Study On The Impact Of Dry Concentrated Liquid Recharge On The Water Quality And Microbial Caommunity Structure Of Landfill

The secondary concentrated solution（also known as dry concentrated solution）will be produced when the concentrated solution of leachate is evaporated at low temperature,and most of them are treated by recharge of landfill.However,the dry concentrated solution is the concentrated product of concentrated solution,which contains a large number of inorganic salts and refractory organics.Whether its recharge affects the water quality and biodegradability of leachate,whether it changes the microbial community structure,function and activity of biochemical system,and whether it impacts the subsequent biochemical treatment system of landfill leachate are still unclear.In this paper,six groups of MSW simulation columns.The effects of dry concentrated liquid recirculation on leachate quality,heavy metal dissolution and release,and microbial community structure were systematically studied.This study provides guidance for the normal operation and scientific management of leachate treatment system.The main conclusions of this paper are as follows:（1）The analysis of the basic physical and chemical properties of leachate showed that the reinjection of dry concentrated liquid had a great influence on the water quality of the leachate.After the reinjection of dry concentrated liquid,the p H,NH₄⁺-N,TN and EC of the leachate increased significantly,and the chloride ion was accumulated in the leachate.The concentrations of COD,TOC and VFA in the leachate decreased,the concentration of BOD₅ in the leachate decreased significantly,and the biodegradability decreased significantly.The DOM and three-dimensional fluorescence spectrum analysis of the leachate showed that the degree of humification of the leachate increased after the reinjection of dry concentrated liquid,the structural degree of humic acid decreased,the degree of polymerization decreased,and the content of aromatic carbon,carboxyl,hydroxyl and ester substituents of humic acid increased.The contents of heavy metals in leachate were analyzed.The concentrations of Co,Cr and Ni in leachate increased after reinjection of dry concentrate,which accelerated the dissolution of some heavy metals in stabilized fly ash of landfill column.（2）The analysis of landfill solid samples showed that p H and EC of landfill solid waste increased significantly and OM degradation rate decreased after reinjection of dry concentrated liquid.The analysis of heavy metal content and morphology showed that reinjection of dry concentrated liquid had little effect on the total amount and morphology of heavy metals in landfill column.（3）The results of high-throughput determination of leachate showed that the recirculation of dry concentrate had a great impact on the microbial community of landfill column.After recirculation of dry concentrate,the diversity and richness of microbial community were significantly reduced,and the dominant bacteria were halophilic bacteria.RDA analysis showed that the microbial community structure in leachate after recirculation of dry concentrate was greatly affected by Cl^-、p H and EC,and the influence degree of environmental factors on the samples was Cl^->p H>EC>NH₄⁺-N>COD>VFAs>ORP>TOC.In summary,the difficulty of leachate treatment is increased after reinjection of dry concentrated liquid,which affects the stabilization process of solid waste in landfill column.The concentration of some heavy metals in leachate is increased,and the change of environmental factors makes the microbial community structure greatly impacted,the microbial diversity is decreased,and the abundance of salt-tolerant microorganisms is increased.