Effect Of Fe²⁺ And Iron-carbon Micro-electrolysis Combined With Persulfate On Treatment Of Effluent From Biochemical Process Of Landfill Leachate

In the field of industrial wastewater treatment,landfill leachate is difficult to be treated as complex compositions,fluctuating water quality and refractory characteristics.Since the effluent quality of the biological treatment process treating landfill leachate cannot satisfy the requirements of Standard for Pollution Control on the Landfill Site of Municipal Solid Waste（GB16889-2008）,the biological treatment process combined with membrane process is commonly used for the treatment of landfill leachate both at home and abroad.The process has some drawbacks,such as high operation and maintenance costs,moreover,the resulting concentrated liquid cannot be treated by the proper technology,which can cause secondary pollution easily.The persulfate oxidation technology is used for the removal of refractory pollutants in water by generating SO₄^-·which has strong oxidizing property.In this study,the effluent of a laboratory-scale four-step feeding anoxic/aerobic（A/O）process treating landfill leachate generated from a domestic landfill in Xi’an City,Shaanxi Province was treated by Fe²⁺and iron-carbon micro-electrolysis process combined with persulfate,respectively.The effects of different factors on the pollutants removal of landfill leachate were studied,and the response surface methodology was employed for optimization of the optimum operation conditions.Moreover,the conversion of the organic matters in the treated landfill leachate was examined by UV spectroscopy,three-dimensional fluorescence,and GC-MS analysis.The following conclusions were drawn:（1）When Fe²⁺was used as the activating agent in the persulfate oxidation process treating the landfill leachate treated by the step-feeding process,the optimum dosages of persulfate(m(S₂O₈^2-:12COD))and Fe²⁺(n(Fe²⁺:S₂O₈^2-))were 0.50 and 2.5 respectively.The optimum pH value is 9.0.When the COD concentration,UV₂₅₄,UV₄₁₀,and NH₄⁺-N concentration of the effluent for the four-step feeding A/O biological contact oxidation process were 2063.39 mg/L,1.296 cm^-1,1.231 cm^-1,and 76.34 mg/L respectively,the COD concentration,UV₂₅₄,UV₄₁₀,and NH₄⁺-N concentration of effluent of the persulfate oxidation process were 647.95 mg/L,0.294 cm^-1,0.067 cm^-1,and 59.91 mg/L respectively while the reaction time was 3 h,correspondingly,the removal efficiencies of COD,UV₂₅₄,UV₄₁₀,and NH₄⁺-N were 68.60%,77.34%,94.57%and 21.53%,respectively.（2）When iron-carbon micro-electrolysis combined with persulfate oxidation process treating the landfill leachate treated by the step-feeding process,the optimum dosages of persulfate(m(S₂O₈^2-:12COD))and Fe-C were 1.00 and 200 g/L respectively.The optimum Fe/C mass ratio is 1:2.The optimum aeration is 0.4 L/min.The optimum pH value is 7.0.When the COD concentration,UV₂₅₄,UV₄₁₀,and NH₄⁺-N concentration of the effluent for the four-step feeding A/O biological contact oxidation process were 2103.83 mg/L,1.403 cm^-1,1.221 cm^-1,and 75.76 mg/L respectively,the COD concentration,UV₂₅₄,UV₄₁₀,and NH₄⁺-N concentration of effluent of the persulfate oxidation process were 374.97 mg/L,0.116 cm^-1,0.048 cm^-1,and52.57 mg/L respectively while the reaction time was 3 h,correspondingly,the removal efficiencies of COD,UV₂₅₄,UV₄₁₀,and NH₄⁺-N were 82.18%,91.71%,96.05%and 30.61%,respectively.（3）When optimizing the experimental conditions of iron-carbon micro-electrolysis combined with persulfate oxidation process using response surface methodology,the model fitting results obtained are significant and have good accuracy,which can effectively predict the removal effect of pollutants in wastewater.Using COD removal rate as the unique response value for prediction,when the dosages of persulfate and Fe-C were 35.60 g/L and 210.69g/L respectively,the initial pH value is 6.70,and the aeration rate is 0.44 L/min,the predicted COD removal rate is 85.99%,and the COD removal rate in the validation experiment is 83.45%.The model can effectively predict COD removal.Meanwhile,the treated effluent is colorless and transparent,with good sensory properties.（4）The continuous flow experiment results show that the iron-carbon micro-electrolysis combined with persulfate oxidation process has an initial COD removal rate of 79.97%when the HRT is 6.0 h and the filler is layered.With the extension of operating time,the COD removal rate gradually decreases.After continuous flow iron-carbon micro-electrolysis combined with persulfate oxidation process treatment,the molecular weight of dissolved organic matter in landfill leachate was reduced,the conjugation effect and the degree of condensation were weakened,and the degree of humification was reduced.Besides,most organic matters were completely mineralized.The large-molecule organic matters in the effluent of the step-feeding process were broken,and small-molecule organic matters were generated,which were refractory organics or unbiodegradable organics was well.