Girish Kumar

Influence of dynamic coupled hydro-bio-mechanical processes on response of municipal solid waste and liner system in bioreactor landfills

A two-dimensional (2-D) mathematical model is presented to predict the response of municipal solid waste (MSW) of conventional as well as bioreactor landfills undergoing coupled hydro-bio-mechanical processes. The newly developed and validated 2-D coupled mathematical modeling framework combines and simultaneously solves a two-phase flow model based on the unsaturated Richards equation, a plain-strain formulation of Mohr-Coulomb mechanical model and first-order decay kinetics biodegradation model. The performance of both conventional and bioreactor landfill was investigated holistically, by evaluating the mechanical settlement, extent of waste degradation with subsequent changes in geotechnical properties, landfill slope stability, and in-plane shear behavior (shear stress-displacement) of composite liner system and final cover system. It is concluded that for the given specific conditions considered, bioreactor landfill attained an overall stabilization after a continuous leachate injection of 16years, whereas the stabilization was observed after around 50years of post-closure in conventional landfills, with a total vertical strain of 36% and 37% for bioreactor and conventional landfills, respectively. The significant changes in landfill settlement, the extent of MSW degradation, MSW geotechnical properties, along with their influence on the in-plane shear response of composite liner and final cover system, between the conventional and bioreactor landfills, observed using the mathematical model proposed in this study, corroborates the importance of considering coupled hydro-bio-mechanical processes while designing and predicting the performance of engineered bioreactor landfills. The study underscores the importance of considering the effect of coupled processes while examining the stability and integrity of the liner and cover systems, which form the integral components of a landfill. Moreover, the spatial and temporal variations in the landfill settlement, the stability of landfill slope under pressurized leachate injection conditions and the rapid changes in the MSW properties with degradation emphasizes the complexity of the bioreactor landfill system and the need for understanding the interrelated processes to design and operate stable and effective bioreactor landfills. A detailed discussion on the results obtained from the numerical simulations along with limitations and key challenges in this study are also presented.

System effects on bioreactor landfill performance based on coupled hydro-bio-mechanical modeling

AbstractA newly developed and validated numerical model that accounts for the coupled hydro-bio-mechanical processes in municipal solid waste (MSW) landfills, was employed to assess influence of va...

Incorporating Thermal Effects in Modeling of MSW Landfills

Heat is one of the primary byproducts of biodegradation of municipal solid waste (MSW). Biodegradation of MSW in landfills induces changes in physical properties, mechanical response of MSW, and flow of leachate within the MSW pore spaces. Moreover, biodegradation of MSW in landfills is temperature dependent and consequently the engineering properties of MSW are all influenced by waste temperatures. Thus, landfills are complex systems with interrelated processes and it is crucial to account for all these interdependencies to accurately predict the coupled behavior of MSW. In this study, a coupled-thermo-hydro-bio-mechanical model was formulated that incorporates the effect of temperature on heat generation and biodegradation of MSW. The model integrates a two-phase flow hydraulic model, a plane-strain formulation of the Mohr-Coulomb mechanical model, a first order decay biodegradation model, and a one-dimensional heat conduction model with temperature-dependent heat generation. Numerical simulations were carried out using a typical landfill configuration with leachate injection simulating a bioreactor landfill. The simulations were carried out with and without temperature effects to determine the influence of temperature on MSW behavior. The results indicate a significant influence of temperature on the MSW response (degradation and settlement) and underscore the importance of incorporating thermal effects in numerical modeling of MSW landfill systems.

Risk, Sustainability and Resiliency Considerations in Polluted Site Remediation

Environmental pollution including the soil and groundwater contamination has been a major problem faced by the U.S., and many other countries across the world. Realizing the impact contaminated sites had on human health and environment, some of the major environmental regulatory agencies were formed that imposed strict regulations to condemn improper waste disposal practices and to clean up the contaminated sites. Over the years, the environmental regulations and policies have evolved from being ambitious and impractical to a more rational risk-based remediation approach. Several remediation technologies have been developed based on their suitability to different site characteristics. However, the choice of the final remedial technology has always been dictated by its ability to reduce the contaminant concentrations to remedial goals, the cost, and speed of implementation of the technology at the contaminated site. The enormous use of energy and resources by the remediation activities and consequently, the broader environmental impacts that follow from various remediation activities goes unaccounted. In recent years, a more holistic approach, the green and sustainable remediation, involving the quantification of net environmental, economic, and social impacts/benefits (the triple bottom line) of site remediation activities is given great importance to achieve sustainable development. Moreover, with the global climate change and regularly occurring extreme events, it is essential that the remediation plan and design is resilient/adaptable to the extreme events. This study presents an overview of risk-based site remediation approach, and green and sustainable remediation and the tools that aid in quantifying the sustainability of remediation alternatives. In addition, the importance of considering resilient design in remediation projects is discussed. Finally, the challenges and opportunities that needs to be addressed to realize sustainable and resilient remediation are highlighted.

Reliability assessment of bioreactor landfills using Monte Carlo simulation and coupled hydro-bio-mechanical model

The performance of a bioreactor landfill is highly influenced by the simultaneous interactions of several coupled processes that occur within the landfill. In addition, the high uncertainty and spatial variability in the geotechnical properties of municipal solid waste (MSW) poses significant challenge in accurately predicting the performance of bioreactor landfills. In this study, a 2D coupled hydro-bio-mechanical (CHBM) model was employed to predict the behavior of MSW in bioreactor landfills. The numerical model integrated a two-phase flow hydraulic model, a plane-strain formulation of Mohr-Coulomb constitutive model, and a first order decay biodegradation model. The statistical ranges (mean and standard deviation) of some of the major influential MSW properties were derived from the published studies. Random fields of spatially variable MSW properties were generated following the log-normal distribution. Reliability-based analysis was carried out by performing several realizations of Monte-Carlo simulations and the statistical response of the output results including the moisture distribution, pore fluid pressures, landfill settlement, and interface shear response of the composite liner system were quantified. The results clearly indicate the importance of considering spatial variability of the geotechnical MSW properties and its influence on the performance of bioreactor landfills during leachate injection operations. A comparison of the results with the deterministic analysis was performed to evaluate the relative benefits and to emphasize the need for reliability-based analysis for effective design of bioreactor landfills.

Addressing Sustainable Technologies in Geotechnical and Geoenvironmental Engineering

Geotechnical and geoenvironmental engineering, which constitutes one of the major tasks of the infrastructure and construction projects, is one of the main contributors to the climate change and other global environmental impacts, due to the use of large amounts of materials and energy. One of the most effective ways to address these challenges is to have the environmental implications integrated into the decisions of a geotechnical/geoenvironmental project. In this regard, the application of life cycle assessment (LCA) has gained major impetus to evaluate the environmental sustainability of such projects. LCA is a comprehensive method for assessing a range of environmental impacts across the full life cycle of a geotechnical and geoenvironmental project, from raw material acquisition, material manufacturing and transport, construction, use and maintenance, and final disposal/recycling. LCA can be challenging due to limited reliable or relevant inventory of data for the assessment. However, it is a systematic and well-accepted tool to develop/design environmentally sustainable geotechnical and geoenvironmental projects. In addition, a triple bottom line assessment which further involves evaluating the economic and social sustainability aspects of the project along with the LCA is essential to holistically evaluate and identify the effectiveness of a geotechnical and geoenvironmental project toward sustainability. This paper presents a review of few studies that demonstrate the application of LCA and triple bottom line assessment to some of the common geotechnical and geoenvironmental projects. The study underscores the importance of LCA in identifying the critical materials and/or operations for the resulting environmental impacts and helps explore different options to improve the net environmental and socioeconomic benefits.

Coupled Hydro-Biomechanical Modeling of Bioreactor Landfills: New Modeling Framework and Research Challenges

Bioreactor landfills are emerging as a sustainable option in place of traditional landfills because of their inherent benefits such as waste to energy conversion, early waste stabilization, landfill space recovery, and its beneficial reuse with no long-term risks of leachate treatment and disposal. However, the performance of a bioreactor landfill is dictated by the coupled processes within the landfill. Understanding the individual system processes and their interdependencies is crucial in order to numerically model this system. Till date, there is no single model which can account for coupled processes to assess the performance of bioreactor landfills holistically. In this paper, a new mathematical modeling approach is presented that incorporates coupled hydraulic, mechanical, and biological processes in bioreactor landfills. Few results obtained from numerical simulations using this mathematical framework are briefly discussed, and major research challenges associated with the numerical modeling are highlighted.

Novel techniques in high speed modem implementation using programmable DSPs

We present the design and performance of a high speed MSK modem that incorporates digital heterodyne processing. A novel table look-up procedure for direct IF/RF modulation, based on a suitable maximal-length shift register sequence, is described. High performance, linear phase, low-complexity mixing and filtering in the receiver is achieved using multirate IFIR filters, where the shaping filter may possibly beM-th-band. The configuration of the IFIR filters is chosen based on the carrier frequency and the filtering requirements.