Modeling of ultrasonic enhancement on membrane distillation (original) (raw)
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Separation and Purification Technology, 2021
This study investigates the efficiency of low-power ultrasound in the range of 3.5-30.0 W to improve permeate flux and alleviate membrane fouling in an air-gap membrane distillation (AGMD) system. Natural groundwater and reverse osmosis (RO) reject water were fed into the AGMD system on which fouling experiments were conducted with hydrophobic polyvinylidene fluoride (PVDF) membrane. After 35 h of AGMD system operation with groundwater and RO reject water, fouling caused the permeate flux to decrease by 30% and 40% respectively. Concentration polarization, intermediate pore blocking, and cake filtration appear to be the main reasons for flux decline with both feedwater types. Ultrasound application for a short period of 15 min resulted in flux improvement by as high as 400% and 250% for RO reject and groundwater, respectively. Modelling of the heat and mass transfers showed that the flux increase was mainly due to membrane permeability improvements under ultrasonic vibration. Fouling visualisation using Scanning Electron Microscopy revealed that ultrasound effectively removed membrane fouling without compromising the membrane's structure. Importantly, permeate flux improvements with targeted low-power ultrasound appears to be proportionally higher than those of high-power ultrasound applied to the whole system, on a flux improvement per ultrasound W/m 2 basis.
Acoustic field-assisted osmotic membrane distillation
Desalination, 2002
Osmotic membrane distillation (OMD) is a novel membrane process that facilitates the concentration of aqueous solutions under mild operating conditions. The main drawback of OMD, like any other membrane process, is relatively low flux. In the present work acoustic field has been applied for the enhancement of transmembrane flux. Acoustic field, using transducer, of the frequency 1.2 MHz was applied perpendicularly to the membrane. Encouraged by the initial results of reasonable enhancement in the transmembrane flux (by 20-30%), further experiments were carried out for 5 M NaCl/pure water, 5 M CaCl 2 /pure water, NaCl/sugarcane juice and CaCl 2 /sugarcane juice systems both in the presence and absence of acoustic field. It was observed that there was about 22-205% enhancement in transmembrane flux with the application of acoustic field. All the experiments have been carried out in a membrane cell using different hydrophobic membranes polytetrafluoroethylene and polypropylene). The effect of various parameters such as concentration (2, 3, 4, 5 M), stirring speed (0, 198, 250, 450 rpm) and temperature (40, 50, 60°C) was studied on transmembrane flux in the absence of acoustic field, and the effect of acoustic field was studied at the best conditions observed. PTFE and PP membrane fluxes for CaCl 2 were both higher in the case of sugarcane juice and water than those for NaCl and K 2 HPO 4 solutions. Results obtained from these experiments were correlated using a modified Nernst film model.
Ultrasonics, 2017
Membrane ultrafiltration is increasingly applied for wastewater treatment and reuse, even though membrane fouling still represents one of the main drawbacks of this technology. In the last years, innovative strategies for membrane fouling control have been developed, such as the combination of membrane processes with ultrasound (US). In present work, the application of membrane ultrafiltration and its combination with US were studied, evaluating the influence on the performance of the treatment and membrane fouling formation of two membrane fluxes, 75 and 150 L/m 2 h, along with two US frequencies, 35 and 150 kHz. The results observed showed that the combination of membrane ultrafiltration with US, respect to the filtration process alone, reduced membrane fouling rates to a greater extent at the higher membrane flux and lower US frequency applied, reaching a reduction of 57.33% at 150 L/m 2 h and 35 kHz. Furthermore, higher organic matter and turbidity removals were observed at higher frequency (130 kHz). The results obtained highlights the applicability of this combined process for the upgrading of membrane ultrafiltration and as an alternative option to conventional tertiary wastewater treatments.
Ultrasonic irradiation control of silica fouling during membrane distillation process
Desalination, 2016
• Ultrasonic irradiation was introduced into membrane distillation process. • Influence of ultrasonic irradiation on silica fouling control was investigated. • Calcium ion would destroy silica colloid stability and aggravate membrane fouling. • Ultrasonic irradiation can mitigate silica fouling and maintain permeate flux.
Ultrasonics sonochemistry, 2006
Ultrasound based on-line cleaning for membrane filtration of industrial wastewater was studied. An ultrasonic transducer was assembled in the membrane module in order to get an efficient cleaning of membranes in fouling conditions. The focus of the studies was on the effects of the ultrasound propagation direction and frequency as well as the transmembrane pressure. The more open the membrane was the easier the membrane became plugged by wastewater colloids, when the ultrasound propagation direction was from the feed flow side of the membrane. If the membrane was tight enough, the ultrasound irradiated from the feed side of the membrane increased the flux significantly. However, in the circumstances studied, the power intensity needed during filtration was so high that the membranes eroded gradually at some spots of the membrane surface. It was discovered that the ultrasonic field produced by the used transducers was uneven in pressurised conditions. On the other hand, the ultrasoun...
Direct contact ultrasound for fouling control and flux enhancement in air-gap membrane distillation
Ultrasonics Sonochemistry, 2019
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Chemical Engineering and Processing - Process Intensification, 2018
Highlights The performance of hollow and flat-sheet polyurethane (PU) membranes synthesized with different additives and solvent were evaluated with oil-in-water emulsion. The steady-state permeate flux and the rejection of oil in percentage (%) at three different modes was determined. Change in morphological properties of the membrane are found to have a significant effect on the permeate flow rate and oil removal. Ultrasonic in O/W emulsion ultrafiltration could be achieved using ultrasonic energy intermittently rather than continuously. Generation of cavitation, microjets and Brownian motion by the ultrasonic were the dominant mechanisms responsible for ultrafiltration.
2023
Despite their compact design and superior effluent quality, resulting from the smart integration of separation processes with biodegradation, the widespread adoption of membrane bioreactors is limited due to the persistent issue of membrane fouling. This mini review encapsulates research on using ultrasound-induced vibration to mitigate membrane fouling in domestic wastewater systems. It discusses the dual physical and chemical mechanisms behind the use of ultrasound and highlights its limitations. Moreover, it proposes several future research directions, including further examination of operating conditions such as ultrasound power and frequency, combining ultrasound with other cleaning strategies scaling up the process, and the need for long-term experiments, where additional emphasis must be given (i) to the influence of ultrasound irradiation on membrane integrity and efficiency and (ii) estimating the cost of sonochemical integration and operation Finally, it underscores the need for a holistic assessment that considers energy and environmental issues and discusses a proposed roadmap toward implementing ultrasound technology in membrane bioreactor systems.
The use of ultrasound to mitigate membrane fouling in desalination and water treatment
Desalination, 2018
Fouling is recognized as a serious challenge in reverse osmosis desalination and in different membrane-based separation technologies. Membrane fouling not only reduces the permeate flux and the membrane productivity but also significantly decreases the membrane lifespan, increases the energy and feed pressure requirement, and increases membrane maintenance and replacement costs. As a result, the consequences of membrane fouling have always stimulated research investigations into different fouling mitigation strategies. In this context, application of ultrasound is an effective technique that can be used as an external aid for both membrane fouling control and membrane cleaning. The purpose of this review paper is to provide an updated and comprehensive review of ultrasound as an effective tool for membrane flux enhancement and membrane cleaning. In addition to briefly discussing the mechanisms of membrane fouling, theories related to ultrasonic waves, acoustic cavitation, cavitational collapse, and ultrasoundinduced effects are addressed. The key challenges in industrial application of ultrasound for flux enhancement and membrane cleaning are also discussed.