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

Response surface methodology-based optimisation of adsorption of diclofenac and treatment of pharmaceutical effluent using combined coagulation-adsorption onto nFe2O3 decorated water chestnut shells biochar

This work involved the preparation of pristine and iron nanoparticle-loaded biochar from a water chestnut shell to remove diclofenac sodium (DCF) containing effluent of pharmaceutical origin. To create suitable forecasting equations for the modelling of the DCF adsorption onto the adsorbent, response surface methodology (RSM) was used. The parameters, e.g. pH, adsorbent mass, DCF concentration and contact time, were used for the modeling of adsorption. The RSM model predicts that for 98.0% DCF removal, the ideal conditions are pH 6, an adsorbent dose of 0.5 g L-1, and a contact time of 60 min with an initial adsorbate concentration of 25 mg L-1 at 303 K. The maximum capacity deduced from the Langmuir model was 75.9 mg g-1 for pristine water chestnut shell biochar (pWCBC) and 122.3 mg g-1 for magnetically modified nano-Fe2O3 biochar (mWCBC). Under equilibrium conditions, the Langmuir model was the best-suited model compared to the Temkin and Freundlich models. The adsorption data in this investigation efficiently fitted the pseudo-second-order model, emphasizing that chemisorption or ion exchange processes may be involved in the process. The WCBC demonstrated recyclability after 10 cycles of repeated adsorption and desorption of DCF. A combined coagulation adsorption process removed COD, NH3-N, NO3-, PO43-, and DCF by 92.50%, 86.41%, 77.57%, 84.54%, and 97.25%, respectively. This study therefore shows that coagulation followed by adsorption onto biochar can be a cost-effective substitute for conventional pharmaceutical wastewater treatment.

Synthesis of sustainable mesoporous sulfur-doped biobased carbon with superior performance sodium diclofenac removal: Kinetic, equilibrium, thermodynamic and mechanism

Over the last years, the strategy of employing inevitable organic waste and residue streams to produce valuable and greener materials for a wide range of applications has been proven an efficient and suitable approach. In this research, sulfur-doped porous biochar was produced through a single-step pyrolysis of birch waste tree in the presence of zinc chloride as chemical activator. The sulfur doping process led to a remarkable impact on the biochar structure. Moreover, it was shown that sulfur doping also had an important impact on sodium diclofenac (S-DCF) removal from aqueous solutions due to the introduction of S-functionalities on biochar surface. The adsorption experiments suggested that General and Liu models offered the best fit for the kinetic and equilibrium studies, respectively. The results showed that the kinetic was faster for the S-doped biochar while the maximum adsorption capacity values at 318 K were 564 mg g-1 (non-doped) and 693 mg g-1 (S-doped); highlighting the better affinity of S-doped biochar for the S-DCF molecule compared to non-doped biochar. The thermodynamic parameters (ΔH0, ΔS0, ΔG0) suggested that the S-DCF removal on both adsorbents was spontaneous, favourable, and endothermic.

Ketorolac removal through photoelectrocatalysis using TiO2 nanotubes in water system

Ketorolac, a highly persistent NSAID of environmental concern, was significantly removed from water (80% removal) through photoelectrocatalysis where titanium dioxide nanotubes prepared by Ti foil electrochemical anodization at 30 V were used as photoanodes. Fifteen milligrams per liter of ketorolac solutions in a 0.05 M Na2SO4 aqueous medium was subjected to irradiation from a 365-nm light with an intensity of 1 mWcm-2 and under an applied potential of 1.3 V (vs. Hg/Hg2SO4/sat.K2SO4) at pH 6.0. When each process (photo and electrocatalysis) was carried out separately, less than 20% drug removal was achieved as monitored through UV-vis spectrophotometry. Through scavenging experiments, direct oxidation on the photogenerated holes and oxidation by hydroxyl radical formation were found to play a key role on ketorolac's degradation. Chemical oxygen demand (COD) analyses also showed a significant COD decreased (68%) since the initial COD value was 31.3 mg O2/L and the final COD value was 10.1 mg O2/L. A 48% mineralization was also achieved, as shown by total organic carbon (TOC) analyses. These results showed that electrodes based on titania nanotubes are a promising alternative material for simultaneous photocatalytic and electrocatalytic processes in water remediation.

Self-cleaning cellulose acetate/crystalline nanocellulose/polyvinylidene fluoride/Mg0.975Ni0.025SiO3membrane for removal of diclofenac sodium and methylene blue dye in water

Recalcitrant pollutants present in wastewater, without an effective treatment, have several effects on aquatic ecosystems and human health due to their chemical structure and persistence. Therefore, it is crucial the development of efficient technologies to eliminate such pollutants in water. Nano-photocatalysts are considered a promising technology for water remediation; however, one common drawback is the difficulty of recovering it after water processing. One effective strategy to overcome such problem is its immobilization into substrates such as polymeric membranes. In this study, a polymeric membrane with embedded Mg0.975Ni0.025SiO3is proposed to remove model pollutants diclofenac sodium and methylene blue dye by synergetic adsorption and photocatalytic processes. Mg0.975Ni0.025SiO3was synthesized by the combustion method. The matrix polymeric blend consisting of a blend of cellulose acetate, crystalline nanocellulose and polyvinylidene fluoride was obtained by the phase inversion method. The composite membranes were characterized by FTIR, x-ray diffraction, and scanning electron microscopy. With pollutant solutions at pH 7, the pollutant adsorption capacity of the membranes reached up to 30% and 45% removal efficiencies for diclofenac sodium and methylene blue, respectively. Under simulated solar irradiation photocatalytic removal performances of 70% for diclofenac sodium pH 7, and of 97% for methylene blue dye at pH 13, were reached. The membrane photocatalytic activity allows the membrane to avoid pollutant accumulation on its surface, given a self-cleaning property that allows the reuse of at least three cycles under sunlight simulator irradiation. These results suggest the high potential of photocatalytic membranes using suitable and economical materials such as cellulosic compounds and magnesium silicates for water remediation.

Is cavitation a truly sensible choice for intensifying photocatalytic oxidation processes? - Implications on phenol degradation using ZnO photocatalysts

Phenols are recalcitrant compounds that constitute the majority of organic contaminants in industrial wastewaters. Their removal at large scales require a combination of various processes to reach the desired discharge quality. An extensive body of work has already been published in the area of phenol removal from wastewater, however none of them have focussed on a truly 'sensible' approach for coupling advanced oxidation processes (AOPs). Rather, a higher removal efficiency was targeted by unduly complicating the process by combining multiple AOPs. The most influential AOP as the primary method typically driven by the nature of the pollutant should form the basis for a hybrid AOP followed by a complementary AOP to intensify the oxidation process. This strategy is lacking in current literature. We address this knowledge gap directly by systematically identifying the best hybrid process for ZnO mediated photocatalysis of phenol. Either a cavitation mediated pre-treatment of ZnO or cavitation-photocatalysis-peroxide based hybrid AOP was investigated. While the pre-treatment approach led to >25% increase in phenol oxidation compared to bare ZnO photocatalysis, the hydrodynamic cavitation-photocatalysis-peroxide based system was found to have a cavitational yield 5 times higher than its acoustic cavitation counterpart. A new phenomenon known as the 'pseudo staggered effect' was also observed and established in hydrodynamic cavitation mediated photocatalysis-peroxide hybrid process for the first time. While we demonstrated that cavitation is a truly 'sensible' choice to enhance photocatalysis, the nature of the pollutant under investigation must always be the key driver when designing such hybrid AOPs.

Numerical Investigation of the Cavitation Characteristics in Venturi Tubes: The Role of Converging and Diverging Sections

Cavitation is a typical physical process that has shown to be highly valuable in the wastewater treatment field. This study aims to investigate the effects of the converging and diverging sections of a Venturi tube on the cavitation flow field. Multiphase flows in tubes are presented using the mixture model and the standard k-ε model. And the Schnerr and Sauer cavitation model is employed to simulate the vapor–liquid phase transition process. Both grid independence and the numerical method’s feasibility were validated before the research. The results showed that the influence of the divergence section length on Venturi cavitation characteristics depends on the provided pressure conditions. As the pressure increases, shorter divergence sections result in more significant cavitation effects. The length of the convergence section displays various cavitation behaviors under different pressure situations. A small contraction section length can achieve better cavitation effects in high-pressure applications, whereas the opposite is true in low-pressure cases. Within the scope of this study, it was observed that the Venturi tube with a divergent section of 14 Lt and a convergent one of 2.4 Lt provided enhanced cavitation performance when subjected to inlet pressures ranging from 0.8 to 1.2 MPa. Our findings indicate that the selection of converging and diverging section lengths in Venturi tubes should consider the corresponding operational pressure conditions, which provides valuable guidance and engineering significance in the research and development of Venturi cavitation devices in hydraulic engineering.

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.

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.

TLC–Densitometry for Determination of Omeprazole in Simple and Combined Pharmaceutical Preparations

TLC combined with densitometry was used and chromatographic conditions developed to separate omeprazole and diclofenac sodium from their potential impurities. The development of the TLC–densitometry method is based on the elaboration of new chromatographic conditions allowing for the simultaneous determination of omeprazole and diclofenac sodium in a pharmaceutical preparation. Identification and quantification of omeprazole in simple and combined (with diclofenac) pharmaceutical preparations was performed on silica gel 60F₂₅₄ using one mobile phase: chloroform–methanol–ammonia (36:4:0.60, v/v). Diclofenac sodium was determined in the presence of omeprazole after 2D separation on silica gel using two mobile phases of the first phase of chloroform–methanol–ammonia (36:4:0.60, v/v) and the second mobile phase cyclohexane–chloroform–methanol–glacial acetic acid (6:3:0.5:0.5 v/v). The developed method is simple, economical, specific, precise, accurate, sensitive, and robust, with a good range of linearity for the quantification of omeprazole and diclofenac sodium. TLC in combination with densitometry can be used as an effective analytical tool for quality control and quantitative determination of omeprazole in simple and combined pharmaceutical preparations containing diclofenac sodium. TLC in combination with densitometry can be recommended for the analysis of omeprazole and diclofenac sodium in the absence of HPLC or spectrophotometer in the laboratory or to confirm results obtained with other analytical techniques.

Pilot-scale hybrid system combining hydrodynamic cavitation and sedimentation for the decolorization of industrial inks and printing ink wastewater

A pilot-scale hydrodynamic cavitation (HC) system followed by sedimentation (SED) was used for the decolorization of 5 industrial-grade inks, a fluid containing a mixture of the five industrial grade inks (MIX) and printing ink wastewater (PIW). The pilot scale HC reactor combines a Venturi tube with a 31 holes orifice plate accommodated in the vena-contracta of Venturi. The study aimed to define optimal operating conditions, i.e., hydrogen peroxide concentration (H₂O₂), pH and combined HC/SED treatment time, to achieve decolorization and reduce HC operation time. Under the optimal conditions at the proposed HC/SED system, color removal reached 92%, 91%, 90%,98% and 90%, for black, red, yellow, cyan, and green ink respectively (at pH 8 without H₂O₂ addition). In the same system, color removal for PIW was 92%, whereas for MIX decolorization reached more than 90% for all the wavelengths in the selected spectrum 300-700 nm at HC/SED system (at pH 8 and 1 g L^-1 hydrogen peroxide). The suspended particles were characterized by measurements of the particle size distribution and of the respective zeta potential. The equivalent cavitation yields, electric energy consumption and operating costs were calculated. The present work's results suggested that HC combined with sedimentation has a great potential for real applications and is superior compared to other technologies (i.e., H₂O₂ alone, sedimentation alone or even HC with or without H₂O).

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.

Recent advances in structural modifications of photo-catalysts for organic pollutants degradation - A comprehensive review

Over the last few years, industrial and anthropogenic activities have increased the presence of organic pollutants such as dyes, herbicides, pesticides, analgesics, and antibiotics in the water that adversely affect human health and the environment worldwide. Photocatalytic treatment is considered a promising, economical, effective, and sustainable process that utilizes light energy to degrade the pollutants in water. However, certain drawbacks like rapid recombination and low migration capability of photogenerated electrons and holes have restricted the use of photo-catalysts in industries. Hence, despite the abundance of lab-scale research, the technology is still not much commercialized in the mainstream. Several structural modifications in the photo-catalysts have been adopted to enhance the pollutant degradation performance to overcome the same. In this context, the present review article outlines the different advanced heterostructures synthesized to date for improved degradation of three major organic pollutants: antibiotics, dyes, and pesticides. Moreover, the article also emphasizes the degradation kinetics of photo-catalysts and the publication trend in the past decade along with the roadblocks preventing the transfer of technology from the laboratory to industry and new age photo-catalysts for the profitable implications in industrial sectors.

Treatment of real industrial-grade dye solutions and printing ink wastewater using a novel pilot-scale hydrodynamic cavitation reactor

A novel pilot-scale hydrodynamic cavitation (HC) reactor was used to decolorize industrial-grade dye solutions and printing ink wastewater (PIW). The effect of the orifice plate geometry (1 hole plate of 1 mm and 2 mm in diameter, 31 holes of 1 mm and 2 mm in diameter, 62 holes of 1 mm and 2 mm in diameter), inlet pressure (4, 5 bar), initial dye concentration (0.3 and 0.6 OD), and the synergistic effect of HC and hydrogen peroxide concentration (0.0, 0.5, 1.0, 2.0 g/L) were investigated. The results showed that the highest color removal was obtained using 31 holes orifice plate of 2 mm holes' diameter, at 4 bar inlet pressure. Furthermore, although HC could not degrade completely all the industrial-grade dyes, efficiency was enhanced in the presence of H₂O₂. The optimum concentration of hydrogen peroxide was 1.0 g/L regardless of the initial concentration of the dyes studied. Under optimum operating conditions, color removal reached up to 68% for black, 39% for red, 43% for yellow, 55% for green, and 51% for cyan dye, while color removal in the PIW reached only 15%. The black dye solution presented almost 100% COD removal, while 38%, 25%, 67%, and 78% COD removal values were obtained for the red, yellow, cyan and green dyes, respectively. 55% COD removal was recorded from the PIW. Concerning cavitation yields, black, red, yellow, green, cyan dye yields reached 2.5E(-7), 1.1E(-7), 1.5E(-7), 2.0E(-7), 1.7E(-7) OD⋅L/J, respectively, while PIW yield was 6.3E(-8) OD⋅L/J. The present study demonstrates that HC combined with green oxidants such as hydrogen peroxide could be an alternative treatment approach for real industrial wastewater streams. However, a combination with a post-treatment method should be applied to maximize both color and COD removal.

Carbamazepine and Diclofenac Removal Double Treatment: Oxidation and Adsorption

In the present research, the effect of two hybrid treatments, ozone followed by powdered activated carbon (PAC) or PAC followed by ozone (O₃), was studied for the removal of two drugs present in water: diclofenac and carbamazepine. In the study, two initial concentrations of each of the contaminants, 0.7 mg L^-1 and 1.8 mg L^-1, were used. Different doses of PAC between 4-20 mg L^-1 were studied as variables, as well as different doses of O₃ between 0.056-0.280 mg L^-1. The evolution of the concentration of each contaminant over time was evaluated. From the results obtained, it was concluded that the combined treatment with ozone followed by PAC reduces between 50% and 75% the time required to achieve 90% removal of diclofenac when compared with the time required when only activated carbon was used. In the case of carbamazepine, the time required was 97% less. For carbamazepine, to achieve reduction percentages of up to 90%, O₃ treatment followed by PAC acted faster than PAC followed by O₃. In the case of diclofenac, PAC treatment followed by O₃ was faster to reach concentrations of up to 90%. However, to reach yields below 80%, O₃ treatment followed by PAC was more efficient.

Application of advanced materials in sonophotocatalytic processes for the remediation of environmental pollutants

Significant advances in various industrial processes have resulted in the discharge of toxic pollutants into the environment. Consequently, it is essential to develop efficient wastewater treatment processes to reduce water contamination and increase recycling/reuse. Photocatalytic degradation is considered as an efficient method for the degradation of toxic pollutants in industrial wastewater. However, the use of photocatalytic approaches is associated with numerous limitations, such as lengthy procedures and the necessity for large amounts of catalysts. Hence, it has been proposed that photocatalysis could be combined with other techniques, including sonolysis, electrochemical, photothermal, microwave, ultrafiltration, and biological reactor. The integration of photocatalysis with sonolysis could be remarkably beneficial for environmental remediation. The combination of these processes has the advantages of using uniformly dispersed catalysts, regeneration of the catalyst surface, improved mass transfer, enhanced surface area due to smaller catalyst particles, and production of more active radicals for the degradation of organic pollutants. In this review, an overview on employing sonophotocatalysis for the removal of toxic organic contaminants from aqueous environments is provided. Additionally, the limitations of photocatalysis alone and the fundamental sonophotocatalytic mechanistic pathways are discussed. The importance of utilizing advanced two-dimensional (2D) semiconductor materials in sonophotocatalysis and the common synthetic approaches for the preparation of 2D materials are also highlighted. Lastly, the review provides comprehensive insights into different materials based on metal oxides, chalcogenides, graphene, and metal organic frameworks (MOFs), which are involved in sonophotocatalytic processes employed for the remediation of environmental pollutants.

Photocatalytic degradation of diclofenac using TiO2-CdS heterojunction catalysts under visible light irradiation

The present study reports the photocatalytic degradation of analgesic drug diclofenac using the hydrothermally prepared TiO₂-CdS heterojunction catalyst. The results suggest that the prepared catalysts exhibited excellent photocatalytic activity under visible light irradiation. The photodegradation kinetics were well fitted to the pseudo-first-order reaction. The apparent reaction rate constant for TC5 catalyst in the diclofenac degradation was 0.02316 min^-1. Mineralisation of diclofenac using TC5 photocatalyst was around 86% within 4 h of irradiation time. The operating parameters such as optimal catalyst dosage, apparent solution pH and the effect of initial diclofenac concentration were also studied using the TC5 catalyst. The role of active species in the degradation mechanism was elucidated and it was found that the hydroxyl radical is the main active species in the diclofenac degradation mechanism. The charge transfer between heterojunction catalysts is facilitated by direct Z-scheme heterojunction structure. The coupled photocatalysts also showed good photochemical stability and reusability over five successive reaction cycles. The tentative degradation pathway has been devised based on LC-MS peaks, and it is found that only m/z 224, m/z 178 and m/z 124 were persisted at the end of the reaction.

Degradation of Antibiotics in Wastewater: New Advances in Cavitational Treatments

Over the past few decades, antibiotics have been considered emerging pollutants due to their persistence in aquatic ecosystems. Even at low concentrations, these pollutants contribute to the phenomenon of antibiotic resistance, while their degradation is still a longstanding challenge for wastewater treatment. In the present literature survey, we review the recent advances in synergistic techniques for antibiotic degradation in wastewater that combine either ultrasound (US) or hydrodynamic cavitation (HC) and oxidative, photo-catalytic, and enzymatic strategies. The degradation of sulfadiazine by HC/persulfate (PS)/H2O2/α-Fe2O3, US/PS/Fe0, and sono-photocatalysis with MgO@CNT nanocomposites processes; the degradation of tetracycline by US/H2O2/Fe3O4, US/O3/goethite, and HC/photocatalysis with TiO2 (P25) sono-photocatalysis with rGO/CdWO4 protocols; and the degradation of amoxicillin by US/Oxone®/Co2+ are discussed. In general, a higher efficiency of antibiotics removal and a faster structure degradation rate are reported under US or HC conditions as compared with the corresponding silent conditions. However, the removal of ciprofloxacin hydrochloride reached only 51% with US-assisted laccase-catalysis, though it was higher than those using US or enzymatic treatment alone. Moreover, a COD removal higher than 85% in several effluents of the pharmaceutical industry (500-7500 mg/L COD) was achieved by the US/O3/CuO process.

Electrochemical oxidation of diclofenac on CNT and M/CNT modified electrodes

Successful electrochemical oxidation of diclofenac, a non-steroidal anti-inflammatory drug considered as an emerging pollutant, was investigated on CNT, Pt/CNT and Ru/CNT modified electrodes based on Carbon Toray in aqueous media.

Experimental and numerical studies on the cavitation in an advanced rotational hydrodynamic cavitation reactor for water treatment

Hydrodynamic cavitation (HC) has emerged as one of the most potential technologies for industrial-scale water treatment. The advanced rotational hydrodynamic cavitation reactors (ARHCRs) that appeared recently have shown their high effectiveness and economical efficiency compared with conventional devices. For the interaction-type ARHCRs where cavitation is generated from the interaction between the cavitation generation units (CGUs) located on the rotor and the stator, their flow field, cavitation generation mechanism, and interaction process are still not well defined. The present study experimentally and numerically investigated the cavitation flow characteristics in a representative interaction-type ARHCR which has been proposed in the past. The cavitation generation mechanism and development process, which was categorized into "coinciding", "leaving", and "approaching" stages, were analyzed explicitly with experimental flow visualization and computational fluid dynamics (CFD) simulations. The changes in the cavitation pattern, area ratio, and sheet cavitation length showed high periodicity with a period of 0.5 ms/cycle at a rotational speed of 3,600 rpm in the flow visualization. The experimental and CFD results indicated that sheet cavitation can be generated on the downstream sides of both the moving and the static CGUs. The sheet cavitation was induced and continuously enlarged in the "leaving" and "approaching" stages and was crushed after the moving CGUs coincided with the static CGUs. In addition, vortex cavitation was formed in the vortex center of each CGU due to high-speed rotating fluid motion. The shape and size of the vortex cavitation were determined by the compression effect produced by the interaction. The findings of this work are important for the fundamental understanding, design, and application of the ARHCRs in water treatment.

Ti-pillared montmorillonite clay for adsorptive removal of amoxicillin, imipramine, diclofenac-sodium, and paracetamol from water

The adsorptive removal of natural montmorillonite (MMT) clay pillared with titanium oxide (Ti-PILC) was examined in this study to see the adsorptive remove of pharmaceutical compounds (PCs): amoxicillin (AMOX), imipramine (IMP), Diclofenac-Sodium (DIF-S), and paracetamol (PCM) from water under a batch-scale study. The post-intercalation changes in clay were investigated with various surface and structural analysis techniques. The results confirm an increase in the surface area, microporosity, and acidic sites (lewis acid) which improved and regulates Ti-PILC interactions with electron-rich PPCPs molecules. The FTIR bands for Si-OH and Al-OH show a shift in MMT, after pillaring, indicates the intercalation of Ti pillared in its interlayer space. The isotherms studies suggested the best fitting of Redlich Peterson models for all pharmaceutical adsorption data. The Langmuir adsorption (maximum) was recorded for Ti-PILC in the order: 82.68 (IMP) > 23.05 (DIF-S) > 20.83 (PCM) > 4.26 (AMOX) mg.g^-1 at a fixed adsorbent dose i.e. 0.1 g·L^-1. The PCs adsorption kinetics was also evaluated by Pseudo-first-, and second-order model and results showed the best curve fitting for all PCs. Results of regeneration studies showed that modified Ti-PILC could be a low-cost cleaner material for adsorption of pharmaceuticals from water.

The removal of bisphenols and other contaminants of emerging concern by hydrodynamic cavitation: From lab-scale to pilot-scale

The rapid growth in the variety and quantity of contaminants of emerging concern (CEC) in wastewater indicates the necessity for developing efficient and environmentally friendly methods for their removal. This study investigates the removal efficiency of 46 CEC, including 12 bisphenols, from wastewater using a lab and pilot-scale hydrodynamic cavitation generator alone and in combination with UV illumination (pilot-scale). During lab-scale cavitation, the highest removal efficiencies of bisphenols (15-63%) for this specific design of cavitator were obtained at a rotational frequency (v_cav) = 9500 rpm and time (t_cav) = 10 min. Temperature and the physicochemical properties (e.g. K_ow) of the studied compounds also had a significant effect on removal efficiency. At the pilot-scale, 11 CECs were quantifiable in the wastewater influent, and the generator operated at ν_cav = 2290 and 2700 rpm. The highest removal efficiencies (15-90%) were obtained at a lower ν_cav = 2290 rpm while neither an increase in ν_cav, t_cav or the presence of UV-C light increased the removal efficiency. A lower ν_cav also reduced the hydrodynamic power of the cavitator from 477 W to 377 W, resulting in reduced energy consumption. Overall, the results show the potential of hydrodynamic cavitation for a large-scale application as a pre-treatment technology and pave the way for future improvements in the design of cavitation reactors.

Photocatalytic degradation of model pharmaceutical pollutant by novel magnetic TiO2@ZnFe2O4/Pd nanocomposite with enhanced photocatalytic activity and stability under solar light irradiation

In the last decades, the use of magnetic nanocomposites as a catalyst was considered for removal of organic pollutants due to its easy separation. Therefore, initially, TiO₂@ZnFe₂O₄/Pd nanocomposite was prepared and then used in the photodegradation of diclofenac under direct solar irradiation in the batch and continuous systems. The structure, morphology and other specifications of produced nanocatalyst were determined via XRD, VSM, FESEM/EDX, FTIR, GTA, UV-Vis, Zeta potential, XPS and ICP-OES. The effective factors on diclofenac removal via nanophotocatalyst viz. pH, catalyst concentration, initial concentration of diclofenac, and flow rate and column length on diclofenac photodegradation were studied. Based on the results, the optimal rate for pH, catalyst concentration, and initial concentration of diclofenac was 4, 0.03 g/l and 10 mg/l respectively. Pd-coated TiO₂@ZnFe₂O₄ magnetic photocatalyst had higher photocatalytic activity in diclofenac photodegradation in relation to ZnFe₂O₄ and TiO₂@ZnFe₂O₄ under solar light irradiation. The findings showed that after five recycles, the photocatalytic efficiency did not show much reduction i.e. the removal efficiency from 86.1% in the first cycle reduced only to 71.38% in the last cycle. Likewise, in this study, with flow rate reduction and column length increase diclofenac degradation rate increased.

Sonophotocatalytic degradation of sodium diclofenac using low power ultrasound and micro sized TiO2

The nonsteroidal anti-inflammatory drug sodium diclofenac (DC) is an emerging water pollutant which resists conventional wastewater treatments. Here the sonophotocatalytic degradation of DC was carried out using micrometric TiO₂ (both pristine and Ag-decorated), UV-A irradiation and 20 kHz pulsed ultrasound. Sonophotocatalytic tests were compared with photolysis, sonolysis, sonophotolysis, sonocatalysis and photocatalysis data performed in the same conditions. A synergy index of over 2 was determined for tests with pristine TiO₂, while values close to 1.3 were observed for Ag-TiO₂. Reaction intermediates were studied by HPLC-MS, showing degradation mechanisms activated by hydroxyl radicals. Similar pathways were identified for photocatalytic and sonophotocatalytic tests, although the latter led to more oxidized compounds. Different reactor configurations (static and dynamic set ups) were studied. Sequential and simultaneous application of UV light and ultrasound led to similar performance. The role of water matrix was investigated using ultrapure and drinking water, showing marked detrimental effects of electrolytes on the DC degradation. Overall, the combined treatment proved more efficient than photocatalysis alone especially in demanding working conditions, like in drinking water matrices.

Adsorption, degradation, and mineralization of emerging pollutants (pharmaceuticals and agrochemicals) by nanostructures: a comprehensive review

This review discusses a fresh pool of research findings reported on the multiple roles played by metal-based, magnetic, graphene-type, chitosan-derived, and sonicated nanoparticles in the treatment of pharmaceutical- and agrochemical-contaminated waters. Some main points from this review are as follows: (i) there is an extensive number of nanoparticles with diverse physicochemical and morphological properties which have been synthesized and then assessed in their respective roles in the degradation and mineralization of many pharmaceuticals and agrochemicals, (ii) the exceptional removal efficiencies of graphene-based nanomaterials for different pharmaceuticals and agrochemicals molecules support arguably well a high potential of these nanomaterials for futuristic applications in remediating water pollution issues, (iii) the need for specific surface modifications and functionalization of parent nanostructures and the design of economically feasible production methods of such tunable nanomaterials tend to hinder their widespread applicability at this stage, (iv) supplementary research is also required to comprehensively elucidate the life cycle ecotoxicity characteristics and behaviors of each type of engineered nanostructures seeded for remediation of pharmaceuticals and agrochemicals in real contaminated media, and last but not the least, (v) real wastewaters are extremely complex in composition due to the mix of inorganic and organic species in different concentrations, and the presence of such mixed species have different radical scavenging effects on the sonocatalytic degradation and mineralization of pharmaceuticals and agrochemicals. Moreover, the formulation of viable full-scale implementation strategies and reactor configurations which can use multifunctional nanostructures for the effective remediation of pharmaceuticals and agrochemicals remains a major area of further research.

Zebrafish toxicity assessment of the photocatalysis-biodegradation of diclofenac using composites of TiO2 and activated carbon from Argania spinosa tree nutshells and Pseudomonas aeruginosa

The occurrence and persistence of pharmaceutical products (PPs) in the environment have recently been well-documented and are a major concern for public health. Their incidence in aquatic ecosystems is the result of their direct release without any prior treatment or insufficient wastewater treatment. Therefore, an efficient and safe posttreatment process for removing PPs must be developed. In this study, we focused on the ability of photocatalysis or combined photocatalysis and biodegradation to effectively and safely remove diclofenac (DCF) and its by-products from water. The heterogeneous photocatalysis system was based on bio-sourced activated carbon obtained from Argania spinosa tree nutshells and Degussa P25 titanium dioxide (ACP-TiO₂), and biodegradation involved Pseudomonas aeruginosa. Toxicity tests were conducted with zebrafish embryos to evaluate the applicability of the treatment processes. The results showed that photocatalytic treatment with 0.1 mg/L of ACP-TiO₂ 9% for 7.5 h is sufficient to eliminate DCF (50 mg L^-1) and its by-products from water. Low levels of malformation (< 20%) were detected in zebrafish embryos treated with photocatalyzed DCF solutions at 1, 5, and 7 mg L^-1 after 4 days of exposure. After 3 h of incubation, P. aeruginosa was found to reduce the toxicity of DCF (10 mg L^-1) photocatalyzed for 2 and 4 h. Additional studies should be conducted to elucidate the biodegradation mechanism.

Use of Ultrasound as an Advanced Oxidation Process for the Degradation of Emerging Pollutants in Water

Emerging pollutants are compounds of increased environmental importance and, as such there is interest among researchers in the evaluation of their presence, continuity and elimination in different environmental matrices. The present work reviews the available scientific data on the degradation of emerging pollutants, mainly pharmaceuticals, through ultrasound, as an advanced oxidation process (AOP). This study analyzes the influence of several parameters, such as the nature of the pollutant, the ultrasonic frequency, the electrical power, the pH, the constituents of the matrix and the temperature of the solution on the efficiency of this AOP through researches previously reported in the literature. Additionally, it informs on the application of the referred process alone and/or in combination with other AOPs focusing on the treatment of domestic and industrial wastewaters containing emerging pollutants, mainly pharmaceuticals, as well as on the economic costs associated with and the future perspectives that make ultrasound a possible candidate to solve the problem of water pollution by these emerging pollutants..

Controlled Hydrodynamic Cavitation: A Review of Recent Advances and Perspectives for Greener Processing

The 20th century has witnessed a remarkable enhancement in the demand for varieties of consumer products, ranging from food, pharmaceutical, cosmetics, to other industries. To enhance the quality of the product and to reduce the production cost, industries are gradually inclined towards greener processing technologies. Cavitation-based technologies are gaining interest among processing technologies due to their cost effectiveness in operation, minimization of toxic solvent usage, and ability to obtain superior processed products compared to conventional methods. Also, following the recent advancements, cavitation technology with large-scale processing applicability is only denoted to the hydrodynamic cavitation (HC)-based method. This review includes a general overview of hydrodynamic cavitation-based processing technologies and a detailed discussion regarding the process effectiveness. HC has demonstrated its usefulness in food processing, extraction of valuable products, biofuel synthesis, emulsification, and waste remediation, including broad-spectrum contaminants such as pharmaceuticals, bacteria, dyes, and organic pollutants of concern. Following the requirement of a specific process, HC has been implemented either alone or in combination with other process-intensifying steps, for example, catalyst, surfactant, ultraviolet (UV), hydrogen peroxide (H2O2), and ozone (O3), for better performance. The reactor set-up of HC includes orifice, slit venturi, rotor-stator, and sonolator type constrictions that initiate and control the formation of bubbles. Moreover, the future directions have also been pointed out with careful consideration of specific drawbacks.

TiO2@C core@shell nanocomposites: A single precursor synthesis of photocatalyst for efficient solar water treatment

This study reports the facile synthesis of highly photoactive TiO₂@C core@shell nanocomposites through a single alkoxide precursor. TiO₂ and carbon-based hybrid nanomaterials are popular photocatalysts owing to their abundance, low toxicity, and high stability, making them strong candidates for practical solar water-treatment applications. However, synthesis of such nanomaterials is often a multi-step process and requires careful control of the external carbon source for producing the desired morphology. In this regard, this study reports the synthesis of well-dispersed TiO₂@C nanocomposites without the need of an external carbon source. The resulting photocatalyst was employed for treatment of various water-borne pollutants including several dyes, pharmaceuticals, and pathogens. Rapid mineralization of pollutants could be achieved even with low amounts of catalyst, with the performance well exceeding that of pristine TiO₂ and P25 Degussa. Results indicate that incorporation of C increases visible-light absorption and greatly improves the separation of photogenerated charge carriers. Given the facile synthesis and the wide scope of operation, the proposed catalyst could be a significant step towards practical photocatalytic solar water-treatment.

Hydrodynamic cavitation degradation of Rhodamine B assisted by Fe3+-doped TiO2: Mechanisms, geometric and operation parameters

In this paper, a novel method, hydrodynamic cavitation (HC) combined with Fe³⁺-doped TiO₂, for the degradation of organic pollutants in aqueous solution is reported. The venturi tubes with different geometric parameters (size, shape and half divergent angle) are designed to obtain a strong HC effect. The structure, morphology and chemical composition of prepared Fe³⁺-doped TiO₂ as catalyst are characterized via using XRD, SEM, TEM, XPS, UV-vis DRS and PL methods. The effects of added TiO₂ (heat-treated at different temperatures for different times) and Fe³⁺-doped TiO₂ (with different mole ratios of Fe and Ti) on the HC catalytic degradation of RhB are discussed. The influences of operation parameters including inlet pressure, initial RhB concentration and operating temperature on the HC catalytic degradation of RhB are studied by Box-Behnken design (BBD) and response surface methodology (RSM). Under 3.0 bar inlet pressure for 10 mg/L initial concentration of RhB solution at 40 °C operating temperature in the presence of Fe³⁺-doped TiO₂ with 0.05:1.00 M ratio of Fe and Ti, the best HC degradation ratio can be obtained (91.11%). Furthermore, a possible mechanism of HC degradation of organic pollutants in the presence of Fe³⁺-doped TiO₂ is proposed. Perhaps, this study may provide a feasible method for a large-scale treatment of dye wastewater.

Investigation of ammonia stripping with a hydrodynamic cavitation reactor

Ammonia is a commonly used compound in the domestic and industrial fields. If ammonia found in wastewater after use is not treated, even at low concentrations it may cause toxic effects in the receiving environment. In this study, a hydrodynamic cavitation reactor (HDC) was designed with the aim of removing ammonia. The effect of parameters like different cavitation numbers, airflow, temperature and initial concentration on NH₃ removal was researched. The potential of hydrodynamic cavitation for removal of volatile gases, like NH₃, was assessed with the aid of two film theory mathematical equations. Experimental studies were performed at fixed pH = 11. Under the conditions of 0.12 cavitation number, 25 L/min airflow, 30 °C temperature and 2500 mg/L initial concentration, in 24 h 98.4% NH₃ removal efficiency was achieved. With the same experimental conditions without any air, the HDC reactor provided 89.5% NH₃ removal at the end of 24 h. The HDC reactor is very effective for the removal of volatile gases from wastewater and it was concluded that even in the absence of aeration, the desired NH₃ removal efficiency was provided.

Decomposition of pharmaceutical micropollutant - diclofenac by photocatalytic nanopowder mixtures in aqueous media: effect of optimization parameters, identification of intermediates and economic considerations

This study evaluates application of three different nanopowder mixtures for decomposition of diclofenac (DCF), one of frequently detected pharmaceutical in wastewater. Analyzed three photocatalytic mixtures ZnO/SnO₂, ZnO/TiO₂ and ZnO/In₂O₃ are for the first time used for diclofenac degradation. A set of experiments were performed in order to investigate influence of catalyst concentration (0.10-0.60 mg mL^-1), initial concentration of diclofenac (0.002-0.010 mg mL^-1) and pH value (5-9). The increase in the catalyst concentration leads to a decrease in the degradation rate constant, which is the most pronounced in the ZnO/TiO₂ and ranges from 0.47 (6) min^-1 to 0.25 (3) min^-1. The influence of pH on efficacy shows completely different effects: ZnO/In₂O₃ is most effective in alkaline environments, ZnO/TiO₂ in neutral environments, while ZnO/SnO₂ efficiency is good in both alkaline and acidic environments. Initial concentrations of diclofenac showed a complex effect on the degradation rate. The four dominant intermediates were detected by LC MS/MS technique. In case of all three nanomaterials, intensive degradation was achieved in first 30 minutes. The economical analysis of photocatalytic treatment was provided where the preparation of nanomaterials does not demand high costs and with the highest diclofenac concentration, total operation costs are the lowest (77.14 US$/kWh).

Intensification of diesel oxidative desulfurization via hydrodynamic cavitation

A Hydrodynamic Cavitation Assisted Oxidative Desulfurization (HCAOD) process was applied for treatment of diesel fuel feedstock using hydrogen peroxide and formic acid as the oxidant and catalyst, respectively. Investigation on the effect of main process variables including pressure drop (3-6 bar), time of treatment (10-30 min) and formic acid to oxidant molar ratio (n_A/n_O) (1-5), was performed through applying Response Surface Methodology (RSM) based on Box-Behnken design. Single and interactive effects of the parameters were recognized. A remarkable 95% extent of desulfurization at optimum conditions with HC pressure drop of 4.2 bar, acid to oxidant ratio (n_A/n_O) of 3.2 at 29 min was achieved. The results were also compared to an oxidation system without the aid of hydrodynamic cavitation. Accordingly, HCAOD can be considered as a promising treatment scheme for intensification of diesel oxidative desulfurization.

Modeling & simulation studies on batch anaerobic digestion of hydrodynamically cavitated tannery waste effluent for higher biogas yield

This study describes the efficacy of the pretreatment method of tannery waste effluent (TWE) by hydrodynamic cavitation (HC) prior to anaerobic digestion (AD) using a slit venturi cavitating device operated at 5 bar pressure for 2 h. The HC effect caused faster disintegration and solubilization of larger organic molecules into smaller ones, so that it could be easily digested by the microbial cells resulting in higher degradation rates, lower acclimatization time, higher COD reduction of the TWE and higher biogas generation. The biogas yield and % COD reduction was almost twice higher in HC treated TWE compared to raw TWE. Biogas yield of 68.57 mL/g volatile solids with 43.17% COD reduction was obtained during AD of HC treated TWE in 2 L bioreactor with 10% seed dosage. 'AD' Simulator developed in MATLAB represented the AD performance for both raw and HC treated TWE feed and predicted for concentrations of organic polymers, monomers, VFA and biogas produced, in which model parameter optimization was done by validations using methane production data from bioreactors. The AD simulator estimated higher hydrolysis rate constants for HC treated TWE than for raw TWE as observed in the experiments. Biogas production increased up to 7.8 and 11.8 folds for raw and HC treated TWE samples respectively by adding food waste to TWE feed with organic loading rate of 48 h. Cost estimations proved that cost of excess biogas produced by anaerobic digestion of HC treated TWE mixed with food waste, recovers the extra cost of HC pretreatment when compared to raw TWE alone, establishing HC as an effective pre-treatment tool prior to AD.

Preparation of a novel Z-scheme KTaO3/FeVO4/Bi2O3 nanocomposite for efficient sonocatalytic degradation of ceftriaxone sodium

In this work, a novel Z-scheme sonocatalyst, KTaO₃/FeVO₄/Bi₂O₃, is prepared via ultrasonic-assisted isoelectric point method. The prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The catalytic activity of Z-scheme KTaO₃/FeVO₄/Bi₂O₃ sonocatalyst is studied in degradation of ceftriaxone sodium under ultrasonic irradiation. In addition, the influences of ultrasonic irradiation time, scavengers and sonocatalyst used times on sonocatalytic degradation of ceftriaxone sodium are examined. Under the experimental conditions of 150 min ultrasonic irradiation time, 1.00 g/L KTaO₃/FeVO₄/Bi₂O₃ addition amount and 10.00 mg/L ceftriaxone sodium concentration, the sonocatalytic degradation ratio of ceftriaxone sodium achieves 81.30%. Finally, the possible sonocatalytic degradation mechanism of ceftriaxone sodium caused by Z-scheme KTaO₃/FeVO₄/Bi₂O₃ sonocatalyst is proposed. The enhanced sonocatalytic activity may be attributed to the fact that the FeVO₄ as a special conductive channel provides a strong driving force to transfer electrons through valence state changes of iron and vanadium, which accelerates electron transfer from conduction band (CB) of Bi₂O₃ to valence band (VB) of KTaO₃. Perhaps, the KTaO₃/FeVO₄/Bi₂O₃ composite is an excellent Z-scheme sonocatalyst which can be used to effectively degrade the organic pollutants in wastewater under ultrasonic irradiation.

Remoción de sulfuros presentes en el agua residual del proceso de curtido mediante cavitación hidrodinámica

El sulfuro presente en el agua residual de la industria del curtido de cueros proviene de la operación de pelambre (depilado de la piel) en concentraciones que afectan significativamente la calidad del agua del cuerpo receptor debido a la toxicidad del vertimiento produciendo la mortandad de flora y fauna, responsable de la presencia de olores desagradables en el cauce y la notable disminución del oxígeno disuelto en el agua del afluente. En la presente investigación, la remoción de sulfuro es evaluada empleando la técnica cavitación hidrodinámica (CH), un proceso de oxidación avanzada analizado desde diferentes parámetros de operación como pH inicial del agua residual y presión de entrada para un tiempo de reacción fijo de 90 minutos; parámetros de diseño fueron establecidos mediante el uso de dos prototipos, variando el número y diámetro de orificios en el punto de estrangulamiento con el objetivo de determinar las condiciones óptimas del reactor para el tratamiento de este tipo de contaminante en las aguas residuales. Se obtuvo una remoción máxima del 32,6 % de la concentración inicial de sulfuro sin aplicar algún tipo de catalizador o reactivo químico; de igual modo se realizó un análisis costobeneficio debido a la eficiencia de la tecnología aplicada en comparación con la energía requerida por el reactor empleado, donde se observa una disminución del 198 % del costo total del tratamiento actual. Finalmente, la cavitación hidrodinámica es una tecnología sustentable para la industria del curtido de cueros.