The application of aqueous sonochemistry and supercritical water oxidation to environmental engineering
Abstract
A clean and safe environment is necessary for sustainable social and economic developments. Every year thousands of toxic chemicals are manufactured and released into the environment, and governments have stricter and stricter regulations. As a result, conventional methods sometimes cannot meet the requirements. Advanced oxidation, a group of innovative technologies utilizing hydroxyl free radical, is developed to meet the challenge. This research investigated two advanced oxidation technologies, namely aqueous sonochemistry and supercritical water oxidation. Both the mechanisms and plausibility to degrade aqueous pollutants in complex matrices were studied. The processes were further optimized via selecting of appropriate operative parameters, including sound frequency, intensity, and flow rate for sonochemistry, and temperature, pressure, and oxygen concentration for supercritical water oxidation. Aqueous sonochemistry demonstrated high degradation rates and effective dehalogenation for polychlorinated biphenyls (PCBs), trichloroacetonitrile, chloropicrin and bromobenzene even in complex matrices involving multiple pollutants, various impurities and high COD loads. Analysis of products and intermediates confirmed that free-radical attack and pyrolysis were the major mechanisms. 358 kHz was the most efficient frequency for all compounds studied. Higher sound intensity and faster flow also benefited sonication. Organic solids decelerated sonication when the targeted compound adsorbed strongly on the solids, but dissolved solids and inorganic solids had minimal effect on sonicaiton. Supercritical water oxidation rapidly destroyed nitrobenzene. Greater than 90% of organic N and 67% of organic C was transformed into inorganic species with high selectivity towards N 2 and CO2 when nitrobenzene was decomposed. Complete mineralization was achieved at 600°C, 346 atm and 160 s.
Degree
Ph.D.
Advisors
Hua, Purdue University.
Subject Area
Environmental engineering|Environmental science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.