Study On Treatment Of Compressed Leachate From Waste Transfer Station By Freezing-Melting Method

With the enforcement of waste classification,the waste classification and recovery system is becoming more and more perfect.When the waste is transported to the landfill or incineration plant,it will be compressed at the waste transfer station to produce waste compression leachate.This part of waste compression leachate has high pollutant concentration and cannot be discharged at will.At present,the traditional treatment methods still have shortcomings.For example,the high concentration of ammonia nitrogen in the waste compression leachate will lead to the inactivation of microorganisms in biological treatment;Physicochemical method can only be used as pretreatment and advanced treatment method of landfill leachate.The combined treatment process is complex and the cost is high.Because of its complex water quality and great difficulty in treatment,the effectiveness and stability of the treatment process should be considered,as well as the future economic rationality of the treatment process.Based on this,the research on the treatment of waste compression leachate in waste transfer station by freezing-melting method was carried out.The static progressive freezing device was used to explore the effect of different freezing temperature and different freezing time on the treatment of waste compression leachate by freezing method;the ice flakes at different freezing temperatures were observed by microscope to find out the mechanism of freezing method;the effects of melting temperature,ice crushing and ultrasound on the treatment of waste compression leachate by melting method were discussed.The conclusions were as follows:（1）The experimental study on the removal of pollutants from the waste compression leachate of waste transfer station by freezing method showed that with the increase of freezing time and the decrease of freezing temperature,the ice thickness and freezing rate gradually increased,and the freezing temperature and freezing time had a significant effect on the ice thickness of the waste compression leachate,and the correlation coefficient was0.92～0.93.The microscopic observation results showed that the pollutants existed in the ice in the form of salt bags,and some salt bags connected into channels,which was similar to the arrangement of pipes.（2）The experimental study on the removal of pollutants(COD_Cr,TOC,NH₃-N and TP)in the waste compression leachate of waste transfer station by freezing method showed that the removal rate of pollutants in the filtrate decreased gradually with the increase of freezing time and the decrease of freezing temperature.Under-5℃and 24h freezing conditions,the removal rate of pollutants was high,which showed that the removal rates of COD_Cr,TOC,NH₃-N and TP in simulated wastewater were 90.75%,92.25%,92.11%and 89.68%respectively,while the removal rates of COD_Cr,TOC,NH₃-N and TP in actual wastewater were 84.46%,76.69%,79.71%and 74.72%respectively.（3）The experimental study on the removal of pollutants(COD_Cr,TOC,NH₃-N,TP)in the waste compression leachate of waste transfer station by melting method showed that for the simulated and actual waste compression leachate,the removal rate of pollutants at the melting temperature of 20℃was greater than that at the melting temperature of 60℃;the removal rate of pollutants under the condition of broken ice melting was greater than that under the condition of whole ice melting.For simulated waste compression leachate,the removal rate of pollutants under ultrasonic melting condition was greater than that under natural melting condition.For actual waste compression leachate,the removal rate of pollutants under ultrasonic melting condition was less than that under natural melting condition.When the ice melting ratio was 30%,about 40%～70%of COD_Cr,TOC,NH₃-N and TP in the waste compression leachate under each melting condition were removed.（4）Under the same freezing conditions,the removal rate of pollutants in the simulated waste compression leachate was better than that in the actual waste compression leachate,perhaps because the composition of the actual waste compression leachate was complex,and the ice crystal structure may be different,and the ice crystal formed by the actual wastewater may grow mostly in dendritic ice,resulting in more pollutants trapped in the ice.Under the same melting conditions,the treatment effect of the melting method on the simulated waste compression leachate was better than that of the actual waste compression leachate.This may be because the composition of the actual water body was complex,and the combination degree of pollutants and ice structure also determined the difficulty of pollutants melting out of the ice.