•Effects of CGU arrangement on ARHCR performance are studied by CFD.•The “simplified flow field” strategy was utilized.•Lower intersection angle and number of rows are benefit to performance.•Proper ...radial and circumferential offsets and radial spacing are advisable.•This work may provide a reference value to the design of ARHCRs.
Hydrodynamic cavitation (HC) is widely considered a promising process intensification technology. The novel advanced rotational hydrodynamic cavitation reactors (ARHCRs), with considerably higher performance compared with traditional devices, have gained increasing attention of academic and industrial communities. The cavitation generation unit (CGU), located on the rotor and/or stator of an ARHCR, is utilized to generate cavitation and consequently, its geometrical structure is vital for the performance. The present work studied, for the first time, the effect of the arrangement of CGU on the performance of a representative ARHCR by employing computational fluid dynamics based on the “simplified flow field” strategy. The effect of CGU arrangement, which was neglected in the past, was evaluated: radial offset distance (c), intersection angle (ω), number of rows (N), circumferential offset angle (γ), and radial spacing (r). The results indicate that the CGU, with an arrangement of a low ω and moderate c, N, γ, and r, performed the highest cavitation efficiency. The corresponding reasons were analyzed by combining the flow field and cavitation pattern. Moreover, the results also exposed a weakness of the “simplified flow field” strategy which may induce the unfavorable “sidewall effect” and cause false high-pressure region. The findings of this work may provide a reference value to the design of ARHCRs.
•Effective approach to disintegrate WAS using a rotor-stator type HCR is performed.•Sludge disintegration performance of a rotor-stator type HCR is evaluated.•Using thermal energy significantly ...increases sludge-disintegration performance.•Inlet pressure does not affect particle decomposition below certain rotational speed.
The sludge disintegration performance of a rotor-stator type hydrodynamic cavitation reactor (HCR) was experimentally investigated. First, the cavitation-generation mechanism was revealed using flow visualization and thermal performance was evaluated. To determine the effects of cavitation (including thermal energy) and shear stress on sludge disintegration, the performance of the HCR with and without the dimples and temperature control was analyzed. Finally, the effects of the operating conditions on the sludge disintegration performance were evaluated via a full factorial design of varying inlet pressures and rotational speeds. The main assessment factors for the sludge disintegration performance were analyzed such as particle decomposition and solubilization performance. The results indicated that when dimples were present and there was no temperature control, the reduction of sludge particles increased by 50%–80%. Additionally, the disintegration performance increased with the rotational speed and was minimized at the highest inlet pressure.
Biodiesel, with its nature of clean, biodegradability, and renewability, is an ideal substitute for fossil diesel. This critical review focuses on the advances in process intensification of biodiesel ...production by the emerging hydrodynamic cavitation (HC) technology. The recent progress in HC reactors and HC-assisted biodiesel production are summarized and discussed. Several key operating factors (i.e., reactor structure, cavitation intensity, temperature, molar ratio of alcohol to oil, catalyst, and duration) and the economic feasibility are analyzed. It is found that HC can effectively enhance acid- and alkali-catalyzed production processes by using various edible and non-edible oils (e.g., waste cooking oil) as feedstocks, and have economic practicability for industrialization. HC can achieve as high as over 99% yields in a short time, and the quality of the high-purity products meets EN 14214 and ASTM D6751 standards. Although the process simulation and life cycle cost analysis (LCCA) validated that the economics of HC process is far superior to that of conventional mechanical stirring at large scales, the experimental research at pilot or industrial scales is absent, and the amplification effect of both the reactor and process is unclear. Moreover, the investigations on the cavitation flow mechanism, structural optimization and design of HCRs, and feasibility (e.g., life cycle analysis (LCA), LCCA, and LCA-LCCA), have to be focused on in the future. At last, the strengths, weaknesses, opportunities, and threats (SWOT) of the HC process are evaluated by a SWOT matrix, which may hopefully provide some inspiration for the future development of this novel technology.
Display omitted
•High yield/conversion can be achieved by HC from edible and non-edible oils.•Rotational-type reactors demonstrate considerably high effectiveness and economics.•Continuous HC process is found to be available on laboratory scales.•LCCA indicates the cost of industrial-scale HC process is reasonable.•Feasibility of HC process is comprehensively assessed by a SWOT matrix.
Display omitted
•High synergism between AOPs and hydrodynamic cavitation.•Significant lowering of treatment costs.•Hybrid technologies for water and wastewater treatment.•Effective activation of ...oxidants for radicals formation.•Sustainable solutions for environmental protection.
High-performance water treatment systems based on cavitational processes have received an increasing interest of scientific community in the past few decades. Numerous studies indicated the advantageous application of hydrodynamic cavitation as an alternative, reagent-free treatment method of various pollutants in water. Both approaches were proved as an effective method to achieve mineralization of many organic contaminants as well as a disinfection method, which is able to eliminate pathogenic microorganisms. This makes cavitation-based methods a promising candidate implemented in a post-treatment stage of water treatment facilities. Nowadays, hybrid methods based on combination of cavitation with advanced oxidation processes (AOPs), possessing enhanced oxidation capacity were proposed. Compared to the individual utilization of cavitation and AOPs (e.g., O3, H2O2, Fenton’s process), hybrid processes are capable to degrade even highly persistent contaminants and shorten the operation time reducing the overall consumption of energy and oxidants. The improved performance of hybrid methods is attributed to the synergistic effect occurring between integrated technologies, which is expressed by the synergistic index. In this paper, recent reports focusing on coupling of cavitation and AOPs were reviewed to reveal major principles and mechanisms governing the synergistic effect. The review discusses the effect of process parameters (oxidant type, pH, hydraulic and ultrasonic properties, Kow) on the oxidation effectiveness. Comparative analysis was provided in order to highlight the advantages and limits laying behind the discussed methods. The analysis of the economic feasibility was performed to assess the potential applicability of hybrid techniques in large-scale wastewater treatment.
Hydrodynamic cavitation (HC) coupled with persulfate (PS)-based that resulted in the synergistic degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated marine sediments. The effects ...of HC injection pressure and ΣPAH: PS on the rate and extent of PAH degradation were studied in the pressure range of 0.5–2.0 bar, PS concentration rage of 2 × 10−4 to 2 × 10−2 M or ΣPAH: PS of 1:10–1000, and reaction time of 20–60 min. A pseudo-first-order rate law fitted PAHs removal kinetics well. The degradation rate constant increased with injection pressure, reaching the maximum level at 0.5 bar, then decreased at injection pressure became greater than 0.5 bar. The results showed that PAH removal was 84% by the combined HC and PS process, whereas, HC alone only achieved a 43% removal of PAHs in marine sediments under the optimal inlet pressure of 0.5 bar at PS concentration of 2 × 10−2 M in 60 min. The HC‒PS system effectively removed PH, PY, FLU, BaA, and CH at 91, 99, 91, 84, and 90%, respectively. The maximum removal of 6-, 5-, 4-, 3-, and 2-ring PAHs was 89, 87, 84, 76, and 34%, respectively. Major reactive oxygen species (ROSs), namely, SO4−• and HO•, were responsible for PAHs degradation. Results clearly highlighted the feasibility of HC−PS system for the clean-up of PAHs-laden sediments in particular and other recalcitrant organic contaminants in general.
Display omitted
•Hydrodynamic cavitation (HC) enhanced persulfate (PS) activation.•Hydrodynamic cavitation decreased the particle size of sediment materials.•HC−PS system effectively degraded polycyclic aromatic hydrocarbons (PAHs).•SO4−.• and HO• were major ROS responsible for PAH degradation.
Hydrodynamic cavitation enables activation of persulfate to generate reactive oxygen species, namely, SO4−• and HO• radicals and effectively degrade PAHs in marine sediment.
Display omitted
•Overview of recent work based on the application of HC for wastewater treatment.•Discussed the factors affecting HC efficiency.•The detailed optimization parameters of HC reactors ...are provided.•Guidelines on optimum conditions for both individual and combined HC processes.•Pertinent proposals on the research trends and directions of HC.
As one of the advanced oxidation processes, the cavitation-based process has become a promising technology for treating industrial effluents due to the advantages of cost-effectiveness in operation, higher energy efficiencies, and large-scale operation. In hydrodynamic cavitation (HC), cavities are generated as a result of local pressure drops caused by various constrictors or by mechanical rotation of the vortex diode and other rotating-type devices. The study on the influence of various geometric parameters of different kinds of HC reactors and the operation conditions is popular among researchers. In the present work, we systematically introduced the formation of HC and the mechanism of degradation of pollutants by HC. Further, for various cavitating devices, the influence of various geometrical and operating parameters affecting the cavitation conditions was discussed in detail. Overviews of earlier work based on the different types of HC reactors including venturi, orifice plate, rotating-type HC devices, and vortex diode were elaborated. Moreover, a detailed summary of HC-based hybrid technologies employed in recent work was presented to better show the synergetic index of different processes. Some recommendations for future work have been proposed.
Display omitted
•Hydrodynamic cavitation is effective in PS and PMS activation.•SO4•− and HO• radicals were predominant reactive species for BTEX degradation.•The inhibitory effect of inorganic ...anions on BTEX degradation ranked Cl− < SO42− < CO32–.•Surprising synergism of PMS and Cl− increased the degradation by formation of Cl-based radical species.•Degradation pathways of BTEX were proposed by intermediates identified by HPLC-DAD.
Hydrodynamic cavitation (HC) is an emerging technology gaining interest in water treatment for use in elimination of a wide range of organic pollutants. The energy released during cavitation phenomenon has number of applications and, particularly, it can be utilized for activation of persulfate (PS) and peroxymonosulfate (PMS). In the present study, hybrid techniques: HC combined with persulfates – HC-PS and HC-PMS were tested for the degradation of BTEX in water. Studies on the effect of initial PS and PMS concentration showed that a molar ratio of the oxidant to BTEX equal to 5 is favorable for both cases. Thus, in 240 min HC-PS-5 process allowed to degrade 91.51%, 95.50%, 94.65%, 94.95% of benzene, toluene, ethylbenzene and o-xylene, respectively, while 90.85%, 94.50%, 94.36%, 93.07% of those compounds were degraded by HC-PMS-5. BTEX degradation pathway was proposed for HC-PS-5 and HC-PMS-5 processes relying on the identification of the main reaction intermediates using liquid chromatography coupled with UV diode array detector (HPLC-UV-DAD). Benzyl alcohol, phenol, benzoic acid, benzaldehyde and o-cresol were the main intermediates of BTEX degradation, which multistep pathway involved H-abstraction, OH addition and dealkylation in route to mineralization. At final time of treatment primary and secondary pollutants were effectively degraded. In terms of kinetics, BTEX degradation followed the pseudo-first-order reaction model and the degradation kinetics were faster in HC-PMS-5 system than in HC-PS-5. Surprisingly, the presence of chloride ions (Cl−) in HC-PMS-5 improved the degradation efficiency of alkylated benzene derivatives indicating a synergistic effect of Cl− with SO4•− radicals.
Advanced oxidation processes (AOPs) have been developed to decompose toxic pollutants to protect the aquatic environment. AOP has been considered an alternative treatment method for wastewater ...treatment. Bromine is present in natural waters posing toxic effects on human health and hence, its removal from drinking water sources is necessary. Of the many techniques advanced oxidation is covered in this review. This review systematically examines literature published from 1997 to April 2024, sourced from Scopus, PubMed, Science Direct, and Web of Science databases, focusing on the efficacy of AOPs for pollutant removal from aqueous solutions containing bromide ions to investigate the impact of bromide ions on AOPs. Data and information extracted from each article eligible for inclusion in the review include the type of AOP, type of pollutants, and removal efficiency of AOP under the presence and absence of bromide ion. Of the 1784 documents screened, 90 studies met inclusion criteria, providing insights into various AOPs, including UV/chlorine, UV/PS, UV/H2O2, UV/catalyst, and visible light/catalyst processes. The observed impact of bromide ion presence on the efficacy of AOP processes, alongside the AOP method under scrutiny, is contingent upon various factors such as the nature of the target pollutant, catalyst type, and bromide ion concentration. These considerations are crucial in selecting the best method for removing specific pollutants under defined conditions. Challenges were encountered during result analysis included variations in experimental setups, disparities in pollutant types and concentrations, and inconsistencies in reporting AOP performance metrics. Addressing these parameters in research reports will enhance the coherence and utility of subsequent systematic reviews.
Display omitted
•AOPs reveal the various mechanisms for radical production.•Brˉ ions affect the removal efficiency of pollutants by AOPs.•Brˉ effect is related to AOPs type, Brˉ concentration and nature of pollutants.•Promoting effect of Brˉ is due to formation of Br2.●ˉ, Br●, Br2●ˉ, and ●ClBrˉ radicals.
Display omitted
•Mass transfer and oxidant utilization are two key issues in SO4•− oxidation.•Hydrodynamic cavitation (HC) is a green, effective solution to solve these issues.•Mass transfer was ...enhanced by HC-induced turbulence via Fe0 → Fe2+→Fe3+→Fe2+.•HC promotes persulfate (PS) utilization in HC-Fe0/PS system.•Mass spectra and theoretical calculations reveal tetracycline degradation pathways.
Mass transfer and oxidant utilization are perhaps two of the most critical issues in sulfate radical (SO4•−) based advanced oxidation technologies (AOTs) and their scaled-up implementation. In this study, we propose using hydrodynamic cavitation (HC), considered a green, effective method, to promote both mass transfer and oxidant utilization in zero-valent iron (Fe0) activated persulfate (PS) system. Whilst the BET surface area of Fe0 was increased by 8 times after HC treatment, concentration of Fe2+ derived from Fe0 oxidation is greatly increased for effective PS activation. The reappearance of Fe0 and Fe2+ after cavitation ensured a good reusability of the catalyst. Likewise, the impact of pH revealed that TC adsorption on catalyst at acidic pH favored its degradation compared with that at higher pH. With respect to oxidant utilization, it is observed that PS even at a high dosage (2.8 mM) was completed converted within 30 min in the HC-Fe0/PS system. According to SEM, TEM, and BET analysis, we conclude that the microjets induced by cavitation bubbles or direct abrasion by HC agitation have contributed to the removal of hydroxide/oxide layers on the Fe0 surface, thus reactivating its catalytic activity. Given these reasons, we observed up to 97.80% removal of Tetracycline (TC), the model pollutant, with a synergistic coefficient as high as 2.62. After confirming SO4•− as the most dominant reactive species, five degradation pathways of TC were proposed given the intermediate evidence from LC-MS/MS analysis and density functional theory (DFT) calculations. Results from this study could provide new insights into the role of HC on PS activation and shed light on the potential implementation of the SO4•−-based AOTs for scaled-up wastewater treatments.
PDF