Landfill Cover System Research Articles

Effect of temperature on gas breakthrough and permeability of compacted loess in landfill cover

In China, municipal solid waste containing large amounts of kitchen waste possesses the characteristics of lower cellulose content (15% on a dry basis) and a faster CH4 generation rate. This promotes the emission of hazardous gases and the increase in gas pressure in landfill cover systems. The higher temperature further aggravates the aforesaid phenomena. The present work investigated the temperature effect on the gas breakthrough pressure (GBP) and permeability of compacted loess. The water permeability kw increases with increasing temperature. The intrinsic water permeability KW independent of pore fluid properties behaves just in an opposite manner. KW would have been increased with increasing temperature if the rigid wall of the permeameter had not been intervened in the permeability tests. The intrinsic permeability KG also decreases with the increase in temperature. Although the higher KG neglects the gas slippage effect, the combination of the thermal expansion of minerals, the transformation of bound water to free water, and the thermal expansion of free water causes pore water to migrate into macropores. Such a pore water migration is accompanied by the water-gas boundary moving to the vadose zone. On the other hand, the capillary pressure shows a correspondence with the GBP value. The higher temperature reduces the difficulty for gas molecules to overcome the surface tension at the water-gas boundary, corresponding to the lower GBP value. The findings provide critical guideposts concerning the design of the gas breakthrough and permeability of compacted loess in landfill covers under the temperature effect.

Metabolic diversity shapes vegetation-enhanced methane oxidation in landfill covers: Multi-omics study of rhizosphere microorganisms

Vegetation root exudates have the ability to shape soil microbial community structures, thereby enhancing CH4 bio-oxidation capacity in landfill cover systems. In this study, the CH4 oxidation capacity of indigenous vegetation rhizosphere microorganisms within operational landfill covers in Chongqing, China, was investigated for the first time, with the objective of identifying suitable plant candidates for CH4 mitigation initiatives within landfill cover systems. Furthermore, a multi-omics methodology was employed to explore microbial community structures and metabolic variances within the rhizospheric environment of diverse vegetation types. The primary aim was to elucidate the fundamental factors contributing to divergent CH4 oxidation capacities observed in rhizosphere soils. The findings demonstrated that herbaceous vegetation predominated in landfill covers. Notably, Rumex acetosa exhibited the highest CH4 oxidation capacity in the rhizosphere soil, approximately 20 times greater than that in non-rhizosphere soil. Root exudates played a crucial role in inducing the colonization of CH4-oxidizing functional microorganisms in the rhizosphere, subsequently prompting the development of specific metabolic pathways. This process, in turn, enhanced the functional activity of the microorganisms while concurrently bolstering their tolerance to microbial pollutants. Consequently, the addition of substances like Limonexic acid strengthened the CH4 bio-oxidation process, thereby underscoring the suitability of Rumex acetosa and similar vegetation species as preferred choices for landfill cover vegetation restoration.

VOCs emission from a final landfill cover system induced by ground surface air temperature and barometric pressure fluctuation

Volatile organic compounds (VOCs) emission flux and their concentration profiles were measured at a final municipal solid waste (MSW) landfill cover in Hangzhou, China. The influencing parameters, especially ground surface air temperature and pressure were monitored concomitantly. Furthermore, a numerical model incorporating coupled thermo-hydro-chemical interaction to assess VOCs emission from this final landfill cover (LFC) system was developed and validated with the field test results. The tested total VOC emission flux from the final cover is 0.0124 μg/m2/s, which indicates that the total amount of VOCs emitted into the atmosphere is 391 mg/m2 annually. Among these, dichloromethane (DCM) dominated VOCs emission flux during May, comprising 51.8% of the total emission flux. The numerical simulation results indicated that the diffusive emission flux of VOCs varied consistently with the fluctuation of atmospheric temperature. Whereas, the advective flux varied inversely with the fluctuation of barometric pressure. The highest difference in diffusive emission flux induced by temperature variation is 183 μg/m2/day and occurred in spring. Moreover, the results demonstrated that the impact of atmospheric temperature and pressure fluctuation on the emission of VOC from final covers is non-negligible when reasonably assessing the risks of landfill and landfill gas emission budget.

Effects of fine aggregate content on the unsaturated hydraulic characteristics of recycled concrete aggregate

Recycled concrete aggregate (RCA) can be used in landfill and slope cover systems, where its unsaturated hydraulic properties play an important role. The hydraulic behavior of RCAs can be potentially controlled through mixing coarse and fine aggregates by a pre-determined proportion, which lacks experimental validation. In this study, water retention curve (WRC) and permeability function (PF) of RCAs with different fine aggregate contents ( fc) were investigated. Experiments on 9 RCAs with different gradations reveal that when fc is between 20% and 30%, a second air entry value appears, and the shape of both WRC and PF becomes bimodal, which is probably resulted from an uneven dual-peak pore size distribution. With an increasing fc, the first air entry value and the residual water content increases. The unsaturated coefficient of permeability decreases with the increasing fc for a low suction level (<0.1 kPa), but increases with the raise of fc for high suction (>10 kPa). Overall, adopting a properly mixed RCA with fc value of less than 10% or over 40%, instead of a narrowly graded RCA, is recommended for coarse- and fine-grained layers in a capillary barrier, respectively.

Quantitative analysis of TCE biodegradation pathway in landfill cover utilizing continuous monitoring, droplet digital PCR and multi-omics sequencing technology

The remediation of volatile chlorinated hydrocarbons in the quasi-vadose zone has become a significant challenge. We applied an integrated approach to assess the biodegradability of trichloroethylene to identify the biotransformation mechanism. The formation of the functional zone biochemical layer was assessed by analyzing the distribution of landfill gas, physical and chemical properties of cover soil, spatial-temporal variations of micro-ecology, biodegradability of landfill cover soil and distributional difference metabolic pathway. Real-time online monitoring showed that trichloroethylene continuously undergoes anaerobic dichlorination and simultaneous aerobic/anaerobic conversion-aerobic co-metabolic degradation on the vertical gradient of the landfill cover system and reduction in trans-1,2-dichloroethylene in the anoxic zone but not 1,1-dichloroethylene. PCR and diversity sequencing revealed the abundance and spatial distribution of known dichlorination-related genes within the landfill cover, with 6.61 ± 0.25 × 104–6.78 ± 0.09 × 106 and 1.17 ± 0.78 × 103–7.82 ± 0.07 × 105 copies per g/soil of pmoA and tceA, respectively. In addition, dominant bacteria and diversity were significantly linked with physicochemical factors, and Mesorhizobium, Pseudoxanthomonas and Gemmatimonas were responsible for biodegradation in the aerobic, anoxic and anaerobic zones. Metagenome sequencing identified 6 degradation pathways of trichloroethylene that may occur in the landfill cover; the main pathway was incomplete dechlorination accompanied by cometabolic degradation. These results indicate that the anoxic zone is important for trichloroethylene degradation.

Analysis of a landfill cover without geomembrane using varied particle sizes of recycled concrete

Previous studies have demonstrated the effectiveness of a novel three-layer landfill cover system constructed with recycled concrete aggregates (RCAs) without geomembrane in both laboratory and field. However, no systematic investigation has been carried out to optimize the combination of the particle sizes for fine-grained RCAs (FRC) and coarse-grained RCAs (CRC) that can be used for the three-layer landfill cover system. The aim of this paper is to assist engineers in designing the three-layer landfill cover system under a rainfall of 100-year return period in humid climate conditions using an easily controlled soil parameter D 10 of RCAs. The numerical study reveals that when D 10 of FRC increases from 0.05 mm to 0.16 mm, its saturated permeability increases by 10 times. As a result, a larger amount of rainwater infiltrates into the cover system, causing a higher lateral diversion in both the top FRC and middle CRC layers. No further changes in the lateral diversion are observed when the D 10 value of FRC is larger than 0.16 mm. Both the particle sizes of FRC and CRC layers are shown to have a minor influence on the percolation under the extreme rainfall event. This implies that the selection of particle sizes for the FRC and CRC layers can be based on the availability of materials. Although it is well known that the bottom layer of the cover system should be constructed with very fine-grained soils if possible, this study provides an upper limit to the particle size that can be used in the bottom layer ( D 10 not larger than 0.02 mm). With this limit, the three-layer system can still minimize the water percolation to meet the design criterion (30 mm/yr) even under a 100-year return period of rainfall in humid climates.

Effects of plant-biochar interaction on the performance of a landfill cover system: field monitoring and numerical modelling

Biochar has been used as a sustainable amendment to moderate the risks of climate change to plant and soil management. A 3-year field monitoring was conducted at Shenzhen Xiaping landfill to evaluate the performance of a three-layer landfill cover using plant and biochar. Coarse-grained completely decomposed granites (CDG) amended with peanut shell biochar at 0%, 5% and 10% (m3/m3) were used for the top layers of three grass plots (10 m×5 m each), respectively. Coarse recycled concrete and fine-grained CDG were used for the middle and bottom layers of all plots. Numerical simulation was conducted to back analyse the monitored results. The results show that the grassed cover with biochar can retain over four times higher negative pore-water pressure than that without biochar. During the monitoring, over 62% of total rainfall was evapotranspirated from biochar amended covers, which was 10% larger than the cover without biochar. With biochar amendments, the infiltration amount was reduced by 13%, but water storage was improved by up to 15%. The measured and computed percolation of the grassed covers with 0%, 5% and 10% biochar meet the recommended criterion by USEPA. It is recommended that 5% biochar content is sufficient to minimise water percolation.

WITHDRAWN: Physical and numerical modelling of a vegetated three-layer landfill cover system using recycled aggregates without a geomembrane

WITHDRAWN: Physical and numerical modelling of a vegetated three-layer landfill cover system using recycled aggregates without a geomembrane

Analytical solution for coupled water–gas transport in unsaturated landfill cover system with different root architectures

This study presents an analytical solution for coupled water–gas transport in a landfill cover system considering four different root architectures (i.e., uniform, triangular, exponential and parabolic architectures), which can consider transient diffusive-advective transport of gas under steady-state water distributions in different condition (e.g., rainfall stage and evaporation stage). The proposed solution is verified against an existing analytical solution, validated against an experiment, and compared with a numerical solution. Using the verified analytical solution, simulations were conducted on the coupled water–gas transport. The results show that ignoring water transport can lead to significant error in gas transport results under various conditions (e.g., the methane flux is underestimated by 45% due to ignoring water transport, when the desaturation coefficient α is 0.1 m−1). The parametric study results indicate that triangular and exponential root architectures have greater effect on water–gas transport (e.g., pore-water pressure, gas emission fluxes) compared with the uniform and parabolic root architectures; vegetation has a significant impact on the water–gas transport, especially in dry conditions (e.g., the gas emission flux through vegetated cover is about 26.3% lower than that through the bare cover); the rainfall intensity and volumetric water content at the bottom boundary have significant effect on water–gas transport in the cover. The proposed analytical solution can be used to aid the design of vegetated soil cover system and the verification of other more complex models.

Life cycle assessment of novel biogeochemical cover versus conventional soil cover

The aim of this study is to evaluate the functional performance and environmental impacts of recently proposed biogeochemical cover (BGCC) system at a municipal solid waste landfill and compare with the conventional soil cover (SC) system. The functional performance of the cover systems was assessed through infiltration, methane emissions and slope stability analyses. In addition, life cycle assessment (LCA) was performed to evaluate the environmental impacts of the cover systems. The study also assessed the effect of various factors such as biochar manufacturing process, mode of transportation (fossil fuel powered vehicles versus electric powered vehicles), and transportation distance for raw materials supply on the environmental impacts. The results showed that the BGCC can significantly reduce the greenhouse gas emissions and global warming in comparison to the SC due to the use of biochar amended soil and basic oxygen furnace (BOF) slag. BGCC had 69 times more reduction in global warming impacts than SC which was attributed to the high methane oxidation potential of the biochar amended soil and carbon dioxide sequestration capacity of BOF slag. Moreover, BGCC had lesser environmental impacts than SC, mainly in the categories of eutrophication, carcinogens, non-carcinogens, respiratory effects, and ecotoxicity. Reducing transportation distance for biochar supply led to further reduction of the environmental impacts associated with the BGCC. For example, reducing the biochar procurement distance from 300 km to 100 km reduced the impacts from smog, acidification, eutrophication, and fossil fuel depletion by 14%, 13%, 5% and 14%, respectively. In addition, switching the vehicle from diesel powered to electric powered for transportation of raw materials led to significant reduction in fossil fuel depletion, smog, acidification and ecotoxicity in both BGCC and SC. For example, the fossil fuel depletion reduced by 97% and 39% in BGCC and SC, respectively by switching the fuel source. In addition, BGCC had overall positive impact on the human health and ecosystem whereas SC showed potential damage to human health. Overall, BGCC system proves to be an environmentally sustainable alternative to landfill cover system with significant potential for mitigation of greenhouse gases and odor from MSW landfills.

Hydraulic performance assessment of a multi-layered landfill cover system under constant water ponding

Abstract The engineered multi-layered cover system (MLCS) is used to minimize rainwater infiltration into the wastes accommodated in near surface waste disposal facility (NSDF). It is important to assess the hydraulic performance of MLCS before deploying it in the field. For this purpose, an instrumented three-layered soil column representing MLCS was subjected to 1.5 m constant ponding head for 400 days. The variation of volumetric water content and soil water potential was monitored as a function of depth and time. The objective of the study is to understand the long-term hydraulic performance and rate of saturation of different layers of MLCS. Under constant water ponding, the time to saturation for 0.3 m in surface layer, 0.6 m in drainage layer and 1.0 m in hydraulic barrier layer was observed as 24, 223 and 262 days, respectively. The numerical analysis of the MLCS predicted comparable time duration of 25, 234 and 272 days, respectively. It was noted that the numerical simulation performed by using measured wetting hydraulic parameters matched well with the experimental observation. The importance of soil specific calibration of water content sensors to improve the accuracy of observations was demonstrated. Percentage error in the estimation of layer specific soil water storage, clearly indicates that the volumetric water content measurements using profile probe was marginally better than 5TM measurements.

A steady-state analytical model for coupled methane transport and oxidation in vegetated landfill cover soil

The biologically active soils covered by plants are widely applied in landfill final covers for controlling the emission of methane from municipal solid waste. The current study focuses on developing alternative formulations of steady-state analytical modeling for coupled methane transport and oxidation in vegetated landfill cover systems considering the effect of mass exchange via plants’ roots. The proposed analytical frameworks are validated by a set of experimental data. The varied examples of coupled methane transport and oxidation are evaluated by the proposed solution to discuss the effects of the properties of roots and soils on the overall performance of vegetated landfill covers. It was shown that the increment of the root depth or root density can effectively contribute to the reduction of CH4 emission from landfill cover systems while coupled effects of advection/diffusion and oxidation rate may influence the overall performance of CH4 transport. For example, increasing root density from 100 m/m3 to 3 × 103 m/m3 can lead to a reduction of CH4 emission rate by a factor of 1.3. This is mainly attributed to the increase of aerobic zone with the root density growing. It is found that the methane removal efficiency is more sensitive to variations of the saturation outside the root zone (S2) than that in the root zone (S1) as gases inlet fluxes are largely reduced and the role of the plant is weakened for a larger S2. The present analytical models may provide an easy-to-use tool for performance evaluation of cover systems, benchmark studies, parameter identification and sensitivity analysis.

Numerical investigation on hydraulic and gas flow response of MSW landfill cover system comprising a geosynthetic clay liner under arid climatic conditions

Municipal solid waste (MSW) landfill cover systems are designed to minimize the infiltration of rainwater into waste and to mitigate the biogas emissions to the atmosphere. In the present study, the efficacy of such a landfill cover system consisting of a Geosynthetic clay liner (GCL)in mitigating the hydraulic flow and gas emissions under arid climatic conditions was investigated critically. For this purpose, the water retention curve (WRC), hydraulic conductivity function, and gas flow characteristics of the chosen GCL were studied through experimental methods in the laboratory. The unsaturated transient state seepage analysis utilizing coupled hydraulic and gas flow mechanisms was performed in the study to assess the performance of the cover system. The results obtained from the experiments were used as input parameters. The effect of drying/desiccation and the self-healing nature of GCL due to climatic changes were also analyzed by exposing the GCL directly to the climatic boundary for one year. It was observed that the GCL present in the chosen cover system effectively functions as a hydraulic barrier in arid climatic conditions. However, during the summer and winter seasons, an increase in gas flow from 0.02 g/h/m2 to 24.7 g/h/m2 was observed, probably due to the drying anddesiccation of GCL. Interestingly, due to the self-healing nature of the GCL, gas flow through the cover system was substantially reduced to 0.02 g/h/m2 during the rainy season. The effect of drying was more pronounced when the GCL was exposed to the climatic condition, leading to an early gas breakthrough and an increase in gas flow from 0.02 g/h/m2 to 957 g/h/m2. The percolation through the cover system remains considerably low throughout the year, mostly due to the unsaturation and low hydraulic conductivity in GCL. A cumulative percolation close to 0.1 m3 was observed at the end of one year in arid climatic conditions.

Long-term field performance of non-vegetated and vegetated three-layer landfill cover systems using construction waste without geomembrane

This paper compares the field performance of non-vegetated and vegetated three-layer landfill cover systems utilising construction waste but without geomembrane at the Shenzhen Xiaping landfill site in humid climates over a monitoring period of 54 months. The top layer of each cover system was constructed using coarse-grained completely decomposed granite (CDG). The middle and bottom layers were compacted with coarse recycled concrete (CRC) and fine-grained CDG, respectively. Numerical analyses were also carried out. During the 54-month monitoring period, the cumulative rainfall recorded was 9800 mm. Retained pore water pressure in the vegetated cover was close to that in the non-vegetated cover after the heaviest rainfall recorded in Shenzhen during the monitoring period. The pore water pressure retained in the vegetated cover can be higher than that in the non-vegetated cover due to the increased saturated water permeability (ks) induced by plant growth over 3 years. Surface runoff and water storage capacity in the vegetated cover were about five times and 9% higher than those in the non-vegetated cover, respectively. However, the long-term behaviour of the cover system in respect of these two aspects was influenced by the increase of ks due to the growth of grass roots. The middle CRC layer diverted infiltrated water by up to 51% of total rainfall. The measured average annual percolation of the non-vegetated and vegetated covers was about 23 mm and 21 mm, respectively. The measured data are supported by numerical analyses and they meet the US recommended criterion.

Numerical model for static chamber measurement of multi-component landfill gas emissions and its application

The quantitative assessment of landfill gas emissions is essential to assess the performance of the landfill cover and gas collection system. The relative error of the measured surface emission of landfill gas may be induced by the static flux chamber technique. This study aims to quantify effects of the size of the chamber, the insertion depth, pressure differential on the relative errors by using an integrated approach of in situ tests, and numerical modeling. A field experiment study of landfill gas emission is conducted by using a static chamber at one landfill site in Xi’an, Northwest China. Additionally, a two-dimensional axisymmetric numerical model for multi-component gas transport in the soil and the static chamber is developed based on the dusty-gas model (DGM). The proposed model is validated by the field data obtained in this study and a set of experimental data in the literature. The results show that DGM model has a better capacity to predict gas transport under a wider range of permeability compared to Blanc’s method. This is due to the fact that DGM model can explain the interaction among gases (e.g., CH4, CO2, O2, and N2) and the Knudsen diffusion process while these mechanisms are not included in Blanc’s model. Increasing the size and the insertion depth of static chambers can reduce the relative error for the flux of CH4 and CO2. For example, increasing the height of chambers from 0.55 to 1.1 m can decrease relative errors of CH4 and CO2 flux by 17% and 18%, respectively. Moreover, we find that gas emission fluxes for the case with positive pressure differential (∆Pin-out) are greater than that of the case without considering pressure fluctuations. The Monte Carlo method was adopted to carry out the statistical analysis for quantifying the range of relative errors. The agreement of the measured field data and predicted results demonstrated that the proposed model has the capacity to quantify the emission of landfill gas from the landfill cover systems.

Transformation mechanism of carbon tetrachloride and the associated micro-ecology in landfill cover, a typical functional layer zone

Landfill is one of the important sources of carbon tetrachloride (CT) pollution, and it is important to understand the degradation mechanism of CT in landfill cover for better control. In this study, a simulated landfill cover system was set up, and the biotransformation mechanism of CT and the associated micro-ecology were investigated. The results showed that three stable functional zones along the depth, i.e., aerobic zone (0-15 cm), anoxic zone (15-45 cm) and anaerobic zone (> 45 cm), were generated because of long-term biological oxidation in landfill cover. There were significant differences in redox condition and microbial community structure in each zone, which provided microbial resources and favorable conditions for CT degradation. The results of biodegradation indicated that dechlorination of CT produced chloroform (CF), dichloromethane (DCM) and Cl- in anaerobic and anoxic zones. The highest concentration of dechlorination products occurred at 30 cm, which were degraded rapidly in aerobic zone. In addition, CT degradation rate was 13.2-103.6 μg/(m2·d), which decreased with the increase of landfill gas flux. The analysis of diversity sequencing revealed that Mesorhizobium, Thiobacillus and Intrasporangium were potential CT-degraders in aerobic, anaerobic and anoxic zone, respectively. Moreover, six species of dechlorination bacteria and eighteen species of methanotrophs were also responsible for anaerobic transformation of CT and aerobic degradation of CF and DCM, respectively. Interestingly, anaerobic dechlorination and aerobic transformation occurred simultaneously in the anoxic zone in landfill cover. Furthermore, analysis of degradation mechanism suggested that generation of stable anaerobic-anoxic-aerobic zone by regulation was very important for the harmless removal of full halogenated hydrocarbon in vadose zone, and the increase of anoxic zone scale enhanced their removal. These results provide theoretical guidance for the removal of chlorinated pollutants in landfills.

Experimental Study on the Effect of Hemp Fiber on Mechanical Properties of Stabilized Clayey Soil

ABSTRACT Clayey soils have fine particles and contain clay minerals. Therefore, they are sensitive to water and cause stability problems. Nowadays, soil stabilization is an accepted method to resolve the problem of stability. In this study, hemp fiber was used as an additive material for stabilization of clayey soil. The use of fibers in the stabilization of clayey soils is becoming widespread, particularly with regard to applications involving the stabilization or reinforcement of shallow steep earth slopes and steep cover systems for landfills. In these applications, the use of natural fibers use is very important due to their environmentally friendly properties. Hemp legally planted in different countries is used in several industries, such as paper, textiles, clothing, biodegradable plastics, construction, body products, health food, and biofuel. In this study, hemp fiber was preferred because of its natural and environmentally friendly properties. To observe the effect of hemp fiber on the compressive strength of clayey soil material, the unconfined compression tests and shear box tests were carried out under laboratory conditions. The experimental results showed that hemp fiber is effective on the compressive strength of clayey soils. As a result, hemp fiber can be used successfully in clayey soil stabilization as an environmentally friendly material.

Field trial of a reinforced landfill cover system: performance and failure

The geotechnical stability of an inclined multilayer capping depends on the shear strength available along the various interfaces. If the slope is very steep an additional reinforcing geosynthetic may be used to obtain a safer condition. Full-scale field trials can provide better resolution data on the reinforcement behaviour than conventional calculation methods based only on laboratory tests. The paper deals with a field trial carried out on multilayer capping, reinforced with a geogrid, in an Italian landfill. The geogrid behaviour was monitored for a month using displacement sensors and pressure cells located along the slope and in the anchor trench. Subsequently, the cover system was led to collapse by cutting the reinforcement and an analysis of the reinforcement behaviour and its relevance in the system stability were studied. This paper discusses in detail the setup of the field trial and the experimental data recorded during installation, monitoring, and failure phases of the system. The deformation behaviour of the geogrid during the entire test was recorded and analysed. The resulting data highlight the effects of the construction process on the geogrid behaviour including the contribution of geogrid creep characteristics until the failure.

Use of methanotrophically activated biochar in novel biogeochemical cover system for carbon sequestration: Microbial characterization

Biochar-amended soils have been explored to enhance microbial methane (CH4) oxidation in landfill cover systems. Recently, research priorities have expanded to include the mitigation of other components of landfill gas such as carbon dioxide (CO2) and hydrogen sulfide (H2S) along with CH4. In this study, column tests were performed to simulate the newly proposed biogeochemical cover systems, which incorporate biochar-amended soil for CH4 oxidation and basic oxygen furnace (BOF) slag for CO2 and H2S mitigation, to evaluate the effect of cover configuration on microbial CH4 oxidation and community composition. Biogeochemical covers included a biochar-amended soil (10% w/w), and methanotroph-enriched activated biochar amended soil (5% or 10% w/w) as a biocover layer or CH4 oxidation layer. The primary outcome measures of interest were CH4 oxidation rates and the structure and abundance of methane-oxidation bacteria in the covers. All column reactors were active in CH4 oxidation, but columns containing activated biochar-amended soils had higher CH4 oxidation rates (133 to 143 μg CH4 g−1 day−1) than those containing non-activated biochar-amended soil (50 μg CH4 g−1 day−1) and no-biochar soil or control soil (43 μg CH4 g−1 day−1). All treatments showed significant increases in the relative abundance of methanotrophs from an average relative abundance of 5.6% before incubation to a maximum of 45% following incubation. In activated biochar, the abundance of Type II methanotrophs, primarily Methylocystis and Methylosinus, was greater than that of Type I methanotrophs (Methylobacter) due to which activated biochar-amended soils also showed higher abundance of Type II methanotrophs. Overall, biogeochemical cover profiles showed promising potential for CH4 oxidation without any adverse effect on microbial community composition and methane oxidation. Biochar activation led to an alteration of the dominant methanotrophic communities and increased CH4 oxidation.

Effects of biochar on soil water retention curves of compacted clay during wetting and drying

Compacted clay possesses a low water permeability and has been widely used in geo-environmental facilities such as landfill cover systems. Recent studies revealed the potential applications of compacted biochar-amended clay (BAC) as an alternative landfill cover soil. However, the effects of biochar on the soil water retention curves (SWRCs) of clay at low suction are not known. This study can help fill this knowledge gap by measuring the wetting and drying SWRCs of clay and BAC (20% biochar). Soils were compacted in instrumented soil columns and subjected to a wetting and drying cycle, and soil water content and suction were measured along with the soil depth. BAC was saturated faster when compared with clay. Upon drying, the soil water content of clay at 65 mm depth dropped to almost zero, while about 5% of water was retained in BAC. It showed that biochar increased the soil water retention capacity of compacted clay upon drying. SWRCs showed that biochar-clay composite possesses a higher soil water retention capacity at a low soil suction range (< 1000 kPa) compared with clay alone. It revealed the benefits of using compacted biochar-clay composite as a hydraulic barrier to minimize desiccation-induced cracks and potentially promote its serviceability, especially in arid and semi-arid regions. The composite is also a carbon sink material that can reduce landfill gas emissions and pollutant leaching.