Decomposition Of Coking Wastewater By Ultrasonic Cavitation And Its Combined Technologies

Since the late of 1980's, the effectiveness of using ultrasonic technology to degrade organic pollutants of wastewater has caught the attention of research fellows worldwide concerned; as a result, intensive research work has been devoted to this approach. Nevertheless, most of the work to date has focused on the sonochemical degradation of single model organic pollutant with lower initial concentration in the simulated wastewater. By contrast, as for the treatment of the real wastewater of a coke plant, co-approach of combining ultrasonic cavitation with other technology was carried out, meanwhile, the degradation efficiency, mechanism, and reaction kinetics of the compounds, such as ammonia, nitrogen-bearing organic compounds, and CODcr-bearing organic compounds, were investigated in this thesis. The degradation efficiency, mechanism, pathway, and kinetics were investigated by taking phenol as the representative of the organic components in the coking wastewater. A combined approach of both ultrasonic cavitation and Fenton reagent was attempted. Particularly, by combining ultrasonic cavitation with oxic microbe, the degradation efficiency of CODcr-bearing organic compounds under various conditions was studied in detail so as to examine the degradability of the coke plant wastewater, which was regarded as a kind of wastewater of difficult-to-treat due to its higher initial concentration of organic compounds. And the explanation of the sonochemical decomposition of the organic pollutants in the wastewater was given by using a new water quality model. Catalysts was introduced to improve the degradation efficiency of CODcrbearing organic compounds in the ultrasonic process.To begin with, as demonstrated by the test results of single ultrasonic approach, ultrasonic cavitation has a stronger degradation effect on ammonia than on the rest nitrogen-bearing organic compounds. The initial pH value, the initial concentration of organic components, the presence of saturated gas, and the energy density of ultrasound consisted of the four key factors to affect the degradation efficiency. The sonochemical decomposition of ammonia and those containing nitrogen element took place via the reactions of thermal decomposition in cavitation bubbles. Consequently, nitrogen gas (Na), which would evaporate to air, was formed by the nitrogen elements coming from ammonia and those organic compounds containing nitrogen elements. The decomposition process follows pseudo second-order kinetics.Secondly, ultrasonic cavitation can also effectively degrade the CODcrbearing organic compounds of the coking wastewater. Again, the four key factors played a key rolein the process of degradation. The refractory substances such as naphthalene and pyridine were degraded considerably. Meanwhile, the concentration of phenol and cresols also fairly decreased. The mechanism was dominated by the reactions between CODCr-bearing organic compounds and -OH radicals of the bulk solution. While, thermal decomposition in cavitation bubbles or in the interfacial region (between the bubbles and bulk solution) played a less important role in the mechanism. The decomposition process is in line with the equation of pseudo first-order kinetics.Thirdly, tests of phenol solution have revealed that impacts of experimental parameters on phenol are as same as the impacts on CODCr of the coking wastewater. The mechanism of ultrasonic degradation of phenol is that -OH radicals produced by ultrasound in aqueous solution attack phenolic cycle at adjacent or para position of the hydroxyl on phenol so that phenol is changed into small organic molecules such as muconic acid, maleic acid and ethane diacid. These small organic molecules will be oxidized to form carbon dioxide and water by -OH radical eventually. According to the reaction pathway of the ultrasonic degradation of phenol, its reaction equation is in line with the equation of first-order kinetics. The mechanism of ultrasonic degradation of most hydrophilic organic compounds such as phenol, cresols in t...