Research Of Landfill Leachate By Coagulation-Fenton-Soil Rapid Infiltration Treatment

With the development of urbanization in China,the number of domestic garbage generated by the city is increasing,and the quality of landfill leachate produced by landfills is complicated and harmful.In the existing landfill leachate treatment methods,the biochemical methods have the disadvantages of low bearing load and weak impact resistance,the high cost of operation and infrastructure.Nanofiltration also has a high cost due to the high loss rate of the membrane and is prone to clogging.In this years,the soil rapid infiltration treatment of landfill leachate is limited to the effect of removal of COD concentration.There are few reports on the removal of NH₃-N and the transformation between different forms of nitrogen.At the same time,there are few relevant references explaining the changes of dissolved organic matter during treatment and the micro-ecological changes before and after water intake.In this project,the landfill leachate is pretreated by coagulation a nd Fenton oxidation,and the pretreated leachate is further treated by two-stage soil rapid infiltration columns.Through the detection of water quality indicators under different process conditions,the operating conditions were optimized.The changes of pollutant concentration and enzyme activity in the system under different contaminant loading conditions were compared.The three-dimensional fluorescence spectroscopy was used to analyze the leachate's dissolved organic fluorescence characteristics.High-throughput sequencing technology was used to analyze the bacterial community within the system.Landfill leachate is treated with coagulation and Fenton before the treatment of siol filtration system to achieve the purpose of removing suspended particulates from leachate and improving biodegradability.Combined with the experimental results and actual conditions,when the pH is 8,the use of FeC l₃ dosage of 0.6g/L,polyacrylamide?PAM?dosage of 4mg/L is a better coagulation pretreatment conditions.In the Fenton process,the p H of 6,the FeSO₄·7H₂O dosage of 2.0 g/L,and the H₂O₂ dosage of 1.5 mL/L is mainly used in the pretreatment.During the process optimization,the FeSO₄·7H₂O dosage and the H₂O₂ dosage will be adjusted according to the process conditions.In experiments of optimize the process conditions,the effects of biodegradability,influent hydraulic loading,wet-dry cycle conditions were investigated by varying the influent B/C ratio,influent water volume and influent frequency.The experimental results show that in addition to the slightly lower COD and NH₃-N removal rates under high hydraulic loading conditions,the COD removal rates of the other three process conditions are all above 72%,and the NH3-N removal rate is over 96%.During the operation of the system,the nitrogen conversion process mainly stays in the nitrification stage of converting NH₃-N to NO₃-N.The concentration of NO₂-N increases in first stage and then decreases.When the B/C ratio is 0.20-0.35,the system performance is better than the B/C ratio of 0.10-0.20,water hydraulic loading of 0.11m³/m²·d is better than 0.23m³/m²·d,the wet-dry cycle of 24h is better than the cycle of 12h.The operating conditions of the follow-up experiments were:the influent B/C ratio was adjusted to 0.20-0.35,the influent hydraulic load was 0.11m3/m2d,and the influent water was once per day,and the wet-dry cycle was 24h.In the influent condition of high concentration load,the removal rate of COD and NH₃-N in the soil rapid infiltration system is not as high as that of low concentration load,the maximum load of COD and NH₃-N that could be degraded by two-stage soil rapid infiltration system was250 mg/L and 300 mg/L.At the same time,under the conditions of high concentration load,the soil rapid infiltration system showed about 5%of the removal rate of TN,while it did not show under low concentration load conditions.Under two loading conditions,catalase,urease,nitrate reductase and nitrite reductase in the infiltration system can maintain a certain activity,and the change trend of enzyme activity in the process is similar.There was no significant correlation between the concentration of pollutants and the four enzyme activities under the condition of low concentration load influent.There was a significant positive correlation between urease activities and TN concentration,and a significant negative correlation with nitrite reductase and the concentration of NO₂-N in the high load condition.The change of dissolved organic matter?DOM?components in landfil l leachate were analyzed by three-dimensional fluorescence spectroscopy.The DOM in the original landfill leachate is dominated by humic acids.The DOM after treatment of the first-stage infiltration column is mainly visible fulvic-like compounds,and there is also the presence of UV fulvic-like compounds.The fluorescence intensity of the two substances after the secondt-stage infiltration column treatment is enhanced.After treatment with two-stage infiltration column,the benzene ring structure of the effluent decreases,and the structure of the organic matter changes.The DOM in the effluent of the infiltration column contains more than one fluorogenic group of fulvic acid.High-throughput sequencing was used to analyze the bacterial communities in the soil rapid infiltration system.The number of bacterial communities in the lower layer of the percolation column was the most,and the diversity of the community was the most abundant.Bacterial community structure on the padding was divided into phylum of 46,class of 61,order of 100,famaily of 213 and genus of 673.The most abundant bacterial communities at each level were Proteobacteria of phylum,?-Proteobacteria of class,Bacillales of order,Bacillales of famaily,Exiguobacterium of genus.There are also many nitrification and denitrification bacterial communities that can promote nitrification and denitrification in the system.