Experimental Study Of Msw Degradation In An "Aerobic-Anaerobic-Aerobic" Three-Stage Landfilling Bioreactor

The municipal solid waste（MSW）has the characteristics of high moisture and high organic matter content in China,which leads to a long operating cycle,low methane recovery efficiency and high pollutant emission in conventional sanitary landfills.In recent years,different types of bioreactor landfills were investigated to make landfills sustainable,such as anaerobic,aerobic,quasi-aerobic,and combined bioreactor landfills with various regulatory measures.Aerobic technology was used for the pretreatment of anaerobic landfill or old-age landfill,which achieves the certain effect.In this paper,an"aerobic-anaerobic-aerobic"three-stage landfilling bioreactor（TSLB）was designed by integrating short-term pre-aeration,anaerobic landfill and in-situ aerobic stabilization stages.In the laboratory,the integrated bioreactors were operated under a semi-continuous mode,with fresh MSW added periodically.Its performance in the degradation of MSW,biogas recovery and leachate control etc,was evaluated.The main results of the thesis are as follows:Different stages of the TSLB have various effects on the removal of diverse organic matter components.Short-term pre-aeration can achieve the targeted degradation of polysaccharides,proteins and fats,and enrich the lignocelluloses;anaerobic landfill produces large quantities of biogas through degradation of proteins,fats,and lignocelluloses;aerobic stabilization can further remove fat,lignocelluloses,and other substances in the MSW.The TSLB can promote the biodegradation of the MSW and accelerate the stabilization of landfill.At the end of the experiment,VS was reduced from 45.60%to12.76%,and the moisture content was decreased from 56.55%to 30.48%.The proportion of C,H,O and N in dry MSW gradually decreased,meanwhile,the proportion of ash increased significantly.The volume of MSW of the TSLB was 21%lower than the control bioreactor,the TSLB significantly improved the space utilization rate of landfill.According to VS and moisture content,the MSW realized stabilization in 120 days basically,and the site achieved the requirements of moderate utilization.The TSLB can shorten the lag time and production cycle of methane production of MSW.The lag time of the TSLB was about 16 days,and the whole production cycle lasted for 80 days.The accumulated biogas production was 193 NL/kgTS,which was more than80%of the production potential.The effective biogas production of the accumulated biogas production（the proportion of CH₄>50%）exceeded 92%.The production rate of biogas was kept within the range of 3.04⁴.34 NL/kgTS.d.Its fluctuation range was very little,which was conducive to the centralized collection and utilization of biogas.The TSLB can change the physical and chemical characteristics of leachate,and effectively reduce the pollutant emission.The concentration of SCOD and VFAs in the leachate produced by the TSLB was relatively low.The concentration of ammonia nitrogen was above 2000 mg/L.Higher initial concentration of ammonia nitrogen can neutralize the VFAs,keeping the leachate pH within the range of 7.0 to 8.0,which provided a suitable pH environment for anaerobic degradation.In the aerobic stabilization stage,the volume of leachate was reduced by 84%through forced aeration for 40 days,and the removal rates of the total mass of SCOD,VFAs and ammonia nitrogen reached71%,78%and 98%respectively,which reduced the difficulty of the subsequent treatment of leachate.