Leachate Injection Research Articles

Effects of concentrated leachate injection modes on stabilization of landfilled waste

Injection of concentrated leachate to landfills is a simple and cost-effective technology for concentrated leachate treatment. In this study, the effects of injection mode of concentrated leachate and its hydraulic loading rate on the stabilization of landfilled waste were investigated. Compared with the injection of concentrated leachate, the joint injection of leachate and concentrated leachate (1:1, v/v) was more beneficial to the degradation of landfilled waste and mitigated the discharge amount of pollutants at the hydraulic loading rate of 5.9 L m(-2) day(-1). As the hydraulic loading rate of the joint injection of leachate and concentrated leachate was increased from 5.9 to 17.6 L m(-2) day(-1), the organic matter, biologically degradable matter, and total nitrogen of landfilled waste were degraded more rapidly, with the degradation constant of the first-order kinetics of 0.005, 0.004, and 0.003, respectively. Additionally, NO2(-)-N and NO3(-)-N in the concentrated leachate could be well removed in the landfill bioreactors. These results showed that a joint injection of concentrated leachate and raw leachate might be a good way to relieve the inhibitory effect of high concentrations of toxic pollutants in the concentrated leachate and accelerate the stabilization of landfilled waste.

Application of food waste leachate to a municipal solid waste incinerator for reduction of NOx emission and ammonia water consumption

This study investigates the possibility of applying food waste leachate to a municipal solid waste incinerator in order to effectively dispose of the material and to reduce the environmental impact. The spray positions and the quantity of the food waste leachate in municipal solid waste incinerator were adjusted to examine the stability of the process and the environmental effect. The rear of the first combustion chamber was found to be the desirable location for an environmental perspective in this study. At a food waste leachate injection rate of 2 m 3 /h, the concentration of the emitted NOx decreased from 130 ppm to 40 ppm. The consumption of ammonia water was reduced by about 36% after adding the food waste leachate. The inclusion of the food waste leachate to the municipal incinerator also increased the amount of steam that was produced. The results of this research indicated that a positive outcome can be expected in terms of diversifying the treatment options for food waste leachate. The results also provide guidance for institutional framework to manage the incineration of the food waste leachate.

Design of horizontal trenches for leachate recirculation in bioreactor landfills using two-phase modelling

Horizontal trenches (HTs) are the simplest form of leachate recirculation systems (LRSs), constructed by excavating a trench to a desired depth and length along the length of a municipal solid waste (MSW) landfill. The performance of HTs is mainly based on few empirical studies. Moreover, previous mathematical models often either considered the MSW as saturated than unsaturated or assumed incorrect MSW properties. Hence, those studies lack the accuracy needed for the efficient design of HT. In this study, parametric studies are performed to develop design charts for HTs considering real field MSW conditions. Heterogeneous-anisotropic MSW resulted in an increase in wetted width and area and a decrease in the pore pressures developed than homogeneous-isotropic waste. Normalised design charts are provided to estimate wetted width, wetted area and pore water pressure at steady-state for a given leachate injection rate, hydraulic conductivity and the dimension and location of HT from a LRS.

Two-Phase Modeling of Leachate Recirculation Using Drainage Blankets in Bioreactor Landfills

A drainage blanket (DB) is a recently introduced leachate recirculation system (LRS) in bioreactor landfills, which involves the use of a blanket of high permeable material that is spread over a large area of the municipal solid waste (MSW). Based on the laboratory and field observations documented in the literature, the results of the performance and efficiency of bioreactor landfills vary greatly due to the empirical method followed to design the LRS. Therefore, a rational LRS design methodology that achieves an efficient bioreactor landfill and creates an optimal and safe environment is necessary. Two-phase flow modeling was performed in this study by representing the relative permeabilities of leachate and landfill gas with the van Genuchten function and fluid flow with Darcy’s law. The effects of heterogeneous-anisotropic MSW, the leachate injection rate, and the saturated and unsaturated hydraulic conductivities of the MSW on the moisture distribution in a typical bioreactor landfill cell using a DB as the LRS were modeled. Those results included saturation levels, maximum pore water and gas pressures, maximum influenced lateral spread (wetted width), maximum influenced wetted area, and outflow collected at leachate collection and removal system at the bottom of the landfill. The results indicate that the variation in the different parameters assumed has a significant influence on the successful distribution of the moisture. Unsaturated hydraulic properties considerably affect moisture flow and distribution in landfilled MSW. And, the intermittent mode of leachate recirculation has the potential for the development of gas pressures that must be considered to evaluate the stability of the landfill slopes.

Design of drainage blankets for leachate recirculation in bioreactor landfills using two-phase flow modeling

Drainage blankets (DB) are used for leachate recirculation in bioreactor landfills and consist of highly permeable material placed over a large area of the landfill with the leachate injection pipe embedded in the material at specified locations. DBs are generally installed at different depth levels during the waste filling operations. Very limited information is reported on performance of DBs, and that which exists is based on a small number of field monitoring and modeling studies. A rational method for the design of landfills using DBs has not been developed. This study performs a parametric analysis based on a validated two-phase flow model and presents design charts to guide the design of DBs for given hydraulic properties of MSW, the leachate injection rate and the dimensions and locations of the DB as measured from the leachate collection and recirculation system (LCRS) located at the bottom of the landfill cell. Numerical simulations were performed for the two established MSW conditions: homogeneous–isotropic and heterogeneous–anisotropic waste. The optimal levels of leachate saturation, wetted width, wetted area and developed pore water and pore gas pressures were determined, and design charts using the normalized parameters were developed. An example is presented on the use of design charts for typical field application.

Slope stability of bioreactor landfills during leachate injection: Effects of geometric configurations of horizontal trench systems

In bioreactor landfills, different configurations of closely spaced horizontal trench (HT) systems are often considered as leachate recirculation systems to achieve uniform and rapid distribution of moisture in municipal solid waste (MSW). In this study, a numerical two-phase flow modelling was adopted to study the effects of geometric configuration of HT systems on the moisture distribution in MSW, and the stability of a simplified bioreactor landfill slope during continuous and intermittent leachate recirculation. Transient variations in pore water and capillary pressures in MSW were assessed, and slope stability analyses were performed using strength reduction technique. MSW was considered as heterogeneous and anisotropic with varied unit weight and saturated hydraulic conductivity. The results demonstrated that geometric configurations of HT systems significantly affected the moisture distribution, generation and distribution of pore water and capillary pressures in MSW, and considerably influenced the mechanical stability of bioreactor landfill slope. It was concluded that staggered configuration of closely spaced HT systems with intermittent sequences of leachate recirculation and subsequent gravity drainage in alternate shallow and deep HT layers should be adopted as they produce uniform moisture distribution and ensure the mechanical stability of landfill slope due to low induced pore pressures near side slope. Overall, this study presents a significant contribution to the understanding of the basic mechanisms controlling the geotechnical stability of bioreactor landfills during leachate operations. Furthermore, the capability of the adopted commercial code was verified with complexities related to bioreactors behaviour. However, further research is needed to validate the model based on field monitoring data at actual bioreactor landfills.

Artificial neural network model for predicting methane percentage in biogas recovered from a landfill upon injection of liquid organic waste

Field-scale investigation for a period of more than four months was conducted to evaluate the performance of a landfill for biogas extraction upon the injection of food waste leachate (FWL), a liquid organic waste generated from the food waste recycling facilities in Korea. The target was set at recovering about 50–60 % methane from the landfill gas (LFG) at extraction rates varying between 10 and 30 m3/h. An application of the artificial neural network (ANN) was presented in this paper to predict the performance parameter namely methane percentage (%). The input parameters to the network were LFG extraction rate (m3/h) and landfill leachate: FWL ratio, respectively, which were obtained from the field-scale investigation. Four different back error propagation learning algorithms were used to train the ANN for a comparative analysis, and the best among them was selected. To substantiate our claim, performance of the network was analyzed for different set of training and test data points. Predictions were attained by appropriately selecting the network parameters and, adequately training the network with 130 set of data points. The accuracy of back propagation neural network (BPNN)-based model predictions was evaluated by calculating the correlation coefficient (R) and mean absolute percentage error values. The results from this predictive modeling work showed that BPNNs were able to predict the methane percentage of the LFG in an acceptable range.

Slope stability of bioreactor landfills during leachate injection: Effects of heterogeneous and anisotropic municipal solid waste conditions

In bioreactor landfills, leachate recirculation can significantly affect the stability of landfill slope due to generation and distribution of excessive pore fluid pressures near side slope. The current design and operation of leachate recirculation systems do not consider the effects of heterogeneous and anisotropic nature of municipal solid waste (MSW) and the increased pore gas pressures in landfilled waste caused due to leachate recirculation on the physical stability of landfill slope. In this study, a numerical two-phase flow model (landfill leachate and gas as immiscible phases) was used to investigate the effects of heterogeneous and anisotropic nature of MSW on moisture distribution and pore-water and capillary pressures and their resulting impacts on the stability of a simplified bioreactor landfill during leachate recirculation using horizontal trench system. The unsaturated hydraulic properties of MSW were considered based on the van Genuchten model. The strength reduction technique was used for slope stability analyses as it takes into account of the transient and spatially varying pore-water and gas pressures. It was concluded that heterogeneous and anisotropic MSW with varied unit weight and saturated hydraulic conductivity significantly influenced the moisture distribution and generation and distribution of pore fluid pressures in landfill and considerably reduced the stability of bioreactor landfill slope. It is recommended that heterogeneous and anisotropic MSW must be considered as it provides a more reliable approach for the design and leachate operations in bioreactor landfills.

Influence of the geomembrane on time-lapse ERT measurements for leachate injection monitoring

Leachate recirculation is a key process in the operation of municipal waste landfills as bioreactors. To quantify the water content and to evaluate the leachate injection system, in situ methods are required to obtain spatially distributed information, usually electrical resistivity tomography (ERT). However, this method can present false variations in the observations due to several parameters. This study investigates the impact of the geomembrane on ERT measurements. Indeed, the geomembrane tends to be ignored in the inversion process in most previously conducted studies. The presence of the geomembrane can change the boundary conditions of the inversion models, which have classically infinite boundary conditions. Using a numerical modelling approach, the authors demonstrate that a minimum distance is required between the electrode line and the geomembrane to satisfy the good conditions of use of the classical inversion tools. This distance is a function of the electrode line length (i.e. of the unit electrode spacing) used, the array type and the orientation of the electrode line. Moreover, this study shows that if this criterion on the minimum distance is not satisfied, it is possible to significantly improve the inversion process by introducing the complex geometry and the geomembrane location into the inversion tools. These results are finally validated on a field data set gathered on a small municipal solid waste landfill cell where this minimum distance criterion cannot be satisfied.

Slope stability of bioreactor landfills during leachate injection: Effects of unsaturated hydraulic properties of municipal solid waste

In bioreactor landfill, the leachate flow and moisture distribution depend upon saturated and unsaturated hydraulic properties of municipal solid waste (MSW). The effects of unsaturated parameters have not been studied because of scarcity of the data and variation in unsaturated parameters due to MSW heterogeneity, degree of decomposition, and pore structure. In this study, a numerical two-phase flow model was used to examine the effects of unsaturated hydraulic properties on the moisture distribution, pore fluid pressures, and the stability of a bioreactor landfill slope with horizontal trench as leachate recirculation system. Unsaturated hydraulic parameters were based on the van Genuchten model and obtained from previously published laboratory studies. The unsaturated hydraulic properties of MSW are found to significantly influence the leachate distribution, pore water and capillary pressures, and landfill slope stability during the operations of leachate injection and subsequent gravity drainage. Further research is needed for better understanding and accurate measurement of hydraulic properties and shear strength parameters of unsaturated MSW.

Two-Phase Modeling of Leachate Recirculation Using Vertical Wells in Bioreactor Landfills

Leachate recirculation or liquid injection is an established practice for operating landfills as bioreactors to enhance the biodegradation of municipal solid waste (MSW). Among other subsurface liquid injection methods, vertical wells (VWs) represent one of the most common methods used for active or closed landfills. The current design and operation of VW systems does not consider the effect of additional liquid injection on the increase in gas pressures. In this study, a two-phase model that assumes landfill leachate and gas as immiscible phases was used to predict the moisture distribution and pore water and pore-gas pressures in a typical bioreactor landfill that uses VWs as its leachate injection or recirculation system. The unsaturated liquid and gas properties of MSW were simulated based on the van Genuchten model. The study evaluates the effect of the unsaturated hydraulic conductivity of MSW, the heterogeneous and anisotropic nature of the MSW, and the geometric configuration of VWs on moisture distribution and pore water and gas pressures. The unsaturated hydraulic properties of MSW significantly influence the wetted area and pore-water pressures during the initial stages of leachate injection and during the gravity drainage that follows. The numerical modeling results show that the gas pressures in the landfill will be of the order of 60 to 150 kPa, which are far above the liquid pressures for most typical liquid injection rates when no gas accumulation in the landfill is assumed due to an active gas extraction system. Hence, the slope stability of bioreactor landfills needs to be assessed by using the effects of gas and liquid pressures, especially when the gas extraction system is operating at below optimum efficiency.

Seismic Imaging of a Leachate-Recirculation Landfill: Spatial Changes in Dynamic Properties of Municipal Solid Waste

Leachate-recirculation landfills enhance waste degradation through percolation of leachate inside the waste mass. In situ monitoring of moisture distribution and changes in mechanical properties (stiffness) of municipal solid waste (MSW) is needed to optimize the safe and effective operation of these types of landfills. Geophysical methods, such as electrical-resistivity tomography, have effectively monitored moisture distribution during and after leachate injection. This study investigates seismic surveys to capture the changes in mechanical properties [shear modulus (via shear-wave velocity) and Poisson’s ratio] of MSW to infer the extent of degradation and provide dynamic properties needed for seismic stability evaluation. To achieve this goal, a series of seismic surveys were performed at the Veolia ES Orchard Hills landfill, 15 km south of Rockford, Illinois, to image seismic velocity structure and the Poisson’s ratio of a recirculation cell, compared with an adjacent newer landfill cell without leachate recirculation. Seismic data were collected using fan shot direct P-wave (compressional wave) surveys and S-wave (shear wave) surveys, conventional P-wave refraction, and the multichannel analysis of surface waves (MASW) method. The fan shot surveys employed a sledgehammer source on one side of the landfill and geophones on the opposite side, thus exploiting the landfill’s topography and geometry to image waste to a depth of approximately 10 m. P-wave-velocity tomographic models and S-wave-velocity tomographic models from these direct-wave (through-pile) raypaths indicate a dramatic velocity increase below 5 m depth, perhaps indicating consolidation and compaction of the waste material. The ratio in P-wave to S-wave velocity ranges from 1.8 to 3.7, with an average of approximately 2.7, and Poisson’s ratio ranges from 0.29 to 0.46, with an average value of 0.42 (standard deviation 0.024). In the upper 5 m S-wave velocity (∼150–170 m/s) is higher at the recirculation cell than in newer portions of the landfill consisting of uncompacted waste (∼110–120 m/s), as derived from analysis of surface waves. The landfill cap, which is present over the recirculation cell, but not over the new waste, may be at least partly responsible for this difference. S-wave velocities are very similar below 5 m depth, whereas P-wave velocity (from seismic-refraction profiling) indicates a slight decrease in velocity between the leachate-recirculation cell and newer portions of the landfill. The refraction and surface wave surveys, however, were depth-limited (less than 8–9 m), compared with the fan shots. Overall, this study showed that seismic surveys have the potential to monitor spatial and temporal variation of dynamic properties of MSW.

Effects of Turbulence and Temperature on Leachate Chemistry

AbstractThis study investigates the role of turbulence and temperature on changes in chemistry (dissolved Ca2+ and pH) of leachate within transmission pipes in bioreactor landfills, using synthetic and real leachate from the Brady Road Landfill in Winnipeg, Manitoba. Sealed reactors with rotating propellers were used to mimic leachate flow through the transmission pipes. The reactors were operated under turbulent conditions at 32, 83, and 180 rpm for 6 h on and 18 h off to represent the daily leachate injection operation of a general landfill. A control reactor was operated parallel to the reactors at 0 rpm. During the Off phase, the reactors were either sealed or open to the atmosphere. Under sealed conditions and pH values lower than 7.2, no significant changes in chemistry were observed for the synthetic or real leachate. However, for the mixers and control reactors containing real leachate at pH values higher than 7.4, pH dropped approximately by 0.3–0.4 units. This is explained by Ca2+ removal as CaC...

Enhanced methane recovery by food waste leachate injection into a landfill in Korea

The current food waste leachate (FWL) disposal practice in Korea warrants urgent attention and necessary action to develop an innovative and sustainable disposal strategy, which is both environmentally friendly and economically beneficial. In this study, methane production by FWL injection into a municipal solid waste landfill with landfill gas (LFG) recovery facility was evaluated for a period of more than 4 months. With the target of recovering LFG with methane content ∼50%, optimum LFG extraction rate was decided by a trial and error approach during the field investigation in five different phases. The results showed that, upon FWL injection, LFG extraction rate of ∼20 m 3/h was reasonable to recover LFG with methane content ∼58%. Considering the estimated methane production potential of 31.7 m 3 CH 4 per ton of FWL, methane recovery from the landfill was enhanced by 14%. The scientific findings of this short-term investigation indicates that FWL can be injected into the existing sanitary landfills to tackle the present issue and such landfills with efficient liner and gas collection facility can be utilized as absolute and sustainable environmental infrastructures.

Temporal and spatial pore water pressure distribution surrounding a vertical landfill leachate recirculation well.

Addition of liquids into landfilled waste can result in an increase in pore water pressure, and this in turn may increase concerns with respect to geotechnical stability of the landfilled waste mass. While the impact of vertical well leachate recirculation on landfill pore water pressures has been mathematically modeled, measurements of these systems in operating landfills have not been reported. Pressure readings from vibrating wire piezometers placed in the waste surrounding a liquids addition well at a full-scale operating landfill in Florida were recorded over a 2-year period. Prior to the addition of liquids, measured pore pressures were found to increase with landfill depth, an indication of gas pressure increase and decreasing waste permeability with depth. When liquid addition commenced, piezometers located closer to either the leachate injection well or the landfill surface responded more rapidly to leachate addition relative to those far from the well and those at deeper locations. After liquid addition stopped, measured pore pressures did not immediately drop, but slowly decreased with time. Despite the large pressures present at the bottom of the liquid addition well, much smaller pressures were measured in the surrounding waste. The spatial variation of the pressures recorded in this study suggests that waste permeability is anisotropic and decreases with depth.

Experimental and theoretical assessment of the multi-domain flow behaviour in a waste body during leachate infiltration

The optimisation of landfill operation is a key challenge for the upcoming years. A promising solution to improve municipal solid waste (MSW) management is the bioreactor technology. A meso-scale (around 1 m 3) experimental set-up was performed to study the effect of moisture control in low density conditions with different leachate injection operations and bioreactor monitoring including the use of a neutron probe. The moisture content distribution evolution demonstrates a multi-domain flow behaviour. A classic van Genuchten–Mualem description of the connected porosity proved insufficient to correctly describe the observed phenomena. A bimodal description of the connected porosity is proposed as solution and a connected/non-connected porosities numerical model was applied to the results. The model explains the experimental results reasonably well.

Contribution of 3-D time-lapse ERT to the study of leachate recirculation in a landfill

Leachate recirculation is a key process in the operation of municipal waste landfills as bioreactors. It aims at increasing the moisture content to optimise the biodegradation. Because waste is a very heterogeneous and anisotropic porous media, the geometry of the leachate plume recirculation is difficult to delineate from the surface at the scale of the bioreactor site. In this study, 3-D time-lapse electrical resistivity tomography (ERT) was used to obtain useful information for understanding leachate recirculation hydrodynamics. The ERT inversion methodology and the electrode arrays were optimised using numerical modelling simulating a 3-D leachate injection scenario. Time-lapse ERT was subsequently applied at the field scale during an experimental injection. We compared ERT images with injected volumes to evaluate the sensitivity of time-lapse ERT to delineate the plume migration. The results show that time-lapse ERT can accomplish the following: (i) accurately locate the injection plume, delineating its depth and lateral extension; (ii) be used to estimate some hydraulic properties of waste.

Decoupling MSW settlement into mechanical and biochemical processes – Modelling and validation on large-scale setups

Forecasting settlements of non-hazardous waste is essential to ensure the integrity and durability of landfill covers over time. Over a short time span, the survey of settlements may also contribute to the investigation of the biodegradation processes. This paper addresses secondary settlements of Municipal Solid Waste (MSW), a heterogeneous and time-evolving material. An analysis of available experimental data from different pilots and the literature was conducted to quantify the influence of biodegradation on MSW secondary settlements. After making assumptions about the various features of the waste and their constitutive relationships, a one-dimensional biomechanical model to predict the secondary settlement has been developed. The determination of the total secondary settlement was obtained by the addition of two separate parts, the mechanical settlement, due to creep, and the biochemical settlement, due to the degradation of the organic matter. The latter has been evaluated based on the observed biogas production. Using the data from different recent large-scale experiments that provide a monitoring of biogas production, a method for predicting the biochemically-induced settlements is proposed and validated on these tests. The relative contributions of mechanical and biochemical settlements are also calculated and discussed as a function of waste pre-treatment and operation conditions (biological pre-treatment, shredding, leachate injection). Finally, settlement may be considered as a relevant indicator for the state of biodegradation.

Effect of leachate injection modes on municipal solid waste degradation in anaerobic bioreactor

Three pilots simulated landfill bioreactors were used to investigate the effect of leachate injection modes on anaerobic digestion and biogas production from municipal solid waste. The technical modes used to increase waste moisture consisted of an initial saturation of the waste by flushing with leachate followed by a quick drainage, or weekly leachate injections with two different rates. The results confirmed that increasing moisture content is a key parameter to boost the biological reactions. Weekly leachate injection with high flow rate led to better results than the initial saturation of the waste in terms of biogas production kinetics. Water percolation was found to be an important factor to accelerate the degradation of solid waste. However, a modelling of the collected data by Gompertz model clearly showed that the intrinsic biogas potential determined on the initial solid waste was not reached with any of the progressive leachate injection modes.

Improvement of electrical resistivity tomography for leachate injection monitoring

Leachate recirculation is a key process in the scope of operating municipal waste landfills as bioreactors, which aims to increase the moisture content to optimize the biodegradation in landfills. Given that liquid flows exhibit a complex behaviour in very heterogeneous porous media, in situ monitoring methods are required. Surface time-lapse electrical resistivity tomography (ERT) is usually proposed. Using numerical modelling with typical 2D and 3D injection plume patterns and 2D and 3D inversion codes, we show that wrong changes of resistivity can be calculated at depth if standard parameters are used for time-lapse ERT inversion. Major artefacts typically exhibit significant increases of resistivity (more than +30%) which can be misinterpreted as gas migration within the waste. In order to eliminate these artefacts, we tested an advanced time-lapse ERT procedure that includes (i) two advanced inversion tools and (ii) two alternative array geometries. The first advanced tool uses invariant regions in the model. The second advanced tool uses an inversion with a “minimum length” constraint. The alternative arrays focus on (i) a pole–dipole array (2D case), and (ii) a star array (3D case). The results show that these two advanced inversion tools and the two alternative arrays remove almost completely the artefacts within +/−5% both for 2D and 3D situations. As a field application, time-lapse ERT is applied using the star array during a 3D leachate injection in a non-hazardous municipal waste landfill. To evaluate the robustness of the two advanced tools, a synthetic model including both true decrease and increase of resistivity is built. The advanced time-lapse ERT procedure eliminates unwanted artefacts, while keeping a satisfactory image of true resistivity variations. This study demonstrates that significant and robust improvements can be obtained for time-lapse ERT monitoring of leachate recirculation in waste landfills.