Study On Treatment Of Leachate Membrane Concentrate With Coagulation-Catalytic Ozone Combined Process

With the promulgation and implementation of GB 16889-2008"Pollution Control Standards for Domestic Waste Landfill Sites",stricter regulations have been imposed on the discharge limits of landfill leachate.The membrane treatment method is often used as an advanced treatment process for landfill leachate because of its small footprint and good treatment effect.However,the application of membrane processing technology will produce a concentrated solution with high organic matter concentration,high heavy metal content,and extremely poor biodegradability,and its proper treatment has become a problem that restricts the application of membrane processing technology.In this study,the concentrated liquid produced after the treatment of the landfill leachate membrane of the Zhengzhou Waste Comprehensive Treatment Plant was taken as the research object,and the coagulation-ozone catalytic oxidation combined process was used for in-depth treatment.The change law of organic matter in concentrated liquid by combined process was explored,and the diatomite-loaded nano-Fe₃O₄heterogeneous ozone catalyst was prepared to explore its effectiveness in catalyzing ozone treatment of concentrated liquid.The results of the coagulation and precipitation test show that the four flocculants of polyaluminum chloride（PAC）,polyferric sulfate（PFS）,polyaluminum ferric chloride（PAFC）and polyaluminum ferric silicate（PSAF）can all pass the coagulation and precipitation Reduce the COD and UV₂₅₄values of the concentrate,but the PAC coagulation removal effect is better than the other three.The optimal treatment effect was obtained under the condition that the initial p H of the concentrate was 5.0 and the dosage of PAC was 1000 mg/L.The dosage of coagulant was 4 mg/L.At this time,the removal rates of COD and UV₂₅₄of the concentrate were:35.65%and 40.34%.Diatomite-loaded nano-Fe₃O₄heterogeneous ozone catalyst was prepared by co-precipitation method,and the catalyst was characterized by XRD,SEM-EDS,FTIR and BET analysis methods.The results showed that nano-Fe₃O₄particles were successfully loaded on diatomite The surface has increased dispersion,and the specific surface area and pore volume of the material have decreased before and after loading.The prepared diatomite-loaded nano-Fe₃O₄material still has a high specific surface area of 71.07 m²/g.The results of the ozone catalytic oxidation test show that the optimal treatment effect is obtained under the conditions that the initial p H of the concentrate is 7,the ozone volume flow rate is 1.0 L/min,the catalyst dosage is 0.8 g/L,and the reaction time is 90 min.The COD and UV₂₅₄removal rates of effluent were 67.8%and 86.3%,respectively.The kinetic analysis results show that the process of ozone-catalyzed oxidation degradation of organic matter in the concentrate is more in line with the pseudo-second-order reaction kinetics.The catalyst reuse test shows that after five times of repeated use,the catalyst can still maintain a removal rate of more than 60%of the concentrated liquid COD.The free radical quenching test verified that diatomite-loaded nano-Fe₃O₄can catalyze ozone to generate hydroxyl radicals,thereby oxidatively degrading organic matter in the concentrate.In this study,ultraviolet-visible absorption spectroscopy,gel chromatography,three-dimensional fluorescence spectroscopy,and gas chromatography-mass spectrometry were used to investigate the changes of organic matter in the concentrated process of the combined process.The results show that the combined process can reduce the concentration in the concentrated liquid.The degree of aromatic structuring of organic matter,substances with large molecular weights are converted into small molecular substances,and refractory organic substances such as fulvic acid and humic acid are decomposed into small molecule intermediate products without fluorescent properties.GC-MS results show that after the combined process,the hard-to-degrade heterocyclic organic compounds in the concentrate can be opened and degraded into alkane derivatives and other degradable substances,and the alkane organic compounds are mineralized into CO₂and H₂O to be removed.The results of biodegradability analysis showed that the BOD₅/COD value of the concentrate increased from 0.02 to 0.32,and the biodegradability of the effluent has been greatly improved.