WELCOME TO MY PERSONAL PAGE.
- I joined NC State University in August 1989 after completing my Ph.D. at the University
of Wisconsin in 1988 and then spending a year as a research scientist at the
U.S. Environmental Protection Agency Laboratory for Groundwater Research (Ada,
OK). I have been serving as Department
Head since 2010.
- My research interests are in the
area of solid waste engineering with a specific emphasis on (1) biological and
chemical processes in landfills and (2) the use life-cycle analysis to evaluate
the economic and environmental performance of integrated solid waste management
Chemical, and Physical Processes in Landfills
- Biological, chemical and physical
processes all affect the decomposition of municipal solid waste(MSW) in
landfills as well as the behavior of trace waste components such as organics
and metals. I am interested in all aspects of solid waste behavior in landfills
and conduct research that ranges from fundamental studies of the microbial
ecology of landfills to more applied studies on the effect of various
industrial wastes on refuse decomposition and gas generation. My research area includes laboratory and
field-scale experimental work as well as mathematical models to describe
various aspects of waste and landfill behavior.
Representative projects are described below, with references to journal
articles that describe the work more fully.Journal articles are listed in my Publication List.
- In collaboration with Dr. Francis
de los Reyes in our department, Ph.D. student Bryan Staley conducted work
to understand the mechanisms by which methane production is initiated in a
landfill. Two hypotheses were explored
including the presence of methanogen-rich microniches and the presence of acid
tolerant methanogens that could grow under the acidic conditions that are typical
soon after the disposal of fresh solid waste.
This work resulted in a series of papers from methods development to a
description of the initiation of refuse methanogenesis in laboratory-scale
simulations (papers 85, 92 98).
- In collaboration with Dr. Detlef
Knappe in our department, I have worked on the behavior of trace organic
contaminants during waste decomposition.
This work began in 2000 when Dr. Dilek Sanin, a postdoctoral research
associate at the time and now a professor in Turkey, worked with waste
excavated from a Superfund Site to measure the behavior of toluene and acetone
during waste decomposition (paper 34).
This work continued with postdoctoral research associate Dr. Shannon
Bartelt-Hunt, now on the faculty at the University of Nebraska, who began to
explore the behavior of chemical warfare agents in landfills (papers 62, 66.) This work was based on mathematical modeling
and was extended to a detailed description of trace contaminant behavior in
landfills in collaboration with Michael Lowry at Research Triangle Institute
(paper 67). In parallel, postdoctoral
research associate Dr. Pascal Saikaly worked on the behavior of surrogate biological warfare
agents in decomposing waste (papers 65, 89).
Most recently, Ph.D. student Jovi Saquing focused on physical and
chemical interactions between municipal waste components and trace organic contaminants
(papers 70, 76, 83). Perfluorinated
compounds have been documented in municipal landfill leachate (paper 91). Currently, with support from the National
Science Foundation, we are working to identify sources of perfluorinatedcompounds
in municipal waste and to evaluate whether landfill leachate is a significant source
of these compounds in the environment.
- I have a
long standing interest in material biodegradability in landfills including both
bulk waste components such as various types of paper (paper 20), wood (paper
94), and newly developed biodegradable polymers (papers 25, 46, 93 as well as
ASTM standard D6776-02). Concurrently, I
am interested in quantifying that fraction of biogenic waste that does not
degrade and is put into long-term carbon storage in landfills (paper 27, 68,
104). I am currently working with 1
Ph.D. students on improved analytical methods for lignin in MSW. The method most commonly employed to quantify
lignin in MSW is the Klason lignin method and we have shown that interferences
(plastics, rubber, synthetic textiles) make this method unreliable for bulk
MSW. I am working with a second Ph.D.
student on factors controlling the anaerobic biodegradability of wood in
simulated landfill systems.
- I am interested in the impact of
various wastes on refuse decomposition and on the analysis of field-scale
landfill performance. This is best
illustrated by work on the effect of industrial wastes on decomposition (papers
72, 73). I have worked on various
aspects of bioreactor landfills for many years (papers 42, 75, 99, 101) and
recently completed a national assessment of the state-of-the practice in
collaboration with Dr. Craig Benson at the University of Wisconsin and Dr.
Chris Bareither, now at Colorado State University (papers 61, 77, 78). We are currently analyzing landfill gas
collection data from landfills across the U.S. in an effort to update the U.S.
EPA’s Landfill gas Emissions Model (LandGEM - http://www.epa.gov/ttncatc1/dir1/landgem-v302-guide.pdf).
- There are many other aspects of
landfills where I am actively working including strategies for the long-term
management of landfills (papers 49, 90, 100, 102) and landfill gas collection
(papers74, 79, 103).
- The Application of Life-Cycle Analysis to Integrated Solid
- I collaborate with Drs. E. Downey Brill, Joe DeCarolis and Ranji Ranjithan in
our department on research to identify optimal strategies for solid waste
management in consideration of cost, energy consumption and environmental emissions
using life-cycle analysis. In the late 1990s, we worked with the Research
Triangle Institute and the U.S. EPA to develop the first solid waste management
life-cycle model in which a user could search all feasible solid waste
management strategies to identify optimal waste management scenarios. The model, often referred to as the Decision
Support Tool, includes process models to describe emissions from individual
unit processes (e.g., waste combustion – paper 35; landfills – paper 36), as
well a systems model (papers 43, 44) and a user interface (paper 38). In subsequent work, we considered uncertainty
in model parameters (paper 56) and later the model was used in a case study to
assist the State of Delaware with solid waste management planning (paper
69). The use of life-cycle analysis to
explore various aspects of the waste management system continues with papers on
industrial wastes (84), commercial food waste (95), and a study on whether
biodegradability is a desirable attribute of a material (paper 93).
- We are currently working on a new
version of the optimization model to enhance its capabilities in several areas
(manuscript submitted). First, all
process models are being updated in consideration of changes in waste
management technologies (e.g., new methods for refuse collection, increased
automation in MRFs, reduced emissions from mass burn combustion systems, a more
sophisticated analysis of landfills). In
addition, new process models for anaerobic digestion and waste gasification have
been developed. Second, the model will have
the capability to consider future changes to the solid waste system such as
increased costs for energy, limits on greenhouse gas emissions and higher
landfill diversion targets. Changes can
be imposed in five year time steps throughout the modeling period. Third, the model will project changes in the
mix of fuels used to generate energy in the U.S. as this has implications for
both the cost of energy and the offset credits attributable to processes in
which energy is recovery from waste (e.g., combustion, landfills, anaerobic