Biocover Performance of Landfill Methane Oxidation: Experimental Results

An experimental passive methane oxidation biocover (PMOB) was constructed within the existing final cover of the St-Nicéphore landfill. Its substrate consisted of a 0.80-m-thick mixture of sand and compost. The goal of this experiment was to evaluate the performance of the PMOB in reducing CH4 emissions when submitted to an increasing methane load. The CH4 load applied started with 9.3?g?CH4?m?2?d?1. When the site had to be closed for the winter, the CH4 input was 820?g?CH4?m?2?d?1. Throughout the study, practically all the CH4 input was oxidized; absolute removal rates were linearly correlated to methane loading; and the oxidation zone was established between 0.6–0.8 m. These results seem to indicate that the upper limit potential of this PMOB to oxidize CH4 was not necessarily reached during the study period. Surface CH4 concentration scans showed no signs of leaks. The substrate offered excellent conditions for the growth of methanotrophs, whose count averaged 3.91×108?CFU?g?dw?1 soil.     

Characterization of Methane Flux and Oxidation at a Solid Waste Landfill

Methane emissions were measured at several locations at a typical solid waste facility using a static chamber technique. At the entire facility, methane flux varied from ?13.6?to?1,755?g?m?2?day?1. The flux data had an arithmetic mean value of 71.3?g?m?2?day?1 and a geometric mean value of 18.6?g?m?2?day?1. At this site, methane emission was generally lower on the side slopes relative to the flat areas of the landfill. The spatial variability of methane flux was characterized by point kriging and inverse distance weighing (IDW) in an intensive study of a 61×61-m area. The geospatial means in this area obtained by both methods were almost identical (20.9 versus 20.8?g?m?2?day?1). These geospatial means for the area were also similar to the arithmetic mean (24.5?g?m?2?day?1), but 3.4 times the geometric mean (6.5?g?m?2?day?1). Methane oxidation was evaluated at the surface of the landfill and at several depths within the cover soil using stable isotope techniques. The δ?13C of CH4 averaged ?55.4% in the anoxic zone. Methane collected in chambers and in surficial soil probes exhibited more 13C enriched values, ranging from ?55.4 to ?34.5%, due to the preferential uptake of 12CH4 by methanotrophic bacteria. Methane oxidation at the landfill averaged 22% and occurred in the upper 70?cm of the landfill cover soil. Oxidation occurred in all tested locations of the landfill and for all ages of buried waste.     

垃圾填埋场沼气电站自动化控制应用技术

以南昌市麦园垃圾填埋场配套的沼气发电工程为例,介绍了该电站采用的国内相同沼气电站没有运用的自动化控制系统。此系统既保证了电站运行的安全性和可靠性,又节省了投资,并减员增效,同时也有利于电厂运行人员的管理,是控制造价和发挥分散控制系统最大功效的最佳方案。     

Gas Transport Parameters for Compacted Reddish-Brown Soil in Sri Lankan Landfill Final Cover

Gas exchange through the compacted final cover soil at landfill sites plays a vital role for emission, fate, and transport of toxic landfill gases. This study involved measuring the soil-gas diffusivity (Dp/Do, the ratio of gas diffusion coefficients in soil and free air) and air permeability (ka) for differently compacted soil samples (reddish-brown soil) from the final cover at the Maharagama landfill in Sri Lanka. The samples were prepared by either standard Proctor compaction or hand compaction to dry bulk densities of 1.60–1.94??g?cm-3. Existing and modified models for predicting Dp/Do and ka were tested against the measured data. The simple, single-parameter Buckingham model predicted measured Dp/Do values across compaction levels equally well or better than a dry bulk density (DBD) dependent model and a soil-water retention (SWR) dependent model. The measured ka values for differently compacted samples were highly affected by the compaction level and the sample moisture preparation method. Also, for air permeability, a single-parameter Buckingham-type ka model was most accurate in predicting ka in the differently compacted soil samples. Equivalent air-filled pore diameters (the effective diameter of the drained pores active in leading air through the sample) for gas flow, deq, were calculated from the measured Dp/D0 and ka values. The deq increased with compaction level, suggesting that a very high compaction level creates well-connected macropores in the reduced total pore space of the cover soil. This is an important consideration when designing cover soils for optimally low water and high oxygen exchange while minimizing climate and toxic gas emissions from the waste layer to the atmosphere.     

填埋场覆盖系统对温室气体释放的影响

在没有沼气收集系统的前提下,填埋场覆盖土壤系统对减少填埋气体的释放非常重要。本文对填埋场应用的覆盖材料及其对填埋场气体释放的影响进行了综述。介绍了覆盖土壤对甲烷的氧化作用,主要包括甲烷氧化作用机理、影响因素等,同时对填埋气体中痕量气体（如N2O,odor、VOCs）在覆盖土壤中的降解进行了总结。     

Hydraulic Performance of Geosynthetic Clay Liners in a Landfill Final Cover

Percolation from a landfill final cover containing a geosynthetic clay liner (GCL) as the hydraulic barrier is described. The GCL was covered with 760?mm of vegetated silty sand and underlain with two gravel-filled lysimeters to monitor percolation from the base of the cover. Higher than anticipated percolation rates were recorded in both lysimeters within 4–15?months after installation of the GCL. The GCL was subsequently replaced with a GCL laminated with a polyethylene geofilm on one surface (a “composite” GCL). The composite GCL was installed in two ways, with the geofilm oriented upwards or downwards. Low percolation rates (2.6–4.1?mm/year) have been transmitted from the composite GCL for more than 5?years regardless of the orientation of the geofilm. Samples of the conventional GCL that were exhumed from the cover ultimately had hydraulic conductivities on the order of 5×10?5?cm/s. These high hydraulic conductivities apparently were caused by exchange of Ca and Mg for Na on the bentonite combined with dehydration. The overlying and underlying soils likely were the source of the Ca and Mg involved in the exchange. Column experiments and numerical modeling indicated that plant roots and hydraulic anomalies caused by the lysimeters were not responsible for the high hydraulic conductivity of the GCL. Despite reports by others, the findings of this study indicate that a surface layer 760?mm thick is unlikely to protect conventional GCLs from damage caused by cation exchange and dehydration. Accordingly, GCLs should be used in final covers with caution unless if cation exchange and dehydration can be prevented or another barrier layer is present (geomembrane or geofilm).     

Extreme Compaction Effects on Gas Transport Parameters and Estimated Climate Gas Exchange for a Landfill Final Cover Soil

Landfill sites have been implicated in greenhouse warming scenarios as a significant source of atmospheric methane. In this study, the effects of extreme compaction on the two main soil-gas transport parameters, the gas diffusion coefficient (Dp) and the intrinsic air permeability (ka), and the cumulative methane oxidation rate in a landfill cover soil were investigated. Extremely compacted landfill cover soil exhibited negligible inactive soil-air contents for both Dp and ka. In addition, greater Dp and ka were observed as compared with normal compacted soils at the same soil-air content (ε), likely because of reduced water-blockage effects under extreme compaction. These phenomena are not included in existing predictive models for Dp(ε) and ka(ε). On the basis of the measured data, new predictive models for Dp(ε) and ka(ε) were developed with model parameters (representing air-filled pore connectivity and water-blockage effects) expressed as functions of dry density (ρb). The developed Dp(ε) and ka(ε) models together with soil-water retention data for soils at normal and extreme compaction (ρb = 1.44 and 1.85??g?cm-3) implied that extremely compacted soils will exhibit lower Dp and ka at natural field-water content (-100??cm H2O of soil-water matric potential) because of much lower soil-air content. Numerical simulations of methane gas transport, including a first-order methane oxidation rate, were performed for differently compacted soils by using the new predictive Dp(ε) model. Model results showed that compaction-induced difference in soil-air content at a given soil-water matric potential condition is likely the most important parameter governing methane oxidation rates in extremely compacted landfill cover soil.     

垃圾填埋场渗沥液调节池的浮盖设计与施工

在调节池设计上采用浮盖技术，并用高密度聚乙烯（HDPE）土工防渗膜作为浮盖材料，结合工程经验对填埋场渗沥液调节池大面积池面加盖的设计与施工进行阐述。     

垃圾渗滤液催化氧化处理技术研究进展

催化氧化技术能有效降解垃圾渗滤液中的难降解有机物.本文对O3类催化氧化、Fenton类催化氧化、电化学氧化、UV/H2O2催化氧化、TiO2光催化氧化等技术的国内外研究进展和发展趋势进行了分析总结,并系统阐述了催化氧化技术降解垃圾渗滤液污染物的作用机理.同时,本文亦对各种新型催化剂的引入对垃圾渗滤液处理的效果进行了探讨,提出新兴高效催化剂的研发和合成是实现渗滤液催化氧化技术发展与应用的关键和核心.     

陈腐垃圾填埋场腐殖土好氧堆肥-浸提技术工艺研究

以某生活垃圾填埋场腐殖土为研究对象,采用好氧堆肥-浸提技术进行腐殖土中可溶性盐类、有机质、重金属的有效处理,探究不同C/N比、微生物菌液添加量、浸提剂添加比例、浸提时间下腐殖土的处理效果,确定最优的好氧堆肥-浸提技术工艺条件。结果表明:调节腐殖土中C/N为25∶1后,添加45 L微生物菌液,保持好氧堆肥条件后,以1∶1体积比添加浸提剂,浸提8 h,反复两次后,再用清水浸提一次,处理后腐殖土能满足《绿化种植土壤》(CJ/T 340-2016)标准。     

Fugitive Methane Emissions from Landfills: Field Comparison of Five Methods on a French Landfill

The study presented in this paper has been initiated by the Veolia Environment research center for waste management and supported by the French Environmental Agency. A comparison of five field-scale measurement methods for measuring fugitive methane emissions has been conducted on a French landfill site. The five methods evaluated consisted of a tracer gas technique, laser radial plume mapping, inverse modeling technique, differential absorption light detection and ranging (LiDAR), and helicopter-borne spectroscopy. These methods are evaluated on their abilities to measure emissions from a practical user-oriented aspect (metrological, technical, and economical criteria). High disparities in terms of quantitative results and applicability were observed from all methods. Techniques that used Gaussian dispersion modeling appeared less applicable to landfill sites due to topographic complexity and did not provide high confidence in the results. However, the method using optical remote sensing (radial plume mapping) methods showed that a spatially detailed analysis is achievable (cell level), and the LiDAR method showed very promising approach and technical performances.     

Results from 18 Years of In Situ Performance Testing of Landfill Cover Systems in Germany

The water balances and the long-term performance of different landfill cover systems have been measured in situ in large-scale lysimeters on the landfill Hamburg-Georgswerder, Germany since 1988. The cover systems including different barrier components for water transport were constructed with state-of-the-art technology and have been excavated at several occasions especially to inspect the structure of the barriers. For the first time, the irreversible impact of crack formation in cohesive soil barriers and geosynthetic clay barriers due to desiccation, shrinkage, ion exchange, and plant root penetration has been observed and quantified in this study. After four years of good performance, these covers began to leak between 90 and 200 mm/year (average precipitation of 860 mm/year). The hydraulic conductivity of the cohesive soil barriers increased from 2×10?10 to 9×10?8?m/s, the daily peaks of the leakage through the geosynthetic clay barriers from initial values around 2×10?11?to?2×10?7?m3/(m2?s). The composite barriers with geomembranes above cohesive soil barriers performed very well, showing no leakage and only very little thermally induced water transport. A capillary barrier also performed well (average annual leakage of 18 mm/year). The data of the past 10 years prove that evapotranspiration can be increased significantly by planting bushes, which also limits the potential leakage through barrier layers.     

Field Performance of a Compacted Clay Landfill Final Cover at a Humid Site

A study was conducted in southern Georgia, USA, to evaluate how the hydraulic properties of the compacted clay barrier layer in a final landfill cover changed over a 4-year service life. The cover was part of a test section constructed in a large drainage lysimeter that allowed continuous monitoring of the water balance. Patterns in the drainage (i.e., flow from the bottom of the cover) record suggest that preferential flow paths developed in the clay barrier soon after construction, apparently in response to desiccation cracking. After four years, the clay barrier was excavated and examined for changes in soil structure and hydraulic conductivity. Tests were conducted in situ with a sealed double-ring infiltrometer and two-stage borehole permeameters and in the laboratory on hand-carved blocks taken during construction and after four years of service. The in situ and laboratory tests indicated that the hydraulic conductivity increased approximately three orders of magnitude (from ≈ 10?7?to? ≈ 10?4?cm?s?1) during the service life. A dye tracer test and soil structure analysis showed that extensive cracking and root development occurred throughout the entire depth of the barrier layer. Laboratory tests on undisturbed specimens of the clay barrier indicated that the hydraulic conductivity of damaged clay barriers can be underestimated significantly if small specimens (e.g., tube samples) are used for hydraulic conductivity assessment. The findings also indicate that clay barriers must be protected from desiccation and root intrusion if they are expected to function as intended, even at sites in warm, humid locations.     

Minimum Depth of Soil Cover above Soil–Steel Bridges

Soil–steel bridges are built of flexible corrugated steel panels buried in well-compacted granular soil. Their design is based on the composite interaction between the soil pressures and the displacements of the conduit wall. The structure failure could be initiated by shear or tension failure in the soil cover above the steel conduit. The provisions for design given in different codes, such as the Canadian Highway Bridge Design Code, managed to avoid some of the problems associated with the failure of soil above soil–steel bridges by requiring a minimum depth of soil cover over the crown of the conduit taking into consideration the geometric shape of the conduit. However, the present code requirements for a minimum depth of cover were developed for a maximum span of 7.62 m and using nonstiffened panels of 51 mm depth of corrugation. The effect of having larger spans or using more rigid corrugated panels has not been examined before and is the subject of this paper. The present study uses the finite-element analysis to re-examine the possible soil failures due to centric live loads (i.e., loads acting symmetrically about the mid span of conduit) or eccentric live loads. The study deals with spans up to 15.24 m of circular conduits and 21.3 m of arches with deep corrugations. It has been found that, in addition to the conduit geometry, the actual dimension of the span should be considered to determine the required depth of soil cover.     

Application of Fuzzy Logic to Estimate Flow of Methane for Energy Generation at a Sanitary Landfill

This paper proposes the use of a multicriteria assessment technique to evaluate the methane flow during gas extraction from a sanitary landfill. A number of parameters determine the gas generation and the feasibility for its extraction from a landfill. These parameters form a complex set of information with unknown mathematical interrelationships making potential gas flow evaluations difficult and elusive. In addition, the data available for a particular landfill are very often imprecise, uncertain, or subjective, making it even more difficult to evaluate the potential for gas extraction without conducting pilot tests. The method proposed in this paper uses fuzzy composite programming that allows for the use of imprecise information. A landfill gas potential index has been defined, which can be determined by easily obtainable climatological, geological, and landfill parameters. The landfill gas (LFG) potential index is related to the landfill gas flow using an empirical equation. The LFG potential model was calibrated and verified using data obtained from 61 landfills where gas extraction is being conducted. A sensitivity analysis was done to study the impact of variations in the input data on model output.     

Influence of High-Permeability Layers for Enhancing Landfill Gas Capture and Reducing Fugitive Methane Emissions from Landfills

Gas collection systems of various designs have been used to control landfill gas emissions, which can be problematic, particularly before installation of final landfill covers. In this work, an innovative gas collection system that includes a permeable layer near the top surface of landfills was evaluated for enhancing capture of landfill gas and reducing fugitive methane emissions. A computational model that accounts for advective and diffusive fluxes of multiple gas components was used to evaluate the efficiency of this new design for intermediate landfill covers. The utility of the high-permeability gas-conductive layer was illustrated for several conditions of interest including varying refuse permeability, varying degrees of permeability anisotropy, and temporal atmospheric pressure changes. Simulations showed that the permeable layer decreased methane emissions by 43% when the horizontal to vertical permeability ratio for refuse was kh/kv = 3 and the domain average kh = 3×10?12?m2, while reductions in methane emissions decreased to 17% for the same anisotropy but with kh = 10?11?m2. With this design, barometric pressure changes did not significantly affect oxygen intrusion or methane emission rates.     

Aerobic Methane Oxidation Coupled to Denitrification: Kinetics and Effect of Oxygen Supply

Aerobic methane oxidation coupled to denitrification (AME-D) is a process in which aerobic methanotrophs oxidize methane and release organic compounds that are used by coexisting denitrifiers as electron donors for denitrification. This process is potentially promising for denitrification of wastewater or landfill leachate poor in organic carbon using methane produced onsite as external electron donor. We studied the kinetics of an aerobic methane-oxidizing denitrifying culture and investigated the effect of dissolved oxygen (DO) concentration and air supply rate on AME-D using a batch reactor and a semicontinuous reactor setup. At methane concentrations of 18–33% in air and air flow rates of 15–35?mL?air?L?1?liquid?min?1, the DO concentration was less than 0.01?mg?L?1 and the nitrate removal reached a maximum value of 56.7?mg?NO3–N?g?1?VSS?d?1 with 79% being attributed to denitrification. When the air supply rate was increased to 70?mL?air?L?1?liquid?min?1 resulting in a drop in methane content to 10%, the DO concentration in the bioreactor rose to about 0.8–1.0?mg?L?1 and the total nitrate removal dropped to about 10?mg?NO3–N?g?1?VSS?d?1 with none of it being attributed to denitrification.     

晶格氧部分氧化甲烷制合成气及其氧扩散行为研究

介绍了一种在熔融盐中利用金属氧化物的晶格氧部分氧化甲烷制合成气的新方法。以NiO为氧载体对其部分氧化甲烷的氧扩散行为进行了初步研究。利用XRD和GC等分析手段,在自行设计的氧扩散行为研究反应器中对熔融盐体系和产物气进行了分析研究。结果表明,在800℃的碳酸熔融盐中,CH4通过不含NiO氧载体的熔融盐层时H2、CO浓度仅为13.67%和20%,而通过含NiO氧载体的熔融盐层时H2、CO浓度明显增至45.9%和24.5%;实验表明NiO能够提供出自身晶格氧把CH4部分氧化成n(H2)/n(CO)接近理论值2的合成气;NiO在熔融碳酸盐体系中虽有少量溶解,但主要不以离子化形式扩散氧,而是CH4与NiO分子间发生气固反应占主导,在这一过程中NiO分子中晶格氧是甲烷部分氧化的活性氧物种。