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.     

Quantifying OH radical generation in hydrodynamic cavitation via coumarin dosimetry: Influence of operating parameters and cavitation devices

Hydrodynamic cavitation (HC) has been extensively investigated for effluent treatment applications. Performance of HC devices or processes is often reported in terms of degradation of organic pollutants rather than quantification of hydroxyl (OH) radicals. In this study, generation of OH radicals in vortex based cavitation device using coumarin dosimetry was quantified. Coumarin was used as the chemical probe with an initial concentration of 100 µM (15 ppm). Generation of OH radicals was quantified by analysing generated single hydroxylated products. The influence of operating parameters such as pH and type of acid used to adjust pH, dissolved oxygen, and inlet and outlet pressures was investigated. Acidic pH was found to be more conducive for generating OH radicals and therefore subsequent experiments were performed at pH of 3. Sulphuric acid was found to be more than three times effective than hydrochloric acid in generating OH radicals. Effect of initial levels of dissolved oxygen was found to influence OH radical generation. Performance of vortex based cavitation device was then compared with other commonly used cavitation devices based on orifice and venturi. The vortex based cavitation device was found to outperform the orifice and venturi based devices in terms of initial per-pass factor. Influence of device scale (nominal flow rate through the device) on performance was then evaluated. The results presented for these devices unambiguously quantifies their cavitational performance. The presented results will be useful for evaluating computational models and stimulate further development of predictive computational models in this challenging area.     

Intensifying extraction of biomolecules from macroalgae using vortex based hydrodynamic cavitation device

Macroalgae have a tremendous potential to become an important renewable resource for valuable biomolecules and chemicals. New and improved ways of cell disruption and of enhancing rate as well as yield of extraction of valuable products from macroalgae are needed to fully realise this potential. In this work, hydrodynamic cavitation (HC) was used for intensifying rate and yield of extraction of phycoerythrin, proteins and carbohydrates from marine macroalgae Palmaria palmata. We use vortex-based HC devices which do not use small restrictions like orifice-based HC devices or moving parts like rotor–stator based HC devices. A bench scale setup with a nominal slurry flow rate of 20 LPM was established. Dried and powdered macroalgae was used. Influence of key operating parameters like pressure drop and number of passes on extraction performance (the rate and yield) was measured. A simple, yet effective model was developed and used for interpreting and describing experimental data. The results indicate that there exists an optimum pressure drop across the device at which extraction performance is maximum. The extraction performance with HC was found to be significantly better than the stirred vessels. HC has resulted in 2 to 20 times improvement in the rate of extraction of phycoerythrin (R-PE), proteins and carbohydrates. Based on the results obtained in this work, pressure drop of 200 kPa and number of passes through the HC devices of about 100 were found to be most effective for HC-assisted intensified extraction from macroalgae. The presented results and model will be useful for harnessing vortex-based HC devices for intensifying the extraction of valuable products from macroalgae.     

Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: A review

Advanced oxidation processes such as cavitation and Fenton chemistry have shown considerable promise for wastewater treatment applications due to the ease of operation and simple reactor design. In this review, hybrid methods based on cavitation coupled with Fenton process for the treatment of wastewater have been discussed. The basics of individual processes (Acoustic cavitation, Hydrodynamic cavitation, Fenton chemistry) have been discussed initially highlighting the need for combined processes. The different types of reactors used for the combined processes have been discussed with some recommendations for large scale operation. The effects of important operating parameters such as solution temperature, initial pH, initial pollutant concentration and Fenton’s reagent dosage have been discussed with guidelines for selection of optimum parameters. The optimization of power density is necessary for ultrasonic processes (US) and combined processes (US/Fenton) whereas the inlet pressure needs to be optimized in the case of Hydrodynamic cavitation (HC) based processes. An overview of different pollutants degraded under optimized conditions using HC/Fenton and US/Fenton process with comparison with individual processes have been presented. It has been observed that the main mechanism for the synergy of the combined process depends on the generation of additional hydroxyl radicals and its proper utilization for the degradation of the pollutant, which is strongly dependent on the loading of hydrogen peroxide. Overall, efficient wastewater treatment with high degree of energy efficiency can be achieved using combined process operating under optimized conditions, as compared to the individual process.     

Effect of geometry of hydrodynamically cavitating device on degradation of orange-G

In this research work, we have carried out geometric optimization of different cavitating devices using degradation of orange-G dye [OG] as a model pollutant. Three different cavitating devices viz. orifice plate, circular venturi and slit venturi were optimized and the degradation of orange-G dye was studied. The optimization of all three cavitating devices was done in terms of fluid inlet pressure to the cavitating devices and cavitation number. The effect of pH and initial concentration of the dye on the degradation rate was also studied. The geometry of cavitating device (flow cross sectional area, perimeter, shape, etc.) was found to be an important parameter in getting the maximum cavitational effect using hydrodynamic cavitation. The cavitational yield of all three cavitating devices were compared on the basis of mg of total organic carbon (TOC) reduction per unit energy supplied. The slit venturi gives almost 50% higher degradation rate and cavitational yield among all three cavitating devices studied for the same amount of energy supplied.     

Oxidation of Sulphur pollutants in model and real fuels using hydrodynamic cavitation

Hydrodynamic Cavitation (HC) offers an attractive platform for intensifying oxidative desulphurization of fuels. In the first part of this work, we present new results on oxidising single ring thiophene in a model fuel over the extended range of volume fraction of organic phase from 2.5 to 80 v/v %. We also present influence of type and scale of HC device on performance of oxidative desulphurization. Further experiments revealed that oxidising radicals generated in-situ by HC alone were not able to oxidise dual ring thiophenes. External catalyst (formic acid) and oxidising agents (hydrogen peroxide, H₂O₂) were therefore used with HC. Based on our prior work with acoustic cavitation (AC), the volumetric ratios for H₂O₂ and formic acid were identified as 0.95 v/v % and 6.25 v/v % respectively. The data of oxidation of dual ring thiophenes with n-dodecane and n-hexane as model fuels and typical transport fuels (diesel, kerosene, and petrol) using these oxidant and catalyst is presented. The observed performance with HC was compared with results obtained from a stirred tank and AC set-up. The presented data indicates that HC is able to intensify oxidation of sulphur species. The presented results provide a sound basis for further developments on HC based oxidative desulphurization processes.     

ANN based surrogate model for key Physico-chemical effects of cavitation

Intense and localised physico-chemical effects realised by cavitation such as generation of hydroxyl radicals, high-speed jets, and very high energy dissipation rates are being harnessed for a wide range of applications from emulsions, crystallisation, reactions to water treatment and waste valorisation. Single cavity models are typically used to quantitatively estimate such localised effects of cavity collapse. However, these models demand significant computing resources for resolving fast dynamics and therefore are very difficult, if not impossible, to integrate with CFD based cavitation device or reactor scale models. This severely limits the utility of device/ reactor scale models in simulating key applications of interest. In this work, we present, for the first time, artificial neural network (ANN) based surrogate models which accurately represent complex physico-chemical effects of cavity collapse. Recently developed cavity dynamics model was used for generating training data set encompassing both acoustic and hydrodynamic cavitation. Appropriate methodology for training ANN was developed. A shallow three hidden layer dense ANN was found to be more effective for estimating three main effects of cavity collapse: jet velocity, •OH generation and localised energy dissipation rate. The performance of trained ANN was then evaluated by comparing the predictions with the totally unseen data obtained from the cavity dynamics model. The developed ANN was shown to simulate unseen data very well not just within the range of training data (interpolation) but also beyond (extrapolation). Algebraic equations representing ANN are included to facilitate incorporation in device/ reactor scale CFD models. The presented methodology and results will be useful for developing high-fidelity CFD models of cavitation devices/ reactors based on key physico-chemical effects of cavity collapse.     

Degradation of benzene present in wastewater using hydrodynamic cavitation in combination with air

The degradation of benzene present in wastewater using hydrodynamic cavitation (HC) alone as well as in combination with air has been studied using nozzles as cavitating device of HC reactor. Initially, the energy efficiency of the HC reactor operated at different inlet pressures was determined using the calorimetric studies. Maximum energy efficiency of 53.4% was obtained at an inlet pressure of 3.9 bar. The treatment processes were compared under adiabatic as well as isothermal conditions and it was observed that under the adiabatic condition, the extent of degradation is higher as compared to isothermal condition. Studies related to the understanding the effect of inlet pressure (range of 1.8–3.9 bar) revealed that the maximum degradation as 98.9% was obtained at 2.4 bar pressure using the individual operation of HC under adiabatic conditions and in 70 min of treatment. The combination of HC with air was investigated at different air flow rates with best results for maximum degradation of benzene achieved at air flow rate of 60 mL/sec. A novel approach of using cavitation for a limited fraction of total treatment time was also demonstrated to be beneficial in terms of the extent of degradation as well as energy requirements and cost of operation. Based on the cavitational intensity, the resonant radius of aggregates of cavitation bubbles was also determined for distilled water as well as for aqueous solution of benzene. Overall, significant benefits of using HC combined with air have been demonstrated for degradation of benzene along with fundamental understanding into cavitation effects.     

Mapping of cavitational activity in a pilot plant dyeing equipment

A large number of papers of the literature quote dyeing intensification based on the application of ultrasound (US) in the dyeing liquor. Mass transfer mechanisms are described and quantified, nevertheless these experimental results in general refer to small laboratory apparatuses with a capacity of a few hundred millilitres and extremely high volumetric energy intensity. With the strategy of overcoming the scale-up inaccuracy consequent to the technological application of ultrasounds, a dyeing pilot-plant prototype of suitable liquor capacity (about 40 L) and properly simulating several liquor to textile hydraulic relationships was designed by including US transducers with different geometries.Optimal dyeing may be obtained by optimising the distance between transducer and textile material, the liquid height being a non-negligible operating parameter. Hence, mapping the cavitation energy in the machinery is expected to provide basic data on the intensity and distribution of the ultrasonic field in the aqueous liquor. A flat ultrasonic transducer (absorbed electrical power of 600 W), equipped with eight devices emitting at 25 kHz, was mounted horizontally at the equipment bottom.Considering industrial scale dyeing, liquor and textile substrate are reciprocally displaced to achieve a uniform colouration. In this technology a non uniform US field could affect the dyeing evenness to a large extent; hence, mapping the cavitation energy distribution in the machinery is expected to provide fundamental data and define optimal operating conditions. Local values of the cavitation intensity were recorded by using a carefully calibrated Ultrasonic Energy Meter, which is able to measure the power per unit surface generated by the cavitation implosion of bubbles. More than 200 measurements were recorded to define the map at each horizontal plane positioned at a different distance from the US transducer; tap water was heated at the same temperature used for dyeing tests (60 °C). Different liquid flow rates were tested to investigate the effect of the hydrodynamics characterising the equipment.The mapping of the cavitation intensity in the pilot-plant machinery was performed to achieve with the following goals: (a) to evaluate the influence of turbulence on the cavitation intensity, and (b) to determine the optimal distance from the ultrasound device at which a fabric should be positioned, this parameter being a compromise between the cavitation intensity (higher next to the transducer) and the US field uniformity (achieved at some distance from this device).By carrying out dyeing tests of wool fabrics in the prototype unit, consistent results were confirmed by comparison with the mapping of cavitation intensity.     

Degradation of reactive orange 4 dye using hydrodynamic cavitation based hybrid techniques

In the present work, degradation of reactive orange 4 dye (RO4) has been investigated using hydrodynamic cavitation (HC) and in combination with other AOP’s. In the hybrid techniques, combination of hydrodynamic cavitation and other oxidizing agents such as H₂O₂ and ozone have been used to get the enhanced degradation efficiency through HC device. The hydrodynamic cavitation was first optimized in terms of different operating parameters such as operating inlet pressure, cavitation number and pH of the operating medium to get the maximum degradation of RO4. Following the optimization of HC parameters, the degradation of RO4 was carried out using the combination of HC with H₂O₂ and ozone. It has been found that the efficiency of the HC can be improved significantly by combining it with H₂O₂ and ozone. The mineralization rate of RO4 increases considerably with 14.67% mineralization taking place using HC alone increases to 31.90% by combining it with H₂O₂ and further increases to 76.25% through the combination of HC and ozone. The synergetic coefficient of greater than one for the hybrid processes of HC + H₂O₂ and HC + Ozone has suggested that the combination of HC with other oxidizing agents is better than the individual processes for the degradation of dye effluent containing RO4. The combination of HC with ozone proves to be the most energy efficient method for the degradation of RO4 as compared to HC alone and the hybrid process of HC and H₂O₂.     

Removal of single and dual ring thiophene’s from dodecane using cavitation based processes

Utilising cavitation for enhancing oxidative desulphurization has been investigated for nearly-two decades with recent investigations shifting focus from low-capacity acoustic cavitation (AC) to scalable hydrodynamic cavitation (HC). This work focuses on developing a viable means for removing thiophene’s from fuels. In the first phase of this work, use of vortex based HC devices for removal of single and dual ring thiophenes from dodecane was investigated. HC was shown to be able to remove single ring thiophene from dodecane without using any external catalyst or additives. However, in absence of catalyst or additives, it was not possible to remove dual ring thiophenes such as dibenzothiophene using HC. Therefore, in the second phase of this work, various strategies based on use of catalyst or additives to augment cavitation based process were investigated. AC based experiments were opted for shortlisting suitable catalysts and additives for intensifying cavitation based processes. The influence of using oxidant (H₂O₂) and carboxylic acid catalysts on efficacy of removal of dual ring thiophenes is presented. Several conditions were tested, and the optimal volumetric ratios of 0.95 v/v % H₂O₂ and 6.25 v/v % HCOOH was identified and utilised throughout the remainder of the study. Regeneration of extractant which accumulates oxidised sulphur species from dodecane was also investigated using AC. The additives and process conditions reported in this work are useful for enhancing desulphurization performance.     

Degradation of organic wastewater by hydrodynamic cavitation combined with acoustic cavitation

In this paper, the decomposition of Rhodamine B (RhB) by hydrodynamic cavitation (HC), acoustic cavitation (AC) and the combination of these individual methods (HAC) have been investigated. The degradation of 20 L RhB aqueous solution was carried out in a self-designed HAC reactor, where hydrodynamic cavitation and acoustic cavitation could take place in the same space simultaneously. The effects of initial concentration, inlet pressure, solution temperature and ultrasonic power were studied and discussed. Obvious synergies were found in the HAC process. The combined method achieved the best conversion, and the synergistic effect in HAC was even up to 119% with the ultrasonic power of 220 W in a treatment time of 30 min. The time-independent synergistic factor based on rate constant was introduced and the maximum value reached 40% in the HAC system. Besides, the hybrid HAC method showed great superiority in energy efficiency at lower ultrasonic power (88–176 W). Therefore, HAC technology can be visualized as a promising method for wastewater treatment with good scale-up possibilities.     

Degradation of a cationic dye (Rhodamine 6G) using hydrodynamic cavitation coupled with other oxidative agents: Reaction mechanism and pathway

In the present study, decolorization and mineralization of a cationic dye, Rhodamine 6G (Rh6G), has been carried out using hydrodynamic cavitation (HC). Two cavitating devices such as slit and circular venturi were used to generate cavitation in HC reactor. The process parameters such as initial dye concentration, solution pH, operating inlet pressure, and cavitation number were investigated in detail to evaluate their effects on the decolorization efficiency of Rh6G. Decolorization of Rh6G was marginally higher in the case of slit venturi as compared to circular venturi. The kinetic study showed that decolorization and mineralization of the dye fitted first-order kinetics. The loadings of H₂O₂ and ozone have been optimized to intensify the decolorization and mineralization efficiency of Rh6G using HC. Nearly 54% decolorization of Rh6G was obtained using a combination of HC and H₂O₂ at a dye to H₂O₂ molar ratio of 1:30. The combination of HC with ozone resulted in 100% decolorization in almost 5–10 min of processing time depending upon the initial dye concentration. To quantify the extent of mineralization, total organic carbon (TOC) analysis was also performed using various processes and almost 84% TOC removal was obtained using HC coupled with 3 g/h of ozone. The degradation by-products formed during the complete degradation process were qualitatively identified by liquid chromatography-mass spectrometry (LC-MS) and a detailed degradation pathway has been proposed.     

Treatment of cyanide containing wastewater using cavitation based approach

Industrial wastewater streams containing high concentrations of biorefractory materials like cyanides should ideally be treated at source. In the present work, degradation of potassium ferrocyanide (K₄F_e(CN)₆) as a model pollutant has been investigated using cavitational reactors with possible intensification studies using different approaches. Effect of different operating parameters such as initial concentration, temperature and pH on the extent of degradation using acoustic cavitation has been investigated. For the case of hydrodynamic cavitation, flow characteristics of cavitating device (venturi) have been established initially followed by the effect of inlet pressure and pH on the extent of degradation. Under the optimized set of operating parameters, the addition of hydrogen peroxide (ratio of K₄F_e(CN)₆:H₂O₂ varied from 1:1 to 1:30 mol basis) as process intensifying approach has been investigated. The present work has conclusively established that under the set of optimized operating parameters, cavitation can be effectively used for degradation of potassium ferrocyanide. The comparative study of hydrodynamic cavitation and acoustic cavitation suggested that hydrodynamic cavitation is more energy efficient and gives higher degradation as compared to acoustic cavitation for equivalent power/energy dissipation. The present work is the first one to report comparison of cavitation based treatment schemes for degradation of cyanide containing wastewaters.     

Physical insights into the sonochemical degradation of recalcitrant organic pollutants with cavitation bubble dynamics

This paper tries to discern the mechanistic features of sonochemical degradation of recalcitrant organic pollutants using five model compounds, viz. phenol (Ph), chlorobenzene (CB), nitrobenzene (NB), p-nitrophenol (PNP) and 2,4-dichlorophenol (2,4-DCP). The sonochemical degradation of the pollutant can occur in three distinct pathways: hydroxylation by OH radicals produced from cavitation bubbles (either in the bubble–bulk interfacial region or in the bulk liquid medium), thermal decomposition in cavitation bubble and thermal decomposition at the bubble–liquid interfacial region. With the methodology of coupling experiments under different conditions (which alter the nature of the cavitation phenomena in the bulk liquid medium) with the simulations of radial motion of cavitation bubbles, we have tried to discern the relative contribution of each of the above pathway to overall degradation of the pollutant. Moreover, we have also tried to correlate the predominant degradation mechanism to the physico-chemical properties of the pollutant. The contribution of secondary factors such as probability of radical–pollutant interaction and extent of radical scavenging (or conservation) in the medium has also been identified. Simultaneous analysis of the trends in degradation with different experimental techniques and simulation results reveals interesting mechanistic features of sonochemical degradation of the model pollutants. The physical properties that determine the predominant degradation pathway are vapor pressure, solubility and hydrophobicity. Degradation of Ph occurs mainly by hydroxylation in bulk medium; degradation of CB occurs via thermal decomposition inside the bubble, degradation of PNP occurs via pyrolytic decomposition at bubble interface, while hydroxylation at bubble interface contributes to degradation of NB and 2,4-DCP.     

Decolourization of Rhodamine B: A swirling jet-induced cavitation combined with NaOCl

A hydrodynamic cavitation reactor (Ecowirl) based on swirling jet-induced cavitation has been used in order to allow the degradation of a waste dye aqueous solution (Rhodamine B, RhB). Cavitation generated by Ecowirl reactor was directly compared with cavitation generated by using multiple hole orifice plates. The effects of operating conditions and parameters such as pressure, pH of dye solution, initial concentration of RhB and geometry of the cavitating devices on the degradation rate of RhB were discussed. In similar operative conditions, higher extents of degradation (ED) were obtained using Ecowirl reactor rather than orifice plate. An increase in the ED from 8.6% to 14.7% was observed moving from hole orifice plates to Ecowirl reactor. Intensification in ED of RhB by using hydrodynamic cavitation in presence of NaOCl as additive has been studied. It was found that the decolourization was most efficient for the combination of hydrodynamic cavitation and chemical oxidation as compared to chemical oxidation and hydrodynamic cavitation alone. The value of ED of 83.4% was reached in 37 min using Ecowirl combined with NaOCl (4.0 mg L⁻¹) as compared to the 100 min needed by only mixing NaOCl at the same concentration. At last, the energetic consumptions of the cavitation devices have been evaluated. Increasing the ED and reducing the treatment time, Ecowirl reactor resulted to be more energy efficient as compared to hole orifice plates, Venturi and other swirling jet-induced cavitation devices, as reported in literature.     

Degradation of 2,4-dinitrophenol using a combination of hydrodynamic cavitation,chemical and advanced oxidation processes

In the present work, degradation of 2,4-dinitrophenol (DNP), a persistent organic contaminant with high toxicity and very low biodegradability has been investigated using combination of hydrodynamic cavitation (HC) and chemical/advanced oxidation. The cavitating conditions have been generated using orifice plate as a cavitating device. Initially, the optimization of basic operating parameters have been done by performing experiments over varying inlet pressure (over the range of 3–6 bar), temperature (30 °C, 35 °C and 40 °C) and solution pH (over the range of 3–11). Subsequently, combined treatment strategies have been investigated for process intensification of the degradation process. The effect of HC combined with chemical oxidation processes such as hydrogen peroxide (HC/H₂O₂), ferrous activated persulfate (HC/Na₂S₂O₈/FeSO₄) and HC coupled with advanced oxidation processes such as conventional Fenton (HC/FeSO₄/H₂O₂), advanced Fenton (HC/Fe/H₂O₂) and Fenton-like process (HC/CuO/H₂O₂) on the extent of degradation of DNP have also been investigated at optimized conditions of pH 4, temperature of 35 °C and inlet pressure of 4 bar. Kinetic study revealed that degradation of DNP fitted first order kinetics for all the approaches under investigation. Complete degradation with maximum rate of DNP degradation has been observed for the combined HC/Fenton process. The energy consumption analysis for hydrodynamic cavitation based process has been done on the basis of cavitational yield. Degradation intermediates have also been identified and quantified in the current work. The synergistic index calculated for all the combined processes indicates HC/Fenton process is more feasible than the combination of HC with other Fenton like processes.     

Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis

Diclofenac sodium, a widely detected pharmaceutical drug in wastewater samples, has been selected as a model pollutant for degradation using novel combined approach of hydrodynamic cavitation and heterogeneous photocatalysis. A slit venturi has been used as cavitating device in the hydrodynamic cavitation reactor. The effect of various operating parameters such as inlet fluid pressure (2–4 bar) and initial pH of the solution (4–7.5) on the extent of degradation have been studied. The maximum extent of degradation of diclofenac sodium was obtained at inlet fluid pressure of 3 bar and initial pH as 4 using hydrodynamic cavitation alone. The loadings of TiO₂ and H₂O₂ have been optimised to maximise the extent of degradation of diclofenac sodium. Kinetic study revealed that the degradation of diclofenac sodium fitted first order kinetics over the selected range of operating protocols. It has been observed that combination of hydrodynamic cavitation with UV, UV/TiO₂ and UV/TiO₂/H₂O₂ results in enhanced extents of degradation as compared to the individual schemes. The maximum extent of degradation as 95% with 76% reduction in TOC has been observed using hydrodynamic cavitation in conjunction with UV/TiO₂/H₂O₂ under the optimised operating conditions. The diclofenac sodium degradation byproducts have been identified using LC/MS analysis.     

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.     

Hydrodynamic cavitation-enhanced photocatalytic activity of P-doped TiO2 for degradation of ciprofloxacin: Synergetic effect and mechanism

Hybrid methods with an enhanced oxidation capacity have been proposed for the removal of organic contaminants based on combining hydrodynamic cavitation (HC) with advanced oxidation processes (AOPs). In this study, we utilize the synergetic effect between photocatalytic processes and HC to strengthen ciprofloxacin (CIP) degradation by P-doped TiO₂ catalysts. In comparison to a degradation ratio of 20.37 % in HC and 55.7 % in P-TiO₂-based photocatalytic processes alone, the CIP degradation ratio reached as high as 90.63 % in HC-assisted photocatalytic processes with the optimal experimental parameters. The mechanic microjets treatment originated from HC make P-TiO₂ nano photocatalysts with significantly increased surface area, smaller particle sizes, cleaner surface and improved dispersion, which were found using SEM, TEM, and BET analysis. Possible degradation mechanisms and reaction pathways of CIP during hybrid HC + photocatalytic processes were explored by coupling free radical capture experiments and liquid chromatography-mass spectrometry . This hybrid HC + photocatalytic technique has a potential application in the treatment of antibiotic sewage at the industrial level.