Study On Selection Of Landfill Bio-covers And The Effect Of Covers On The Methane Reduction

Waste landfills were the third anthropogenic methane emission source on earth which effecton the global climate. At present1billion tons of municipal solid wastes are produced a year inchina,80%of refuse was treated by a sanitary landfill according to the conditions of our country.Landfill gas（LFG） which mainly consisting from methane and carbon dioxide was produced inlandfills and a great amount of LFG was emitted into the air. How to control LFG emission has agreat significance in help reduce global warming. The object of this research is Xingfeng wastelandfill in Guangzhou, LFG collection and emission system was realized and methane emissionsource of landfill was found out by monitoring the methane emission rate. On this basis, thelandfill bio-cover which meets the engineering demand and methane oxidation were selectedthrough simulation columns experiment, optimize material compositions and exam dynamicmechanism can provide theoretical basis and technical support for engineering application. Themain conclusions are as follows:（1） Xingfeng waste landfill is providing electricity to the local power grid through thecollection and recovery of landfill gas for power generation. The landfill divided into fourdistricts, each district set three layers pipeline for collection LFG. The third and fourth districtsare in gas generation phase, the LFG collection rate reached37.8%and43.9%. Because thepipeline get clogged and unreasonable layout, the LFG collection rate decreases which cause agreat amount of LFG was emitted into the air.The emission rates of methane in fresh andmatured refuses were0.29mol·m-2·h^-1and4.17mol·m-2·h^-1, respectively. The emission rate ofmethane was0.175×10⁷m³·a^-1. The methane emission from operating area should be controlledin order to promote methane reduction.（2） The methane oxidation of3bio-covers （sewage, aged refuse and soil） was studiedthrough simulation experiment. The results showed that average daily methane oxidation rate,methane conversion and reaction rate V（CH₄） of sewage, aged refuse and soil were10.27%,75.82%,1.76mmol/（kg·d）;11.05%,75.61%,2.04mmol/（kg·d） and9.05%,68.15%,1.33mmol/（kg·d） respectively. The methane oxidation capacity of sludge and aged refuse were betterthan soil. Methane oxidation and physicochemical property of sludge which were modified by3solid modifiers （coal ash, construction wastes and soil） were also studied. Sludge modified by coal ash presented best ability for methane oxidation among the3modifier, which average dailyoxidation rate, methane conversion and V（CH₄） were17.27%,92.37%,2.35mmol/（kg·d）. Notonly coal ash plays fertilizer effect, and makes the sludge loose and expands. The sludgemodified by coal ash ameliorated physical and chemical properties and improved methaneoxidation ability. Taking the bio-cover as landfill cover can oxidize methane more effectivelythan traditional soil cover layer, and maybe a latent technology for landfill methane emissionreduction.（3）The engineering requirements of osmotic coefficient and compressive strength for covermaterial of landfill site were satisfied when the maxed ratio of coal ash and sludge are1:1^-1.5:1.Full factorial34experimental design using simulation columns was conducted to investigatestatistically the effects of mixed ratio, moisture content, nutrient addition and cover thickness onthe CH₄oxidation efficiency through a landfill bio-cover sewage sludge modified by coal ash.The results from all experiment sets showed that the optimal conditions was1:1mixed ratio ofcoal ash and sewage sludge, added0.05mL/g NMS nutrients to400mm thickness in landfillbio-cover which made moisture content of material reached40%. The maximum CH₄oxidationefficiency was88.6%under the optimal conditions.（4） The methane oxidation efficiency of landfill bio-cover was influenced by methanecontent in LFG and oxygen content in air, the more of methane and oxygen, the higher ofmethane oxidation efficiency. Kinetic equation and parameter were also determined, resultsshowed that the kinetics of methane oxidation was conformed to the second-order reaction,which equation was-dV（CH₄）/dt=kV（CH₄）V（O₂）. The kinetic parameter were done byMichaelis-Menten equation, V（CH₄） initially with methane concentrations increases, until thebio-cover of methane concentrations saturated. The largest methane oxidation rate（V max）was2.54μmol CH₄g^-1h^-1,the apparent half saturation constant（K m） was0.49μmol.