Study On Treatment Of Landfill Leachate And Organic Pollutants By Ultrasonic Irradiation

In this dissertation, the recent research on the treatment of landfill leachate and persistent organic pollutants and ultrasound technology were reviewed at first. The research on the determination of organic pollutants in landfill leachate by gas chromatography-mass spectrometry was carried out. Then the research on the removal mechanism and kinetics of COD and ammonia nitrogen in landfill leachate by ultrasound irradiation was studied, and the sonolysis mechanism of o-DCB in solution was also studied. Meanwhile, the comparison of enhancement effect of pentachlorophenol sonolysis at 20 kHz by different dual-frequency ultrasonic irradiations was investigated.1)Results of the determination of organic pollutants in landfill leachate are summarized as follows:39 kinds of main organic pollutants in landfill leachate by GC-MS were identified. In the detected organic matters, 4-methyl-phenol has been confirmed to be cancer-boosting substance or assisting, and another two, dichloromethane and methylbenzene belong to the blacklist of environmental priority control pollutants in China.2)Results of the removal mechanism and kinetics of COD and ammonia nitrogen in landfill leachate by ultrasound irradiation are summarized as follows:①The removal mechanism and kinetics of COD in landfill leachate by ultrasound irradiationCOD removal efficiency increases with increased ultrasound power input. Decreased initial COD concentration makes for COD removal efficiency, but the COD removal gross is smaller than that of higher initial COD concentration. The effect of initial pH on COD removal is not obvious. Air aeration and the dosage of TiO2 can enhance COD removal efficiency. COD removal efficiency increases with dosage of NaCl, but overdoses may cause efficiency retardation.The main sonolysis of landfill leachate proceeds via reaction with·OH radicals, a thermal reaction also occurs, although its contribution is small. The kinetics mode of removal of COD from landfill leachate could be explained by the complexity of organic pollutant sonolysis and organic pollutants in landfill leachate and COD measurement based on K2Cr2O7 methods.②The removal mechanism and kinetics of ammonia nitrogen in landfill leachate by ultrasound irradiationAmmonia nitrogen removal efficiency increases with increased initial pH. Ammonia nitrogen removal efficiency increases gradually with extended reaction time, but increases little after 180min reaction. Increased ultrasound power input makes for ammonia nitrogen removal efficiency. Air aeration can enhance ammonia nitrogen removal efficiency.The mechanism of ammonia-nitrogen removal by ultrasound irradiation may mainly be that the ammonia molecules in leachate enter into the cavitation bubbles and transform into nitrogen molecules and hydrogen molecules via pyrolysis under instant high temperature and high pressure in the cavitation bubbles. The pseudo-first-order removal kinetics of ammonia nitrogen in landfill leachate by ultrasound irradiation was observed.3)Results of the removal of o-DCB in solution by ultrasound irradiation are summarized as follows:Removal efficiency of o-DCB increases little with increased ultrasound power input. Decreased initial o-DCB concentration makes for o-DCB removal efficiency, but the o-DCB removal gross is smaller than that of higher initial o-DCB concentration. The effect of initial pH on o-DCB removal is not obvious. Air aeration can enhance o-DCB removal efficiency. The o-DCB removal by ultrasound irradiation mainly dissociates by pyrolysis to CO2 and H2O under instant high temperature and high pressure in the cavitation bubbles. The pseudo-first-order removal kinetics of o-DCB by ultrasound irradiation was observed.4)Results of the degradation of pentachlorophenol in solution by dual-frequency ultrasound irradiation are summarized as follows:As to the actual power dissipated in the solution, different frequency ultrasound combined with 20kHz appears to be frequency sensitive. Pentachlorophenol degradation rates were different at mono-frequency ultrasound irradiation with the same actual dissipated power.Pentachlorophenol degradation rate at dual-frequency ultrasonic irradiation is the highest compared to mono-frequency ultrasonic systems. The combination of dual-frequency systems has synergistic effect and the enhancement effect of sonochemical degradation of pentachlorophenol at 20 kHz by dual-frequency systems appears to be remarkable frequency sensitive. The order of contribution to the enhancement effect of sonochemical degradation of pentachlorophenol at 20 kHz is as follows: 530kHz >800kHz>40 kHz >1040kHz.