Study On The Degradation Of Landfill Leachate By Ultrasound

Ultrasound has been successfully used in wastewater treatment and many environmental scientists pay more attention to the application and study at the ultrasonic degradation techniques. In this dissertation the recent research on the degradation of organic pollutants by ultrasound and associated technologies for the treatment of paper mill wastewater were reviewed. The flocculation and the ultrasonic irradiation techniques were used to degrade landfill leachate. The influence of the operation parameters on the efficiency of degradation were investigated, such as flocculation kind, pH, the amount of drug, sedimentation time, ultrasonic frequency, power intensity, duration time, ultrasonic reactor, different NH^3-N and aeration stripping. 1. Results of flocculation degradation of landfill leachate are summarized as follows: (1) The flocculation efficiency at landfill leachate by using containing Fe-salt is better than that by Al-salt. In the study, a best result could be achieved by using 2.4g/L PFS as flocculation. At the pH of 6.0, the decrease rate of COD and chromaticty did not change after 25 minutes of treatment. (2) Under the optimum condition, CODcr,SS and chromaticty all decreases, but NH^3-N did not. It is not helpful to the removal of COD by adding PAM. 2. After flocculated, ultrasonic degradation techniques were applied in the landfill leachate. Several results were obtained: (1) With the increasing of pH of the waste water, the removal of NH^3-N was to rised; In thi study, the landfill leachate were adjusted to pH of 11 before ultrasonic degradation. (2) The power and intensity of the ultrasound obviously affect on the removal of NH^3-N and the degradation effectiveness of the organic pollutants. The removal of NH^3-N rised with the increaseing of the power. But for landfill leachate, there is an optimal power at a certain intensity. In this study, the optimal power when frequency is 20KHz and 40KHz is 200W and 80W, respectively. (3) In this study: with the same type of ultrasonic reactor and the same acoustic power, the use of intensity of 20KHz is more efficient for the removal of NH3-N and degradation of organic pollutants than of 40KHz. (4) The ultrasonic degradation is a very simple and affective method for the treatment of landfill leachate with high concentration of ammonia nitrogen. After 3hr of ultrasonic treatment, the concentration of ammonia nitrogen was decreased from 1643mg/L to 225mg/L, a removal of NH3-N of more than 86 percent was achieved. (5) To combine with ultrasonic degradation technique, the time when combination technique applied could be significant shorten, as well as the efficience of aeration technique increased. After applying the combination technique for 1.5 hours, the removal of NH3-N is almost the same as that by just using ultrasonic treatment alone for 3 hours. The combination technique can also increase the degradation of organic pollutants in landfill leachate than that by just using ultrasonic method. (6) The mechanism study of the ultrasonice degradation shows that aeration purge plays a key role in the removal of NH3-N in landfill leachate. (7) Addition of 0.15mg/L n-C4H9OH in the landfill leachate, the organic compounds could not be degraded. This shows that the hydroxyl radical oxidation plays a key role in the degradation of organic compounds, because the C4H9OH destroys the hydroryl radicals.