Hanumanth S. Kulkarni

Prediction of Long-Term Municipal Solid Waste Landfill Settlement Using Constitutive Model

This paper proposes a generalized constitutive model for municipal solid waste, based on the framework derived from critical state concepts and incorporating the effects of mechanical creep and time-dependent biodegradation, to predict total landfill compression under incremental loading and with time. The model parameters are calculated based on laboratory one-dimensional compression and triaxial compression tests, and data available from published literature. To illustrate the applicability of the proposed model, settlements due to incremental loading of waste with time are predicted for typical landfill conditions. The predicted settlement results using the proposed model are compared with the predicted settlement results using 14 different reported models. It is shown that the predicted settlements can vary significantly depending on the model used and the parameter values selected. The proposed model predicts the total settlement in a range similar to the reported models that consider all three compo...

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

AbstractLeachate 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 moi...

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.

Influence of Spatial Variation of Hydraulic Conductivity of Municipal Solid Waste on Performance of Bioreactor Landfill

The current study analyzes the leachate distribution in the Orchard Hills Landfill, Davis Junction, Illinois, using a two-phase flow model to assess the influence of variability in hydraulic conductivity on the effectiveness of the existing leachate recirculation system and its operations through reliability analysis. Numerical modeling, using finite-difference code, is performed with due consideration to the spatial variation of hydraulic conductivity of the municipal solid waste (MSW). The inhomogeneous and anisotropic waste condition is assumed because it is a more realistic representation of the MSW. For the reliability analysis, the landfill is divided into 10 MSW layers with different mean values of vertical and horizontal hydraulic conductivities (decreasing from top to bottom), and the parametric study is performed by taking the coefficients of variation (COVs) as 50, 100, 150, and 200%. Monte Carlo simulations are performed to obtain statistical information (mean and COV) of output parameters of the (1) wetted area of the MSW, (2) maximum induced pore pressure, and (3) leachate outflow. The results of the reliability analysis are used to determine the influence of hydraulic conductivity on the effectiveness of the leachate recirculation and are discussed in the light of a deterministic approach. The study is useful in understanding the efficiency of the leachate recirculation system

Validation of Two-Phase Flow Model for Leachate Recirculation in Bioreactor Landfills

A numerical two-phase flow model is presented to determine the moisture distribution and pore water and gas pressures within unsaturated municipal solid waste (MSW) in bioreactor landfills during leachate recirculation. The numerical model used is the Fast Lagrangian Analysis of Continua (FLAC), which is based on finite difference approach. The model governing equations and mathematical formulations is briefly explained. Validation of the model is examined by simulating the published laboratory and field studies and published modeling studies. Overall, the two-phase flow model is found to produce results comparable with those of the published studies. This assures that the model can be used for the prediction of moisture distribution and for the rational design of leachate recirculation systems in bioreactor landfills.

Modeling coupled hydromechanical behavior of landfilled waste in bioreactor landfills: Numerical formulation and validation

AbstractBioreactor landfills involving leachate recirculation are emerging as the preferred option for managing municipal solid waste (MSW). Effective bioreactor landfill performance can be achieved by ensuring uniform and adequate moisture (leachate) distribution in landfilled MSW. This paper presents a numerical two-phase flow model as a tool to predict hydraulic behavior (moisture distribution and pore fluid pressures) in unsaturated MSW under leachate recirculation, mechanical response (stress-strain behavior), and coupled hydromechanical interactions of MSW in landfills. The selected mathematical model is the Fast Lagrangian Analysis of Continua (FLAC), which assumes leachate and landfill gas as two immiscible phases. The governing equations and numerical implementation are presented along with the general model implementation considerations. The model is validated by simulating the published laboratory studies, field studies, and published modeled studies. Overall, it is shown that the mathematical ...

Effects of unsaturated hydraulic properties of municipal solid waste on moisture distribution in bioreactor landfills

Moisture distribution in a bioreactor landfill depends on various parameters such as the leachate recirculation system and its geometric configuration, hydraulic properties of municipal solid waste (MSW), and others. Hydraulic properties of MSW are the most important parameters that govern leachate distribution. Studies on the effect of saturated hydraulic properties of MSW on moisture distribution are documented in literature; however, studies on the effect of unsaturated hydraulic properties are scarce. The main objective of this paper is to model the effect of unsaturated hydraulic properties of MSW on leachate distribution. Since MSW is unsaturated, flow of two immiscible fluids (leachate and landfill gas) is expected; therefore, a mathematical model that accounts for a two-phase system is implemented which considers leachate as wetting fluid and landfill gas as non-wetting fluid. This model is validated based on reported laboratory test results and mathematical modeling studies. The effect of unsaturated hydraulic properties of MSW indicates significant variations in leachate distribution under steady state and gravity drainage conditions, which shows that its consideration is essential in the design of leachate recirculation systems in bioreactor landfills.

Horizontal trench system effects on leachate recirculation in bioreactor landfills

ABSTRACT Horizontal trenches (HTs) are constructed during the waste filling for leachate recirculation in bioreactor landfills. Leachate distribution depends on HT configuration (i.e., spacing between successive HTs), leachate injection rate, modes of injection, and hydraulic properties and MSW heterogeneity. Presently, the effects of these variables on the moisture distribution have not been studied systematically. This study provides a systematic evaluation of the effect of the HTs variables on the moisture distribution and pore fluid pressures. A two-phase flow model is used to model a bioreactor landfill having an HT leachate injection system. It quantifies the effects of the unsaturated hydraulic properties and MSW heterogeneity, trench configuration, leachate injection flux, and mode of injection on hydraulic behaviour. The results show that unsaturated hydraulic conductivity and MSW heterogeneity significantly shape the zone of influence and excess pore pressures. Under heterogeneous-anisotropic conditions, the leachate migrates more laterally and the developed pore-pressures are lower than for homogeneous MSW. A closely-spaced, multi-level, staggered HT system is found to provide uniform and adequate moisture distribution in MSW. An intermittent mode of injection that alternates between the shallow and deep trenches with a higher leachate injection flow rate is found to be effective to control the excess pore pressures.

Effect of leachate recirculation and extent of degradation on the Stability of bioreactor landfill slopes

The stability of a bioreactor landfill slope is influenced by the quantity and method of leachate recirculation as well as on the degree of decomposition. Other factors include properties variation of waste material and geometrical configurations, i.e., height and slope of landfills. Conventionally, the stability of slopes is evaluated using factor of safety approach, in which the variability in the engineering properties of MSW is not considered directly and stability issues are resolved from past experiences and good engineering judgments. On the other hand, probabilistic approach considers variability in mathematical framework and provides stability in a rational manner that helps in decision making. The objective of the present study is to perform a parametric study on the stability of a bioreactor landfill slope in probabilistic framework considering important influencing factors, such as, variation in MSW properties, amount of leachate recirculation, and age of degradation, in a systematic manner. The results are discussed in the light of existing relevant regulations, design and operation issues.