw sides were analyzed through the fluorescence excitation-emission matrix (FEEM) spectrophotometry to confirm that the humic acid-like materials were the primary membrane fouling components in this AnOMBR. Additionally, 16S rRNA metagenomics analysis indicated that Methanosaeta was the predominant contributor to methanogenesis and proliferated during the long-term operation. The methane yield was increased from 0.2 to 0.26 L CH4/g COD when the methanogen species acclimatized to the saline system.

A study on dynamic volatile organic compound emission characterization of water-based paints.

Volatile organic compounds (VOCs) emitted from surface coatings have caused growing public concern for air quality. Even the low-emitted VOC impact from water-based paints on indoor air quality in urban areas has caused concern. This paper presents experimental data using a mathematical model to simulate dynamic VOC emissions from water-based paints that is based on mass transfer and molecular diffusion theories. A series of field-analogous experiments were carried out to continuously measure the VOCs emitted from two typical water-based paints using a gas chromatography-flame-ionization detector monitor in an artificial wind tunnel system. In the study cases, the mass flux of VOCs emitted from the water-based paints was up to 50 microg/m2sec. It was found that the time needed to completely emit VOCs from water-based paints is just hundreds of seconds. However, the order of magnitude of the VOC emission rate from water-based paints is not lower than that from some dry building materials and solvent-based paints. The experimental data were used to produce a useful semiempirical correlation to estimate the VOC emission rates for water-based paints. This correlation is valid under appropriate conditions as suggested by this work with a statistical deviation of +/- 7.6%. With this correlation, it seems feasible to predict the dynamic emission rates for VOCs during a painting process. This correlation is applicable for assessing the hazardous air pollutant impact on indoor air quality or for environmental risk assessment. Associated with the dynamic VOC emission characterization, the air-exchange rate effect on the VOC emission rates is also discussed.

Aqueous Oxytetracycline and Norfloxacin Sonocatalytic Degradation in the Presence of Peroxydisulfate with Multilayer Sheet-Like Zinc Oxide.

Multilayer ZnO sheet-like flakes were synthesized by a simple method of precipitation and characterized by the techniques of X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The findings are proven that the SEM images show the overall morphology of a single sheet-like ZnO nanostructure made from uniformly thick nano-sheets. In an aqueous environment, the acoustic ability of the prepared material was assessed using ultrasound (US) radiation to degrade oxytetracycline (OTC) and norfloxacin (NF). To increase the degradation efficiency, a US/ZnO/peroxodisulfate system was developed by introducing ammonium persulfate ((NH4)2S2O8) and sodium persulfate (Na2S2O8), exhibiting excellent synergistic effects. Result show the decomposition efficiency for NF removal with Na2S2O8 (64%) appeared to be slightly better than with (NH4)2S2O8 (56%). By contrast, the ultrasonic catalytic efficiency of Na2S2O8 (98%) was slightly better than that of (NH4)2S2O8 (94%) for OTC removal. The addition of scavengers to the US/ZnO/peroxodisulfate system through the NF and OTC results in the largest effect of holes. The degradation is considered to be often caused by holes. In this system, the Na2S2O8 can have two roles to increase the rate of degradation: (1) The SO4- formed by Na2S2O8 under ultrasonic irradiation directly degraded to norfloxacin on ZnO surface; and (2) S2O82- behaved as an electron acceptor, inhibiting recombination of electron hole pairs, enabling the development of more ·OH. Therefore, the synergistic effect significantly increases US/ZnO/peroxodisulfate sonocatalytic activity (Hu, S.B., et al., 2017. Aqueous norfloxacin sonocatalytic degradation with multilayer flower-like ZnO in the presence of peroxydisulfate. Ultrasonics Sonochemistry, 38(1), pp.446-454).