| The increasing proportion of MSW incineration treatment has led to a large number of incineration fly ash.The MSW Landfill Pollution Control Standard(GB16889-2008)and the National Hazardous Waste List(2016 Edition)have provided convenient ways for the treatment and disposal of waste incineration fly ash: waste incineration fly ash after stabilization pretreatment If the content or leaching amount of harmful components(dioxin and heavy metals)meets the requirements of the standard limits,it can enter the MSW landfill for landfill disposal.However,in the actual disposal,due to the large amount of fly ash,the difficulty in site selection of the landfill,the delay in construction timing,and the irregular management,there is a phenomenon of stabilizing fly ash and MSW Co-landfill.In the Co-landfill environment,flying The dissolution characteristics of heavy metals in ash and the complexity of waste degradation mechanisms lack systematic research.This study studied the simulation of natural rainfall conditions by constructing three anaerobic landfill columns,HY(separate MSW),HA(chelating agent stabilized fly ash-MSW),and HP(phosphate stabilized fly ash-MSW).The dissolution of leachate water quality,heavy metals(Pb,Zn,Cu,Cd,Cr,Ni)and the evolution characteristics of microbial community structure in the following landfill columns,and the degradation characteristics of the "stabilized fly ash-residual waste" Co-landfill And the law of stabilization.The main findings are as follows:(1)During the whole Co-landfill process,Cd,Cu,Pb,Zn,Cr and Ni all showed a trend of increasing first and then decreasing.There was no significant difference in the concentration of Cu and Zn in the leachate of the three landfill columns.The landfill leachate Cd,Pb,Cr and Ni filled with stabilized fly ash were significantly higher than the landfill column packed with individual MSW.The Pb of the HY landfill column leachate exceeded the standard at 0～163d,and the HA landfill column Cd(20～122d)and Pb(0～163d)exceeded the standard.The HP landfill column Cd(0～60d),Pb(0)～122d),Ni(60～185d)Exceeded the standard phenomenon.Therefore,there is still a certain risk of heavy metal dissolution in stabilizing fly ash into the landfill.(2)During the experiment,the environment in the landfill column was always in the stage of hydrolysis and acidification,and the p H of the leachate remained below 6.0;ammonia nitrogen and VFA showed a downward trend and then increased;COD showed a rise and then decreased and then maintained a wave balance;SO42-,KN The fluctuations vary greatly.The p H、COD、VFA、NH4+-N of HA and HP landfill leachate were significantly higher than HY landfill column in the middle and late stages.Correlation analysis results show that ORP、COD、KN、VFA are the main factors affecting the dissolution of heavy metals.Cd is mainly related to ORP、KN 、NH4+-N.Cu and Zn are mainly related to p H、ORP、KN、VFA.Pb is mainly related to COD、KN.Cr is mainly related to ORP、COD.Ni is mainly related to ORP、COD、VFA.Related.(3)The microbial diversity of the landfill column was higher than that of the previous stage,and the microbial diversity of the HY landfill column was lower than that of the HA and HP landfill columns.In the medium term,the microbial diversity of the stabilized fly ash under the waste was higher than that of the upper layer,and the HP landfill column showed the opposite law in the later stage.The dominant bacteria of bacteria are: Firmicutes,Bacteroidetes,Proteobacteria.The fermicutes in the microbial communities of different landfill columns were the most dominant bacteria,and the relative abundances of Bacteroidetes and Proteobacteria were significantly reduced in the lower layer of fly ash.The dominant bacteria of the bacteria are Clostridia,Bacteroidia,Bacilli,and Gammaproteobacteria.The proportion of Clostridia and Bacteroidia in different periods was significantly higher than that of other fungi.Clostridia was dominant in the late stage,and the relative abundance of Bacteroidia and Bacilli was significantly decreased in the later stage.Gammaproteobacteria showed the opposite trend.In the mid-term,the Clostridia abundance in the HY landfill column is lower than that in the HA and HP landfill columns.The Bacteroidia abundance is higher than that in the HA and HP landfill columns.The Clostridia abundance is not much different in the later period,and the Bacteroidia abundance is not much different(The abundance of waste in the lower layer of fly ash is higher).The dominant species are Prevotella、Clostridium IV、Lactobacillus、Rummeliibacillus.The relative abundance of Prevotella、Lactobacillus in the fly ash is significantly lower than that in the upper part of the fly ash and the MSW.Clostridium IV 、 Rummeliibacillus have opposite distribution characteristics,indicating that the stabilized fly ash affects the microbial community structure in the waste.(4)Correlation analysis showed that the main environmental factors affecting microbial community structure at different stages were different.The medium term was mainly related to p H、NH4+-N,and the latter was mainly related to COD、NH4+-N.The lower level of fly ash is more significantly affected by heavy metals than the upper level of fly ash.It is mainly affected by Cr and Ni in the middle stage and is mainly related to Cu and Pb in the later stage.As the waste in the landfill is degraded continuously,the microbial community structure also shows a significant change trend.In the later system,the microbial community structure gradually adapts to the hydrolysis and acidification environment,and the microbial composition tends to be similar.In summary,the stabilized fly ash-MSW Co-landfill system has heavy metal dissolution in the hydrolysis and acidification stage,and there are still certain environmental risks.When stabilized fly ash and MSW are layered and landfilled without recharge operation,there is no significant impact on the waste degradation in the landfill system,but it has a great impact on the leachate water quality and microbial community structure. |
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