Study On The Pretreatment Of Aged Landfill Leachate By Electrocatalytic Oxidation

With the increase of population and rapid economic growth,people’s consumption level is increasing day by day.The amount of garbage in our country is increasing at an average rate of 8%to 10%per year.Most of the domestic garbage is treated by sanitary landfill.There are many aged landfills with a landfill time of more than 10 years.The leachate produced contains high concentration of ammonia nitrogen and many refractory organics,which are directly treated by biological method It is very difficult and expensive to deal with.The purpose of this study is to explore the feasibility of electrocatalytic oxidation in the pretreatment of Landfill Leachate for the aged to reduce the difficulty of biochemical treatment.The main contents of the study are:to clarify the main components and contents of pollutants in the leachate,to explore the main factors affecting the removal of pollutants by electrocatalytic oxidation,the electrochemical performance of titanium based metal oxide electrode,pollutant removal mechanism and reaction kinetics,to optimize the reaction conditions,and to evaluate the electrocatalytic oxidation technology from both technical and economic aspects.The main conclusions are as follows:（1）The aged landfill leachate has high ammonia nitrogen content（concentration is about 2.60×10³ mg/L,accounting for more than 90%of total nitrogen）,high organic content(COD_cr≈5.20×10³ mg/L,TOC≈1.82×10³ mg/L,in which water-soluble humus accounts for about 65%of total dissolved organic carbon),and high conductivity of 4.24×10⁴μS/cm（the concentration of chloride ion and bicarbonate is about 5.89×10³ mg/L and 8.60×10³ mg/L respectively）,which is weakly alkaline（p H≈7.9）.（2）The higher the current density,the longer the reaction time,the better the pollutant removal effect,and the more the chloride ion loss.Compared with Ti/Pb O₂ and Ti/Sn O₂-Sb2O₅ electrodes,Ti/Ir O₂-Ru O₂ electrode has better chlorine evolution performance,stability,and ammonia nitrogen removal effect.Although low p H is beneficial to the oxidation of organic matters,it is not conducive to the circulation of chloride ions in the system,and chlorine gas is separated out seriously.There was no significant effect on the removal of pollutants by changing the chloride concentration in the range of 5500-8500 mg/L.（3）The removal of pollutants by electrocatalytic oxidation mainly depends on the active chlorine species with strong oxidizability generated in the reaction process.The ring breaking and chain breaking of macromolecular organics are the main characteristics of the initial stage of the reaction and the average reaction rate is relatively low.The removal rate of ammonia nitrogen accords with zero order reaction kinetics and is higher than that of organic matter.Under the condition of current density of 60 m A/cm²,plate spacing of 0.5 cm,and no adjustment of p H value and chloride ion concentration,the aged landfill leachate was treated to 4.5 h,the removal rate of ammonia nitrogen and chroma is close to 100%,the macromolecular organics are almost completely degraded,and the reaction time continues to be prolonged.The removal rate of total organic carbon is slow,and the removal rate stays at about 50%,and the loss of chloride ion and the content of polychlorinated compounds increase sharply.The reaction time should be set between 4 and 5 hours,which can not only reduce the main pollutants in the leachate and improve its biodegradability,but also avoid energy waste and increase the content of by-products.（4）By comparison,although the energy consumption cost of this technology is high,it has better pretreatment effect,can receive higher economic benefits,and has application value.