| At present,the most commonly used advanced treatment technology of landfill leachate in China is the biological method-ultrafiltration-reverse osmosis membrane separation process.In the process of treatment,reverse osmosis concentrate will be produced,which accounts for 20%30%of the total landfill leachate.Therefore,in order to avoid the generation of reverse osmosis concentrate,aiming at the biochemical effluent of landfill leachate after ultrafiltration treatment,and at the same time,for the existing waste leachate reverse osmosis concentrate processing research has become a research emphasis.At present,the effect and efficiency of the existing methods are very limited.The ozonation method has been paid more and more attention by researchers because it is not limited by wastewater chroma,wastewater pH and other conditions,and it will not produce secondary pollution.However,it has the disadvantages of low utilization rate,weak mineralization and degradation effect on organic matters.Therefore,the combination of ozonation and other processes is widely used in the treatment of refractory wastewater.In this paper,the microbubble technology and catalytic ozonation were used to study the process of treating biologically-treated leachate by catalytic ozonation of active carbon?AC?;the mechanism of enhanced ozonation of the biologically-treated leachate by catalytic materials.On this basis,the ozonation treatment technology of reverse osmosis concentrate of landfill leachate was further studied,and the combination process of ozone for biochemical effluent and reverse osmosis effluent was investigated The removal effect of COD and chroma of the permeate concentrate and the improvement of its biodegradability,and the degradation mechanism of organic matters were studied.The main results of this paper are as follows:?1?The combination system of O3+AC was used to treat the biologically-treated leachate.When the dosage of activated carbon was 350g,the ozone concentration at the inlet was 60 g/m3,the ozone flow at the inlet was 3 L/min,the reaction temperature was25°C,and the reaction pressure was 0.1 MPa.In the O3+AC system,the COD removal rate of the biologically-treated leachate could reach 89.87%,and the final COD value of effluent could reach the national discharge standard?less than 100 mg/L?,the same strip the removal efficiency of COD was only 37.33%and 65.16%after AC and O3treatment.The mechanism of degradation of the biologically-treated leachate in the O3+AC system was studied by UV-vis and GC-MS,and the stability,deactivation mechanism and regeneration method of AC were studied.After 5 times of recycling,the catalytic activity of AC was still stable.A large number of organic pollutants adsorbed on the surface of activated carbon occupy the active sites on the surface of AC,resulting in its deactivation.The specific surface area and catalytic activity of AC after deactivation can be recovered by HCl acid leaching.?2?When the ozone concentration in the liquid phase increased to a stable level,the dissolved ozone concentration,the apparent mass transfer coefficient of ozone?KLa?and the·OH concentration in the liquid phase were 21 mg/L,0.7255 min-1 and 683?mol/L,respectively,which were 14%,51%and 60?mol/L higher than those in the alone O3 system.The effects of the operating parameters,such as ozone concentration,ozone flow rate,reactor pressure and liquid reaction temperature,on the mass transfer performance were investigated.The results show that the concentration of ozone and the production of hydroxyl radicals in the liquid phase increase with the increase of ozone concentration and flow rate.KLa has nothing to do with the concentration of ozone at the inlet,but increases with the increase of ozone flow rate at the inlet.The concentration of ozone,KLa and the production of hydroxyl radicals in the liquid phase are less affected by pressure.The temperature has a greater impact,and the concentration of ozone and KLa in the water decrease with the increase of temperature The amount of hydroxyl radicals increased with the increase of temperature.In addition,O3+SSWM system was used to treat the biologically-treated leachate.After 120 min of reaction,the removal efficiency of COD was about 10%higher than that of O3 system alone.?3?Three different combined processes of ozonation were used:1)O3+Ca?OH?2treatment,then O3+AC system treatment;2)Ca?OH?2 flocculation,then O3+AC system treatment;3)O3+AC treatment of landfill leachate reverse osmosis concentrate.The final removal efficiency of COD was 95.84%,92.88%and 87.62%respectively;the removal efficiency of concentrated solution chroma?CN?are 93.6%,91.84%and 84.95%respectively;BOD5/COD was 7.2,6.4 and 4.7 times higher than the original solution.Combined with the comprehensive consideration of operation cost,process 2 was the best process.The process parameters of process 2 were optimized,and the optimal amount of AC was determined to be 60 g/L.the COD value of the treated effluent could meet the national discharge standard.UV-vis,3D-EMM and GC-MS were used to analyze the degradation mechanism of organics in the concentration solution treated by process 2.The results showed that the humic acids in the concentration solution were greatly reduced,the aromatization degree was significantly reduced,and the heterocyclic macromolecules in the concentration solution were effectively removed. |
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