Cavitation based treatment of industrial wastewater: A critical review focusing on mechanisms, design aspects, operating conditions and application to real effluents

Advances in chemical removal and degradation technologies for microplastics in the aquatic environment: A review

In recent years, global attention has been extensively focused on the water pollution and health risks caused by microplastics(MPs), thereby making the treatment of microplastics a key area of research. Chemical removal and degradation present effective approaches to addressing this issue. Consequently, this review summarizes the latest research advancements in the chemical removal and degradation of microplastics in water, comparing the treatment efficacy and advantages and disadvantages of various removal/degradation techniques. It elucidates the chemical mechanisms underlying the removal/degradation of microplastics and identifies the primary influencing factors during the treatment process. A systematic analysis of the performance of microplastic treatment technologies is conducted, examining the impact of microplastic characteristics, operational conditions, and other parameters on the effectiveness of microplastic treatment.

CdBi2S4-Decorated Aminated Polyacrylonitrile Nanofiber for Photocatalytic Treatment of Cr(VI) and Tetracycline Wastewater

The significant threat posed by the high toxicity of heavy metals and antibiotics in water pollutants has prompted a growing emphasis on the development of highly efficient removal methods for these pollutants. In this paper, flexible electrospinning polyacrylonitrile (PAN) nanofiber-supported CdBi2S4 was synthesized via a hydrothermal method, followed by amination treatment with diethylenetriamine (DETA). The as-prepared CdBi2S4/NH2-PAN nanofiber, enriched with sulfur vacancies, demonstrated outstanding visible-light trapping ability and a suitable band gap, leading to efficient separation and transport of photogenerated carriers, ultimately resulting in exceptional photocatalytic capability. The optimal 3-CdBi2S4/NH2-PAN nanofiber achieved impressive reduction rates of 92.26% for Cr(VI) and 96.45% for tetracycline hydrochloride (TCH) within 120 min, which were much higher than those for CdS/NH2-PAN, Bi2S3/NH2-PAN, and CdBi2S4/PAN nanofibers. After five cycles, the removal rate of the CdBi2S4/NH2-PAN nanofiber consistently remained above 90%. Their ease of separation and recovery from the application environment contributes to their practicality. Additionally, compared with conventional suspended particle catalyzers, the composite nanofiber exhibited remarkable flexibility and self-supporting properties.

Ultrasound for the degradation of endocrine disrupting compounds in aqueous solution: A review on mechanisms, influence of operating parameters and cost estimation

Availability of drinking water is one of the basic humanitarian goals but remains as a grand challenge that the world is facing today. Currently, water bodies are contaminated not only with conventional pollutants but also with numerous recalcitrant pollutants, such as PPCPs, endocrine disrupting compounds, etc. These emerging pollutants require special attention because of their toxicity to living organisms, bio-resistant and can sustain even after primary and secondary treatments of wastewater. Among different treatment technologies, sonolysis is found to be an innovative and promising technique for the treatment of emerging pollutants present in aqueous solution. Sonolysis is the use of ultrasound to enhance or alter chemical reactions by the formation of free radicals and shock waves which ultimately helps in degradation of pollutants. This review summarizes several studies in the sonochemical literature, including mechanisms of sonochemical process, physical and chemical effects of ultrasound, and the influence of several process variables such as ultrasound frequency, power density, temperature and pH of the medium on degradation performance for endocrine disrupting compounds. In addition, this review highlighted techno-economic perspectives focusing on the total cost required for translating the ultrasound-based processes on a large scale. Overall, the objective of this study is to exhibit a critical review of information available in the literature to encourage and promote future research on sonolysis for the degradation of Endocrine Disrupting Compounds (EDCs).

Boron removal in seawater desalination by progressive freezing-melting

Desalination plays a crucial role in addressing water scarcity and promoting sustainable development. However, the presence of high boron content in seawater poses a significant challenge. This study introduces a progressive freezing-melting method that effectively removes boron while desalinating seawater. The experimental results indicated that salinity and boron rate of removal increased with freezing temperature and decreased with freezing duration. Among the experimental melting methods, ultrasonic melting (UM) and oscillatory melting (OM) were superior to natural melting (NM) for boron removal and desalination, with oscillatory melting proving to be the most effective. Specifically, when seawater was frozen at - 20 °C for 44 h followed by OM of 55% of the ice, salinity and boron removal rates reached 96.79% and 97.60%, respectively. The concentrations of boron and salinity in the treated seawater were only 0.777‰ and 0.149 mg/L. Moreover, the estimated theoretical energy consumption for treating 1 m3 of seawater was calculated to be 5.95 kWh. This study not only contributes to environmental sustainability but also holds significant potential due to its high efficiency in desalination and boron removal.

Effect of the arrangement of cavitation generation unit on the performance of an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC) is widely considered a promising process intensification technology. The novel advanced rotational hydrodynamic cavitation reactors (ARHCRs), with considerably higher performance compared with traditional devices, have gained increasing attention of academic and industrial communities. The cavitation generation unit (CGU), located on the rotor and/or stator of an ARHCR, is utilized to generate cavitation and consequently, its geometrical structure is vital for the performance. The present work studied, for the first time, the effect of the arrangement of CGU on the performance of a representative ARHCR by employing computational fluid dynamics based on the "simplified flow field" strategy. The effect of CGU arrangement, which was neglected in the past, was evaluated: radial offset distance (c), intersection angle (ω), number of rows (N), circumferential offset angle (γ), and radial spacing (r). The results indicate that the CGU, with an arrangement of a low ω and moderate c, N, γ, and r, performed the highest cavitation efficiency. The corresponding reasons were analyzed by combining the flow field and cavitation pattern. Moreover, the results also exposed a weakness of the "simplified flow field" strategy which may induce the unfavorable "sidewall effect" and cause false high-pressure region. The findings of this work may provide a reference value to the design of ARHCRs.

Extensive investigation of geometric effects in sonoreactors: Analysis by luminol mapping and comparison with numerical predictions

This investigation focuses on the influence of geometric factors on cavitational activity within a 20kHz sonoreactor containing water. Three vessels with different shapes were used, and the transducer immersion depth and liquid height were varied, resulting in a total of 126 experiments conducted under constant driving current. For each one, the dissipated power was quantified using calorimetry, while luminol mapping was employed to identify the shape and location of cavitation zones. The raw images of blueish light emission were transformed into false colors and corrected to compensate for refraction by the water-glass and glass-air interfaces. Additionally, all configurations were simulated using a sonoreactor model that incorporates a nonlinear propagation of acoustic waves in cavitating liquids. A systematic visual comparison between luminol maps and color-plots displaying the computed bubble collapse temperature in bubbly regions was conducted. The calorimetric power exhibited a nearly constant yield of approximately 70% across all experiments, thus validating the transducer command strategy. However, the numerical predictions consistently overestimated the electrical and calorimetric powers by a factor of roughly 2, indicating an overestimation of dissipation in the cavitating liquid model. Geometric variations revealed non-monotonic relationships between transducer immersion depth and dissipated power, emphasizing the importance of geometric effects in sonoreactor. Complex features were revealed by luminol maps, exhibiting appearance, disappearance, and merging of different luminol zones. In certain parametric regions, the luminol bright regions are reminiscent of linear eigenmodes of the water/vessel system. In the complementary parametric space, these structures either combine with, or are obliterated by typical elongated axial structures. The latter were found to coincide with an increased calorimetric power, and are conjectured to result from a strong cavitation field beneath the transducer producing acoustic streaming. Similar methods were applied to an additional set of 57 experiments conducted under constant geometry but with varying current, and suggested that the transition to elongated structures occurs above some amplitude threshold. While the model partially reproduced some experimental observations, further refinement is required to accurately account for the intricate acoustic phenomena involved.

Hydrodynamic cavitation degradation of hydroquinone using swirl-type micro-nano bubble reactor

This study reports the degradation of hydroquinone using lab-scale hydrodynamic cavitation approach (aswirl-type micro-nano bubble reactor), which is considered a green and effective method. The effects of inlet pressure, gas flow rate, pH and initial hydroquinone concentration on hydroquinone degradation were analysed based on experimental research. After experiments investigation, it was concluded that with pH 7.38, hydroquinone concentration of 50 mg/L, and int pressure of 0.2 MPa, the degradation efficiency of hydroquinone reached 91.25% in wastewater. Furthermore, this study also investigated the degradation effect of hydroquinone wastewater by hydrodynamic cavitation combined with persulfate oxidation (HC + PS). The kinetics of hydroquinone degradation by HC or PS oxidation alone and HC + PS oxidation were also examined. Compared with the degradation method alone, the degradation of hydroquinone by HC + PS was more pronounced, and the enhancement factor was 4.55, which indicates that HC greatly enhances the oxidation capacity of PS. In additon, from viewpoint of energy consumption and operating cost, the synergy of HC + PS (1.05 mM) is also the most promising combination. Based on the detection results of the Gas chromatography-mass spectrometry (GC-MS) the possible degradation pathways of hydroquinone were analysed: under the action of ·OH and the high temperature and pressure by cavitation process, the hydroquinone molecule undergoes dehydrogenation and ring-opening reaction, demethylation and decarboxylation reaction to produce intermediate products, which are finally converted into CO2 and H2O in micro-nano bubble cavitation process.

A novel method for the remediation of wastewater containing acid red 131 dye using acoustic cavitation combined with sulphur-doped TiO2 and oxidants

The present study investigated the degradation of Acid Red 131 (AR131) dye using a combination of ultrasound-induced cavitation, ultraviolet (UV) irradiation, chemical oxidants, and photocatalyst, focusing on the effect of operating parameters. It was established that acidic pH, higher input power, and lower initial concentration resulted in higher degradation. Sulphur-doped titanium dioxide (S-TiO2) synthesized using a novel ultrasound-assisted method showed an optimum dosage of 300 ppm for the AR131 degradation with sulphur to titanium ratio of 2:1. In the combination approach, the optimum dosage of hydrogen peroxide (H2O2) and potassium persulfate (KPS) was established as 100 ppm and 400 ppm respectively. The maximum degradation of 90.3% was obtained using a combined approach of US + KPS + UV/S-TiO2 whereas, a maximum synergetic coefficient of 1.57 was obtained for the approach of US + UV/S-TiO2 with degradation of 86.96%. It was also elucidated that for combination approaches of US + H2O2, US + H2O2 + KPS, and US + H2O2 + KPS + UV/S-TiO2, the synergetic coefficients were lower than one due to undesirable side reactions and radical scavenging. Scale-up studies performed at 15 times of the laboratory scale volume, elucidated that the maximum degradation was obtained as 58.01% for the approach of US + KPS + UV/S-TiO2. Therefore, the approach of US + KPS + UV/S-TiO2 was elucidated as the most efficient in degrading the AR131 dye at both small and large scale of operation. In terms of synergy, the approach of US + UV/S-TiO2 was more efficient. Overall, an optimized combination approach was successfully demonstrated for the effective degradation of AR131 dye with synergism and better results at a large scale.

New insights into the mechanism of Fered-Fenton treatment of industrial wastewater with high chloride content: Role of multiple reactive species

Hydroxyl radical (OH) is considered the dominant reactive species in the electro-Fenton (EF) and Fered-Fenton (EF-Fere) processes for wastewater treatment. However, in chloride-rich media, this is arguable due to the obscure mechanisms for the oxidant speciation and pollutant degradation. Herein, the role of active chlorine and Fe(IV)-oxo species (Fe^IVO²⁺) as primary oxidizing agents in HClO-mediated Fered-Fenton (EF-Fere-HClO) process is discussed, along with the dependence of their contribution on the pollutant structure. HClO generated from anodic oxidation of Cl^- can be consumed by added H₂O₂ to form singlet oxygen (¹O₂), which is detrimental because this species is quickly deactivated by water. The reaction between HClO and Fe²⁺ was proved to generate Fe^IVO²⁺, rather than OH or Cl suggested in the literature. The yield of Fe^IVO²⁺ species was proportional to the Cl^- concentration and barely affected by solution pH. The long-lived HClO and Fe^IVO²⁺ can selectively react with electron-rich compounds, which occurs simultaneously to the non-selective attack of OH formed from Fenton's reaction. The Fe^IVO²⁺ and OH concentration profiles were successfully modelled. Although the accumulation of toxic chlorinated by-products from HClO-mediated oxidation might cause new environmental concerns, the toxicity of pesticide wastewater with 508 mM Cl^- was halved upon EF-Fere-HClO treatment.

Hydrodynamic cavitation-assisted preparation of porous carbon from garlic peels for supercapacitors

Hydrodynamic cavitation (HC), which can effectively induce sonochemical effects, is widely considered a promising process intensification technology. In the present study, HC was successfully utilized to intensify the alkali activation of GPs for SCs, for the first time. Five BDCMs were synthesized following the method reported in the literature. For comparison, four more BDCMs with HC-treated, among which a sample was further doped with nitrogen during the HC treatment, were prepared. Then all the samples were compared from microscopical characteristics to electrochemical performance as SCs materials. The morphology study demonstrated that the HC treatment had created many defects and amorphous carbon structures on the GP-based BDCMs, with the highest SSA reaching 3272 m²/g (1:6-HCGP), which 32 folded that of the Raw carbon sample's. The HC treatment also intensified the N-doping process. XRD and XPS results manifested that the N content had been increased and consequently changed the electronic structure of the carbon atoms, leading to the increase of specific capacitance (1:6-HCGP+N-based SC, 227 F/g at 10 A/g). The cycle performance proved that the GP-based BDCMs have long-term stability, indicating that the HC-treated BDCMs were good choices for energy storage technologies. Compared with the ultrasound-assisted method, which may have a high energy density, the HC-assisted method enables high production and energy efficiency. This work is a first time attempt towards the industrial application of HC method in energy-related materials synthesis and encourages more in-depth studies in the future.

CFD-assisted modeling of the hydrodynamic cavitation reactors for wastewater treatment - A review

Hydrodynamic cavitation has been a promising method and technology in wastewater treatment, while the principles based on the design of cavitational reactors to optimize cavitation yield and performance remains lacking. Computational fluid dynamics (CFD), a supplementation of experimental optimization, has become an essential tool for this issue, owing to the merits of low investment and operating costs. Nevertheless, researchers with a non-engineering background or few CFD fundamentals used straightforward numerical strategies to treat cavitating flows, and this might result in many misinterpretations and consequently poor computations. This review paper presents the rationale behind hydrodynamic cavitation and application of cavitation modeling specific to the reactors in wastewater treatment. In particular, the mathematical models of multiphase flow simulation, including turbulence closures and cavitation models, are comprehensively described, whilst the advantages and shortcomings of each model are also identified and discussed. Examples and methods of the coupling of CFD technology, with experimental observations to investigate into the hydrodynamic behavior of cavitating devices that feature linear and swirling flows, are also critically summarized. Modeling issues, which remain unaddressed, i.e., the implementation strategies of numerical models, and the definition of cavitation numbers are identified and discussed. Finally, the advantages of CFD modeling are discussed and the future of CFD applications in this research area is also outlined. It is expected that the present paper would provide decision-making support for CFD beginners to efficiently perform CFD modeling and promote the advancement of cavitation simulation of reactors in the field of wastewater treatment.

Intensification of Red-G dye degradation used in the dyeing of alpaca wool by advanced oxidation processes assisted by hydrodynamic cavitation

Red-G dye is one of the main dyes used in the textile industry to dye alpaca wool. Therefore, considering the large volume of processed wool in Perú, the development of efficient technologies for its removal is a present scientific issue. In this study, an integrated system based on hydrodynamic cavitation (HC) and photo-Fenton process was evaluated to remove the Red-G dye. Using a hybrid cavitation device (venturi + orifice plate), the effect of pH was evaluated, achieving 21 % of removal at pH 2 which was more than 80 % higher compared to pH 4 and 6. The effect of temperature was also evaluated in HC-system at pH 2, where percentage of dye degradation increased at lower temperatures (around 20 °C). Then, 50.7 % of dye was removed under optimized condition of HC-assisted Fenton process (FeSO₄:H₂O₂ of 1:30), that value was improved strongly by UV-light incorporation in the HC-system, increasing to 99 % removal efficiency with respect to HC-assisted Fenton process and reducing the time to 15 min. Finally, the developed cavitation device in combination with photo-Fenton process removed efficiently the dye and thus could be considered an interesting option for application to real wastewater.

A critical review on the sonochemical degradation of organic pollutants in urine, seawater, and mineral water

Substances such as pharmaceuticals, pesticides, dyes, synthetic and natural hormones, plasticizers, and industrial chemicals enter the environment daily. Many of them are a matter of growing concern worldwide. The use of ultrasound to eliminate these compounds arises as an interesting alternative for treating mineral water, seawater, and urine. Thereby, this work presents a systematic and critical review of the literature on the elimination of organic contaminants in these particular matrices, using ultrasound-based processes. The degradation efficiency of the sonochemical systems, the influence of the nature of the pollutant (volatile, hydrophobic, or hydrophilic character), matrix effects (enhancement or detrimental ability compared to pure water), and the role of the contaminant concentration were considered. The combinations of ultrasound with other degradation processes, to overcome the intrinsic limitations of the sonochemical process, were considered. Also, energy consumptions and energy costs associated with pollutants degradation in the target matrices were estimated. Moreover, the gaps that should be developed in future works, on the sonodegradation of organic contaminants in mineral water, seawater, and urine, were discussed.