A comprehensive study of temperature data during the filling and post-closure phases at a landfill in Québec, Canada: Application of a thermal-mechanical-biological model.

A 12-year field study on municipal solid waste (MSW) stabilization in Northern climates was conducted at Ste. Sophie landfill in Québec, Canada. Temperature and settlement data were collected from 12 instrument bundles placed at varying depths in two vertical columns within the waste during the filling and post-closure phases. The data demonstrated a 12-18 month delay in temperature rise during the filling stages due to frozen or partially frozen MSW and highlighted ambient temperature effects at shallow depths. A thermal-mechanical-biological (TMB) model was developed and calibrated to simulate the impact of temperatures on MSW stabilization, particularly emphasizing landfills without leachate recirculation in Northern climates. The biological model related anaerobic heat generation from MSW with temperature and expended energy from biodegradation. The resultant heat was integrated into the thermal model, allowing for the simulation of heat transfer through conduction. The thermal parameters were expressed as a function of density, which was updated in the mechanical model that combined a Generalized Kelvin-Voigt model with a biodegradation-induced strain term. This term was represented as the ratio of expended energy over time to total potential expended energy of the waste. The TMB model effectively predicted MSW behaviour, considering temperature rise delays in cold and sharp rises in warm conditions. This is essential for optimizing landfill operations by promoting waste stabilization before applying the final cover.

A comprehensive study of settlement during the filling and post-closure phases at a landfill in Québec, Canada: Field data and TMB modelling.

In Northern climates, waste placed curbside the evening before waste collection can lead to partially frozen waste at placement, which delays biodegradation and biodegradation-induced settlement. A 12-year settlement dataset collected during the filling and post-closure phases at a landfill in Québec, Canada was analyzed. The dataset showed a delay in biodegradation-induced settlement due to the first three waste lifts being placed in the winter months and exhibited an increase in the settlement rate at later times when the waste temperatures increased to values that support biodegradation. The field data also demonstrated that the stiffness of MSW increased in response to confined stress as subsequent waste lifts were added. A thermal-mechanical-biological (TMB) model was developed, in COMSOL Multiphysics, to simulate the settlement dataset. TMB integrates a Generalized Kelvin-Voigt (GKV) model, simulating instantaneous and mechanical creep settlements, with a biodegradation-induced settlement model that relates heat/gas generation with time to biodegradation-induced settlement. The thermal model simulates heat transfer through conduction and includes a biodegradation heat generation source term. The GKV stiffness parameters are expressed as a function of the applied stress to account for waste compressibility effects on mechanical response, which is consistent with field data and the research literature. The paper focuses solely on the MSW settlement field data and model predictions, with thermal response analysis presented in a separate publication. The TMB model effectively predicted waste behaviour, including resistance to compressibility under higher stress and the delay in waste settlement for waste placed in winter. The temperature and settlement data provide a valuable dataset to validate different models that can be used to predict waste settlement in cold regions.

Impact of temperature on the performance of compost-based landfill biocovers.

Methane (CH4) emissions from landfills are a major contributor to global greenhouse gas emissions. Compost-based biocovers offer a viable approach to reduce CH4 emissions from landfills; however, the effectiveness in climates with varying temperatures is not well understood. The methane removal performances of two compost-based biocover materials (food and yard waste compost) were examined under different temperature conditions using laboratory column experiments. A reactive transport model was used to simulate the experimental results to develop a better quantitative understanding of the effect of temperature on overall methane removal efficiency. As expected, experimental results indicated that the oxidation rate was influenced by temperature, as it was reduced when the temperature decreased from 22 °C to 8 °C. However, some oxidation was observed at a lower temperature, which was confirmed by CO2 concentrations above the initial level and the observed temperatures above the exposure temperature along the height of biocover column. Furthermore, results showed that when the compost-based materials were subjected to 8 °C and then increased to 22 °C, methane oxidation within the material recovered quickly and returned to similar oxidation rates as observed before the temperature was reduced, suggesting that compost-based biocovers may not be affected by cyclic temperature variations when used in colder climates. Methane oxidation capacity was limited by the maximum oxidation rate, the biocover porosity, and the gas saturation profile that affects residence time and overall methane oxidation in the columns. The model results show that the CH4 oxidation rate was reduced by one order of magnitude when the temperature decreased from 22 °C to 8 °C. Therefore, the calculated Q10 values were 4.19 and 5.18 for the food and yard waste compost, respectively. Overall, compost-based landfill biocovers, such as food and yard waste compost, are capable of mitigate CH4 emissions from old and small landfills under different temperature conditions.

Investigation of the Different Regimes Associated with the Growth of an Interface at the Exit of a Capillary Tube into a Reservoir: Analytical Solutions and CFD Validation.

The emergence of a droplet from a capillary tube opening into a reservoir is an important phenomenon in several applications. In this work, we are particularly interested in this phenomenon in an attempt to highlight the physics behind droplet appearance. The emergence of a droplet from a tube opening into a reservoir under quasi-static conditions passes through three stages. The first stage starts when the meniscus in the tube reaches the exit. At this moment, the meniscus intersects the wall of the tube at the equilibrium contact angle. The interface then develops until its radius of curvature becomes equal to the tube radius. During this stage, the capillary pressure increases. In the second stage, the interface continues to evolve with its radius of curvature increasing until the static contact angle with respect to the surface of the reservoir is achieved. This marks the end of the second stage and the start of the third in which the contact line (CL) starts to depart the tube opening along the reservoir surface and the contact angle remains constant. Analytical models for the three stages have been derived based on the law of conservation of linear momentum. The models account for pressure, gravitational, capillary, and viscous forces, while inertia force is ignored. The model can predict the profiles of the mean velocity in the tube, the capillary pressure, and the evolution of the contact angle. In addition, a computational fluid dynamics (CFD) simulation has been conducted to provide a framework for validation and verification of the developed model. The CFD simulation shows qualitative behavior in terms of snapshots of the emerging droplet with time similar to that speculated by the analytical model. In addition, quantitative comparisons with respect to velocity, pressure, and volume profiles of the droplet show very good agreement, which builds confidence in the modeling approach.

Simulating temperature-dependent biodegradation-induced settlement at a landfill with waste lifts placed under frozen conditions.

Instrument bundles placed within the Ste. Sophie landfill (Quebec, Canada) have been collecting temperature and settlement data since January 2010. Previous modelling efforts simulated settlement based on a three-component model to account for primary or instantaneous compression, secondary compression or mechanical creep and time-dependent biodegradation-induced settlement. In northern climates where waste may be placed under frozen conditions, a time-dependent biodegradation-induced settlement term is unable to simulate settlement due to biodegradation as waste temperatures transition from below zero to optimal values for anaerobic degradation. This paper presents a temperature-dependent biodegration-induced settlement model. The model simulates heat generation as a function of temperature and tracks the expended energy as the waste degrades. The ratio of the expended energy to the total potential expended energy is used in the proposed temperature-dependent biodegradation-induced settlement term. The new term better accounts for the delayed biodegradation process observed in wastes placed under frozen conditions. The model was able to simulate the settlement trends observed at the Ste. Sophie landfill. The goal of developing and including a temperature-dependent biodegradation-induced settlement term in the model was to study the effects of operating conditions on waste settlement and stabilization. An optimized waste lift placement strategy could enhance waste stabilization and improve the airspace utilization within a landfill, simultaneously bringing increased revenues to landfill operators while decreasing the post closure environmental burden of landfills.

Simulating the heat budget for waste as it is placed within a landfill operating in a northern climate.

A landfill gas to energy (LFGTE) facility in Ste. Sophie, Quebec was instrumented with sensors which measure temperature, oxygen, moisture content, settlement, total earth pressure, electrical conductivity and mounding of leachate. These parameters were monitored during the operating phase of the landfill in order to better understand the biodegradation and waste stabilization processes occurring within a LFGTE facility. Conceptual and numerical models were created to describe the heat transfer processes which occur within five waste lifts placed over a two-year period. A finite element model was created to simulate the temperatures within the waste and estimate the heat budget over a four and a half year period. The calibrated model was able to simulate the temperatures measured to date within the instrumented waste profile at the site. The model was used to evaluate the overall heat budget for the waste profile. The model simulations and heat budget provide a better understanding of the heat transfer processes occurring within the landfill and the relative impact of the various heat source/sink and storage terms. Aerobic biodegradation appears to play an important role in the overall heat budget at this site generating 36% of the total heat generated within the waste profile during the waste placement stages of landfill operations.

Simulating settlement during waste placement at a landfill with waste lifts placed under frozen conditions.

Twelve instrument bundles were placed within two waste profiles as waste was placed in an operating landfill in Ste. Sophie, Quebec, Canada. The settlement data were simulated using a three-component model to account for primary or instantaneous compression, secondary compression or mechanical creep and biodegradation induced settlement. The regressed model parameters from the first waste layer were able to predict the settlement of the remaining four waste layers with good agreement. The model parameters were compared to values published in the literature. A MSW landfill scenario referenced in the literature was used to illustrate how the parameter values from the different studies predicted settlement. The parameters determined in this study and other studies with total waste heights between 15 and 60 m provided similar estimates of total settlement in the long term while the settlement rates and relative magnitudes of the three components varied. The parameters determined based on studies with total waste heights less than 15m resulted in larger secondary compression indices and lower biodegradation induced settlements. When these were applied to a MSW landfill scenario with a total waste height of 30 m, the settlement was overestimated and provided unrealistic values. This study concludes that more field studies are needed to measure waste settlement during the filling stage of landfill operations and more field data are needed to assess different settlement models and their respective parameters.

Simulating waste temperatures in an operating landfill in Québec, Canada.

A bioreactor landfill operated in Sainte-Sophie, Québec, Canada was instrumented to better understand the waste stabilization process in northern climates. Instrument bundles were placed within the waste to monitor temperature, oxygen, moisture content, settlement, total load, mounding of leachate and electrical conductivity. A finite element model was developed to simulate the heat fluxes to and from the waste, as well as heat generation within the waste from both anaerobic and aerobic processes. The results of the analysis suggest the majority of the aerobic activity occurs in the top portion of the waste lift exposed to ambient air. In addition, the model indicates that frozen waste lifts require a significant amount of heat to thaw the liquid fraction. The model also demonstrates that when a lift of cold waste is placed at the bottom of the landfill, the subsurface acts as a significant source of heat.

Heat budget for a waste lift placed under freezing conditions at a landfill operated in a northern climate.

A landfill operated in Ste. Sophie, Québec, Canada was instrumented to better understand the waste stabilization process in northern climates. Instrument bundles were placed within the waste to monitor temperature, settlement, oxygen, moisture content, total load, mounding of leachate and electrical conductivity. A finite element model was developed to simulate the heat budget for the first waste lift placed in the winter months and was calibrated using the first 10.5 months of collected temperature data. The calibrated model was then used to complete a sensitivity analysis for the various parameters that impact the heat budget. The results of the analysis indicated that the heat required for phase change to thaw the liquid fraction within frozen waste had a significant impact on the heat budget causing sections of waste to remain frozen throughout the simulation period. This was supported by the data collected to date at Ste. Sophie and by other researchers indicating that frozen waste placed during the winter months can remain frozen for periods in access of 1.5 years.

Potential concerns related to using octadecyltrichlorosilane (OTS) in rendering soils and porous ceramics hydrophobic.

The treatment of hydrophilic porous ceramics to render them hydrophobic and wetting to non-aqueous phase liquids (NAPLs) is frequently needed in multiphase flow experiments to control the flow or to measure the pressure of the NAPL. In addition, research dealing with soil wettability implies a need for hydrophobic or NAPL-wet soils. The traditional procedure, which has been widely used in literature, to render hydrophilic porous ceramics and soils hydrophobic is achieved by placing the hydrophilic solid in a 5% (by volume) octadecyltrichlorosilane (OTS) solution in ethanol followed by rinsing in ethanol. This research assesses the use of this procedure as it was found that this treatment procedure resulted in excess OTS on the surface of treated hydrophobic solids which can dissolve in an organic phase and in turn alter the wettability condition of adjacent hydrophilic soils. A modified procedure, which results in hydrophobic solids free of excess OTS, is presented.

Modeling of biological clogging in unsaturated porous media.

A two-dimensional unsaturated flow and transport model, which includes microbial growth and decay, has been developed to simulate biological clogging in unsaturated soils, specifically biofilters. The bacterial growth and rate of solute reduction due to biodegradation is estimated using the Monod equation. The effect of microbial growth is considered in the proposed conceptual model that relates the relative permeability term for unsaturated flow to the microbial growth. Two applications of the model are presented in this study. Using the model, the clogging mechanism in different soils has been simulated. The results of the model indicate that the time to reach a clogged state is influenced by the hydraulic properties of the soil. Clogging is delayed in soils with higher saturated hydraulic conductivities, and higher porosities. For the relative permeability model proposed, higher van Genuchten n values lead to a delay in clogging. The model was also used to simulate the progressive clogging of a septic bed as the biomat initially forms at the up-gradient end of the distribution pipe, displacing wastewater infiltration and biomat formation further down-gradient over time.

Effect of saline water and sludge addition on biodegradation of municipal solid waste in bioreactor landfills.

Bioreactor landfills require sufficient moisture to optimize the biodegradation processes and methane generation. In arid regions, this is problematic given the lack of fresh water supplies. Saline water can be used but may inhibit the biodegradation of the municipal solid waste (MSW) in landfills. Sludge may be used to enhance the biodegradation of MSW under saline conditions. For this study, two groups of laboratory-scale bioreactor cells were used to study the impact of saline water and sludge addition on the biodegradation of MSW in bioreactor landfills. The first group (four bioreactors) operated without sludge addition. The second group (four bioreactors) operated with the addition of sludge. The salt concentrations in the two groups were 0, 0.5, 1 and 3% (w/v), respectively. All bioreactors were operated at neutral pH levels with leachate recycling. The methane yield was 70.6, 61.7 and 47.5 L kg(-1) dry waste for bioreactors R1, R2 and R4, respectively; and 84.7, 78.7, 72.6 and 59 L kg(-1) dry waste for bioreactors R5, R6, R7 and R8, respectively. The high salt content (3%) inhibited the MSW biodegradation as evidenced by the methane yield, the percentage reduction in leachate concentration and the settlement that occurred during the study. Sludge addition was able to improve the methane yield at all salt concentrations.