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Geosynthetic clay liners (GCLs) are widely used in landfill and heap-leach facility cover system for mitigating rainfall infiltration and gas migration into atmosphere. Laboratory tests were conducted to investigate methane diffusion and advection through GCLs. Gas permeability coefficient of GCL for the case with moisture content = 47.5% is one and two orders of magnitude greater than the cases with moisture content = 68.5% and 80.9%, respectively, when 20 kPa vertical stress was applied. The batch adsorption tests indicated that adsorption of methane onto bentonite is negligible. The concentration variation for the adsorption of methane onto bentonite can be neglected. However, methane concentration decreased by 14.2% for the test of methane adsorption onto GCL during the first 2–3 days. This is because methane was adsorbed by the geotextiles rather than by the bentonite in GCL. The large porosity and surface area of geotextiles provide lots of micropores for methane adsorption. Analytical model was then developed to analyze the performance of GCL-based liners system with respect to methane transport. The results indicate that methane emission fluxes for the case with SL + GCL are 7.8 and 5.1 times less than the cases with SL + CCL when the moisture contents were 25.9% and 35.1%, respectively. The methane emission fluxes for both of the SL + GCL and SL + CCL can be neglected when they are fully saturated. GCL is recommended to be used in arid and semi-arid regions rather than CCL. GCL is recommended to be used in arid and semi-arid areas rather than CCL. Advection plays a more important role in methane migration through SL + GCL and SL + CCL than that of diffusion. With moisture contents = 25.9% and 32%, methane emission flux attributed to advection accounts for more than 90% of the total emission flux for both cases of SL + GCL and SL + CCL. With the increase of moisture content of SL, the effectiveness of SL in reducing methane emission increases. The saved space for using GCL + SL composite cover compared with using a single SL cover is 0.7 m when the moisture content equals 25.9%, which is 0.5 m greater than the case when moisture content equals 32%. GMB plays a dominant role in inhibiting methane migration and reducing methane emission flux. When moisture content equals 25.9%, the methane emission fluxes for SL + GMB + GCL and SL + GMB + CCL are 343 times and 2643 times less than the cases with SL + GCL and SL + CCL, respectively.

The methane emission in a loess-gravel capillary barrier cover (CBC) in winter and summer was investigated by constructing a full-scale testing facility (20 m × 30 m) with a slope angle of 14.5° at a landfill in Xi’an, China. Weather conditions, methane emission, gas concentration, temperature, and volumetric water content (VWC) in the CBC were measured. The temperature and moisture in the CBC showed a typical seasonal pattern of warm and dry in summer and cold and wet in winter. Accordingly, the maximum methane oxidation rate and methane emission were higher in summer. The mean methane influx and methane emission decreased significantly as the VWC increased beyond 40% (i.e., a degree of saturation 0.85) at a depth of 0.85 m, which was near the loess/gravel interface. At this depth, more water was presented in the loess layer in the downslope direction due to capillary barrier effects, which increased the upslope methane emission. More dominant methane emission in the middle- and upper-section of the CBC occurred in summer than in winter as there was less soil moisture to facilitate methane transfer. The LFG balance showed that a significant fraction of the loaded LFG was not accounted in the flux chamber measurements due to the preferential flow along the edges of the CBC. The maximum methane oxidation rate was 93.3 g CH4 m−2 d−1, indicating the loess-gravel CBC could mitigate methane emissions after landfill closure.

Microbial aerobic methane oxidation (MAMO) has been considered as an environmental-friendly method for mitigating methane emission from municipal landfill sites. Soil column has in a landfill cover under one-dimensional (1-D) condition. However, most of the published soil column tests failed to simulate 1-D heat transfer due to the use of thermal conductive boundary at the sidewall. In the present study, a heavily instrumented soil column was developed to quantify the effects of thermal boundary condition on the methane oxidation efficiency under different ambient temperatures in landfill cover soil. The sidewall of the soil column was thermally insulated to ensure 1-D heat transport as would have been typically expected in the field condition. Two soil column tests with and without thermal insulation were conducted at a range of controlled ambient temperatures from 15 to 30°C, for studying how soil moisture, matric suction, gas pressure, soil temperature and gas concentration evolve with MAMO. The test results reveal that ignoring thermal insulation in a soil column test would result in a greater loss of soil heat generation by MAMO and hence oxidation efficiency by up to 100% for the range of temperature considered. When the ambient temperature increased to 30°C (but less than the optimum temperature for MAMO), the MAMO efficiency increased abruptly at first but then decreased substantially with time, and this is likely due to the accumulation of biomass generated by MAMO.

Gaseous emissions from municipal solid waste (MSW) disposal plants pose serious odor pollution and health risks. In this study, the emission of volatile organic compounds and carbon disulfide was compared in the main processing units of three disposal methods, i.e., landfilling, eco-mechanical biological treatment (EMBT) and anaerobic fermentation in a MSW disposal plant. Among the detected volatile compounds (VCs), the top ten odor compounds were methanethiol, dimethyl sulfide, dimethyl disulfide, carbon disulfide, styrene, m-xylene, 4-ethyltoluene, ethylbenzene, 2-hexyl ketone and n-hexane in the MSW disposal plant. Sulfur compounds were the main source of odor at the majority of sampling sites, and aromatic compounds were the dominant odor substrates at the tipping unit and sorting system of EMBT, while 2-hexanone was the major odor substrate at the tipping unit (AT) and sorting system (AS) of anaerobic fermentation and the landfill working surface. At AS and AT, the lifetime cancer risk values for 1,2-dichloroethane and trichloroethylene exceeded the carcinogenic risk value (>1.0E-04), and the hazard index values of naphthalene, trichloroethylene and acrolein all exceeded the acceptable level (>1). Therefore, special attention should be paid to VC emissions from MSW disposal facilities, and protection measures should be adopted for on-site workers to minimize health risks.

The variation characteristics and influence factors of methane emission at Jiangchungou landfill, one of the largest landfill in China, has been investigated by a one-year field monitoring campaign during 2015-2016. The methane concentration above the landfill surface varied widely from negligible to 33,975 ppm. At least 75% of the methane concentration values of the sampling points are lower than the allowed limit (500 ppm). More than 95% of the high concentration zones (500 ppm) were located in the temporary cover area (TA). Several environmental factors were found to be related to the variation of the concentration values. A clear correlation was observed between barometric pressure and exceeding-standard areas with a correlation coefficient of -0.743 (p 0.1). The concentration values in the final cover area (FA) were about one order of magnitude lower than those observed in the TA due to the fact that rapid methane production rate happened in the first 180 days after the high kitchen content wastes were landfilled. The percentages of the measured concentration values exceeding 500 ppm near the gas collection wells in TA zone were 71.5% in November, 2015 and 55.7% in January, 2016 due to the leakage from the sides of gas collection wells. The average methane concentration values on the HDPE geomembrane was higher than those observed on the loess cover due to the fact that the geomembrane was relatively thin (0.5 mm) and can be easily damaged by the operation vehicles. Thicker geomembranes (1.5 mm) with a good construction quality control are expected to provide better performance at this site.

Aiming at the serious shortage of landfill storage capacity and the urgent need for simple dumps treatment in China, a method to realize the recycling of landfill storage capacity and the environmental treatment of simple dumps is proposed, which determines the stabilization degree of landfill by in-site full-section borehole sampling to test the degradation stabilization index of solid phase of waste, and uses the basically stabilized waste by excavation and screening. Waste samples were taken at different depths by drilling from the Tianziling Landfill (Phase I) which is the first generation sanitary landfill. The construction fractions, combustible fractions and fine fractions were obtained by manual screening, then the determination and analysis of the fine fraction content, particle size distribution, physicochemical characteristic parameters varied with depth were conducted. After that, the variation of fine fraction and contaminant content with the degradation stabilization index, which was proposed herein, were analysed. The feasibility of landfill mining was discussed in the end. The following conclusions were drawn obtained: when the degradation stabilization index, which was suitable to characterize the degree of biochemical degradation of landfilled waste, was over 0.83, the landfilled waste was almost stabilized, the values of electrical conductivity (EC) and chemical oxygen demand (COD) of the leaching solution became stable as well; while the content of heavy metals and organic matter in the fine fractions dissatisfied the requirements of standards. If the fine fractions were treated with re-landfilling, the reduction rate of the fresh waste collected in a mixing way could reach 83% after basically stabilizing through the process of landfilling and mining, therefore landfill mining can effectively realize the recycling of the storage capacity of sanitary landfills.

A newly developed static chamber method with a laser methane detector and a biogas analyser was proposed to measure the landfill gas emissions and methane (CH4) oxidation rates in landfill covers. The method relied on a laser methane detector for measuring CH4 concentration, avoiding gas samplings during test and hence the potential interference of gas compositions inside the chamber. All the measurements could be obtained on site. The method was applied to determine the landfill gas emissions and CH4 oxidation rates in a full-scale loess gravel capillary barrier cover constructed in landfill. Both laboratory calibration and in-situ tests demonstrated that fast (i.e. 4 oxidation rates in landfill site.

Waste mechanics focuses on the degradation characteristics and mechanical behaviors of municipal solid waste (MSW). Knowledge of waste mechanics helps solve the severe geoenvironmental challenges for MSW landfills. This paper first summarized and compared the physical components and chemical composition of MSWs from 20 countries, including developed and developing countries, and proposed a MSW classification system based on the food waste content and the ratio of cellulose to lignin. Secondly, the degradation characteristics between high food waste content (HFWC) and low food waste content (LFWC) MSWs, originated from their differences in chemical composition due to the distinctions in physical components of MSWs, were compared quantitatively by mass loss, leachate generation, landfill gas (LFG) generation, and contaminants in leachate. Thirdly, mechanical behaviors closely related to the degradation characteristics of both HFWC and LFWC MSWs, including permeability, compressibility, shear strength, and lateral pressure, were elaborated on. Fourthly, degrees of hydrolysis, methane generation, and consolidation, calculated by the stabilization-consolidation model, were introduced to characterize the stabilization process of HFWC MSW landfills, which provided a basis for sustainable landfilling for HFWC MSW landfills. The obtained features of HFWC MSW landfills, including the distributions of leachate mounds and LFG, settlement, and slope stability, showed the causes of main geo-challenges at HFWC MSW landfills, including high risks of leachate leakage and slope instability, and low LFG collection efficiency, were consistent with the monitoring results of several cases. Finally, technologies, practices, and designs towards sustainable landfilling for HFWC MSW landfills in China were presented, which could also serve as useful references and guidelines for other countries in similar situations.

Based on the principles of electron currents conservation and mass conservation, this paper considers the two kinds biochemical reactions of organic aerobic oxidation and simultaneous nitrification-denitrification under the condition of aerobic degradation of municipal solid waste (MSW). Select rapid degradation cellulose (RDC), slow degradation cellulose (SDC), total sugar, fat, protein, and microorganisms as the limiting substrates, and write an aerobic biochemical reaction stoichiometric equation that can reflect the mass linkages among various substances. First-order kinetic equations were used to describe the kinetic behavior of biodegradable organics in the process of aerobic degradation, meanwhile the effects of temperature, water content, and oxygen concentration on the aerobic degradation rate of organic matter were also considered. The microorganism decay was described using a first-order kinetic equation. A model with a clear physical meaning and capable of simulating the time-varying process of aerobic degradation of MSW has been established. The robustness of the model still requires instance validation.

In order to have a better understanding of solidified sludge in a sewage sludge disposal pit, field and laboratory investigation were conducted on the geotechnical properties of the solidified sludge at the Qizishan Landfill in Suzhou, China. The field investigation included borehole sampling. The laboratory test involved the measurements of water content, organic matter content and shear strength for the borehole samples taken from Qizishan landfill sludge pit. The tests results demonstrated that the cohesive intercept (c) of the solidified sludge mostly range from 15 to 60 kPa; friction angle (φ) mostly range from 6° to 40°. The unconfined compressive strength for sludge normally about 180 kPa, but the unconfined compressive strength for some cement-like samples up to 250–300 kPa. Above analysis are useful for the in-situ sludge reinforcement methods, such as first in-situ vacuum preloading combined with subsequent solidification treatment. And it can provide the necessary geotechnical parameter and partly basis for sludge disposal design.

This paper examines the effect of temperature, with the range of 20 to 70 °C, on the hydraulic conductivities of remolded sewage sludge from different regions compared with the kaolin and clay. And the hydraulic conductivities of the heated sludge were measured with the confining stress of 60,100 and 200 kPa. The measured values of hydraulic conductivities for all the sludge increase with increasing temperature, and the hydraulic conductivities at 70 °C increase up to about 25–60 times those at 20 °C, while kaolin and clay are 2–4 times. When cooling from 70 °C to 20 °C, the hydraulic conductivities of sludge were about 7 times the initial values at 20 °C, revealing a hysteresis phenomenon. The changes in viscosity of water, the amount of bound water and organic matter contents with increasing temperature contribute greatly to the significant increase of hydraulic conductivity of sludge. The study also showed the hydraulic conductivities of sludge did not decrease with increasing confining stress.

A new simple system for accurately measuring overall total volume changes in unsaturated soil specimens with a triaxial apparatus is introduced in this paper. The basic principle of the measuring system is to record changes in the differential pressure due to changes in the water level inside an open-ended, bottle-shaped inner cell caused by volume change in the specimen and inside a reference tube using an accurate differential pressure transducer. Several important steps were taken to improve the accuracy and sensitivity of the measuring system. Detailed calibrations were carried out to account for apparent volume changes as a result of changes in cell pressure, fluctuation in the ambient temperatures, creep in the inner cell wall, and relative movement between the loading ram and the inner cell. The calibration results demonstrate that the measuring system is reasonably linear, reversible, and repeatable. The estimated accuracy of the measuring system is in the order of 32 mm3 (or 0.04% volumetric strain for a triaxial specimen 38 mm in diameter and 76 mm in height) once the system is properly calibrated.Key words: unsaturated soils, volume-change measurement, open-ended, bottle-shaped, inner cell, differential pressure, calibration.

One field pump test with passive and active condition was conducted in Qingxilu landfill, Hefei city. In passive condition test, the water level and LFG quality of the constructed extraction wells were tested, and it was revealed that the high water level lead to low LFG quality. Through the active pump test implemented in four extraction wells, the following discipline was discovered: (1) There was large volume LFG stored in waste body; (2) the LFG generation rate for the entire landfill above water level could be 1449m3/h at 50% methane in 2008. The Scholl-Canyon model was then employed to estimate annual LFG generation rate over a time period and it could be predicted that the actual LFG collection potential was more than 600 m3/h before 2015 without water drawdown, however, under condition of the water in waste body pumped out, the actual LFG collection potential would be more than 600 m3/h before 2020.

The adsorption of contaminants onto soil particles typically is nonlinear if the contaminant concentration is sufficiently high. A simplified piecewise linear adsorption isotherm consistent with experimental results is proposed as an approximation for nonlinear adsorption behavior. This approximation allows for the use of analytical solution to model solute diffusion of contaminants that exhibit nonlinear adsorption. A moving boundary is introduced to represent significant changes in the retardation factor of clay with an increase in solute concentration. The proposed analytical solutions were validated using experimental data presented in the literature. There is negligible difference between the results obtained by the proposed analytical solution and those obtained by the linear model when C(m)/C(0) reached 0.5. The results also show that the model based on linear adsorption using the initial secant of the Freundlich isotherm leads to significantly lower estimated breakthrough time for the contaminant of interest than that obtained using the proposed model. The earlier breakthrough is due to an under-estimation of the amount of adsorption. The proposed method is relatively simple to apply and can be used for evaluating experimental results and verifying more complex numerical models.

Cadmium is a toxic heavy metal that has caused serious public health problems. It is necessary to find a cost effective method to deal with wastewater containing Cd(II). Loess soils in China have proven to be a potential adsorbent for Cd(II) removal from wastewater. The adsorption capacity of loess towards Cd(II) has been determined to be about 9.37 mg g(-1). Slurry concentration, initial solution pH, reaction time and temperature have also been found to significantly influence the efficiency of Cd(II) removal. The adsorption isotherms and kinetics of loess soil from China can be best-fit with the Langmuir model and pseudo-second order kinetics model, respectively. The thermodynamic analysis revealed that the adsorption process was spontaneous, endothermic and the system disorder increased with duration. The natural organic matter in loess soil is mainly responsible for Cd(II) removal at pH4.2, while clay minerals contribute to a further gradual adsorption process. Chemical precipitation dominates the adsorption stage at pH8.97. Further studies using X-ray diffraction, Fourier transform infrared spectra of Cd(II) laden loess soil and Cd(II) species distribution have confirmed the adsorption mechanism.