Study On The Reformation Of Middle-aged Landfill Leachate Treatment Process In Xinhua County

Xinhua County landfill was put into operation in January 2011,and its landfill leachate had been treated by a two-stage A/O+Fenton+biological aerated filter?BAF?combination process with a treatment scale of 100m³/d.As the garbage in the landfill matures,the landfill leachate has a high concentration of ammonia nitrogen,and the biodegradability was poor.The effluent of the original process had been unable to meet the discharge standard.In order to avoid the damage of landfill leachate to the surrounding environment,Xinhua landfill modified the original leachate treatment process.This paper mainly studied:determination of the transformation process of the leachate treatment system of Xinhua County landfill;productive operation effect and improvement measures of the leachate treatment system after the completion of the transformation.Firstly,through the investigation of the operation status of the original process,it was found that the main problem of the original process was that the biochemical system had a low processing efficiency.According to the mature characteristics of the landfill leachate and the existing site conditions,the transformation plan was determined to transform the original secondary settling tank into an biological aerated filter?MBR?membrane tank.Then it was combined with the original two-stage A/O process to form the MBR biochemical treatment system.At the same time,in order to ensure the stability of the effluent water quality,nanofiltration?NF?and reverse osmosis?RO?processes were added as advanced treatment.Secondly,after the completion of the transformation work,the productivity test of the combined process with MBR+NF+RO as the core showed that when the COD concentration in the influent water was 1800⁴470mg/L,the ammonia nitrogen concentration was 1612²480mg/L,the reflux ratio of nitrifying liquid was 300%,and the dissolved oxygen was 1.5².5mg/L.The removal rates of ammonia nitrogen were97.34%and 99.2%,the COD content in the effluent was less than 60mg/L,the ammonia nitrogen content was lower than 20mg/L,and the effluent quality was stable.All the indicators of effluent could meet the requirements of emission standards.Finally,the concentrated leachate from the nanofiltration and reverse osmosis equipment were treated by coagulation+oxidation process to optimize the leachate process.The results of the coagulation test indicated that:the polymeric ferric sulfate?PFS?phase was more suitable as the pretreatment for the landfill leachate concentrate of reforming process than the polyaluminum sulfate?PAS?and ferric chloride?FC?.When the pH value value was 5.5 and the dosage of PFS was 1200 mg/L,the optimal removal rates of COD,UV₂₅₄ and chromaticity were 52.1%,71.9%and 78.8%,respectively.After coagulation,H2O2 oxidation and Fenton oxidation method were carried out for advanced treatment.In the H₂O₂ oxidation method,with initial pH=4,100mmol/L hydrogen peroxide?H₂O₂?,and 150min reaction time,the optimal removal rates of COD and chromaticity were 35.6%and 62.3%,respectively,and the B/C value increased from 0.08 to 0.15.In Fenton oxidation method,with initial pH=4,100mmol/L hydrogen peroxide?H₂O₂?,[H₂O₂]:[Fe²⁺]molar ratio of 5:1,120min reaction time,and two steps dosing ratio of 3:1,the removal rates of COD and chromaticity in the concentration were 68.1%and 97.5%,respectively,and the B/C value increased from 0.08 to 0.36.In the case of the same optimum process parameters,the Fenton advanced oxidation process was 9%higher than that of the H2O2 oxidation process,but the COD removal effect could be increased by 85%and biodegradability could be improved by 75%.Therefore,the treatment plan of the concentrated leachate from the nanofiltration and reverse osmosis equipment was determined as follows:after the biodegradability was improved by the coagulation-Fenton advanced oxidation process,the concentrated leachate was then returned to the leachate biochemical system for treatment.