Study On The Combination Process Of Electrooxidation-electrocoagulation For The Advanced Treatment Of Bio-treated Landfill Leachate

With the rapid development of economy and society,resulting in the increase of municipal solid waste year by year.These waste is usually disposed in a sanitary landfill,which produces a large amount of landfill leachate.Landfill leachate contains various pollutants with high concentration and threats the environment seriously.Normally,A combination of biological treatment and membrane filtration is used to treat it.However,due to the high content of refractory pollutants and high salinity in the bio-treated landfill leachate（BTLL）,there are many difficulties such as serious membrane pollution,high treatment costs and secondary pollution.In order to effectively solve the above problems,we conducted the preliminary research using electrocoagulation（EC）and electrooxidation（EO）techniques to treat the BTLL,aiming at the efficient removal of organic matter,chroma,UV₂₅₄ and phosphorus.Firstly,the process performance of single EC and single EO to treat BTLL was investigated.The effects of different electrode combinations of iron-aluminum plates,plate spacing and current density were studied in the single EC process.In the single EO treatment using Ti/Ru O₂ mesh as anode and graphite plate as cathode,the effects of initial p H,current intensity,plate spacing and immersion depth were explored.The experimental results showed that the both processes displayed good treatment performance.EC had an excellent removal towards phosphate（>99%）.When the EC reaction was 1 h,the removal efficiency of COD and chroma reached 59.8%,85%,respectively,with Fe electrode under 0.9 cm plate spacing,5.5 A/m² current density.The removal efficiency of UV₂₅₄ was below 50%,whereas it reached67%via the EO treatment under 4 A of current intensity,0.9 cm plate spacing and 23.7 cm of immersion depth.At this time,COD and chroma could be reduced by 55.4%and 89.2%,indicating the effective degradation of organic matters in the BTLL via direct and/or indirect oxidation.Combined process of EO-EC for the treatment of BTLL was further investigated under continuous flow operation.Results showed that COD,TOC and chroma in EO effluent could be further reduced by subsequent EC.And the total treatment performance of combined process was stable.The average removal efficiency of COD,TOC,UV₂₅₄ and chroma arrived at 48.5%,54%,71.2%,96.2%,respectively.The chroma of final effluent was around 15,which met the emission standard in China.However,the removal of UV₂₅₄ of the electrocoagulation effluent was not significantly improved compared to the electrooxidation.The energy consumption cost of electrocoagulation and electrooxidation was 0.135 RMB/m³ and 3.385RMB/m³,respectively.The loss cost of iron plate was 1.08 RMB/m³.In addition to strong oxidizing properties,The EDS diagram showed that the metal ions could be turned into solid substances and thus removed at the EO cathode.Three-dimensional fluorescence spectra indicated that there was a large amount of humic-like acid and fulvic-like acid,microbial byproducts and aromatic amino acids in BTLL.After electro-oxidation treatment,the content of humic-like acid was significantly reduced.And the fluorescence intensity of aromatic amino acids had basically disappeared.Fulvic-like acid had been partially removed.The electrocoagulation process could remove a small amount of fulvic-like acid.The microbial by-products occupied the main fluorescence intensity of the effluent.GC/MS analysis showed the possible organic components in BTLL and their removal.In summary,the combined electrocoagulation-electrooxidation treatment could degrade most of the organic matter.