Study On Treatment Of Leachate By Combined Coagulation-Flocculation And Different Fenton Oxidation Method

Landfill leachate was still difficult to satisfy the requirements of environmental protection standard about discharging after biological treatments. Thus, an effective treatment technology combined Coagulation-flocculation and different Fenton oxidation method of landfill leachate was investigated to emprove the treatment efficiencies. After anaerobia biological treatment, ammonium tripping was employed to attain COD concentration of 2.37×10³ mg/L and NH3-N concentration of 295.7 mg/L, respectively.Subsequently, flocculation process was undertaken to remove color,turbidity and COD using ferric sulphate, polyferric sulphate(PFS) and polyaluminium ferric chloride (PAFC). The results showed that PFS was superior to the other coagulants for the removal of color,turbidity and COD at 5 of pH value. The addition of organic macromolecule flocculate polyacrylamide(CPAM) was found to be effective for the removal of color,turbidity and COD. The optimal conditions of flocculation process obtained by orthogonal experiment were 5.2 of pH value, 9.1mmol/L of PFS and 5 mg/L of CPAM at 8 min. 75.6% of color removal rate and 93.6% of turbidity removal rate, as well as 56.7% of COD removal rate were attained in this condition.After flocculation treatment of landfill leachate, Photo/Fenton and US/Fenton process, were carried out to attain their optimal conditions. Color and COD removal efficiency of them were compared, and their degradation mechanisms were further investigated in optimal conditions. The results suggested that 99.1% color and 86.2% COD removal were achieved by using 5 mmol/L of Fe²⁺ and 570 mmol/L of H₂O₂ at pH 2.5 in 120 min in Photo/Fenton process. Under the optimal conditions, apparent kinetics equation of landfill leachate was V=-dP/dt=2.6×10^-8×P^1.92×F^1.79×E^1.67. For US/Fenton process, the optimal conditions of landfill leachate were ultrasonic frequency of 45 kHz, power input of 100 W, Fe²⁺ concentration of 5 mmol/L, H₂O₂ concentration of 570 mmol/L and pH value of 2.5. Under this condition, maximum color and COD removal of 99.1% and 83.4% were achieved in 90 min, and its apparent kinetics equation was V=-dP/dt= 1.0×10-⁷×P^0.86×F^2.34×E^0.87×H^0.82. A comparative study of them indicated that Photo/Fenton and US/Fenton attained more color and COD removal rate than Fenton process, and photo,ultrasonic has synergistic effect with Fenton reagent. Photo/Fenton process achieved maximum COD removal and the longest react time, while US/Fenton process attained minimum COD removal and the shortest react time.The UV-vis spectrum of landfill leachate reveals that UV-vis absorption peak of degradation product ranges from 210 nm to 220 nm regardless of their different degradation mechanisms, and high molecular mass compounds can be oxidized into biodegradable compounds or CO₂ and H₂O after Photo/Fenton and US/Fenton treatment.