| Landfill is one of the main methods in disposal of municipal solid waste(MSW)in China.Due to slow development of MSW separation collection,the MSW entering into landfills has been characterized typically by high moisture content(40%~70%)and high degradable organic matter content(> 50%),which cause traditional landfilling suffered from a few challenges such as secondary pollution of leachate and malodorous gas,low biogas recycle efficiency,wide area coverage etc.Based on these issues,this thesis has proposed a technological concept of three-stage bioreactor landfill technique(short-term pre-aeration-anaerobic landfill-in-situ aerobic stabilization acceleration),through precise control and sequence operation,the objectives,such as accelerated degradation of MSW,reduction in pollutants and greenhouse gas emissions,increase of energy recycle efficiency,could be realized.Finally,this technology could promote the transformation of trdational landfills into sustainable ones with the purposes of low pollution,low risk and low carbon emissions.Main results from this research are as follows:Short-term pre-aeration could achieve the targeted modification of organic components in MSW.Different organic components have distinguished degradation rates: degradation of carbohydrates,proteins and lignocelluloses dominate during temperature increasing stage,thermophilic stage and cooling down stage of pre-aeration process,respectively.Short-term pre-aeration has a significant enhancing effect on anaerobic degradation of MSW.A 6~8 days pre-aeration could have methane production of 123.4 and 108.8 NL/kg dry waste,respectively,with methane content in landfill gas generated of ~56%.The waste weigh loss and volume loss were 28.1% and 30.3%,respectively.Particularly,ammonia generated from accelerated ammoniation of proteins in waste during thermophilic stage could neutralize VFAs generated in early stage of anaerobic landfilling,which is the main mechanism to promote subsequent methane production.While,during cooling down stage,large amount of lignocellulose degradation causes a significant reduction in anaerobic production of methane.Therefore,it is recommended to interrupt pre-aeration after its thermophilic period to switch to anaerobic landfilling.In-situ aeration has different stablization acceleration effects on different aged MSW.For young MSW,in-situ aeration resulted in a raipd decrease of dissolved organic carbon(DOC)in leachate,with removal rate of 0.076/d;while for old MSW the average DOC removal rate was only 0.02/d during the whole experimental period.After aerobic stabilization,the HA in leachate from aged MSW has a higher aromatic degree,indicating that post-aeration further promotes humification of aged MSW.Meanwhile,the removal rate of leachate ammonia from aged MSW could achieve more than 99% by using aerobic stabilization.When considering both landfill gases recycling and leachate pollutants removal efficiency,it is recommended to select the yield of landfill gases reached 80% of its production potential as switching point from anaerobic landfill stage to in-situ aerobic stabilization stage.Compared to traditional MSW landfill,three-stage landfill process reduced ~89% of greenhouse gas(GHGs)emissions,reduced ~76% of waste stabilization duration and achieved ~3 times higher of landfill space efficiency.Under controlled conditions,the exhaust gas generated by the aerobic ventilation process is easy to control and treat,landfill gas collection efficiency in anaerobic landfill stage increased and leachate generated during pre-aeration stage is easily-degradable etc contributed to three-stage landfill technique in achieve overall pollution reduction and GHGs emission reduction. |
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