Earth Sciences Division Berkeley Lab
Environmental Remediation Technology Program
Annual Report 2000–2001
NUMERICAL SIMULATION OF LANDFILL BIODEGRADATION PROCESSES Curtis M. Oldenburg, Sharon E. Borglin, and Terry C. Hazen Contact: Curtis M. Oldenburg, 510/486-7419, cmoldenburg@lbl.gov
RESEARCH OBJECTIVES
The need to control gas and leachate production while minimizing refuse volume in municipal solid waste (MSW) landfills has motivated the development of landfill simulation models that can be used by operators to predict and design optimal treatment processes. Prior models of landfill processes are either batch models (zero-dimensional), multilayer batch models (onedimensional), or do not consider gas production as part of biodegradation. The objective of this research is to develop fully three-dimensional numerical simulation capabilities for landfill biodegradation processes, including gas production. In this effort, we have developed T2LBM, a module for the TOUGH2 simulator. This module implements a landfill bioreactor model to provide simulation capability for the processes of aerobic or anaerobic biodegradation of municipal solid waste and the associated flow and transport of gas and liquid.
landfill. Shown in Figure 1 are four panels representing liquid saturation, temperature, acetic acid mass fraction, and aerobicity for the sample problem after one day. At this time, liquid saturation is variable, corresponding to the heterogeneous permeability field as shown in the upper-left panel. The temperature field (upper-right panel) reflects the heating caused by aerobic biodegradation as oxygen in the ambient air is consumed. The low-temperature region in the right-hand side of the domain corresponds to the high-liquid saturation region, where there is less ambient air and more liquid to be heated. At this location, anaerobic conditions prevail, with correspondingly smaller heat production. The mass fraction of acetic acid shown in the lower-left panel reveals that the anaerobic reaction has biodegraded more acetic acid than the aerobic reaction. In the final panel, the quantity called aerobicity is shown, in which aerobicity APPROACH equal to one indicates Biodegradation and gas aerobic conditions, and aeroproduction in MSW landfills bicity equal to zero indicates is an enormously complex anaerobic conditions. Most Figure 1. Liquid saturation (Sl), temperature (T), mass fraction acetic and variable process. To of the domain is weakly acid (XHAcliq), and aerobicity with liquid velocity vectors at t = 1 day make progress in the simulaaerobic as oxygen in the tion of landfill processes, simplifications must be made. The ambient air is still being consumed, while in the low-permeapproach chosen for T2LBM couples the process modeling of the ability, high-liquid saturation region, conditions have already flow and transport of gas and aqueous phases inherent in become anaerobic. Methane and CO2 mass fractions in the gas (not shown) confirm these interpretations. TOUGH2, with biodegradation and gas-generation processes. For simplicity, T2LBM models the biodegradation of a single SIGNIFICANCE OF FINDINGS substrate component (acetic acid, CH3COOH) as a proxy for all Our simulations to date point out the complexity of landfill of the biodegradable fractions in MSW. T2LBM includes six biodegradation processes and demonstrate that numerical simuchemical components (H2O, CH3COOH, CO2, CH4, O2, N2) and heat distributed in gaseous and aqueous phases with partilation of these processes is possible. Application of T2LBM is tioning by Henry’s law. This approach assumes implicitly that ongoing and aimed at simulating results of laboratory experihydrolysis reactions occur to produce acetic acid and places the ments and field tests of landfill biodegradation processes. model focus on biodegradation and associated gas production, RELATED PUBLICATION along with flow and transport processes (including nonOldenburg, C.M., T2LBM: Landfill bioreactor model for TOUGH2, isothermal effects). Version 1.0, Berkeley Lab Report LBNL-47961, 2001.
ACCOMPLISHMENTS
We have developed T2LBM and verified its performance against results from published laboratory studies of aerobic and anaerobic biodegradation. In addition, we have simulated a hypothetical MSW landfill with leachate recirculation and subsequent air injection into the bottom of the
ACKNOWLEDGMENTS
This work has been supported by the Laboratory Directed Research and Development Program of Berkeley Lab, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.
85