Study On Pretreatment Of Mature Landitu Leach Ate By Electrochemical Oxidation Process

Sanitary landfill is nowadays the main process of the municipal solid wastes（MSW）treatment. Landfill leachate is a kind of organic wastewater producing during the course ofrubbish landfill, presenting significant variations in both volumetric flow and chemicalcomposition, it contains large amounts of organic pollutants, ammonia nitrogen, heavymetals and a serious imbalance in microbial nutrient elements ratio. If not properly treatedand safely disposed, landfill leachate could have adverse effects on the environment. As akind of effective method on refractory organic wastewater treatment, electrochemicaloxidation have attracted a great deal of attention basically due to its effectiveness, ease inoperate and control, and no or little secondary pollution.Proceeding from the reality problem on landfill leachate treatment by electrochemicaloxidation, aim to the characteristics of landfill leachate with high ammonia nitrogen andrefractory, a study on electrochemical oxidation process was carried out for treatingsimulate ammonia wastewater, simulate organic wastewater and actual landfill leachate. Theinfluence of several operation parameters on the ammonia and COD removal were analysed,such as electrode material, current density, Cl-concentration, pH value, interelectrode gapand so on. The dynamic kinetics and oxidation mechanism of ammonia electro-oxidationwere investigated. Energy consumption and current efficiency of leachate treatment byelectrochemical oxidation were analyzed, SEM images and XRD pattern of original andused Ti/RuO₂-IrO₂-TiO₂electrode were analyzed. The main results are as follows:Compare the electrochemical oxidation efficiency of simulated ammonia wastewater,simulated organic wastewater and actual leachate with different electrode material. Theresult showed that electrode material had insignificant influence on ammonia and CODremoval efficiency for different wastewater. As for simulated ammonia wastewater andleachate, the performance of the process by using Ti/RuO₂-IrO₂-TiO₂as an anode issuperior to that by using Ti/IrO₂-TaO₂-TiO₂and Ti/PbO₂, while the efficiency of Ti/PbO₂isthe best for simulated organic wastewater. Using Ti as a cathode and Ti/RuO₂-IrO₂-TiO₂as an anode, the direct oxidationefficiency of ammonia was not evidence, and indirect oxidation played a leading role. Thecurrent density and chloride ion concentration were the important influence factors forammonia electro-oxidation. The interelectrode gap and initial ammonia concentration hadlittle effect to ammonia removal. It was found that electrolysis was a little more efficientunder neutral to moderate alkaline conditions than acid one, because it is benefit for therecycle of Cl-â†'Cl₂â†'ClO-â†'Cl-under the moderate alkaline condition. While initialammonia concentration is about500mg/L, the optimal reaction condition was determined asfollows: Under the conditions with current density15mA/cm², chloride concentration4000mg/L, interelectrode gap2cm and initial pH neutral, ammonia removal rate reached99.5%after electrolysis for2hours. The positive ion such as Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺andanion NO₃^-, NO₂^-had little effect on ammonia electro-oxidation removal, CO32-hadsignificant effect, while SO₄^2-and PO₄^3-would block ammonia oxidation. During theelectrolysis process, nitrate and nitrite concentrations were very low, most ammonianitrogens were translated into N2. The concentrations of free chlorines and chloramineswere significantly affected by pH, trichloramine and free chlorines were mainly produced inthe reaction without pH controlling, while monochloramine was mainly produced in a stablealkalescene.The ammonia and COD removal rate increased with current density and Cl-concentration rising, it was benefit for leachate oxidation under the moderate alkalinecondition, whereas it remained almost unaffected by S/V and dilution multiple, butincreasing S/V could reduce the voltage, thus reduce the energy consumption. Under theconditions of current density30mA/cm², chloride concentration5000mg/L, pH8, andarea/volum17.8m²/m3,99.9%of the NH₃-N,49.1%of the COD and90%of the color in thelandfill leachate could be removed after electrolysis for6hours with a Ti/RuO₂-IrO₂-TiO₂anode, BOD₅/COD increased from0.1to0.25, the specific energy consumption of ammoniaand COD were91.8kW·h/kgNH₃-N and146.35kW·h/kgCOD.