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Membrane fouling is one of the major problems encountered during the application of membrane filtration. While power ultrasound has been used as a cleaning mechanism for many decades it has only recently been applied to membrane systems. This review provides an overview of the application of ultrasound in membrane filtration processes on both flux enhancement and membrane cleaning. The ultrasonic cleaning mechanisms, influence of operating parameters and effects of ultrasound on membrane and feed solutions have been examined. Most reports indicate that ultrasound increases membrane permeation by either reducing the depth of the foulant cake layer or by increasing turbulence in the concentration polarisation layer. There is ongoing debate as to whether these effects arise from acoustic cavitation or microstreaming. The main experimental parameters that alter the efficiency of ultrasonic treatment such as external pressure, power density, cross-flow velocity, frequency, temperature and feed properties have also been reviewed. There is a discrepancy in the literature regarding the integrity of membranes following sonication. Hence larger scale trials of ultrasonic application to different membrane modules over a number of years of operation are required to confirm that these impacts do not reduce the total membrane life. Furthermore, work is required to confirm the ultimate effect

This study evaluates the effectiveness of green and cool roofs as potential Urban Heat Island (UHI) mitigation strategies, and the impacts of these strategies on human thermal comfort during one of the most extreme heatwave events (27 th -30 th January 2009) in the city of Melbourne in southeast Australia. The Weather Research and Forecasting model coupled with the Single Layer Urban Canopy Model including different physical parameterization for various types of roofs (conventional, green and cool roofs) is used to investigate the impacts of green and cool roofs. Results show that the maximum roof surface UHI is reduced during the day by 1°C to 3.8°C by increasing green roof fractions from 30% to 90%, and by 2.2°C to 5.2°C by increasing the albedo of cool roofs from 0.50 to 0.85. Cool roofs are more efficient than the green roofs in reducing the UHI with maximum differences of up to 1.4°C. The reductions of the UHI vary linearly with the increasing green roof fractions, but slightly nonlinearly with the increasing albedo of cool roofs. The maximum reductions in wind speed are 1.25 m s -1 and 1.75 m s -1 with 90% green and cool roofs (albedo 0.85) respectively. While previous studies report that the advection of moist air from rural areas is a key mechanism, this study shows that this is not the case for the extreme heatwave event due to the very dry and warm conditions, and instead, convective rolls play a more important role. This study also shows that initial soil moisture for green roofs does not have a substantial impact on the UHI. Finally, green roofs improve human thermal comfort by reducing the Universal Thermal Comfort Index by up to 1.5°C and 5.7°C for pedestrian and roof surface levels respectively, and by 2.4°C and 8°C for cool roofs for the same levels.

Ultrafiltration (UF) of whey is a major membrane based process in the dairy industry. However, commercialization of this application has been limited by membrane fouling, which has a detrimental influence on the permeation rate. There are a number of different chemical and physical cleaning methods currently used for cleaning a fouled membrane. It has been suggested that the cleaning frequency and the severity of such cleaning procedures control the membrane lifetime. The development of an optimal cleaning strategy should therefore have a direct implication on the process economics. Recently, the use of ultrasound has attracted considerable interest as an alternative approach to the conventional methods. In the present study, we have studied the ultrasonic cleaning of polysulfone ultrafiltration membranes fouled with dairy whey solutions. The effects of a number of cleaning process parameters have been examined in the presence of ultrasound and results compared with the conventional operation. Experiments were conducted using a small single sheet membrane unit that was immersed totally within an ultrasonic bath. Results show that ultrasonic cleaning improves the cleaning efficiency under all experimental conditions. The ultrasonic effect is more significant in the absence of surfactant, but is less influenced by temperature and transmembrane pressure. Our results suggest that the ultrasonic energy acts primarily by increasing the turbulence within the cleaning solution.