Pollution Control Technology Of Off-site Fermentation Based On Municipal Solid Waste Leaching

The main method of collecting landfill gas in sanitary landfills is to derive the landfill gas from the landfill reservoir area through the air-conducting stone cage,and then collect it in the gas collection box through the gas collection pipe network.After purification,landfill gas can be used for power generation or torch combustion.At present,the problems facing the collection of landfill gas are:（1）if the landfill gas is not discharged in time,it will lead to excessive pressure and increase the hidden danger to safety;（2）due to the sealing problem in the landfill reservoir area,it is easy to cause the natural escape of landfill gas,which leads to the deterioration of the air environment near the landfill site and increases the emission of greenhouse gases;（3）the landfill gas collected by this method is a mixed gas produced by the decomposition of different landfill ages,which is mixed with malodorous gases such as N₂,CO₂,NH_3,and H₂S produced in the middle stage of garbage degradation and reduces gases such as CH₄and H₂ produced in the later stage of garbage degradation.The complex composition of the gas makes it difficult to recover.Given the problems faced in the collection of landfill gas,this study proposes to use leachate to leach the fresh garbage at the initial stage of landfill.After the garbage in the hydrolysis stage is leached,the leachate carries soluble small molecular organic pollutants hydrolyzed by garbage to start off-site fermentation.CH₄ can be recovered for resource utilization in the process of off-site fermentation,and the leachate can be recycled again after off-site fermentation.Laboratory simulation studies show that off-site fermentation not only effectively controls the COD concentration of leachate but also enables efficient recovery of landfill gas,which can provide new ideas for the development of new landfill gas collection and utilization technology.The main conclusions are as follows:（1）Through the experiment of organic matter leaching of municipal solid waste,the leaching solution was studied.The experimental data show that the concentration of COD in the leachate increased by 136.38%,the concentration of volatile fatty acids（VFAs）increased by 190.70%,the concentration of protein increased by 59.17%,and the p H value decreased by 16.89%.It is proven that the leachate can flush out the soluble small molecular organic pollutants in the garbage heap.In addition,the perishable components of fresh domestic waste will be hydrolyzed and acidified in the landfill column,and the products such as VFAs can also play a role in reducing p H,which is more conducive to the off-site anaerobic fermentation of the leachate.（2）In the experiment of anaerobic fermentation outside the eluent field,the highest daily gas production was 9.25 m L/g COD·d in group A（35℃）and 8.79 m L/g COD·d in group B（40℃）,and the COD degradation rate of 91.60 m L/g COD,B group 89.39m L/g COD;The COD degradation rate of A group was 71.56%,and the B group was76.17%.The change curve of the detection indexes of the two groups was similar,and the difference was small,but the fermentation temperature of group A was lower than that of group B（35℃<40℃）,the cumulative gas production was higher and the fermentation process was more energy-saving,so it was the best experimental scheme.（3）The results of high-throughput sequencing showed that at the level of bacteria,the relative abundance of Firmicutes in CASS sludge was the highest,and the relative abundance of Proteobacteria in oxidation ditch sludge decreased from 60.40%to56.64%,and that of sludge after acclimation decreased from 53.74%to 47.48%.At the bacterial level,the relative abundance of Thauera in the oxidation ditch sludge samples was higher,and the relative abundance increased from 2.15%to 7.47%after domestication,indicating that the COD removal ability of the acclimated oxidation ditch sludge was significantly improved.（4）In the experiment of off-site anaerobic fermentation of activated sludge inoculated with eluent,the cumulative gas production of group C（T=35℃,V_L:V_S=8:2）inoculated with CASS sludge was the highest,with total gas production of 582.08 m L/g COD after 58 days.The degradation rate of COD concentration was the highest（85.4%）in group D（T=40℃,V_L:V_S=8:2）inoculated with CASS sludge.The cumulative gas production of group B（T=40℃,V_L:V_S=9:1）in the off-site fermentation of oxidation ditch sludge was the highest,and the degradation rate of 1177.05 m L/g COD and the COD concentration was the highest（78.48%）.To sum up,in the off-site fermentation experiment of leachate inoculated with activated sludge,group B（the leachate inoculated with oxidation ditch sludge outside the anaerobic fermentation experiment）had the highest COD degradation rate,the highest cumulative gas production,the short anaerobic fermentation cycle,less sludge inoculation,and the highest energy consumption conversion ratio.（5）The results（the cumulative gas production of off-site fermentation of leaching solution is 91.60 m L/g COD;the cumulative gas production of off-site fermentation of activated sludge inoculated with leaching solution is 1177.05 m L/g COD）showed that inoculation of activated sludge could increase the gas production of off-site anaerobic fermentation,and the cumulative gas production of off-site fermentation was 12.85times higher than that of non-inoculated sludge.（6）The analysis of the technical scheme of anaerobic fermentation outside the leachate site shows that the sanitary landfill with a service period of 15 years and a total landfill volume of about 16.8718 million tons can produce 1.8178 million cubic meters of leachate.The leachate off-site anaerobic fermentation technology can collect a total of 41.4051 million cubic meters of landfill gas under the optimal conditions of the first anaerobic fermentation.after separation and purification,the landfill gas can produce economic benefits of 44.1331 million yuan.