Use of hydrodynamic cavitation in (waste)water treatment

A review of chloride ions removal from high chloride industrial wastewater: Sources, hazards, and mechanisms

To reduce metal pipe corrosion, improve product quality, and meet zero liquid discharge (ZLD) criteria, managing chloride ion concentrations in industrial wastewaters from metallurgical and chemical sectors has become increasingly important. This review provides detailed information on the sources, concentration levels, and deleterious effects of chloride ions in representative industrial wastewaters, and also summarizes and discusses various chloride ion removal techniques, including precipitation, ion exchange, physical separation, and advanced oxidation (AOPs). Among these, AOPs are particularly promising due to their ability to couple with other technologies and the diversity of their auxiliary technologies. The development of dechlorination electrode materials by electro-adsorption (CDI) can be inspired by the electrode materials used in chloride ion battery (CIB). This review also provides insights into exploring the effective combination of multiple chloride removal mechanisms, as well as the development of environmentally friendly composite materials. This review provides a theoretical basis and development direction for the effective treatment and secondary utilization of chlorine-containing industrial wastewater in the future.

Bio-inspired apparatus to produce luminescent cavitation in a rigid walled chamber

A mechanical device inspired by the rapid rotational motion of the pistol shrimp plunger has been developed to experimentally study the contraction/expansion dynamics of a gas bubble inside a confined liquid volume and in the vicinity of solid surfaces. The apparatus consists of a limb with a V-shaped end, which fits into a socket forming a cylindrical compression chamber. Air bubbles of different sizes and in different positions inside the chamber were seeded to study their shape evolution in liquids when subjected to pressure pulses induced by the limb closure. By changing the standoff and curvature parameters, as well as the closing power of the limb it was possible to control the dynamical behavior of the cavity. Four stages describing the dynamic behavior of the bubble were found: 1) A slight expansion-contraction stage accompanied by very weak volumetric oscillations. 2) First compression stage. The formation of gas and liquid micro-jets is observed when the vertical symmetry axis of the bubble is initially located outside of the chamber symmetry axis, on the other hand, when there is a coincidence between these axes, the bubble only contracts exhibiting non-spherical shapes, alternating between oblate and prolate spheroidal structures. 3) An expansion stage where the cavity reaches the walls of the chamber exhibiting irregular shapes on its surface. 4) Second compression stage. This process begins when the limb rebounds and stops sealing the chamber allowing a jet of liquid to enter from the fluid medium outside, inducing a very violent collapse accompanied by the emission of light. The proposed technique represents a novel alternative to study the dynamic evolution of bubbles near and on solid boundaries of various geometries. Other attractive features of the apparatus are its low manufacturing cost, simple design and compact size which makes it easily portable.

Thermal Oscillations of Nanobubbles

Nanobubble cavitation is advancing technologies in enhanced wastewater treatment, cancer therapy and diagnosis, and microfluidic cleaning. Current macroscale models predict that nanobubble oscillations should be isothermal, yet recent studies suggest that they are adiabatic with an associated increase in natural frequency, which becomes challenging when characterizing nanobubble sizes using ultrasound in experiments. We derive a new theoretical model that considers the nonideal nature of the nanobubble's internal gas phase and nonequilibrium effects, by employing the van der Waals (vdW) equation of state and implementing a temperature jump term at the liquid-gas interface, respectively, finding excellent agreement with molecular dynamics (MD) simulations. Our results reveal how adiabatic behavior could be erroneously interpreted when analyzing the thermal response of the gas using the commonly employed polytropic process and explain instead how nanobubble oscillations are physically closer to their isothermal limit.

Hydrodynamic cavitation-enhanced activation of sodium percarbonate for estrogen removal

The present paper investigated the potential of hydrodynamic cavitation (HC) as an effective tool for activating sodium percarbonate (SPC). The method's efficiency was demonstrated by effectively removing estrogens, which are pollutants that have adverse impacts on aquatic ecosystems. The effects of the SPC concentration, temperature of solution, and cavitation time were evaluated. After SPC/HC treatment, the removal of estrogens was monitored by liquid chromatography-tandem mass spectrometry (LC -MS/MS). Already after 4 s of treatment and 24 h of reaction time, more than 97% of estrogens (initial concentration of 300 ng/L) were removed. The effect of post-treatment time is not considered in several papers, even though it seems to be crucial and is discussed here. The results were supported by the values of degradation rate constants, which fit the pseudo-first-order kinetic model. We also verified that HC alone was not effective for estrogen removal under the selected conditions. The sustainability of the SPC/HC system was evaluated based on electric energy per order calculation. The combination of SPC and HC is a promising approach for rapidly degrading micropollutants such as estrogenic compounds without the need for additional technological steps, such as pH or temperature adjustment.

Numerical investigation of the cavitation bubble near the solid wall with a gas-entrapping hole based on a fully compressible three-phase model

The solid surface with several cavities containing gas strongly influences the bubble's dynamical behaviors. To reveal the underlying physical mechanism of the cavitation bubble near a rigid boundary with a gas-entrapping hole, a fully compressible three-phase model, accounting for the three-phase volume transport equation, was implemented in OpenFOAM. The predicted bubble shape was validated with the corresponding experimental photos, and good agreement was achieved. The bubble's primary physical features (e.g., the expanding shock wave, upward and downward liquid jet, and high-pressure region) are well reproduced, which helps understand the underlying mechanisms. The numerical results show that the solid wall with a gas-entrapping hole could affect the morphology of both the bubble and liquid jet, as well as shortens the bubble's first oscillation period in comparison to an intact rigid wall. The relationship among the prolongation factor, the standoff distance, and the relative size ratio is analyzed. It is found the prolongation factor increases as the relative size ratio decrease. As the standoff distance decreases, the gas entrapping hole plays a significant role in the oscillation period of the bubble. The current model can be further extended to reveal the microscopic mechanism of aeration avoiding cavitation damage and investigate the interaction between air bubbles and cavitation bubbles, which is of great interest to practical applications.

Investigation of free fatty acid reduction from mixed crude palm oil using 3D-printed rotor-stator hydrodynamic cavitation: An experimental study of geometric characteristics of the inner hole

A continuous esterification process is employed to decrease the free fatty acid (FFA) concentration of FFA-rich mixed crude palm oil. Both optimal and recommended conditions are determined for the esterification reaction conditions and the geometry of the 3D-printed rotor design in the rotor-stator hydrodynamic cavitation reactor. This study is primarily concerned with the effect of the cavitation device configuration, especially the rotor design, on FFA reduction. Instead of conventional spherical or cylindrical drilled holes, a point angle cone-shaped hole is used to create cavities over the rotor surface. These point angles are adjusted to clarify their effect on FFA reduction. The response surface methodology is applied to determine the optimal concentrations of methanol and sulfuric acid, rotor speed, hole diameter and depth, and cone point angle. The recommended conditions are 20.8 wt% methanol, 2.6 wt% sulfuric acid, 3000 rpm, 5 mm hole diameter, 5 mm hole depth, and 110°, respectively. Under this configuration, the FFA content is reduced from 12.014 wt% to around 1 wt%. A maximum yield of 97.34 vol% esterified oil is obtained through a completed phase separation step, and 93.31 vol% pure oil is collected after the cleansing step. The recommended conditions result in reduced chemical usage, cheaper FFA reduction, and lower environmental impact. This creative rotor design effectively improves our understanding of the geometry of the cavitation device, thus enhancing the cavitation effect in industrial operations.

Degradation of ammonia nitrogen by an economic combined hydrodynamic cavitation method

Hydrodynamic cavitation (HC) was a kind of advanced oxidation mode. There were defects in the common HC devices, such as high energy consumption, low efficiency, and easy plugging. In order to effectively utilize HC, it was urgent to research new HC devices and used them together with other traditional water treatment methods. Ozone was widely used as a water treatment agent that does not produce harmful by-products. Sodium hypochlorite (NaClO) was efficient and cheap, but too much chlorine will be harmful to water. The combination of ozone and NaClO with the HC device of propeller orifice plate can improve the dissolution and utilization rate of ozone in wastewater, reduce the use of NaClO, and avoid the generation of residual chlorine. The degradation rate reached 99.9% when the mole ratio γ of NaClO to ammonia nitrogen (NH3-N) was 1.5 and the residual chlorine was near zero. As for the degradation rate of NH3-N or COD of actual river water and real wastewater after biological treatment, the ideal mole ratio γ was also 1.5 and the ideal O3 flow rates were 1.0 L/min. The combined method has been preliminarily applied to actual water treatment and was expected to be used in more and more scenarios.

Comparative evaluation of advanced oxidation processes (AOPs) for reducing SARS-CoV-2 viral load from campus sewage water

Presence of SARS-CoV-2 in wastewater is a major concern as the wastewater meets rivers and other water bodies and is used by the population for various purposes. Hence it is very important to treat sewage water in an efficient manner in order to reduce the public health risk. In the present work, various advanced oxidation processes (AOPs) have been evaluated for disinfection of SARS-CoV-2 from sewage water collected from STP inlet of academic institutional residential. The sewage water was subjected to ten AOPs, which include Ozone (O₃), Hydrodynamic cavitation (HC), Ultraviolet radiation (UV), and their hybrid combinations like HC/O₃, HC/O₃/H₂O₂, HC/H₂O_2, O₃/UV, UV/H₂O₂, UV/H₂O₂/O_3, and O₃/H₂O₂ to reduce SARS-CoV-2 viral load. Further, AOP treated sewage water was subjected to total nucleic acid isolation followed by RT-qPCR for viral load estimation. The sewage water treatment techniques were evaluated based on their viral concentration-reducing efficiency. It was found that ozone and ozone-coupled hybrid AOPs showed the most promising result with more than 98 % SARS-CoV-2 viral load reducing efficiency from sewage water. Interestingly, the best six AOPs used in this study significantly reduced both the SARS-CoV-2 and PMMoV (faecal indicator) viral load and improved water quality in terms of increasing DO and decreasing TOC.

Pretreatment of herbal waste using sonication

The effect of hydrodynamic cavitation (HC) and the manner it affects the biodegradability of herbal waste suspended on municipal wastewater subjected to mechanical pre-treatment was examined in this paper. The HC was performed at an optimal inlet pressure equal to 3.5 bar and with the cavitation number of 0.11; the number of recirculation passes through the cavitation zone amounted to 30.5. The BOD₅/COD ratio was enhanced by more than 70% between the 5th and 10th minute of the process, indicating the enhanced biodegradability of herbal waste shortly. Fiber component analysis, FT-IR/ATR, TGA and SEM analysis were conducted to check the findings and to demonstrate changes in the chemical and morphological structure of herbal waste. It confirmed that hydrodynamic cavitation visibly influenced the herbal composition and their structural morphology, decreased hemicellulose, cellulose and lignin content, but did not form the by-products affecting the subsequent biological treatment of herbal waste.

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.

A Review on Rotary Generators of Hydrodynamic Cavitation for Wastewater Treatment and Enhancement of Anaerobic Digestion Process

The issue of ever-increasing amounts of waste activated sludge (WAS) produced from biological wastewater treatment plants (WWTPs) is pointed out. WAS can be effectively reduced in the anaerobic digestion (AD) process, where methanogens break down organic matter and simultaneously produce biogas in the absence of oxygen, mainly methane and CO2. Biomethane can then be effectively used in gas turbines to produce electricity and power a part of WWTPs. Hydrodynamic cavitation (HC) has been identified as a potential technique that can improve the AD process and enhance biogas yield. Rotary generators of hydrodynamic cavitation (RGHCs) that have gained considerable popularity due to their promising results and scalability are presented. Operation, their underlying mechanisms, parameters for performance evaluation, and their division based on geometry of cavitation generation units (CGUs) are presented. Their current use in the field of wastewater treatment is presented, with the focus on WAS pre/treatment. In addition, comparison of achieved results with RGHCs relevant to the enhancement of AD process is presented.

Recent Advances in Supercritical CO2 Extraction of Pigments, Lipids and Bioactive Compounds from Microalgae

Supercritical CO₂ extraction is a green method that combines economic and environmental benefits. Microalgae, on the other hand, is a biomass in abundance, capable of providing a vast variety of valuable compounds, finding applications in the food industry, cosmetics, pharmaceuticals and biofuels. An extensive study on the existing literature concerning supercritical fluid extraction (SFE) of microalgae has been carried out focusing on carotenoids, chlorophylls, lipids and fatty acids recovery, as well as the bioactivity of the extracts. Moreover, kinetic models used to describe SFE process and experimental design are included. Finally, biomass pretreatment processes applied prior to SFE are mentioned, and other extraction methods used as benchmarks are also presented.

Trends and characteristics of employing cavitation technology for water and wastewater treatment with a focus on hydrodynamic and ultrasonic cavitation over the past two decades: A Scientometric analysis

Cavitation-based technologies have emerged as a sustainable and effective way to treat natural waters and wastewater, considering their increasing scarcity due to pollution and climate change. For this reason, this work aimed to conduct a scientometric analysis on the topic of cavitation for water and wastewater treatment during the last 20 years, from 2001 to August 2022. We focused on hydrodynamic and ultrasonic cavitation as the prevalent methods of inducing cavitation. Furthermore, an in-depth study on the main trends regarding the number of publications and citations, keywords co-occurrence and evolution, and countries' publication trends was carried out to investigate the future direction of this research topic. The data was gathered from the Web of Science database and analyzed by the Visualization Of Similarities software. This work focused on: i) publication and citation trends, ii) scientific categories, iii) countries' contribution to the topic of cavitation, iv) prominent journals, v) keyword co-occurrence and cluster analysis, and vi) keyword evolution analysis. Results showed a significant increase in publications during the past 5 years. The scientific categories with the highest number of publications were "environmental sciences" and "environmental engineering," with a combined share of 19.4 % of publications. Keywords evolution analysis showed that limited focus was given to topics related to "energy" and "energy efficiency" in the field of cavitation, but with the rising importance of each process's sustainability, the attention given to these concepts will increase in the future. Future directions for the topic of cavitation-related water and wastewater treatments will shift towards more environmentally friendly applications of hydrodynamic and ultrasonic cavitation as well as towards more green and sustainable approaches to address the increasing water pollution problems and shortage. Moreover, it will include other uses besides water treatment such as manufacturing nanomaterials food production and medicine.

Numerical investigation of the translational motion of bubbles: The comparison of capabilities of the time-resolved and the time-averaged methods

In the present study, the accuracies of two different numerical approaches used to model the translational motion of acoustic cavitational bubble in a standing acoustic field are compared. The less accurate but less computational demanding approach is to decouple the equation of translational motion from the radial oscillation, and solve it by calculating the time-averaged forces exerted on the bubble for one acoustic cycle. The second approach is to solve the coupled ordinary differential equations directly, which provides more accurate results with higher computational effort. The investigations are carried out in the parameter space of the driving frequency, pressure amplitude and equilibrium radius. Results showed that both models are capable to reveal stable equilibrium positions; however, in the case of oscillatory solutions, the difference in terms of translational frequency may be more than three fold, and the amplitude of translational motion obtained by the time-averaged method is roughly 1.5 times higher compared to the time-resolved solution at particular sets of parameters. This observation implies that where the transient behaviour is important, the time-resolved approach is the proper choice for reliable results.

Simulations of a full sonoreactor accounting for cavitation

In spite of the increasing interest in ultrasound processing applications, industrial scale-up remains limited, in particular by the unavailability of predictive computer tools. In this study, using a previously published model of cavitating liquids implementable as a non-linear Helmholtz equation, it is shown that a full sonoreactor can be modelled and simulated. The model includes the full transducer and the vibrations of the vessel walls, using the physics of elastic solids and piezo-electricity. The control-loop used by the generator to set the optimal frequency is also accounted for. Apart from the geometry, the unique input of the model is the current feeding the transducer whereas the dissipated electrical power, transducer complex impedance and working frequency are available as outputs. The model is put to the test against experiments realized in different geometries, varying either the input current or the transducer immersion depth. Despite the overestimation of the power dissipated in the liquid, the evolution of the acoustic load in both cases is reasonably well reproduced by simulation, which partially validates the method used.

Microbubbles Remove Listeria monocytogenes from the Surface of Stainless Steel, Cucumber, and Avocado

Fresh produce may be contaminated by bacterial pathogens, including Listeria monocytogenes, during harvesting, packaging, or transporting. A low-intensity cavitation process with air being injected into water was studied to determine the microbubbles' efficiency when detaching L. monocytogenes from stainless steel and the surface of fresh cucumber and avocado. Stainless steel coupons (1″ × 2″), cucumber, and avocado surfaces were inoculated with L. monocytogenes (LCDC strain). After 1, 24 or 48 h, loosely attached cells were washed off, and inoculated areas were targeted by microbubbles (~0.1-0.5 mm dia.) through a bubble diffuser (1.0 L air/min) for 1, 2, 5, or 10 min. For steel, L. monocytogenes (48 h drying) detachment peaked at 2.95 mean log reduction after 10 min of microbubbles when compared to a no-bubble treatment. After 48 h pathogen drying, cucumbers treated for 10 min showed a 1.78 mean log reduction of L. monocytogenes. For avocados, L. monocytogenes (24 h drying) detachment peaked at 1.65 log reduction after 10 min of microbubbles. Microbubble applications may be an effective, economical, and environmentally friendly way to remove L. monocytogenes, and possibly other bacterial pathogens, from food contact surfaces and the surfaces of whole, intact fresh produce.

Remediation of pharmaceutical pollutants using graphene-based materials - A review on operating conditions, mechanism and toxicology

Graphene is a high surface area special carbon compound with exceptional biological, electronic and mechanical properties. Graphene-based materials are potential components used in water treatment on different modes and processes. Ibuprofen and ciprofloxacin are two commonly found pharmaceutical contaminants discharged into water bodies from industrial, domestic and hospital sources. Their concentration levels in water bodies are reported in the range of 1 μg/L to 6.5 mg/L and 0.050-100 μg/L respectively. Their toxic effects pose very high risk to the inhabiting organisms. Their ability to resist biodegradation and capacity to bioaccumulate makes the conventional methods less effective in removal. In the present article, treatment of these compounds via three methods, adsorption, photocatalytic degradation and electro-fenton reactions using graphene-based materials along with the methods adopted for synthesis and treatment are reviewed. The uptakes obtained by graphene-derived adsorbents are presented along with the optimal operating conditions. Studies reported complete removal of ibuprofen from wastewater was achieved at 7 pH for 60 min using graphene membrane as adsorbent and uptake of 99% of ciprofloxacin was exhibited for graphene nanoplates/boron nitrate aerogel at a pH of 7 and 60 min. The reduced graphene oxide surface exhibits higher affinity to light adsorption which leads to the formation of photo generated electrons. The future perspectives for improved applications of graphene-based materials and the research gap currently existing are highlighted.

Combined ultrasound cavitation and persulfate for the treatment of pharmaceutical wastewater

In recent years industrialization has caused magnificent leaps in the high profitable growth of pharmaceutical industries, and simultaneously given rise to environmental pollution. Pharmaceutical processes like extraction, purification, formulation, etc., generate a large volume of wastewater that contains high chemical oxygen demand (COD), biological oxygen demand, auxiliary chemicals, and different pharmaceutical substances or their metabolites in their active or inactive form. Its metabolites impart non-biodegradable toxic pollutants as a byproduct and intense color, which increases ecotoxicity into the water, thus this requires proper treatment before being discharged. This study focuses on the feasibility analysis of the utilization of ultrasound cavitation (20 kHz frequency) together with a persulfate oxidation approach for the treatment of complex pharmaceutical effluent. Process parameters like pH, amplitude intensity, oxidant dosage were optimized for COD removal applying response surface methodology-based Box-Behnken design. The optimum value observed for pH, amplitude intensity and oxidant dosage are 5, 20% and 100 mg/L respectively with 39.5% removal of COD in 60 min of fixed processing time. This study confirms that a combination of ultrasound cavitation and persulfate is a viable option for the treatment of pharmaceutical wastewater and can be used as an intensification technology in existing effluent treatment plants to achieve the highest amount of COD removal.

Cavitation erosion by shockwave self-focusing of a single bubble

The ability of cavitation bubbles to effectively focus energy is made responsible for cavitation erosion, traumatic brain injury, and even for catalyse chemical reactions. Yet, the mechanism through which material is eroded remains vague, and the extremely fast and localized dynamics that lead to material damage has not been resolved. Here, we reveal the decisive mechanism that leads to energy focusing during the non-spherical collapse of cavitation bubbles and eventually results to the erosion of hardened metals. We show that a single cavitation bubble at ambient pressure close to a metal surface causes erosion only if a non-axisymmetric energy self-focusing is at play. The bubble during its collapse emits shockwaves that under certain conditions converge to a single point where the remaining gas phase is driven to a shockwave-intensified collapse. We resolve the conditions under which this self-focusing enhances the collapse and damages the solid. High-speed imaging of bubble and shock wave dynamics at sub-picosecond exposure times is correlated to the shockwaves recorded with large bandwidth hydrophones. The material damage from several metallic materials is detected in situ and quantified ex-situ via scanning electron microscopy and confocal profilometry. With this knowledge, approaches to mitigate cavitation erosion or to even enhance the energy focusing are within reach.

Recent advances in aqueous virus removal technologies

The COVID-19 outbreak has triggered a massive research, but still urgent detection and treatment of this virus seems a public concern. The spread of viruses in aqueous environments underlined efficient virus treatment processes as a hot challenge. This review critically and comprehensively enables identifying and classifying advanced biochemical, membrane-based and disinfection processes for effective treatment of virus-contaminated water and wastewater. Understanding the functions of individual and combined/multi-stage processes in terms of manufacturing and economical parameters makes this contribution a different story from available review papers. Moreover, this review discusses challenges of combining biochemical, membrane and disinfection processes for synergistic treatment of viruses in order to reduce the dissemination of waterborne diseases. Certainly, the combination technologies are proactive in minimizing and restraining the outbreaks of the virus. It emphasizes the importance of health authorities to confront the outbreaks of unknown viruses in the future.

A review on disinfection methods for inactivation of waterborne viruses

Water contamination is a global health problem, and the need for safe water is ever-growing due to the public health implications of unsafe water. Contaminated water could contain pathogenic bacteria, protozoa, and viruses that are implicated in several debilitating human diseases. The prevalence and survival of waterborne viruses differ from bacteria and other waterborne microorganisms. In addition, viruses are responsible for more severe waterborne diseases such as gastroenteritis, myocarditis, and encephalitis among others, hence the need for dedicated attention to viral inactivation. Disinfection is vital to water treatment because it removes pathogens, including viruses. The commonly used methods and techniques of disinfection for viral inactivation in water comprise physical disinfection such as membrane filtration, ultraviolet (UV) irradiation, and conventional chemical processes such as chlorine, monochloramine, chlorine dioxide, and ozone among others. However, the production of disinfection by-products (DBPs) that accompanies chemical methods of disinfection is an issue of great concern due to the increase in the risks of harm to humans, for example, the development of cancer of the bladder and adverse reproductive outcomes. Therefore, this review examines the conventional disinfection approaches alongside emerging disinfection technologies, such as photocatalytic disinfection, cavitation, and electrochemical disinfection. Moreover, the merits, limitations, and log reduction values (LRVs) of the different disinfection methods discussed were compared concerning virus removal efficiency. Future research needs to merge single disinfection techniques into one to achieve improved viral disinfection, and the development of medicinal plant-based materials as disinfectants due to their antimicrobial and safety benefits to avoid toxicity is also highlighted.

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.

Advanced oxidation processes: Performance, advantages, and scale-up of emerging technologies

Advanced oxidation processes (AOPs) are promising technologies for partial or complete mineralization of contaminants of emerging concern by highly reactive hydroxyl, hydroperoxyl, superoxide, and sulphate radicals. Detailed investigations and reviews have been reported for conventional AOP systems that have been installed in full-scale wastewater treatment plants. However, recent efforts have focused on the peroxymonosulphate, persulphate, catalytic ozonation, ultrasonication and hydrodynamic cavitation, gamma radiation, electrochemical oxidation, modified Fenton, and plasma-assisted AOPs. This critical review presents the detailed mechanisms of emerging AOP technologies, their performance for treatment of contaminants of emerging concern, the relative advantages and disadvantages of each technology, and the remaining challenges to scale-up and implementation. Among the evaluated technologies, the modified electrochemical oxidation, gamma radiation, and plasma-assisted systems demonstrated the greatest potential for successful and sustainable implementation in wastewater treatment due to their environmental safety, compatibility, and efficient transformation of contaminants of emerging concern by a variety of reactive species. The other emerging AOP systems were also promising, but additional scale-up trials and a deeper understanding of their reaction kinetics in complex wastewater matrices are necessary to determine the technical and economic feasibility of full-scale processes.

Prediction of vascular injury by cavitation microbubbles in a focused ultrasound field

Many studies have shown that microbubble cavitation is one mechanism for vascular injury under ultrasonic excitation. Previous work has attributed vascular damage to vessel expansions and invaginations due to the expansion and contraction of microbubbles. However, the mechanisms of vascular damage are not fully understood. In this paper, we investigate, theoretically and experimentally, the vessel injury due to stress induced by ultrasound-induced cavitation (UIC). A bubble-fluid-vessel coupling model is constructed to investigate the interactions of the coupling system. The dynamics process of vessel damage due to UIC is theoretically simulated with a finite element method, and a focused ultrasound (FU) setup is carried out and used to assess the vessel damage. The results show that shear stress contributes to vessel injury by cell detachment while normal stress mainly causes distention injury. Similar changes in cell detachment in a vessel over time can be observed with the experimental setup. The severity of vascular injury is correlated to acoustic parameters, bubble-wall distance, and microbubble sizes, and the duration of insonation..

Fundamentals, biomedical applications and future potential of micro-scale cavitation-a review

Thanks to the developments in the area of microfluidics, the cavitation-on-a-chip concept enabled researchers to control and closely monitor the cavitation phenomenon in micro-scale. In contrast to conventional scale, where cavitation bubbles are hard to be steered and manipulated, lab-on-a-chip devices provide suitable platforms to conduct smart experiments and design reliable devices to carefully harness the collapse energy of cavitation bubbles in different bio-related and industrial applications. However, bubble behavior deviates to some extent when confined to micro-scale geometries in comparison to macro-scale. Therefore, fundamentals of micro-scale cavitation deserve in-depth investigations. In this review, first we discussed the physics and fundamentals of cavitation induced by tension-based as well as energy deposition-based methods within microfluidic devices and discussed the similarities and differences in micro and macro-scale cavitation. We then covered and discussed recent developments in bio-related applications of micro-scale cavitation chips. Lastly, current challenges and future research directions towards the implementation of micro-scale cavitation phenomenon to emerging applications are presented.

Cavitation bubble interaction with compliant structures on a microscale: A contribution to the understanding of bacterial cell lysis by cavitation treatment

Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-assisted water treatment on a scale of a single bubble, the present paper numerically addresses interaction between a collapsing microbubble and a nearby compliant structure, that mechanically and structurally resembles a bacterial cell. A fluid-structure interaction methodology is employed, where compressible multiphase flow is considered and the bacterial cell wall is modeled as a multi-layered shell structure. Simulations are performed for two selected model structures, each resembling the main structural features of Gram-negative and Gram-positive bacterial cell envelopes. The contribution of two independent dimensionless geometric parameters is investigated, namely the bubble-cell distance δ and their size ratio ς. Three characteristic modes of bubble collapse dynamics and four modes of spatiotemporal occurrence of peak local stresses in the bacterial cell membrane are identified throughout the parameter space considered. The former range from the development of a weak and thin jet away from the cell to spherical bubble collapses. The results show that local stresses arising from bubble-induced loads can exceed poration thresholds of cell membranes and that bacterial cell damage could be explained solely by mechanical effects in absence of thermal and chemical ones. Based on this, the damage potential of a single microbubble for bacteria eradication is estimated, showing a higher resistance of the Gram-positive model organism to the nearby bubble collapse. Microstreaming is identified as the primary mechanical mechanism of bacterial cell damage, which in certain cases may be enhanced by the occurrence of shock waves during bubble collapse. The results are also discussed in the scope of bacteria eradication by cavitation treatment on a macro scale, where processes of hydrodynamic and ultrasonic cavitation are being employed.

Combined suppression effects on hydrodynamic cavitation performance in Venturi-type reactor for process intensification

Hydrodynamic cavitation is an emerging intensification technology in water treatment or chemical processing, and Venturi-type cavitation reactors exhibit advantages for industrial-scale production. The effects of temperature on hydrodynamic cavitating flows are investigated to find the optimum reaction conditions enhancing cavitating treatment intensity. Results show that the cavitation performance, including the cavitation intensity and cavitation unsteady behavior, is influenced by (1) cavitation number σ (the pressure difference affecting the vaporization process), (2) Reynolds number Re (the inertial/viscous ratio affecting the bubble size and liquid-vapor interface area), and (3) thermodynamic parameter Σ (the thermal effect affecting the temperature drop). With increasing temperature, the cavitation length first increases and then decreases, with a cavitation intensity peak at the transition temperature of 58 °C. With the growth of cavitation extent, the cavity-shedding regimes tend to transition from the attached sheet cavity to the periodic cloud cavity, and the vapor volume fluctuating frequency decreases accordingly. A combined suppression parameter (CSP) is provided to predict that, with increasing CSP value, the cavitation intensity can be decreased. Recommendations are given that working under the low-CSP range (55-60 °C) could enhance the intensification of the cavitation process.

Characteristics of cavitation onset and development in a self-excited fluidic oscillator

Hydrodynamic cavitation has been widely employed in modern chemical technology. A high-speed camera experiment is conducted to reveal the characteristics of hydrodynamic cavitation generated in one self-excited fluidic oscillator. The images obtained from the high-speed camera system are employed to describe several development stages of the hydrodynamic cavitation. The gray intensity of the images which is the volume of bubbles formed is extracted to distinguish the cavitation bubbles from the water. It is found that three regions in the fluidic oscillator could be divided according to the distance from the entrance. The inception of cavitation occurs in the region nearest the entrance. For a relatively low inlet flow rate, the whole process of cavitation could complete within the region that is the second nearest the entrance as a low pressure area appears periodically in this region. For a high inlet flow rate, the vortexes in the region farthest from the entrance are able to generate sufficient low pressures to induce the generation of cavitation. In addition, the intensity of cavitation could be reflected by the cavitation number in a self-excited fluidic oscillator.

Experimental Investigation on the Characteristic of Hydrodynamic-Acoustic Cavitation (HAC)

This study aimed to investigate the Cavitation dynamics of Hydrodynamic-acoustic cavitation by employing experimental methods. The spatial distribution of cavitation clouds, the temporal and spatial distribution achieved by cavitation clouds, and the main flow structure in the flow field were extracted and analyzed by complying with the cavitating flow image captured with the high-speed camera. As indicated from the results, the widened cavitation region and the strength of cavitation under the synergy of ultrasound were reported. When the inlet pressure is 2 MPa, the average value of the volume-averaging cavitation intensity variable is 0.029, 0.058, and 0.092, respectively, and the corresponding growth rate is 95% and 58.5%. By adopting the Proper Orthogonal Decomposition method (POD), the ultrasound was revealed to primarily enhance the cavitation intensity by downregulating the cavitation threshold other than altering the large-scale vortex structure in the flow field. The high-frequency pressure pulsation of ultrasound strengthened the instability exhibited by the shear layer and induced small-scale vortex structures at the shear layer, which was suggested to be the more violently shed and collapse.

Removal of field-collected Microcystis aeruginosa in pilot-scale by a jet pump cavitation reactor

Hydrodynamic cavitation has been investigated extensively in the field of water treatment in the last decade and a well-designed hydrodynamic cavitation reactor is critical to the efficient removal of algal and large-scale application. In this paper, a jet pump cavitation reactor (JPCR) is developed for the removal of cyanobacteria Microcystis aeruginos in a pilot scale. The results demonstrate that the photosynthetic activity of M. aeruginosa is greatly inhibited immediately after treatment in the JPCR, and the growth is also hindered after 3 days culture. Moreover, a high cell disruptions of M. aeruginosa is detected after treated by JPCR. The release of chlorophyll-a indicates that the JPCR caused serious rupture to M. aeruginosa cells. The plausible cell disruption mechanisms are proposed in accordance with a fluorescence microscope and scanning electron microscope. Then, the optimization of cell disruption efficiency is also investigated for various operating conditions. The results showed that the algal cell disruption efficiency is improved at higher inlet pressure and the cavitation stage between the unstable limited operation cavitation stage and stable limited operation cavitation stage. The effect and optimization of JPCR on algal reduction are highlighted. The results of the study promote the application of hydrodynamic cavitation on algal removal and provide strong support for JPCR application in algal removal.

Hydrodynamic cavitation for micropollutant degradation in water - Correlation of bisphenol A degradation with fluid mechanical properties

The present work addresses the correlation of bisphenol A (BPA) degradation by hydrodynamic cavitation with the fluid mechanical properties of the cavitating jet in the reactor. The effects of inlet pressure and two orifices were investigated. The fluid mechanics conditions during the reaction were evaluated by optical measurements to determine the jet length, bubble volume, number of bubbles, and bubble size distribution. In addition, chemiluminescence of luminol is used to localize chemically active bubbles due to the generation of hydroxyl radicals in the reactor chamber. The correlation between the rate constants of BPA degradation and the mechanical properties of the liquid is discussed. Here, linear dependencies between the degradation of BPA and the volume expansion of the bubble volume and chemiluminescence are found, allowing prediction of the rate constants and the hydroxyl radicals generated. BPA degradation of 50% was achieved in 30 min with the 1.7 mm nozzle at 25 bar. However, the 1 mm nozzle has been demonstrated to be more energetically efficient, achieving 10% degradation with 30% less power per 100 passes. There is a tendency for the number of small bubbles in the reactor to increase with smaller nozzle and increasing pressure difference.

Hydrodynamic cavitation efficiently inactivates potato virus Y in water

Waterborne plant viruses can destroy entire crops, leading not only to high financial losses but also to food shortages. Potato virus Y (PVY) is the most important potato viral pathogen that can also affect other valuable crops. Recently, it has been confirmed that this virus is capable of infecting host plants via water, emphasizing the relevance of using proper strategies to treat recycled water in order to prevent the spread of the infectious agents. Emerging environmentally friendly methods such as hydrodynamic cavitation (HC) provide a great alternative for treating recycled water used for irrigation. In the experiments conducted in this study, laboratory HC based on Venturi constriction with a sample volume of 1 L was used to treat water samples spiked with purified PVY virions. The ability of the virus to infect plants was abolished after 500 HC passes, corresponding to 50 min of treatment under pressure difference of 7 bar. In some cases, shorter treatments of 125 or 250 passes were also sufficient for virus inactivation. The HC treatment disrupted the integrity of viral particles, which also led to a minor damage of viral RNA. Reactive species, including singlet oxygen, hydroxyl radicals, and hydrogen peroxide, were not primarily responsible for PVY inactivation during HC treatment, suggesting that mechanical effects are likely the driving force of virus inactivation. This pioneering study, the first to investigate eukaryotic virus inactivation by HC, will inspire additional research in this field enabling further improvement of HC as a water decontamination technology.

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

Acoustic cavitation (AC) and hydrodynamic cavitation (HC) coupled with advanced oxidation processes (AOPs) are prominent techniques used for industrial wastewater treatment though most studies have focused on simulated effluents. The present review mainly focuses on the analysis of studies related to real industrial effluent treatment using acoustic and hydrodynamic cavitation operated individually and coupled with H₂O₂, ozone, ultraviolet, Fenton, persulfate and peroxymonosulfate, and other emerging AOPs. The necessity of using optimum loadings of oxidants in the various AOPs for obtaining maximum COD reduction of industrial effluent have been demonstrated. The review also presents critical analysis of designs of various HCRs that have been or can be used for the treatment of industrial effluents. The impact of operating conditions such as dilution, inlet pressure, ultrasonic power, pH, and operating temperature have been also discussed. The economic aspects of the industrial effluent treatment have been analyzed. HC can be considered as cost-efficient approach compared to AC on the basis of the lower operating costs and better transfer efficiencies. Overall, HC combined with AOPs appears to be an effective treatment strategy that can be successfully implemented at industrial-scale of operation.

Liposome destruction by a collapsing cavitation microbubble: A numerical study

Hydrodynamic cavitation poses as a promising new method for wastewater treatment as it has been shown to be able to eradicate bacteria, inactivate viruses, and destroy other biological structures, such as liposomes. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What exactly are the damaging mechanisms of hydrodynamic cavitation in various applications? In this light, the present paper numerically addresses the interaction between a single cavitation microbubble and a nearby lipid vesicle of a similar size. A coupled fluid-structure interaction model is employed, from which three critical modes of vesicle deformation are identified and temporally placed in relation to their corresponding driving mechanisms: (a) unilateral stretching at the waist of the liposome during the first bubble collapse and subsequent shock wave propagation, (b) local wrinkling at the tip until the bubble rebounds, and (c) bilateral stretching at the tip of the liposome during the phase of a second bubble contraction. Here, unilateral and bilateral stretching refer to the local in-plane extension of the bilayer in one and both principal directions, respectively. Results are discussed with respect to critical dimensionless distance for vesicle poration and rupture. Liposomes with initially equilibrated envelopes are not expected to be structurally compromised in cases with δ>1.0, when a nearby collapsing bubble is not in their direct contact. However, the critical dimensionless distance for the case of an envelope with pre-existing pores is identified at δ=1.9. Additionally, the influence of liposome-bubble size ratio is addressed, from which a higher potential of larger bubbles for causing stretching-induced liposome destruction can be identified.

The occurrence and control of waterborne viruses in drinking water treatment: A review

As the coronavirus disease 2019 continues to spread globally, its culprit, the severe acute respiratory syndrome coronavirus 2 has been brought under scrutiny. In addition to inhalation transmission, the possible fecal-oral viral transmission via water/wastewater has also been brought under the spotlight, necessitating a timely global review on the current knowledge about waterborne viruses in drinking water treatment system - the very barrier that intercepts waterborne pathogens to terminal water users. In this article we reviewed the occurrence, concentration methods, and control strategies, also, treatment performance on waterborne viruses during drinking water treatment were summarized. Additionally, we emphasized the potential of applying the quantitative microbial risk assessment to guide drinking water treatment to mitigate the viral exposure risks, especially when the unregulated novel viral pathogens are of concern. This review paves road for better control of viruses at drinking water treatment plants to protect public health.

Towards the development of cavitation technology for gas hydrate prevention

In offshore gas well drilling and production, methane hydrate may block the tubing, resulting in the stoppage of gas production. Conventional methods such as injection of thermal hydrate inhibitors, thermal insulating or heating, gas dehydration and reducing pressure are time-consuming and expensive, and sometimes, they are not realistic in production conditions. New methods are needed to lower the cost of gas hydrate prevention and to overcome these limitations. The thermal effect of cavitation was applied to the prevention of gas hydrate in this study. The thermal impact of cavitation, supposed to heat the fluids and prevent the formation of gas hydrate, was evaluated. Numerical simulation was performed to study the thermal performance of cavitation. Furthermore, experimental studies of the influence of initial temperature, flow rate, fluid volume and fluid viscosity on the thermal effect of cavitation were performed, and the results were analysed.

Physical field simulation of the ultrasonic radiation method: An investigation of the vessel, probe position and power

In this paper, the effects of ultrasonic probe position, vessel shape, and ultrasonic input power on the sound pressure distribution in the reactor were investigated by solving the Helmholtz equation using COMSOL Multiphysis@ software. Three different types of glass containers were used in the study, which are beaker, Erlenmeyer flask, and round bottom flask. The maximum value of sound pressure in the three containers will gradually increase when the distance between the probe and the bottom of the container decreases. When the distance decreases, the area of the high acoustic pressure region in the round bottom flask does not change significantly, while the area of the high acoustic pressure region in the beaker and Erlenmeyer flask increases sharply, which means that the use of the round bottom flask can reduce the influence of the dead zone on the preparation of nanomaterials. In addition, the change in power increases the value of the peak negative acoustic pressure in the vessel, enhancing the response efficiency of ultrasonic cavitation.

A Flexible Cystoscope Based on Hydrodynamic Cavitation for Tumor Tissue Ablation

OBJECTIVE

Hydrodynamic cavitation is characterized by the formation of bubbles inside a flow due to local reduction of pressure below the saturation vapor pressure. The resulting growth and violent collapse of bubbles lead to a huge amount of released energy. This energy can be implemented in different fields such as heat transfer enhancement, wastewater treatment and chemical reactions. In this study, a cystoscope based on small scale hydrodynamic cavitation was designed and fabricated to exploit the destructive energy of cavitation bubbles for treatment of tumor tissues. The developed device is equipped with a control system, which regulates the movement of the cystoscope in different directions. According to our experiments, the fabricated cystoscope was able to locate the target and expose cavitating flow to the target continuously and accurately. The designed cavitation probe embedded into the cystoscope caused a significant damage to prostate cancer and bladder cancer tissues within less than 15 minutes. The results of our experiments showed that the cavitation probe could be easily coupled with endoscopic devices because of its small diameter. We successfully integrated a biomedical camera, a suction tube, tendon cables, and the cavitation probe into a 6.7 mm diameter cystoscope, which could be controlled smoothly and accurately via a control system. The developed device is considered as a mechanical ablation therapy, can be a solid alternative for minimally invasive tissue ablation methods such as radiofrequency (RF) and laser ablation, and could have lower side effects compared to ultrasound therapy and cryoablation.

Shock-induced collapse of surface nanobubbles

The collapse of cavitation bubbles often releases high-speed liquid jets capable of surface damage, with applications in drug delivery, cancer treatment, and surface cleaning. Spherical cap-shaped surface nanobubbles have previously been found to exist on immersed substrates. Despite being known nucleation sites for cavitation, their collapsing dynamics are currently unexplored. Here, we use molecular dynamics simulations to model the shock-induced collapse of different surface nanobubble sizes and contact angles. Comparisons are made with additional collapsing spherical nanobubble simulations near a substrate, to investigate the differences in their jet formation and resulting substrate pitting damage. Our main finding is that the pitting damage in the surface nanobubble simulations is greatly reduced, when compared to the spherical nanobubbles, which is primarily caused by the weaker jets formed during their collapse. Furthermore, the pit depths for surface nanobubble collapse do not depend on bubble size, unlike in the spherical nanobubble cases, but instead depend only on their contact angle. We also find a linear scaling relationship for all bubble cases between the final substrate damage and the peak pressure impulse at the impact centre, which can now be exploited to assess the relative damage in other computational studies of collapsing bubbles. We anticipate the more controlled surface-damage features produced by surface nanobubble cavitation jets will open up new applications in advanced manufacturing, medicine, and precision cleaning.

Precise micro-particle and bubble manipulation by tunable ultrasonic bottle beams

This paper reports a method to generate tunable bottle beams using an ultrasonic lens, by which the bottle position can be precisely adjusted with the change of the acoustic frequency. Therefore, the position of a single particle or bubble in liquid can be manipulated without using phased array which is costly and huge with complex circuits. Furthermore, we introduced this method to multiple bubble manipulation using acoustic holography. The bottle properties against frequency are theoretically and experimentally analyzed. It is shown that the bottle position depends almost linearly on the operating frequency, which provides a basis for the precise manipulation of bubbles and particles. In addition, the relationship between the acoustic radiation force and the drag force under different incident acoustic pressures is considered, establishing a limit on the moving velocity of the trapped particles. The ultrasonic field observation is further demonstrated by Schlieren imaging system. The proposed method has potential biomedical applications, such as more flexible cell manipulation and targeted drug delivery in vivo, as well as potential applications in the study of chemical reactions between micro objects.

Ashwathanarayanaiah B, Kulkarni S, Udayakishore Y, Halyal A, Chavan A. Intensification of advanced oxidation processes (AOPs) for the degradation of bisphenol-A

Bisphenol-A (BPA), a precursor for many polymers, is a harmful compound for living organisms if present beyond permissible limits in aqueous streams. The combinations of oxidation processes like Hydrodynamic Cavitation (HC), hydrogen peroxide (H2O2), and Fenton’s reagent (H2O2 + FeSO4) were examined for the degradation of BPA in the present study. The effects of operating parameters like inlet pressure, initial concentration of BPA, orifice geometry were investigated on BPA degradation. The degradation rates of BPA increased with inlet pressure up to 0.5 MPa and then showed a decreasing trend beyond 0.5 MPa. The initial concentration of BPA had an inverse relation with the degradation percentage. The multiple hole orifice plate showed better degradation of BPA compared to the single hole orifice plate. In the intensification studies, the addition of hydrogen peroxide to BPA in the cavitation reactor favored BPA degradation. A combination of HC + Fenton’s reagent (0.1 M H2O2 + 0.01 M FeSO4) significantly degraded BPA present in the aqueous streams.

Disinfection characteristics of an advanced rotational hydrodynamic cavitation reactor in pilot scale

Hydrodynamic cavitation is a promising technique for water disinfection. In the present paper, the disinfection characteristics of an advanced hydrodynamic cavitation reactor (ARHCR) in pilot scale were studied. The effects of various flow rates (1.4-2.6 m³/h) and rotational speeds (2600-4200 rpm) on the removal of Escherichia coli (E. coli) were revealed and analyzed. The variation regularities of the log reduction and reaction rate constant at various cavitation numbers were established. A disinfection rate of 100% was achieved in only 4 min for 15 L of simulated effluent under 4200 rpm and 1.4 m³/h, with energy efficiency at 0.0499 kWh/L. A comprehensive comparison with previously introduced HCRs demonstrates the superior performance of the presented ARHCR system. The morphological changes in E. coli were studied by scanning electron microscopy. The results indicate that the ARHCR can lead to serious cleavage and surface damages to E. coli, which cannot be obtained by conventional HCRs. Finally, a possible damage mechanism of the ARHCR, including both the hydrodynamical and sonochemical effects, was proposed. The findings of the present study can provide strong support to the fundamental understanding and applications of ARHCRs for water disinfection.

Quality and cost analysis of a wastewater treatment plant using GPS-X and CapdetWorks simulation programs

Wastewater management is a significant challenge, especially for arid and semiarid countries due to the water scarcity crisis. Considering human health, environmental regulations, wastewater treatment plant expenses, and water reusability, this study aims to assist in designing an efficient and economical WWTP. Technical and economic simulation and modeling are important for designing, constructing, and predicting the requirements of wastewater treatment plant designs. Simulation of a project before its implementation, in the first place, reduces additional costs, and from another point of view, a project is examined and researched from different aspects. In this study, three wastewater treatment plants based on conventional activated sludge, contact stabilization, and step aeration were simulated and evaluated technically and economically using the Zargandeh treatment plant data in Tehran. In three scenarios, GPS-X software investigated the effect of raw wastewater variations between their minimum and maximum intervals on effluent quality, and because the range of inlet effluent was different, more precise results were obtained. Then, the economic costs of the project, including implementation, maintenance, and also energy use, were calculated by Capdetwork software, and contact stabilization was found to be more cost-effective.

ANN based modelling of hydrodynamic cavitation processes: Biomass pre-treatment and wastewater treatment

We have developed artificial neural network (ANN) based models for simulating two application examples of hydrodynamic cavitation (HC) namely, biomass pre-treatment to enhance biogas and degradation of organic pollutants in water. The first case reports data on influence of number of passes through HC reactor on bio-methane generation from bagasse. The second case reports data on influence of HC reactor scale on degradation of dichloroaniline (DCA). Similar to most of the HC based applications, the availability of experimental data for these two applications is rather limited. In this work a systematic methodology for developing ANN model is presented. The models were shown to describe the experimental data very well. The ANN models were then evaluated for their ability to interpolate and extrapolate. Despite the limited data, the ANN models were able to simulate and interpolate the data for two very different and complex HC applications very well. The extrapolated results of biomethane generation in terms of number of passes were consistent with the intuitive understanding. The extrapolated results in terms of elapsed time were however not consistent with the intuitive understanding. The ANN model was able to generate intuitively consistent extrapolated results for degradation of DCA in terms of number of passes as well as scale of HC reactor. The results will be useful for developing quantitative models of complex HC applications.

Role of nanocatalyst in the treatment of organochlorine compounds - A review

Since a few centuries ago, organochlorine compounds (OCs) become one of the threatened contaminants in the world. Due to the lipophilic and hydrophobic properties, OCs always discover in fat or lipid layers through bioaccumulation and biomagnification. The OCs are able to retain in soil, sediment and water for long time as it is volatile, OCs will evaporate from soil and condense in water easily and frequently, which pollute the shelter of aquatic life and it affects the function of organs and damage system in human body. Photocatalysis that employs the usage of semiconductor nanophotocatalyst and solar energy can be the possible alternative for current conventional water remediation technologies. With the benefits of utilizing renewable energy, no production of harmful by-products and easy operation, degradation of organic pollutants in rural water bodies can be established. Besides, nanophotocatalyst that is synthesized with nanotechnology outnumbered conventional catalyst with larger surface area to volume ratio, thus higher photocatalytic activity is observed. In contrast, disadvantages particularly no residual effect in water distribution network, requirement of post-treatment and easily affected by various factors accompanied with photocatalysis method cannot be ignored. These various factors constrained the photocatalytic efficiency via nanocatalysts which causes the full capacity of solar photocatalysis has yet to be put into practice. Therefore, further modifications and research are still required in nanophotocatalysts' synthesis to overcome limitations such as large band gaps and photodecontamination.

Dynamics of bubbles under stochastic pressure forcing

Several studies have investigated the dynamics of a single spherical bubble at rest under a nonstationary pressure forcing. However, attention has almost always been focused on periodic pressure oscillations, neglecting the case of stochastic forcing. This fact is quite surprising, as random pressure fluctuations are widespread in many applications involving bubbles (e.g., hydrodynamic cavitation in turbulent flows or bubble dynamics in acoustic cavitation), and noise, in general, is known to induce a variety of counterintuitive phenomena in nonlinear dynamical systems such as bubble oscillators. To shed light on this unexplored topic, here we study bubble dynamics as described by the Keller-Miksis equation, under a pressure forcing described by a Gaussian colored noise modeled as an Ornstein-Uhlenbeck process. Results indicate that, depending on noise intensity, bubbles display two peculiar behaviors: when intensity is low, the fluctuating pressure forcing mainly excites the free oscillations of the bubble, and the bubble's radius undergoes small amplitude oscillations with a rather regular periodicity. Differently, high noise intensity induces chaotic bubble dynamics, whereby nonlinear effects are exacerbated and the bubble behaves as an amplifier of the external random forcing.