Coking of Pt/γ-Al_(2)O_(3) catalyst in landfill gas deoxygen and its effects on catalytic performance

Catalytic oxidation of CH_(4) has been proved to be an attractive option for landfill gas(LFG) upgrading.However, coking of catalysts in catalytic LFG deoxygen has been clearly observed in industrial applications. In this regard, it is necessary to investigate whether coke deposition originates from CH_(4) or volatile organic compounds present in LFG, and the influence of coke deposition on catalytic performance. Herein,we evaluate the LFG deoxygen on Pt/γ-Al_(2)O_(3) catalyst in simulated LFG(CH_(4), CO_(2), O_(2), N_(2)) and its co-feed with representative volatile organic compounds, ethylbenzene, toluene, benzene and cyclohexane. The results show that the coking of the catalyst is originated from volatile organic compounds rather than CH_(4). The Pt/γ-Al_(2)O_(3) catalyst does not deactivate during LFG deoxygen process, even significant amount of coke deposited, up to 18.15%(mass). Characterization analyses reveal that although coke deposition overall covers the catalyst surface, resulting in mesopores blockage and a reduced number of accessible Pt sites, however, the coke formed, H-rich carbonaceous components, behaves as counterpart for O_(2) elimination. Besides, the coke deposited is mainly filamentous. Thus, coke formation has little negative effect on the overall catalytic performance of Pt/γ-Al_(2)O_(3) catalyst ultimately. The results obtained in this work are helpful for the rational design of robust Pt based catalysts for LFG deoxygen without undue attention to their coking properties, and also favor the innovation of more attractive purification scheme configurations.

Evolution on qualities of leachate and landfill gas in the semi-aerobic landfill

To study the characteristics of stabilization in semi-aerobic landfill, large-scale simulated landfill was constructed based on the semi- aerobic landfill theory. Consequently, the concentrations of chemical oxygen demand （COD）, ammonia nitrogen, and nitrite nitrogen, and the pH value in leachate, as well as the component contents of landfill gas composition （methane, carbon dioxide, and oxygen） in landfill were regularly monitored for 52 weeks. The restflts showed that COD and ammonia concentrations declined rapidly and did not show the accumulating rule like anaerobic landfill, and remained at about 300 and 100 mg/L, respectively, after 48 weeks. Meanwhile, the descending rate reached 98.9% and 96.9%, respectively. Nitrate concentration increased rapidly after 24 weeks and fluctuated between 220-280 mg/L after 43 weeks. The pH values were below 7 during the first 8 weeks and after that leachates appeared to be alkaline. Carbon dioxide was the main composition in landfill gas and its concentration remained at a high level through the whole stabilization process. The average contents of carbon dioxide, oxygen, and methane varied between 19 vol.%-28 vol.%, 2 vol.%-8 vol.%, and 5 vol.%-13 vol.%, respectively. A relative equilibrium was reached after 48 weeks. The highest temperature in the landfill chamber could amount to 75.8 degrees centigrade.

Emission of landfill gas in Qingdao, China

A study on landfill gas emission in Qingdao,China was carried out. The results showed that the generation of landfill gas with maximum methane concentration occurred several months after the refuse was disposed and the steady emission of landfill gas could remain two years.The variation of landfill gas production was associated with temperature. In June, the emission of landfill gas rose gradually from morning to evening, but in September, it rose in the morning, and then fell in the afternoon. From June to August, the emission of landfill gas showed rising trend,but it declined quite quickly from September to December. In different seasons,the outflow rate of landfill gas varied from depth to depth in the refuse site. When earth temperature was higher in summer, the emission of landfill gas did not correspond with the depth of refuse sites, but when temperature fell in winter, and the temperature became a limited factor to the gas production,the outflow of landfill gas increased with increasing in depth of refuse piling.

SLIPPAGE SOLUTION OF GAS PRESSURE DISTRIBUTION IN PROCESS OF LANDFILL GAS SEEPAGE

A mathematical model of landfill gas migration was established under presumption of the effect of gas slippage. The slippage solutions to the nonlinear mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of gas pressure in landfill site was presented under the conditions of considering and neglecting slippage effect. Sensitivity of the model input parameters was analyzed. The model solutions were compared to observation values. Results show that gas slippage effect has a large impact on gas pressure distribution. Landfill gas pressure and pressure gradient considering slippage effect is lower than that neglecting slippage effect, with reasonable agreement between model solution and measured data. It makes clear that the difference between considering and neglecting slippage effect is obvious and the effects of coupling cannot be ignored. The theoretical basis is provided for engineering design of security control and decision making of gas exploitation in landfill site. The solutions give scientific foundation to analyzing well test data in the process of low-permeability oil gas reservoir exploitation.

Municipal solid waste degradation and landfill gas resources characteristics in self-recirculating sequencing batch bioreactor landfill

Based on the degradation characteristics of municipal solid waste(MSW)in China,the traditional anaerobic sequencing batch bioreactor landfill(ASBRL)was optimized,and an improved anaerobic sequencing batch bioreactor landfill(IASBRL)was put forward on the basis of leachate self-recirculation.By monitoring MSW composition,leachate characteristics variation and landfill gas(LFG)generation,the effect of IASBRL was comparatively studied by simulation landfill.Based on the adjusting,scouring and carrying effects of leachate self-recirculation,IASBRL can rapidly decrease Eh value to about-500mV and form a suitable biochemical environment for methanogens,which provides a precondition for stable cooperation between non-methanogens and methanogens.IASBRL can avoid the accumulation of organic acids,make VFA(volatile fatty acid)concentration and CODCr decrease along with the small range fluctuations,and form a stable decomposition-consumption synergy during MSW degradation,therefore,the hydrolysis rate of easy hydrolyze material reaches 71.2% in IASBRL.From the viewpoint of LFG resources in IASBRL,the cumulative LFG production increases to 2327.0L,CH4 mass fraction stabilizes at about 50%,and these provide a favorable precondition for LFG development.

High Efficiency Landfill Gas Fired Power Plant Process with ORC

Helsinki Environmental Services Authority HSY ,Ammaissuo waste management centre consists of two landfill sites. The old land filling area was established in 1987 and closed in 2007. The landfilling at the new landfill section started in November 2007. Until spring 2014 the main treatment method for source separated MSW （municipal solid＇waste） collected from Helsinki Metropolitan area households was landfilling. Approximately 250,000 tonnes of MSW was landfilled annually. From April 2014 on all of the MWS has been utilized in heat and electricity production at new Waste to Energy plant owned and operated by energy company Vantaa Energy Ltd. The landscaping of the landfills is currently ongoing. The construction of the landfill gas collection system was started in 1994 and from 1996 on landfill gas from old landfill area was recovered and burned in torches to reduce the greenhouse gas effect caused by methane in landfill gas. In the end of year （2004） new landfill gas utilisation system was taken in use Gas was used as a fuel in HOB （heat only boiler） to generate district heating for nearby community as well as commercial and industrial sites. The capacity of the system was 7,000 Nm3/h that corresponded to app. 30 MW of heat. Since district heat was mainly needed only during the cold season of the year only about half of the landfill gas produced by the landfill was able to utilize and rest of the gas was still flared leading to relatively low utilization rate of the gas. The construction work of the new 15 MW ＋ 1.2 MW electricity power plant started in spring 2009. The power plant consists of four gas engines and generators and organic rankine cycle process utilizing thermal oil for heat transfer from exhaust gas and steam turbine with hexamethyldisiloxane （silicone oil） as a medium agent. The ORC （Organic Rankine Cycle）-process was commissioned in August 2011 and the operational experiences have been very good. Based on current knowledge the HSY power plant is the biggest landfill gas fired power plant in Europe and probably even in the whole world. Also the combined engine and ORC-process is unique for landfill gas power plants. The third phase of the biogas utilization took place in summer 2015 when the anaerobic digestion biowaste treatment plant was introduced. At the moment the product gas from digestion plant is utilized at landfill gas power plant. In the future gas will be used as a fuel for new power plant process consisting two gas engines and ORC process. Commissioning of the new power plant will take place in October 2016. This paper presents detailed description of the landfill gas utilization system of HSY waste treatment centre and information on operational experiences of landfill gas fired power plant process.

Assessment of Risk to Human Health from Landfill Gas at Sharra Landfill, Tirana--Albania

Urban waste management and particularly dumpsites represents one of the most significant problems tot the long term protection of public health and environment in Albania. All waste management options, including landfilling, involve an element of risk to human health. This article addresses the question, if sources of emissions from Sharra landfill lead theoretically to public exposures exceeding health criteria？ This question is approached using an exposure pathway analysis framework, which link a source of one or more harmful pollutants at a site with a human receptor that inhales the pollutant. The risk posed to human health from HCHO （formaldehyde） and dioxin is estimated for on-site and off-site receptors in Sharra landfill. For on-site receptors, the average risk to get harm through the inhalation pathway from HCHO is in the range of 20 times to 300 times greater than allowed risk value, while for off-site receptors the average risk is in the range of 10 times to 180 times greater. While for dioxin the risk is in the range from 50 to 600 for on-site receptors and 10 to 35 for off-site receptors, times greater than often allowed risk.

Bioenergy recovery from landfill gas:A case study in China

Landfill gas(LFG)utilization which means a synergy between environmental protection and bioenergy recovery was investigated in this study.Pressure swing adsorption technology was used in LFG purification,and laboratory experiment,pilot-scale test,and on-site demonstration were carried out in Shenzhen,China.In the laboratory experiment,A-type carbon molecular sieve was selected as the adsorbent by comparison of several other adsorbents.The optimal adsorption pressure and adsorption time were 0.25 MPa and 2 min,respectively,under which the product generation rate was 4.5 m^(3)/h and the methane concentration was above 90%.The process and optimization of the pilot-scale test were also reported in the paper.The product gas was of high quality compared with the National Standard of Compressed Natural Gas as Vehicle Fuel(GB18047-2000),when the air concentration in feed gas was under 10.96%.The demonstration project was composed of a collection system,production system,and utilization system.The drive performance,environmental protection performance,and economic feasibility of the product gas—as alternative fuel in passenger car,truck,and bulldozer—were tested,showing the feasibility technology for LFG utilization.

Modeling and simulation of landfill gas production from pretreated MSW landfill simulator

The cumulative landfill gas （LFG） production and its rate were simulated for pretreated municipal solid waste （MSW） landfill using four models namely first order exponential model, modified Gompertz model, single component combined growth and decay model and Gaussian function. Considering the behavior of the pretreated MSW landfill, a new multi component model was based on biochemical processes that occurring in landfilled pretreated MSW. The model was developed on the basis of single component combined growth and decay model using an anaerobic landfill simulator reactor which treats the pretreated MSW. It includes three components of the degradation i.e. quickly degradable, moderately degradable and slowly degradable. Moreover, the devel- oped model was statistically analyzed for its goodness of fit. The results show that the multi components LFG production model is more suitable in comparison to the simulated models and can efficiently be used as a modeling tool for pretreated MSW landfills. The proposed model is likely to give assistance in sizing of LFG collection system, generates speedy results at lower cost, improves cost-benefit analysis and decreases LFG project risk. It also indicates the stabilization of the landfill and helps the managers in the reuse of the landfill space. The proposed model is limited to aerobically pretreated MSW landfill and also requires the values of delay times in LFG productions from moderately and slowly degradable fractions ofpretreated MSW.

Spatio-temporal variation of landfill gas in pilot-scale semi-aerobic and anaerobic landfills over 5 years

Variation of CH4, CO2, and O2 concentrations in layers of different depths in semi-aerobic and anaerobic landfills was analyzed over a period of 5 years. The results showed that most of the municipal solid waste became basically stable after 5 years of landfill disposal. In the upper and middle layer, the concentration of CH4 in the semi-aerobic landfill was significantly lower than that in the anaerobic landfill in different landfill periods, while in the lower layer, there was little difference in the CH4 concentration between the semi-aerobic and anaerobic landfills. The average concentration of CH4 and CO2in the anaerobic landfill was always higher than that in the semi-aerobic landfill, while the O2 concentration showed an opposite variation in different landfill periods. This was related to the aerobic reaction of landfill waste around the perforated pipe in the semi-aerobic landfill,which inhibited effective landfill gas generation.

Modified landfill gas generation rate model of first-order kinetics and two-stage reaction

This investigation was carried out to establish a new domestic landfill gas(LFG)generation rate model that takes into account the impact of leachate recirculation.The first-order kinetics and two-stage reaction(FKTSR)model of the LFG generation rate includes mechanisms of the nutrient balance for biochemical reaction in two main stages.In this study,the FKTSR model was modified by the introduction of the outflow function and the organic acid conversion coefficient in order to represent the in-situ condition of nutrient loss through leachate.Laboratory experiments were carried out to simulate the impact of leachate recirculation and verify the modified FKTSR model.The model calibration was then calculated by using the experimental data.The results suggested that the new model was in line with the experimental data.The main parameters of the modified FKTSR model,including the LFG production potential(L0),the reaction rate constant in the first stage(K1),and the reaction rate constant in the second stage(K2)of 64.746 L,0.202 d^(–1),and 0.338 d^(–1),respectively,were comparable to the old ones of 42.069 L,0.231 d^(–1),and 0.231 d^(–1).The new model is better able to explain the mechanisms involved in LFG generation.

Environmental factors affecting growth of grasses，herbs and woody plants on a sanitary landfill

The present study aims at studying relationships between various environmental factors andplant performance on a completed sanitary landfill. Three sites were chosen for comparison: an on-sitelow landfill gas region with a rich vegetation growth (Site L) , an on-site high landfill gas region with apoor vegetation growth (Site H), an off site control region (Site N) which located close to the GinDrinkers' Bay landfill. In Site H, where the levels of methane and carbon dioxide were higher, growth oftrees, shrubs and climbing plants are adversely affected, but not herbs and grasses. Analysis of correla-tion coefficient indicated that carbon dioxide and methane showed a negative correlation with the growth oftrees and shrubs. In Site H, the higher levels of conductivity, Kjeldah-N, Ammonium-N, and variousheavy metals, such as Mn were also exerted their adverse effect on plant growth. Trees tolerant to land-fill gas , e. g. Acacia confusa . would be a better choice for planting on sanitary landfills , in addition to theuse of shallow-rooted trees. Grasses and herbs are less susceptible to landfill gas due to their shallow-rootsystems. Hydroseeding of grasses would ensure a better plant coverage in areas with a moderate level oflandfill gas. Installation of a ventilation system might be needed for areas with a high level of landfill gas.

Numerical model of compressible gas flow in soil pollution control

Based on the theory of fluid dynamics in porous media, a numerical model of gas flow in unsaturated zone is developed with the consideration of gas density change due to variation of air pressure. This model is characterized of its wider range of availability. The accuracy of this numerical model is analyzed through comparison with modeling results by previous model with presumption of little pressure variation and the validity of this numerical model is shown. Thus it provides basis for the designing and management of landfill gas control system or soil vapor extraction system in soil pollution control.

Energy Recovery from MSW Treatment by Gasification and Melting Technology

The increase of waste production, joined to the difficulties concerning both the identification of new disposal sites and the construction of big conventional incinerators, led in recent years to the development of new technologies for waste management such as gasification and melting treatments. The possibility to introduce in the Italian context the DMS （direct melting system） technology, designed and manufactured by Nippon Steel Engineering Co. Ltd., has been taken into account for the scope of proposed work. DMS technology consists in MSW gasification, slags melting and combustion of the syngas produced, with the consequent generation of electric energy through a steam cycle. The system minimizes environmental impact, thanks to an effective recycling of useful resources such as inert melted slags and metals, featuring high flexibility in terms of treatment capacity due to its modular design. The aim of this article is to consider different plant configurations in order to optimize the energy recovery downstream the DMS module. As a case study, landfill gas exploitation integrated in the DMS plant will be considered as a typical situation that could occur in the Italian scenario. The energetic input provided by the biogas allows improving the thermo-economic performances according to market incentives.