Effect Of Mixed Landfill Of Incineration Bottom Ash And Municipal Solid Waste On Methane Production And Its Microbiological Mechanism

With the increase of the proportion of municipal solid waste incinerator（MSWI）in China,the output of incineration bottom ash（BA）is increasing year by year.The municipal solid waste（MSW）Landfill Pollution Control Standard（GB16889-2008）has provided provide a suitable direction for the treatment and disposal of incineration bottom ash:domestic MSWI BA can be directly sent to the MSW landfill for landfill disposal.Incinerator BA-primary waste mixed landfill is gradually becoming a new type of landfill mode,but its stabilization process and methane production law are affected by the operation mode of mixed landfill,and due to the complexity of the waste degradation process and the various types of slag The two-way nature of the impact of key components on waste stabilization leads to the ambiguity of the CH₄generation law during the mixed landfill process,which makes it difficult to effectively control the CH₄generation and emission from mixed landfills.Based on this,this research had constructed five simulated anaerobic landfill systems A（MSW）,B（5%BA-MSW）,C（10%BA-MSW）,D（20%BA-MSW）and E（10%BA、5%decomposed sludge-MSW）,studied the change mechanism of leachate water quality,solid waste characteristics,CH₄and other landfill gas and microbial community structure under completely mixed conditions,and clarified the relationship and difference between the addition ratio of incinerator BA and the degradation characteristics,stabilization degree,CH₄production changes and microbial community structure changes in the simulated domestic waste landfill system.The main conclusions are as follows:（1）In leachate,p H was acidic at the initial stage of landfill and gradually increases with landfill time.ORP showed a steadily increasing trend;EC and alkalinity increased rapidly at a specific time,and then showed a significant decreasing trend.The values of VFA、COD、TOC、TN、NH₄⁺-N、S^2-、SO₄^2-、Ca²⁺and TP showed a trend of first rising and then falling,and kept fluctuation balance in the later stage of landfill.In the DOM change,SUVA₂₅₄and SUVA₂₈₀had a limited change range,and the overall fluctuation increases,indicating that the degree of garbage humification was increasing continuously;E_300/400showed a decreasing trend,indicating that the degree of humification and molecular weight gradually increased.In solid waste,with the advance of landfill time,the p H value showed an obvious upward trend;The EC value basically decreased until the end of the reaction.The values of organic matter and biodegradability showed an obvious downward trend,which indicated that at the end of landfill,the garbage in each landfill system basically stabilized.Adding a proper proportion of incinerator BA can accelerate the stabilization process of the landfill,and the higher the proportion of incinerator BA filling,the faster and greater the stabilization speed.The low proportion of incinerator BA had no significant effect on the stabilization process of garbage,and the addition of high proportion of incinerator BA significantly accelerateed the stage of acid and methane production and the stabilization speed of garbage.The stabilization process of garbage in anaerobic sludge adding device was faster than that in other landfill systems,which indicated that inoculation of microorganisms can make up for the influence of insufficient addition of incineration BA and further improve the degradation rate of domestic garbage.（2）The CH₄gas content showed a trend of rising first and then falling.Adding slag can accelerate the garbage to reach the methane production stage,and the CH₄partial pressure of BA column was much higher than that of single MSW column.The decomposed sludge further shortens the time of garbage degradation and increases the gas content.The peak of methane production first appeared in the systems with 10%BA and 5%decomposed sludge,followed by the systems with 20%and 10%BA addition ratios.For the leachate,the content of CH₄gas in the landfill systems B、C and D had a significant correlation with environmental factors in the middle stage of the landfill,and there was a significant correlation between p H、EC、NH₄⁺-N、VFA、Ca²⁺、SO₄^2-and TP concentration and the content of CH₄gas.For solid waste,only in the late stage of landfill,p H and ORP values were significantly negatively correlated with CH₄gas.The content of CH₄in landfills is significantly different under different BA addition ratios.The content of CH₄gas had a significant positive correlation with E_300/400,and a significant negative correlation with VFA、Ca²⁺and COD.（3）The abundance and diversity of bacteria increased first and then decreased with landfill time.The addition of incineration slag had a certain inhibitory effect on the abundance and diversity of bacterial community.The dominant phylum of bacteria are Firmicutes、Proteobacteria、Actinobacteria and Bacteroidetes.Firmicutes and Actinobacteria were the dominant phylum during the middle stage of landfill,while Bacteroidetes and Proteobacteria were the dominant phylum during the middle and late stage of landfill.The dominant classes of bacteria are Bacilli、Actinobacteria、Gammaproteobacteria、Clostridia and Bacteroidia.Bacilli、Actinobacteria and Clostridia were the dominant classes in the early stage of landfill,and Gammaproteobacteria and Bacteroidia were the dominant classes in the late stage of landfill.Bacilli、Actinobacteria and Clostridia are the dominant bacteria classes of separate domestic waste landfill devices.Among the devices with a higher proportion of BA,Bacilli had an absolute advantage in the early stage of landfilling,and Gammaproteobacteria and Bacteroidia had an absolute advantage in the middle and late stages of landfilling.The dominant genus are mainly Lactobacillus、Propionibacterium、Acinetobacter、Proteiniclasticum and Prevotella.Lactobacillus and Propionibacterium had an absolute predominance in the early landfilling.In the middle and late stages of landfilling,Proteiniclasticum、Acinetobacter and Prevotella had advantages in different periods.The composition of the genus in the separate MSW landfill column and the landfill column with a low proportion of BA was similar,and the composition of the bacteria in the landfill column with a high proportion of BA was also similar.The addition of BA and sludge device The composition of the genus in the landfill column E was significantly different.（4）With the increase of landfill time,the abundance of archaea decreased first and then increased,and the diversity increased first,then decreased and then increased.The diversity of archaea community in the high proportion BA adding column had increased to a certain extent,which showed that the addition of incineration BA can promote the diversity of archaea community to a certain extent.Euryarcharota and Thaumarchaeota are dominant phylum of archaea.Euryarcharota dominates in the later stage of landfill,Thaumarchaeota dominates in the early and middle stages of landfill.Compared with systems with different BA addition ratios,with the increase of BA addition,the advantages of Euryarcharota become more and more obvious,and the content of Thaumarchaeota gradually decreases.Methanosarcinales、Methanomicrobiales and Nitrososphaerales are the dominant orders.Methanosarcinales was dominant in the middle and late stage of landfill,Nitrososphaerales was the dominant bacteria in the early stage of landfill,and Methanomicrobiales was the dominant bacteria in the late stage of landfill.With the increased of BA proportion,the relative abundance of Methanosarcinales first increased and then decreased,the relative abundance of Methanosarcinales gradually increased,and the relative abundance of Nitrososphaerales gradually decreased.Methanosarcina and Nitrososphaera are dominant at the genus level.With the increase of landfill time,the relative abundance of Methanosarcina gradually increased,and the relative abundance of Nitrososphaera gradually decreased,indicating that acetic acid-trophic methanogens began to gradually dominate.In the primary waste device,the relative abundance of Nitrososphaera had an absolute advantage,indicating that the production of CH₄in the separate domestic waste landfill device was mainly through the H₂/CO₂reduction methane production pathway.In the BA addition device,the relative abundance of Methanosarcina gradually increased with the addition of BA,indicating that with the increase in the addition of BA,the acetic acid nutritive methane production pathway began to occupy a dominant position.（5）Correlation analysis showed that OM、TOC、EC were the main environmental factors affecting the bacterial community structure at the initial stage of landfill,and p H、alkalinity、ORP were the main environmental factors affecting the bacterial community structure at the middle and late stage of landfill.The influence degree of waste physical and chemical properties on bacterial community structure was OM>p H>TOC>EC>E_300/400>alkalinity>ORP.ORP、TOC and EC were the main environmental factors affecting the community structure of archaea in the early stage of landfill,and p H was the main environmental factor affecting the community structure of archaea in the middle and late stage of landfill.The order of the impact of the physical and chemical properties of garbage on the structure of the archaeal community was OM>p H>alkalinity>TOC>ORP>EC>E_300/400.In summary,in the anaerobic landfill device with complete mixing of incineration slag and domestic garbage,the mixing of incineration slag and domestic garbage with appropriate proportion can accelerate the stabilization process of the landfill.Adding10%BA into an anaerobic landfill with complete mixing of BA and MSW can accelerate the degradation of garbage to the greatest extent,increase the yield and content of CH₄gas,have great influence on the structure of bacteria and archaea,and change the nutritional metabolism pathway of methanogens.At the same time,appropriate amount of decomposed sludge can further promote the reaction,make up for the influence of insufficient amount of incineration slag,and increase CH₄gas content.