Can ultrasonic be used to degrade chemical pollutants in water?
Water pollution is one of the most urgent problems facing all countries in the world. China's water resources are not only facing shortage and water quality degradation, but also water environmental pollution is becoming more and more serious. In particular, the treatment of biodegradable organic pollutants has always been an important research topic in the field of environmental protection. Some separation methods, such as filtration, gas blowing, coagulation and adsorption, have been put into use, usually transferring pollutants from liquid phase to solid phase (such as activated carbon adsorption) or from liquid phase to gas phase (such as gas blowing). Organic pollutants have not been completely eliminated. As a new interdisciplinary subject, sonochemistry has made remarkable progress in water pollution treatment, especially in the treatment of refractory toxic organic pollutants in wastewater, showing its good application prospects.
The sonochemical degradation of a variety of chemical contaminants in aqueous solution has been investigated. Substrates such as chlorinated hydrocarbons, pesticides, phenols, explosives such as TNT, and esters are transformed into short-chain organic acids, CO2, and inorganic ions as the final products. Time scales of treatment in simple batch reactors over the frequency range of 20 to 500 Khz are reported to range from minutes to hours for complete degradation. Ultrasonic irradiation appears to be an effective method for the rapid destruction of organic contaminants in water because of localized high concentrations of oxidizing species such as hydroxyl radical and hydrogen peroxide in solution, high localized temperatures and pressures, and the formation of transient supercritical water.
The degradation of chemical compounds by acoustic cavitation is shown to involve three distinct pathways: 1) oxidation by hydroxyl radicals, 2) pyrolytic decomposition and 3) supercritical water oxidation. Detailed reaction mechanisms for the degradation of p-nitrophenol, carbon tetrachloride, parathion, p-nitrophenyl acetate and trinitrotoluene are presented.