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Article

Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover

by
Tariq M. Bajwa
1,*,
Mamadou Fall
2 and
Fahad Alshawmar
3
1
Institute of Civil Engineering, School of Civil and Environmental Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan
2
Department of Civil Engineering, University of Ottawa, Ottawa, ON K1N 6N5, Canada
3
Department of Civil Engineering, College of Engineering, Qassim University, Buraydah 51452, Saudi Arabia
*
Author to whom correspondence should be addressed.
Appl. Sci. 2022, 12(9), 4276; https://doi.org/10.3390/app12094276
Submission received: 2 March 2022 / Revised: 8 April 2022 / Accepted: 18 April 2022 / Published: 23 April 2022
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Abstract

:
A landfill biocover system optimizes environmental conditions for biotic methane (CH4) consumption that controls the fugitive and residual emissions from landfills. Research shows that wasted compost material has more (CH4) oxidation potential than other materials. Thus, in this study, the authors investigate the engineering properties of compacted compost to test its suitability for CH4 oxidation capacity. Different laboratory and analytical approaches are employed to attain the set objectives. The biochemical tests show that the studied material indicates the presence of methanotrophs with sufficient organic contents. The compacted compost also shows adequate diffusivity potential to free air space for a wide range of water content. The data also imply that compacting compost to low hydraulic conductivity can be accomplished for a wide range of water content, according to the suggested values for a landfill hydraulic barrier. Furthermore, the low thermal properties of compost as compared to other mineral materials seem more beneficial, as specifically, during the winter season, when the atmospheric temperature is low, low thermal conductivity enables it to sustain a stable temperature for the activities of the microbial organisms, which therefore extends the CH4 oxidation process right through a long period in the winter.

1. Introduction

Municipal solid waste landfills are the third-largest source of anthropogenic methane (CH4) emissions in the atmosphere [1,2], which contribute 9 to 70 Tg/year of CH4 to the environment [3,4], and which therefore have a significant adverse impact on global climate change [5]. Enormous health benefits are associated with climate change mitigation [6]. The occurrence of the anaerobic degradation of municipal solid waste results in the production of two essential gases, namely, carbon dioxide (CO2) and CH4, and CH4 has 25 to 28 times more global warming potential (GWP) than CO2 due to its more significant molar absorption coefficient, despite its smaller quantity in the atmosphere according to the IPCC’s 4th and 5th assessment reports, respectively [7,8]. CH4 is second in order after CO2 for atmospheric concentration [9]. According to Yuan [4], landfills in the USA contribute about 30–35% of CH4 to the atmosphere. Two main approaches can be used to mitigate landfill gas (LFG). From 40% to 90% of LFG can be used for commercial recovery utilizing a network of collection pipes. The remaining gas passes through an intermediate, final cover and, in some cases, through adjoining lateral areas [10]. However, commercial recovery is not economically feasible if the landfills are small or biodegradation is slow.
In such scenarios, a layer of biocover is incorporated into the landfill cover system. The biocover is an integral part of the landfill system. The CH4 gas that passes through a biocover transforms into CO2. Methanotrophs are bacteria that actively convert CH4 into CO2 under aerobic conditions through microbial oxidation [11]. These bacteria consume methane as their food and release it in carbon dioxide, utilizing their metabolism under aerobic conditions. The process is known as microbial methane oxidation. Different materials, such as soil, compost, and mixtures of sand and compost, can construct landfill biocovers. According to [12,13,14,15], compost material has more oxidation capability than other materials. The basic principle of a landfill biocover is to keep the landfill CH4 emission at zero, or a negligible amount for a specified thickness, which can be achieved by establishing a balance between the quantities of CH4 gas generation and consumption. However, biocover design is quite complex due to the number of parameters involved, such as thermal (T; temperature, thermal conductivity, thermal diffusivity, specific heat), hydraulic (H; hydraulic conductivity, water content and degree of saturation, diffusivity, so forth), biological (B; methanotrophs) and chemical (C; organic and inorganic contents) factors that can affect its performance. Figure 1 shows the scheme of a compost-based landfill biocover.
Various research studies, e.g., [4,9,13,16,17,18], have reported the strong impact of water content variations on the performance of covers for CH4 oxidation and stressed a need to define a proper range of water content for the microbial oxidation process in a cover medium. The degree of saturation may affect the landfill cover in different aspects such as (i) the degradation phenomenon, (ii) the gas flow through a medium, and (iii) geotechnical stability of the cover. Yuan [4] explains that CH4 oxidation occurs at a certain water content. For high water content, the gaseous phase molecular diffusion is transformed into aqueous phase molecular diffusion due to filling the pores with water, which considerably reduces the oxidation process.
Similarly, at low water content, the CH4 oxidation capability is also reduced due to insufficient microbial activity in the cover materials. The study further reports that aqueous diffusion is 104 times slower than gaseous phase diffusion. Huber-Humer et al. [13] show that methanotrophic microorganisms tend to become inactive enzymes at less than 13% water content. According to Yuan [4], oxidation tends to become zero at less than 6% water content and increases up to 56% under saturation conditions. The optimal oxidation water content is different for different cover materials such as soil, compost, and a combination of compost and soil.
Gas transport is another crucial process that may considerably affect the CH4 oxidation rate, as the availability of O2 is essential for CH4 oxidation purposes [19]. According to Scheutz et al. [14], the CH4 oxidation process is directly associated with the O2 penetration potential of landfill cover soil, and Diaz et al. [20] report that O2 is the primary element that maintains the respiratory and metabolic activities of microbes, which actively take part in the CH4 oxidation process. Haug [21] highlights the importance of O2 for a compost-based cover, reporting that methane oxidation potential is directly related to water content and free air space. According to studies, such as [9,21,22], the free air space ranging from 20% to 35% establishes the maximum oxygen consumption rate, i.e., 95%. Pokhrel [9] suggests that a water content between 25% and 75% in the landfill cover provides maximum CH4 oxidation potential. The optimum conditions for microbial biodegradation occur at a water content level and free air space level of 60% and 22%, respectively. Gas transport is generally governed by diffusion. The diffusion coefficient is employed in transport and reaction-based mathematical models to predict gas transport and microbial degradation [23], directly linked with the free air space [3,24]. It means that it is essential to identify optimum conditions for water content, free air space, and relative diffusion coefficient regarding the CH4 oxidation potential of landfill biocovers, as inadequate free air space and low or high water content/degree of saturation may undoubtedly reduce the CH4 oxidation process in landfill biocover, due to insufficient supply of O2 to microbial organisms.
The hydraulic conductivity of traditional (soil cover) and biocover is another critical parameter for a cover design regarding its structural suitability and methane oxidation potential. It is well understood that a low permeable cover reduces rainfall infiltration, which results in the saturation of cover material during the rainy season [25]. Studies have shown that when saturation reaches approximately 85%, gas diffusion should be completed in the liquid phase, much slower than in the gas phase [14,26]. It can radically decrease CH4 oxidation due to the lack of both O2 and CH4 in the biocover [14]. It means that optimum hydraulic conductivity of biocover can support an appropriate gas exchange process and minimize rainfall infiltration and subsequent biocover saturation, which can drastically reduce the CH4 oxidation rate.
Furthermore, the research studies [4,7,27,28] state that CH4 oxidation in biocovers is considerably correlated with temperature. Haug [21] states that compost material’s chemical reaction and biological activity occur within a specific temperature range. The temperature beyond this range produces inactive enzymes, insufficient to generate the desired response for microbes. According to Pokhrel [8], CH4 oxidation of various media is different at different temperatures, and the optimal temperature for CH4 oxidation varies from 20 °C to 35 °C. Cabral et al. [27] report that the optimum temperature for CH4 oxidation is 25 °C in landfill cover material, and according to Pokhrel [9], the growth rates of microbial species are highly related to thermal properties along with some other parameters, such as water content, porosity, and permeability. Other studies such as Majdinasab and Yuan [16], Cabral et al. [27], Tan [29], Chandrakanthi et al. [30], and Abu-Hamdeh [31] report that the thermal properties of cover materials depend upon water content, porosity, dry density, organic matter, free air space, contact surface area, air-dry wetness, and degree of saturation. Thermal properties such as thermal conductivity (λ), thermal diffusivity (α), and specific heat (Cp) express the rate of heat dissipation and thus can control the temperature and therefore the microbial oxidation process in the cover media [27,30]. The optimum range of thermal properties is considered essential in designing landfill biocovers. Furthermore, the thermal properties of compost are also considered critical for the determination and the modelling of the heat transfer between the biocover and the atmosphere and between the biocover and the underlying landfill waste. However, heat transfer modelling is out of scope at this stage of the study, and the thermal properties are examined for various initial conditions only.
Some recommendations are available in the literature on compost materials for geotechnical properties, but the data are not explicit regarding CH4 oxidation potential. Thus, the main objective of this paper is to investigate the engineering properties of the compost-based landfill biocover for wide ranges of water content and dry unit weight (compaction curve). Different laboratory protocols and empirical methods are employed to attain the set objectives. Before a detailed investigation, the compost was tested for organic contents initially. The test results show that the studied material is a better option to be used as a cover material. It shows favorable hydraulic and thermal properties, considering the CH4 oxidation mechanisms, compared to other compost and mineral materials under similar conditions.

2. Materials and Methods

2.1. Materials Used

Composting is an aerobic breakdown of organic materials by microorganisms under controlled conditions [32]. The compost materials used in this study were received from Lafleche Inc. of Canada, which processes organic materials in its state-of-the-art compost facility. The compost facility utilizes an aerated and agitated channel arrangement within a primary enclosure for environmental control of moisture, air, and odor. All handling areas, including channels within the primary containment, are further contained within a secondary structure for protection against the elements (wind, rain, snow), containment of materials, and supplementary control of air and odor. The compost facility is constructed on a poured reinforced concrete slab, entirely enclosed by a fabric shelter building. The facility receives biodegradable feedstock and bulking agents, including food scraps, processing residues, municipal-separated organics, paper/cardboard, and leaf and yard waste. The process mechanically agitates the materials in channels equipped with forced aeration. The composting process, including the blending of organics and the active composting process, is carried out indoors. The above-noted organic materials are mixed in an industrial-grade mixer to achieve a homogeneous blend with a proper carbon-to-nitrogen ratio and moisture content. The compost feedstock and bulking agents undergo an active composting phase for a minimum of 25 days. It can also undergo a curing phase before being beneficially used as an agricultural soil amendment, soil additive, or cover material.
The compost with a bulk density of 650 gm/cm3 was received from Lafleche Inc., Canada, and stored in a cold room at the University of Ottawa, Canada, maintaining a temperature of 2~3 °C. A required quantity of samples was transferred to the geotechnical laboratory for each testing program. The compost was placed in the covered pails in the laboratory to preserve the natural water content and other properties. The thermal and hydraulic tests were not performed in the standard effort compaction molds due to the sensitive nature of the compost. The samples were damaged while being pulled out of the mold with a hydraulic jack, so special molds were manufactured, keeping in view the sensitive nature of the tested material and other requirements of these tests.

2.2. Methods Employed

2.2.1. Chemo-Biological Tests

Figure 2 shows the processes and parameters involved in chemo-biological tests of compost materials. Figure A1 in the Appendix A shows the schematic sketch of agarose gel electrophoresis, and Figure A2 shows the wavelength for chromium in the compost sample during ICP tests.

2.2.2. Moisture Density Relationship Tests

Standard Proctor tests were performed at different water contents to obtain the compaction curve of compost material, following the guidelines as discussed in ASTM D 698-07 standard [34]. First, the desired quantity of compost was passed through the #4 sieve and placed back in the covered pail to preserve the existing water content. Before performing the test, each sample was mixed uniformly in a large mixing pan with the specified water content. Each addition of water resulted in clods of different sizes in the beginning. However, each test was performed after assuring uniform mixing of the sample with water. The compaction tests were carried out for a wide range of water content on both sides of optimum water content, which was due to examining the behavior of compost material (porosity, free air space, and relative diffusion coefficient) for a lower and higher degree of saturation. Replicate samples were prepared at each water content level to ensure the repeatability of test data. Each sample was used only once and discarded after the test. The compost material showed different behavior at a high and low degree of saturation. For wet optimum, the specimen started to jump out of the compaction mold while hammering, and this situation arose for samples with more than 100% water content. Similarly, the finer particles of the sample were also observed coming out of the compaction mold during compaction for the dry optimum segment. However, no issues were noticed for water contents ranging from 55% to 100%.

2.2.3. Relative Diffusion Coefficient

Fick’s law describes the rate at which the air can pass through any medium. The diffusion theory of gases depends on the kinetic molecular theory of gases, and the design of biocover demands an understanding of physical processes such as gas transport and microbial degradation. According to Pokhrel et al. [24], the effects of molecular diffusion are much higher than mechanical dispersion in biocover systems. The molecular diffusion coefficient of a gas in a porous medium, such as compost and soil, is less than that in the atmosphere due to the reduced cross-sectional area available for gas movement and tortuosity of flow paths. Therefore, the molecular diffusion coefficient is expressed in terms of relative diffusion coefficient, i.e., ξ = D/Do, where D = gas diffusion coefficient in a porous medium (L2/T) and Do = atmospheric gas diffusion coefficient (L2/T), which is independent of the nature of the diffusing gas. Still, it is a function of media properties, such as air and porosity. The model in [35] was employed to determine the relative diffusion coefficient with free air space for the compaction curve of the compost materials.

2.2.4. Hydraulic Conductivity Tests

Hydraulic conductivity tests were performed following the procedure described in ASTM D 5084-10 standard [36]. A flexible wall constant head method was employed to determine the hydraulic conductivity of compost materials. First, the compost sample was mixed thoroughly in a mixing pan with a specified quantity of water following the compaction curve. After that, the sample was transferred to a small metallic compaction mold with a 5 cm diameter and 11.5 cm depth, and a small metallic tamper was used to compact the specimen. The specimen was compacted in three equal layers with 30 blows for each layer, adjusted by the trial and error method before starting the test with original samples. The compaction was performed to reach the same dry unit weight and water content as determined in the standard compaction effort (ASTM D 698-07) [34]. The compacted sample was taken out of the mold and trimmed with a sharp knife to remove the anomalies and make it per permeameter specifications. The trimming was also necessary to eliminate the blockage of pores, which occurred due to blows of the tamper at the top surface. Sometimes, the sample was broken into pieces, especially at low water content, and the test had to be repeated. The prepared sample was carefully transferred into a triaxial cell without damaging its edges. The sample was fixed in the test cell with extreme care to eliminate any chances of air inside the cell. The cell was filled with water and connected to a triplex device through the lateral, upper, and lower ports.
Benson and Othman [25] reported that the seepage force produces effective stress of 15–20 kPa in a landfill cover. They suggested using a hydraulic gradient of 10 or higher to examine the hydraulic conductivity of landfill cover materials. Thus, a hydraulic gradient of 20 was maintained in this study during the test, adjusting the upper and lower burette of permeater channels. Saturation was achieved by bridging the influent and effluent lines and applying backpressure. Saturation was considered complete after verifying influent intake against effluent water volume supply until they became equal.
Furthermore, post-test determination of the degree of saturation for some samples was undertaken to confirm the complete saturation of the samples tested. The head difference was generated in a specimen by adjusting the upper and lower burettes of the channels. After saturation was completed, the upper and lower burettes were bridged to the same pressure for a few minutes to equalize the pressure inside the specimen. A hydraulic gradient was applied to the sample placed in a triaxial cell to determine its permeability. The water level in the upper and lower burettes was recorded at increased time intervals. Finally, an average was taken to obtain accurate results. The same process was repeated for all samples. Figure 3 shows the equilibrium condition for the saturation of the specimen. Equation (1) was employed to determine the hydraulic conductivity of the studied material as in ASTM D 5084-10 standard [36].
k = V(t1,t2)·L/(PB·A·t)
In Equation (1), k = hydraulic conductivity (cm/s), V(t1,t2) = volume of flow from t1 to t2 (cm3), L = length of sample (cm), PB = bias pressure, psi × 70.37 cm/psi (cm of H2O), A = area of sample (cm2), t = time from t1 to t2. Replicate samples were prepared at each water content level to ensure the repeatability of test data. Due to the sensitive nature of the specimen, the tests were noticed to be time-consuming. At high water content, the particles of compost materials started to dissolve in water and came out of the sample. In contrast, at low water content, the sample collapsed into small pieces during testing, and in both cases, the tests were repeated. However, the samples with low water contents showed more complexities than high water contents.

2.2.5. Thermal Tests

For thermal conductivity tests, each sample was prepared at a certain water content level and dry unit weight of the compaction curve, following the procedure discussed in Section 2.2.3. The compacted samples were taken out of the mold, wrapped in sealed polythene bags, and placed for at least two hours to attain thermal equilibrium before the test. A KD2 Pro device was used to determine the thermal conductivity of the prepared specimens under isothermal conditions, which calculates values for thermal conductivity (K) by monitoring the dissipation of heat from a line heat source given a known voltage (KD2 Pro Manual, 2006). The principle is based on the transient line heat conduction in a homogeneous, isotropic medium. The thermal conductivity is measured with a relative error of 5%. KD2 analyzer allows a quick determination of the thermal conductivity compared to the differential scanning calorimeter (DSC), which requires a relatively long equilibrium time [37]. KD2 Pro device consists of a TR1 sensor, consisting of a large single needle with 2.4 mm diameter and 100 mm length. The sensor needle was inserted into the compacted sample slowly and steadily, to avoid any chances of bend in the needle and reduce any chances of a gap between the needle and compost particles. It was assured that the sample surrounding the needle was more than 1.5 cm from all sides (KD2 Pro Manual, 2006). The default reading time for the TR1 sensor is 5 min but a 10 min reading time was adjusted. The longer reading time provides more reliable results because it minimizes the chances of error, which occurs due to the large needle diameter and contact resistance between the sensor and compost materials. Replicate samples were prepared for each sample to obtain accurate test data.
Chandrakanthi et al. [30] and Agnew and Leonard [38] state that thermal diffusivity (α) and heat capacity (Cp) are essential thermal properties that need to be addressed while examining the thermal behavior of compost materials. Agnew and Leonard [38] report a mathematical relationship as in Equation (2) to determine the specific heat of an organic medium.
Cp = 1.48 − 0.64 (Ash) + 4.18 (M·Cd,b)
In Equation (2), Cp = specific heat of compost (kJ/kg·K), M·Cd,b = moisture content of compost materials as per dry basis, and ash is the mineral content or ash of the material. Furthermore, Chandrakanthi et al. [30] report a relationship as in Equation (3) to estimate the thermal diffusivity in relation to specific heat and thermal conductivity of an organic medium. In Equation (3); α = thermal diffusivity (m2/s), λ = thermal conductivity (w/m·K), ρ = bulk density (kg/m3), Cp = specific heat of material (kJ/kg·K):
α = λ/(ρ·Cp) .

3. Results and Discussions

3.1. Chemo-Biological Characteristics

Figure 4 shows that a band of 250 bp is observed in the study samples for methanotrophs. A band length of 500 bp assures the presence of a large number of methanotrophs in the samples. Methanotrophs may be present in the compost in a more significant band length. Yet, the testing method and molecular kit cannot recognize the bacteria, as the process needs optimization to precisely quantify the methanotrophic bacteria in the compost material.
The compost materials provide 40% organic content per dry mass, showing good potential for methane oxidation. Research studies by Huber-Humer et al. [13] and Yuan [4] report that the material with only 15% organic matter per dry mass basis is considered suitable for landfill biocover. Thus, the compost used in this study indicates sufficient CH4 oxidation potential due to its high percentage of organic contents. The compost materials show a pH of 8.15, as in the findings of Huber-Humer et al. [13]. Silica (SiO2) was relatively high in the samples, about 39% out of 60% inorganic ingredients. SiO2 is also recognized as silicon oxide, well-known for its hardness. SiO2 is most often found in sand or quartz. The present study also indicates that calcium and phosphorous are the other major elements present in the compost, which are found to be 4.28% and 3% of the inorganic materials, respectively.

3.2. Moisture and Density Relationships

Figure 5 shows the compaction curve of the compost material. The compaction tests were carried out for a wide range of water content on both sides of optimum water content, which was conducted to observe the behavior of compost for a lower and higher degree of saturation.
As expected and similar to other studies, in Benson and Othman [25] and Puppala et al. [39], it can be seen that the dry density increases as the water content increases until it attains a maximum value of 1200 kg/m3 at an optimal water content level of 79%. After that, the dry density decreases with increased water content, and this behavior continues for the wet optimum segment. The Proctor curve on the optimum dry side represents a gradual rise to the optimal water content, showing a wide range of changes in water content from 38% to 79% on the dry optimum segment rather than on the wet optimum segment from 79% to 107%. This is because for the wet optimum segment, the water added only fills the pores and water drainage is needed to obtain larger density for the higher water content.
Generally, as in Figure 6, the porosity of the studied material varies from 57 to 65% for water content from 38% to 107%, and these values are in good agreement as reported by Gonzaleze et al. [40] and Wallah et al. [41] for two manure composts and red tuff derived from volcanic ash, respectively. Scheutz et al. [14] stated that the CH4 oxidation process is associated with the O2 penetration capability of landfill cover soil. The soil composition, particle size, and porosity are considered to have significant influences on O2 transport and thus on the CH4 oxidizing capacity of the biocover material [19]. It is well understood that a low permeable cover reduces rainfall infiltration, which results in the saturation of cover material during the rainy season. The cover may also face a desiccation problem during the dry season [25]. The diffusion coefficient is a function of degree of saturation and free air space which may significantly affect the performance properties of landfill biocover material for CH4 oxidation potential. Figure 7 illustrates the relationship between water content and degree of saturation of the compaction curve, and Figure 8 represents the relationship between water content and FAS of compost materials.
It can be seen from Figure 7 that, as expected, S increases with an increase in water content up to the optimal water content. The S increases gradually for the dry optimum segment until reaching the Proctor optimum. After this point, the S is almost the same for the wet optimum segment, showing that most voids are filled with water. Studies have shown that when the degree of saturation reaches approximately 85%, gas diffusion should be completed in the liquid phase, which is much slower than the gas phase [4,14,27], and similar to this, as in Figure 9, the studied material also shows minimal diffusivity potential at 85% degree of saturation. It can radically decrease CH4 oxidation due to the lack of both O2 and CH4 in the biocover [14].
Thus, from an analysis of Figure 7 and Figure 9, it can be concluded that the compacted compost materials with an initial water content higher than 74% (corresponding to the point with a degree of saturation of 85%) show low CH4 oxidation capacity and are thereby unsuitable for landfill biocovers. From Figure 8, it can be observed that as the water content increases up to the optimal water content, the FAS curve sharply decreases, which shows the reduction of voids in the compost materials. Then, the FAS continues to decrease slowly with increased water content until it attains a value close to zero. This means that most voids are filled with water. The compost does not allow sufficient gas flux to pass through the sample at a certain water content level, affecting the microbial oxidation phenomenon due to an insufficient supply of O2. Now in Figure 9, the relative diffusion coefficient is strongly correlated to the free air space and degree of saturation, which shows a gradual decrease with a decrease in free air space and with an increase in the degree of saturation, similar to the findings of Pokhrel et al. [24], until it attains a value of 0.062 at 85% degree of saturation.
Furthermore, the test data of the studied material show a high relative diffusion coefficient of 0.20 to that of 0.17 for soil, 0.10 for soil:compost = 30:70, and 0.10 for soil:compost = 70:30 [24], at a particular free air space of 0.31. Generally, the relative diffusion coefficient varies from 0.204 to 0.12 for changes in free air space from 31 to 20%, corresponding to water content from 38 to 65% and degree of saturation between 46% and 71%. The 20% to 35% FAS values in compost established the maximum O2 consumption rate, i.e., 95% according to previous field and experimental studies [9,22]. The test data presented in Figure 6, Figure 7, Figure 8 and Figure 9 highlight that the studied compost material with water content of 38% to 71% shows the highest consumption rate and thereby highest CH4 oxidation potential; thus, it can effectively be used as landfill cover materials in compacted conditions for methane oxidation.

3.3. Hydraulic Behavior of Compost Material

It can be seen from Figure 10a that the hydraulic conductivity of compost material shows a gradual decrease with an increase in water content for the dry optimum. Minimum hydraulic conductivity occurs at a water content of 86%, slightly above the optimum moisture content, similar to [42]. Beyond this point, k initiates to increase with water content. This hydraulic behavior of compost materials can directly be associated with the adsorption of water on solid surfaces, i.e., electrostatic forces. Though water is continuously added to the sample on the dry optimum side, k decreases gradually. The added water is used to increase the dry unit weight and degree of saturation of the specimen (Figure 7), which compels the compost particles closer to each other. Alternately, the free air space squeezes (Figure 8), and due to this, the attractive interfacial force between water cations and colloid anions gradually increases due to high solid-water interactions. Alternately, hydraulic conductivity decreases, or in other words, at low water content, the diffuse double layer of ions surrounding the particle is not freely developed. The cation concentration increases with increased water content, which therefore diffuses toward the colloid surface to equalize concentrations [43]. As in this study, the ions equalization has taken place at a water content of 86%.
The hydraulic conductivity increases beyond this water content, i.e., 86%, as the water is added to the compost specimens. At this point, the compost material has almost reached close to saturation, as can be seen in Figure 10b. Due to a higher degree of saturation, the added water dilutes/reduces the concentration of soil solids per unit volume, providing a gradual decrease in dry unit weight and increase in porosity as well (Figure 6), or in other words, beyond the optimal water content, the diffuse double layer of ions surrounding the clay particles expands significantly, which consequently reduces the interfacial attractive forces between solid particles and water molecules, as the repulsive forces of water molecules dominate the attractive forces between water molecules and solid colloids, and due to which, the swelling of the compost materials occurs, as seen from the porosity profile (Figure 6), which therefore opens easy paths for water to flow through the pores due to less interfacial attractive force, so k starts to increase.
Furthermore, it can also be seen from Figure 10a that similar to other materials, k of compost material is relatively high for the dry optimum segment in comparison to the wet optimum segment, which is because on the dry optimum side, the compost has lower water content/degree of saturation, it seems to have a flocculated structure with continuous voids and due to this it provides higher hydraulic conductivity than the wet optimum, for which the compost has a higher water content/degree of saturation. However, the structure appears to be dispersed, providing a more tortuous path, so the hydraulic conductivity is less, as in Lambe [42] and Seed and Chen [44]. The studies stated that the degree of particle orientation changed with changes in moisture content of compacted Boston Blue clay and kaolinite soil minerals. Compaction induced changes in the structure of the cohesive soil, which influenced the hydraulic conductivity of the clayey soil [42].
Generally, the hydraulic conductivity of the studied material varies between 7 × 10−6 and 2 × 10−9 cm/s. This trend is in agreement with the data published in [25,45,46] for landfill covers, and it also falls in the range of natural clayey soil (1 × 10−6–1 × 10−8 cm/s) [43]. The test data imply that compacting compost to low hydraulic conductivity can be accomplished for a wide range of water content. However, the water contents needed to achieve low hydraulic conductivity are typically more than those used for compacted clays due to more expansion of diffuse double layer theory. Furthermore, it should be emphasized that some physical and structural changes may occur in landfill cover material due to freezing-thawing and other environmental factors that can lead to the cracking of the cover material after some time and can thus change the hydraulic conductivity values as in [25]. Furthermore, it should be expected that the compost cover experiences settlement in time, which results in the refinement of the compost’s pore structure and thus influences the hydraulic conductivity.

3.4. Thermal Behavior of Compost Materials

Figure 11 shows the compost material’s thermal conductivity (λ) with the compaction curve. As in Figure 11, the thermal conductivity increases almost linearly for the dry optimum, whereas the rate of increase is minimal for the wet optimum. The dry unit weight increases with increased water content for the dry optimum, resulting in close interaction among compost particles. According to Fourier’s law, the conduction of heat is a function of contact surface area [47], and as the compost particles come in close interaction, they gradually decrease in free air space (Figure 8). The contact surface area alternately increases, which increases the conduction of heat, and correspondingly, the thermal conductivity increases [3], or it can be said that the increase in thermal conductivity is also because the thermal conductivity of water (0.6) is approximately 25 times more than that of air (0.024).
Other studies, such as Chandrakanthi et al. [30], showed that the thermal conductivity of compost materials is a function of dry density and a linear relationship exists between the degree of saturation and thermal conductivity. However, in this study, as in Figure 11 and Figure 12, the studied materials provide a linear relationship between thermal conductivity and dry density up to optimal water content, but after this point, the relationship is nonlinear. However, Agnew and Leonard [38] revealed a linear relationship between water content and thermal conductivity. Furthermore, Tang and Cui [48] reported that the thermal conductivity increased with an increase in water content, as well as with dry unit weight for compacted MX80 bentonite specimens. For the wet optimum, the compost particles are almost saturated with a sufficient addition of water (Figure 7), and due to a high degree of saturation, the added water dilutes/reduces the concentration of soil solids per unit volume, which results in a decrease in the contact surface area and particle-to-particle interactions. Now, the thermal conductivity of water (0.59 w/m·K) is smaller than that of mineral soil particles, i.e., 2.9 for silt and clay, 3 for sandstone, and 3.8 for dolostone [49,50], due to which, the rate of increase in the thermal conductivity is minimal for this segment as water dominates the process of heat conduction. The test data show a similar trend as in [51].
Figure 12 provides a clearer picture of the test data. The material shows abrupt changes in thermal conductivity at a high degree of saturation, i.e., close to saturation, and the rate of increase in λ is quite high. Hettiarachchi [52] reports that the thermal conductivity of the compost materials is relatively low when compared to that of the mineral soils, i.e., 2.9 for silt and clay, 3 for sandstone [49], and 2.74 for sandy loam [38], and as depicted in Figure 11, the thermal conductivity of studied materials generally varies between 0.12 and 0.53 w/m·K for changes in water content from 38% to 107%. The general trend is almost similar to sludge compost, for which λ varies from 0.218 to 0.815 w/m·K [38], and the slight differences are generally due to a difference in the degree of saturation and biodegradable materials.
The compost materials tend to conduct heat at a low rate, providing more heat retention capacity than other mineral materials [52]. Consequently, during the winter season, when the atmospheric temperature is low, this low thermal conductivity enables it to sustain a stable temperature for the activities of the microbial organisms, which therefore extends the CH4 oxidation process right through a long period in the winter, similar to the findings in [53], which means that the compost materials can effectively be used as landfill cover materials for CH4 oxidation purposes. The experimental data set was validated with the theoretical data set, estimated with the model as reported in [54] and Figure 13; both data sets show close agreement. The model data set shows a slightly higher peak at low water content, and this slight difference is because compost is a combination of various ingredients with different properties. Figure 14 shows that the specific heat of compost material increases with an increase in water content in a linear fashion, similar to Mears et al. [55] and Kodesova et al. [56]. This is because the specific heat of water (4.18 kJ/kg·K) is almost four times that of air (1 kJ/kg·K) [56]. Consequently, a gradual increase in water content increases water-filled pores, therefore reducing the fraction of air-filled pores, consequently increasing the specific heat [38].
Generally, the specific heat of the studied material varies from 1.58 to 4.48 kJ/kg·K for water content variations between 38% and 107% (Figure 14), showing comparatively high values compared to other compost materials; 1.9 kJ/kg·K for soil organic matter [56], 1.40 for sawdust, and 1.57 for oat straw [57], and soils as well; 0.9 for soil minerals, 0.86 for clay, and 0.775 for sandstone [56]. The test data also agree with the findings of [38], in which the specific heat of compost materials, made of cattle manure with sawdust and rice hulls, varied from 1.59 to 3.14 kJ/kg·K. According to Kodesova et al. [56], soil with high specific heat provides ample heat storage. This means that the studied material comparatively shows a greater tendency to store heat than soils and other compost materials, which may alternately provide a better tendency to maintain a specific temperature within the cover for microbial organisms over the more extended period during winter, preceding the summer season in colder regions.
The thermal diffusivity of compost material, as in Figure 15, increases with an increase in water content, in an almost similar fashion to that of the thermal conductivity profile in Figure 11. The mechanisms responsible for this trend are also the same, which have already been discussed above. It is evident from Figure 15 that the thermal diffusivity varies from 4.0 × 10−8 to 7.96 × 10−8 m2/s for variations in water content from 38% to 107%, which is in close agreement with the data set of other compost materials, i.e., silage (1 × 10−8 m2/s) [57] and oat straw (6 × 10−8 m2/s) [38]. Furthermore, the studied material shows more diffusivity potential than other compacted clays, i.e., 1 × 10−11 for compacted wastewater clay and 3 × 10−10 for kaolinite clay [58].
It can be concluded from test results that the studied material tends to attain thermal equilibrium quickly, spreading heat within the medium faster than other materials. The thermal properties of compost in this study have been examined for initial conditions only. They may therefore change with changes in the extrinsic climatic conditions, intrinsic behavior of biocover, and underlying landfill waste over time. The study suggests a need to simulate the heat transfer between the biocover and the atmosphere and between the biocover and the underlying landfill waste over a longer period for changed conditions. A similar study conducted by the authors Bajwa and Fall [59] showed that similar compost materials enabled the maintenance of a temperature between 21.5 and 22.5 °C when monitored as landfill cover material at different depths for more than 80 days, which highlighted its capacity to continually sustain the temperature within the optimal conditions for methanotrophs, as an optimal temperature for maximum oxidation potential lies between 20 and 35 °C [7,9,18], and between 15 and 35 °C [16]. In addition to this, the temperature outside a specific range produces inactive enzymes, insufficient to generate the desired reaction for microbes [21]. It can be concluded from Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13, Figure 14 and Figure 15 that the studied material is a better option to be used as a landfill biocover than other materials, considering its engineering properties.

4. Conclusions

The test data show that compost is a suitable material for landfill biocover as it provides sufficient organic matter contents, essential for the growth of microbial organisms/methanotrophs. The polymerase chain reaction test shows the existence of a large number of methanotrophs in the compost materials. The moisture content and dry density relationships show that the compacted compost material shows adequate free air space and O2 diffusivity potential for a wide range of water content, providing a better environment for methanotrophs to participate in the CH4 oxidation process under aerobic conditions. The low thermal conductivity, high thermal diffusivity, and high specific heat of the studied material compared to other soil minerals highlight its potential to sustain sufficient temperature for the microbial organisms within the cover, even in cold regions over a more extended period. The hydraulic conductivity of compacted compost material is also per the specifications of landfill covers, as reported in other studies. Based on the findings of this study, a landfill biocover for water content ranging from 38% to 71% is suggested as a design recommendation as it can be seen from the test results that the studied material meets most of the requirements for maximum biotic CH4 consumption. However, despite the presented results, there is still a need to conduct a detailed parametric study and field investigations of the long-term performance of compost-based landfill biocover. The evaluation of the CH4 oxidation capacity of the studied material is also required.

Author Contributions

Conceptualization, T.M.B. and M.F.; Data curation, T.M.B. and F.A.; Formal analysis, T.M.B. and F.A.; Funding acquisition, M.F.; Investigation, T.M.B.; Methodology, T.M.B. and M.F.; Project administration, M.F.; Resources, M.F.; Supervision, M.F.; Validation, T.M.B. and M.F.; Visualization, T.M.B. and F.A.; Writing—original draft, T.M.B.; Writing—review and editing, M.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data presented in this study are available upon request.

Acknowledgments

The authors are immensely thankful to National Scientific Research Council Canada, Ministry of Research and Innovation, Ontario, Canada, Lafleche Environment Inc., Canada, and the University of Ottawa, Canada, for providing financial support to complete this research work.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

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Figure A1. Schematic drawing of agarose gel electrophoresis.
Figure A1. Schematic drawing of agarose gel electrophoresis.
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Figure A2. Wavelength of chromium for ICP (AES) test.
Figure A2. Wavelength of chromium for ICP (AES) test.
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References

  1. Bajar, S.; Sing, A.; Kaushik, C.P.; Kaushik, A. Suitability assessment of dumpsite biocover to reduce methane emissions from landfills under the interactive influence of nutrients. Environ. Sci. Pollut. Res. 2021, 28, 1519–1532. [Google Scholar] [CrossRef] [PubMed]
  2. Parsaeifard, N.; Sattler, M.; Nasirian, N.; Chen, V.C.P. Enhancing anaerobic oxidation of methane in municipal solid waste landfill cover soil. Waste Manag. 2020, 1, 44–54. [Google Scholar] [CrossRef] [PubMed]
  3. Khoshand, A.; Fall, M. Geotechnical characterization of compost-based biocover materials 2014. Geotech. Geol. Eng. 2014, 32, 489–503. [Google Scholar] [CrossRef]
  4. Yuan, L. Methane Emission and Oxidation through Landfill Covers. Ph.D. Thesis, College of Engineering, Florida State University, Tallahassee, FL, USA, 2006. [Google Scholar]
  5. Reddy, K.R.; Yargicoglu, E.N.; Chetri, J.K. Effects of biochar on methane oxidation and properties of landfill cover soil: Long term column incubation tests. J. Environ. Eng. 2021, 147, 04020144. [Google Scholar] [CrossRef]
  6. Phillips, D. Ambient air quality synergies with a 2050 carbon neutrality pathway in South Korea. Climate 2022, 10, 1. [Google Scholar] [CrossRef]
  7. IPCC. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change; Core Writing Team, Pachauri, R.K., Reisinger, A., Eds.; IPCC: Geneva, Switzerland, 2007; 104p. [Google Scholar]
  8. IPCC. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change; Core Writing Team, Pachauri, R.K., Meyer, L.A., Eds.; IPCC: Geneva, Switzerland, 2014; 151p. [Google Scholar]
  9. Pokhrel, D. Compost-Based Biocap Performance. Ph.D. Thesis, Department of Civil Engineering, University of Calgary, Calgary, AB, Canada, 2006; pp. 1–290. [Google Scholar]
  10. Huber-Humer, M.H.; Gebret, J.; Hilger, H. Biotic systems to mitigate landfill methane emissions. Waste Manag. Res. 2008, 26, 33–46. [Google Scholar] [CrossRef]
  11. Ait-Benichou, S.; Jugnia, L.B.; Greer, C.W.; Cabrel, A.R. Methanotrophs and methanotrophic activity in engineered landfill biocovers. Waste Manag. 2009, 29, 2509–2517. [Google Scholar] [CrossRef]
  12. Abichou, T.; Mahieu, K.; Yuan, L.; Chanton, J.; Hater, G. Effects of compost biocovers on gas flow and CH4 oxidation in a landfill cover. Waste Manag. 2009, 29, 1595–1601. [Google Scholar] [CrossRef]
  13. Huber-Humer, M.; Roder, S.; Lechner, P. Approaches to assess biocover performance on landfills. Waste Manag. 2009, 29, 2092–2104. [Google Scholar] [CrossRef]
  14. Scheutz, C.; Kjeldsen, P.; Bogner, J.E.; Visscher, A.D.; Gebert, J.; Hilger, H.A.; Huber-Humer, M.; Spokas, K. Microbial methane oxidation process and technologies for mitigation of landfill gas emissions. Waste Manag. Res. 2009, 27, 409–455. [Google Scholar]
  15. Tanthachoon, N.; Cheimchaisri, W. Alternative approach for encouraging methane oxidation in compost-based landfill cover layer with vegetation. In Proceedings of the International Conference on Sustainable Solid Waste Management, Chennai, India, 5–7 September 2007; pp. 202–209. [Google Scholar]
  16. Majdinasab, A.; Yuan, Q. performance of the biotic systems for reducing methane emissions from landfill sites: A review. Ecol. Eng. 2017, 104, 116–130. [Google Scholar] [CrossRef]
  17. Albana, M.; Fernandes, L. Effects of temperature, moisture content, and fertilizer addition on biological methane oxidation in landfill cover soils. Toxic Radioact. Waste Manag. 2009, 13, 187–195. [Google Scholar] [CrossRef]
  18. Visvanathan, C.; Pokhrel, D.; Cheimchaisri, W.; Hettiaratchi, J.P.A.; Wu, J.S. Methanotrophic activities in tropical landfill cover soils: Effects of temperature, moisture content and methane concentration. Waste Manag. Res. 1999, 17, 1313–1323. [Google Scholar] [CrossRef]
  19. Maanoja, S.T.; Rintala, J.A. Evaluation of methods for enhancing methane oxidation via increased soil air capacity and nutrient content in simulated soil cover. Waste Manag. 2018, 82, 82–92. [Google Scholar] [CrossRef] [PubMed]
  20. Diaz, L.F.; Savage, G.M.; Golueke, C.G. Composting of municipal solid wastes. In Handbook of Solid Waste Management, 2nd ed.; The McGraw Hill Companies Inc.: New York, NY, USA, 2002; ISBN 9780071356237. [Google Scholar]
  21. Haug, R.T. Compost Engineering, Principles and Practice; Ann Arbor Science Publishing Inc.: Detroit, MI, USA, 1980. [Google Scholar]
  22. Tim, R. The Practical Handbook of Compost Engineering; Taylor & Francis Inc.: Boca Raton, FL, USA, 1993. [Google Scholar]
  23. Hettiarachchi, J.P.A.; Hettiaratchi, A.; Mehrotra, A. Comprehensive one-dimensional mathematical model for heat, gas and moisture transport in methane biofilters. Waste Manag. 2007, 11, 225–234. [Google Scholar] [CrossRef]
  24. Pokhrel, D.; Hettiaratchi, P.; Kumar, S. Methane diffusion coefficient in compost and soil—Compost mixtures in gas phase biofilter. Chem. Eng. J. 2011, 169, 200–206. [Google Scholar] [CrossRef]
  25. Benson, C.H.; Othman, M.A. Hydraulic and mechanical characteristics of compacted municipal solid waste compost. Waste Manag. Res. 1993, 11, 127–142. [Google Scholar] [CrossRef]
  26. Cabrel, A.R.; Burnotte, F.; Lefebvre, G. Geotechnical characterization of a pulp and paper (deinking) residue used in cover systems. Environ. Geotech. 2002, 1, 207–212. [Google Scholar]
  27. Cabrel, A.R.; Capanema, M.A.; Gebert, J.; Moreira, J.F.; Jugnia, L.B. Quantifying microbial methane oxidation efficiencies in two experimental landfill bio covers using stable isotopes. Water Air Soil Pollut. 2010, 209, 157–172. [Google Scholar] [CrossRef]
  28. Chanton, J.P.; Lipay, K. Seasonal variation in methane oxidation in a landfill cover soil as determined by an in-situ isotope technique. Glob. Biogeochem Cycles 2000, 14, 51–60. [Google Scholar] [CrossRef]
  29. Tan, K.H. Environmental Soil Science, 3rd ed.; Taylor and Francis Group: Boca Raton, FL, USA, 2009. [Google Scholar]
  30. Chandrakanthi, M.A.; Mehrotra, A.K.; Hettiaratchi, J.P.A. Thermal conductivity of leaf compost used in biofilters: An experimental and theoretical investigation. Environ. Pollut. 2005, 136, 167–174. [Google Scholar] [CrossRef] [PubMed]
  31. Abu-Hamdeh, N.H. Thermal properties of soil as affected by density and water content. Bio-Syst. Eng. 2003, 86, 97–102. [Google Scholar] [CrossRef]
  32. Shimizu, N. Process optimization of the composting system, In Robotics and Mechatronics for Agriculture; CRC Press: Boca Raton, FL, USA, 2017. [Google Scholar]
  33. ASTM D 2974-07a; Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils. ASTM International: West Conshohocken, PA, USA, 2007.
  34. ASTM D 698-07; Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort. ASTM International: West Conshohocken, PA, USA, 2007.
  35. Penman, H.L. Gas and vapor movement in soil: The diffusion of vapors through porous solids. J. Agric. Sci. 1940, 30, 437–462. [Google Scholar] [CrossRef]
  36. ASTM D5084-03; Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter. ASTM International: West Conshohocken, PA, USA, 2003.
  37. Célestin, J.C.; Fall, M. Thermal conductivity of cemented paste backfill materials and factors affecting it. Int. J. Min. Reclam. Environ. 2009, 274–290. [Google Scholar] [CrossRef]
  38. Agnew, J.M.; Leonard, J.J. The physical properties of compost. Compost Sci. Util. 2003, 11, 238–264. [Google Scholar] [CrossRef]
  39. Puppala, A.J.; Pokala, S.P.; Intharasombat, N.; Williammee, R. Effects of organic matter on physical strength, and volume change properties of compost amended expansive clay. J. Geotech. Geoenviron. Eng. 2007, 133, 1449–1461. [Google Scholar] [CrossRef]
  40. Gonzalez, J.L.; Medina, M.; Benitez, I.C. Slurry composting options. BioCycle 1989, 30, 53–55. [Google Scholar]
  41. Wallach, R.; Da Silva, F.F.; Chen, Y. Unsaturated hydraulic characteristics of composted agricultural waste, tuff, and their mixtures. Soil Sci. 1992, 153, 434–441. [Google Scholar] [CrossRef]
  42. Lambe, T.W. The structure of compacted clay. J. Soil Mech. Found. Div. 1958, 84, 1–34. [Google Scholar] [CrossRef]
  43. Mitchell, J.K.; Soga, K. Fundamentals of Soil Behavior; John Wiley & Sons Inc.: Hoboken, NJ, USA, 2005. [Google Scholar]
  44. Seed, H.B.; Chen, C.K. Structure and strength characteristics of compacted clays. J. Soil Mech. Found. Div. 1959, 85, 87–128. [Google Scholar] [CrossRef]
  45. Daniel, D.E. Landfill Impoundments. In Geotechnical Practice for Waste Disposal; Springer: New York, NY, USA, 1993; pp. 97–112. [Google Scholar]
  46. Kamon, M.; Inazumi, S.; Inui, T. Durability of compacted sludge landfill over-under wetting drying cycle. Environ. Geotech. 2002, 1, 661–666. [Google Scholar]
  47. Li, Z.; Yu, X. Multi physical simulation of freezing unsaturated soil. Geotech. Spec. Publ. 2010, 199, 157–166. [Google Scholar]
  48. Tang, A.M.; Cui, Y.J. Determining the thermal conductivity of compacted MX80 clay. In Unsaturated Soil; American Society of Civil Engineers: Reston, VA, USA, 2006; pp. 1695–1706. [Google Scholar]
  49. Cote, J.; Konrad, J.M. A generalized thermal conductivity model for soils and construction materials. Can. Geotech. J. 2005, 42, 443–458. [Google Scholar] [CrossRef]
  50. Ramires, M.L.V.; Neito de Castro, C.A.; Nagasaka, Y.; Nagashima, A.; Assael, M.J.; Wakeham, W.A. Standard reference data for the thermal conductivity of water. J. Phys. Chem. Ref. Data 1995, 24, 1377–1381. [Google Scholar] [CrossRef]
  51. Al Nakashabandia, G.; Kohnke, H. Thermal conductivity and diffusivity of soils as related to moisture tension and other physical properties. Agric. Meteorol. 1964, 2, 271–279. [Google Scholar] [CrossRef]
  52. Hettiarachchi, V.C. Mass, Heat and Moisture Transport in Methane Biofilters. Ph.D. Thesis, University of Calgary, Calgary, AB, Canada, 2005. [Google Scholar]
  53. Mor, S.; De Visscher, A.; Ravindra, K.; Dahiya, R.P.; Chandra, A.; Van Cleemput, O. Induction of enhanced methane oxidation in compost: Temperature and moisture response. Waste Manag. 2006, 26, 381–388. [Google Scholar] [CrossRef] [Green Version]
  54. Cosenza, P.; Guerin, R.; Tabbagh, A. Relationship between thermal conductivity and water content of soils using numerical modelling. Eur. J. Soil Sci. 2003, 54, 581–587. [Google Scholar] [CrossRef]
  55. Mears, D.R.; Singley, M.E.; Ali, G. Thermal and physical properties of compost. In Proceedings of the 7th National Agricultural Waste Management Conference: Energy, Agriculture and Waste Management, Syracuse, NY, USA, 1975; Ann Arbor Science Publishers, Inc.: Detroit, MA, USA; pp. 515–527. [Google Scholar]
  56. Kodesova, R.; Fer, M.; Neuberger, P. Thermal properties of representative soils of the Czech Republic. Soil Water Resour. 2014, 8, 141–150. [Google Scholar] [CrossRef] [Green Version]
  57. Ahn, H.K.; Sauer, T.J.; Richard, T.L.; Glanville, T.D. Determination of thermal properties of composting bulk materials. Biosci. Technol. 2009, 100, 3974–3981. [Google Scholar] [CrossRef]
  58. Fredlund, D.G.; Rahardjo, H. Phase Properties and Relationships, In Soil Mechanics for Unsaturated Soils; John Wiley & Sons, Inc.: New York, NY, USA, 1993. [Google Scholar]
  59. Bajwa, T.; Fall, M. Coupled thermal-hydraulic and mechanical (THM) evolution of compost materials in the column. In Proceedings of the 66th Canadian Geotechnical Conference and the 11th Joint CGS/IAH-CNC Groundwater Conference, GeoMontreal, Montréal, QC, Canada, 29 September–3 October 2013. [Google Scholar]
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Figure 1. Schematic sketch of compost-based landfill biocover.
Figure 1. Schematic sketch of compost-based landfill biocover.
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Figure 2. Processes and parameters involved in biochemical tests of compost materials [33].
Figure 2. Processes and parameters involved in biochemical tests of compost materials [33].
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Figure 3. Equilibrium condition for saturation of specimen at 71.85% water content and a dry density of 1075 kg/m3.
Figure 3. Equilibrium condition for saturation of specimen at 71.85% water content and a dry density of 1075 kg/m3.
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Figure 4. Methanotrophs in the compost material.
Figure 4. Methanotrophs in the compost material.
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Figure 5. Standard compaction curve for compost material.
Figure 5. Standard compaction curve for compost material.
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Figure 6. Relationship between porosity vs. compaction curve of compost material.
Figure 6. Relationship between porosity vs. compaction curve of compost material.
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Figure 7. Relationship between the degrees of saturation vs. compaction curve of compost.
Figure 7. Relationship between the degrees of saturation vs. compaction curve of compost.
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Figure 8. Relationship between free air space vs. compaction curve of compost material.
Figure 8. Relationship between free air space vs. compaction curve of compost material.
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Figure 9. Free air space, relative diffusion coefficient, and degree of saturation relationships of compost material.
Figure 9. Free air space, relative diffusion coefficient, and degree of saturation relationships of compost material.
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Figure 10. Hydraulic conductivity of the compost materials: (a). hydraulic conductivity vs. compaction curve; (b). hydraulic conductivity vs. degree of saturation.
Figure 10. Hydraulic conductivity of the compost materials: (a). hydraulic conductivity vs. compaction curve; (b). hydraulic conductivity vs. degree of saturation.
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Figure 11. Thermal conductivity vs. compaction curve of compost material.
Figure 11. Thermal conductivity vs. compaction curve of compost material.
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Figure 12. Relationship between thermal conductivity and degree of saturation of compost material.
Figure 12. Relationship between thermal conductivity and degree of saturation of compost material.
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Figure 13. Comparison of experimental and theoretical test data of compost material.
Figure 13. Comparison of experimental and theoretical test data of compost material.
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Figure 14. Relationship between specific heat and water content of compost material.
Figure 14. Relationship between specific heat and water content of compost material.
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Figure 15. Relationship between thermal diffusivity vs. compaction curve of compost material.
Figure 15. Relationship between thermal diffusivity vs. compaction curve of compost material.
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Bajwa, T.M.; Fall, M.; Alshawmar, F. Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover. Appl. Sci. 2022, 12, 4276. https://doi.org/10.3390/app12094276

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Bajwa TM, Fall M, Alshawmar F. Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover. Applied Sciences. 2022; 12(9):4276. https://doi.org/10.3390/app12094276

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Bajwa, Tariq M., Mamadou Fall, and Fahad Alshawmar. 2022. "Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover" Applied Sciences 12, no. 9: 4276. https://doi.org/10.3390/app12094276

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