Determination of the ultrasonic effectiveness in advanced wastewater treatment
Biological treatment is the most commonly applied method for treatment of wastewaters. However, biological treatment can be inhibited by bacteriotoxic or persistent pollutants present in wastewater (Lifka et at., 2003). As a result, this technology may be incapable of reducing the levels of contaminants below which they are not considered as a potential threat to public health. Therefore, new technologies that offer significant improved levels of treatment or constituent reduction need to be tested and evaluated (Metcalf and Eddy, 2003). Advanced oxidation processes (AOPs) are used to oxidize organic constituents found in wastewater that are difficult to degrade biologically. AOPs typically involve the generation and use of hydroxyl free radical as a strong oxidant to destroy compounds (Metcalf and Eddy, 2003). Ultrasonic technology (as an AOP) has been used for water and wastewater treatment (Naffrechoux et at., 2000). Ultrasound (US) was defined as the sound of a frequency that is beyond human hearing above 16 kHz. The ultrasound energy which has been used in sonochemistry is in the distinct ranges of 16-1000 kHz i.e. power ultrasound (Zheng, 2004). Ultrasonic irradiation of aqueous solutions can result in the growth and collapse of gas bubbles (cavitation) so producing high transient temperatures and pressures, which leads to the formation of free radicals (°OH , °OOH) via thermal dissociation of water and oxygen.