Research Interests

Introduction

The decomposition of lignocellulosic materials in solid waste disposal systems has implications for both methane emissions and long-term carbon storage, which in turn impact global carbon cycling. Lignocellulosic biomass is estimated to represent 0.95×1018g, or 29% of the active global organic carbon reservoir. 1 The overall objective of my research is to understand the reactivity of organic carbon in solid waste treatment and disposal systems and its role in carbon cycling, with an emphasis on describing the fundamental basis for various macro-processes.  I am also interested in understanding the interaction of solid waste management systems such as landfills with natural and other engineered systems including impacts on air quality (e.g. organic compounds and methane) and water quality (e. g. UV absorbance and ammonia).

I plan research that will improve our current understanding of the waste management system with an emphasis on the responsible and sustainable utilization of resources.  This will require a more holistic approach to solid waste management by applying life-cycle concepts from product conception, design, use/re-use/recycle and end-of-life management (i.e., recycling or disposal). Moreover, I am interested in research that will impact developing countries where improvement of health and sanitation will not be complete without addressing solid waste. For example, solid waste, when not disposed in engineered systems, will release leachate that contaminates drinking water sources.

Summary of Previous and Ongoing Work

The research described here has resulted in publications with researchers from different disciplines and different sectors including academia, government and industry.

Carbon Balance. Carbon balance modeling is important for evaluating the environmental impact of waste management alternatives and identifying areas for improvement. For example, landfilling remains a major disposal option in many countries and landfills are considered the third and fourth largest sources of anthropogenic methane in the U.S. and globally, respectively. 2, 3 Thus, it is important to quantify the environmental impact of landfilling by (1) parameterizing models to estimate methane emissions; and (2) evaluating the performance of existing models to determine the variables controlling a landfill’s carbon footprint. I have conducted research to study the anaerobic decomposition of different components of municipal solid wastes (e.g. wood, paper and food waste) and to improve on the model parameters required to describe methane production. 4-7

In 2010, I published a paper detailing an approach to estimate decay rate constants (k) from the laboratory decomposition data. 8 Prior to this work, there was no quantitative basis for assignment of decay rates to individual biodegradable waste components. These parameters are important in estimation of the climate impact of landfilling globally. The parameters that I developed have been adopted by the US EPA in the Waste Reduction Model (WARM) to estimate greenhouse gas (GHG) emissions from landfilling of solid waste 9 and in their GHG emissions inventory 2, as well as by other researchers in models to evaluate landfills and other solid waste management alternatives 10-13.  In further work, I compared measured landfill emissions with emissions predicted by existing models commonly used for GHG inventories, including models used by the Intergovernmental Panel on Climate Change (IPCC), and US EPA. 14 Results showed that for the study landfill, modeled emissions are orders of magnitude greater than measured emissions. This study underscores the need to conduct more extensive validation of current models used for emissions estimation. Similarly, the derived model parameters have been used to develop a model to assess the relative sensitivity of variables controlling the carbon footprint of a landfill. Monte Carlo analysis showed that methane production and carbon storage control a landfill’s carbon footprint. These types of analyses are important in making well-informed decisions to guide both policy development and future research.

Tracer correlation method allows for the direct measurement of methane emissions from a non point source such as a landfill (Above) . Along with methane oxidation measurements, mass balance can be conducted to calculate for the methane production (below)

Comparison of measured methane production with modeled methane production using different landfill gas modelling protocol.

 

Understanding Anaerobic Decomposition of Lignocellulosic Wastes. The core of my dissertation research was to understand substrate reactivity during the anaerobic decomposition of solid wastes that contain lignocellulosic substrates, and to develop tools for studying these processes at both laboratory- and field-scale. While differences in the decomposition behavior of different lignocellulosic materials are well-documented, the fundamental basis for the recalcitrance of some fractions of lignocellulose has not been fully studied. In my research, I applied 2D-NMR to study chemical changes during the anaerobic decomposition of lignocelluloses. Results showed that while significant cellulose and hemicellulose were converted to methane and carbon dioxide, lignin was generally preserved. This work represents the first application of 2D NMR of a fully dissolved cell wall in characterizing chemical changes during the anaerobic decomposition of lignocellulose in which the associations between lignin and structural carbohydrates are retained in a more native state. This study fills up a knowledge gap on the role anaerobic decomposition of plant tissues on global carbon cycling.


Aliphatic Region of the HSQC spectra showing the cross-peak corresponding to substructures of lignocellulose in its “native” state.

Aromatic region of the HSQC spectra showing crosspeaks corresponding to C9 units of lignin.

 

I have also conducted research to develop tools to improve our understanding of chemical and biological process in landfills. For example, I have adopted a CuO oxidation method to measure lignin in municipal solid waste. Because lignin is conserved during anaerobic decomposition, lignin can be used as a biomarker for waste decomposition.

I am currently leading two projects on landfill processes. The goal of the first project is to understand the impact of temperature on the anaerobic decomposition and methane generation in solid waste that was excavated from an elevated temperature landfill, and to determine whether microbial populations adapt to elevated temperatures over time.  I am applying biochemical assays and metagenomics to characterize methane generation and microbial communities in excavated samples.

 

Biochemical assay demonstrates the occurrence thermophilic methanogens in samples obtained from a landfill experiencing elevated temperatures (left). This observation was further supported by the microbial community characterizations (right)

The diversion of food waste from landfills is increasing due to the enactment of policies banning food waste disposal, as well as goals to reduce landfill methane emissions and to recover the energy potential of food waste in anaerobic digesters. Landfill leachate increasingly requires pre-treatment because it contains high levels of refractory organic matter (ROM) and ammonia that impact WWTP operations. 15, 16 ROM (i.e. humic- and fulvic-like substances) in leachate reduces the effectiveness of UV disinfection. Thus, understanding sources of ROM and exploration of alternatives to reduce its presence in leachates are needed.  I serve as the principal investigator on a project to determine the effect of food waste diversion from landfills on leachate quality, with an emphasis on UV absorbance and ammonia concentrations. I also plan to characterize UV absorbing species in leachate by 2D NMR and mass spectrometry. In this project. I am running reactors to characterize leachate quality in mixtures of MSW and specific sources of food waste.

Future Research

My future research will emphasize studies to reduce waste and improve the sustainable recovery of resources and energy from waste. It is also central to my future research to address issues relating to environmental inequity.

  1. Plastic Waste Management
  2. Management of Alternative Waste Streams such as Coal Combustion Residuals (CCR)
  3. Emerging contaminants
  4. Landfills as a Source of Materials and Energy
  5. Solid Waste Management in Developing Countries

References

  1. Hedges, J.I. Global biogeochemical cycles: progress and problems. Mar. Chem. 1992, 39 (1-3), 67-93.
  2. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 – 2012: Washington, D.C. https://www.epa.gov/sites/production/files/2017-02/documents/2017_complete_report.pdf (accessed 1/27/18)
  3. Denman, K.L.; Brasseux, G.; Chidthaisong, A.; Ciais, P.; Cox, P.M.; Dickinson, R.E.; Hauglustaine, D.; Heinze, C.; Holland, E.; Jacob, D.; Lohmann, U.; Ramachandran, S.; da Silva Dias, P.L.; Wofsy, S.C.; Zhang, X. Couplings between changes in the climate system and biogeochemistry, In Climate Change 2007: The Physical Science Basis Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Solomon, S.; Qin, D.; Manning, M., et al, Eds.; Cambridge University Press: Cambridge, U.K., 2007.
  4. Wang, X.; Padgett, J.M.; De la Cruz, Florentino B.; Barlaz, M.A. Wood biodegradation in laboratory-scale landfills. Environ. Sci. Technol. 2011, 45, 6864-6871.
  5. Lopez, V.M.; De la Cruz, F.B.; Barlaz, M.A. Chemical composition and methane potential of commercial food wastes. Waste Manage. 2016, 56, 477-490.
  6. Wang, X.; De la Cruz, F.B.; Ximenes, F.; Barlaz, M.A. Decomposition and carbon storage of selected paper products in laboratory-scale landfills. Sci. Total Environ. 2015, 532, 70-79.
  7. De la Cruz, F.B.; Chanton, J.P.; Barlaz, M.A. Measurement of carbon storage in landfills from the biogenic carbon content of excavated waste samples. Waste Manage. 2013, 33 (10), 2001-2005.
  8. De la Cruz, F.B.; Barlaz, M.A. Estimation of Waste Component-Specific Landfill Decay Rates Using Laboratory-Scale Decomposition Data. Environ. Sci. Technol. 2010, 44 (12), 4722-4728.
  9. Documentation for Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model (WARM). https://www.epa.gov/sites/production/files/2016-03/documents/warm_decay_rate_structure_10_30_2009.pdf. (accessed 1/27/18).
  10. Levis, J.W.; Barlaz, M.A. Is Biodegradability a Desirable Attribute for Discarded Solid Waste? Perspectives from a National Landfill Greenhouse Gas Inventory Model. Environ. Sci. Technol. 2011, 45 (13), 5470-5476.
  11. Levis, J.W.; Barlaz, M.A. What Is the Most Environmentally Beneficial Way to Treat Commercial Food Waste? Environmental Science \& Technology 2011, 45 (17), 7438-7444.
  12. Morris, J.; Scott Matthews, H.; Morawski, C. Review and meta-analysis of 82 studies on end-of-life management methods for source separated organics. Waste Manage. 2013, 33 (3), 545-551.
  13. Amini, H.R.; Reinhart, D.R. Regional prediction of long-term landfill gas to energy potential. Waste Manage. 2011, 31 (9–10), 2020-2026.
  14. De la Cruz, F.B.; Green, R.B.; Hater, G.R.; Chanton, J.P.; Thoma, E.D.; Harvey, T.A.; Barlaz, M.A. Comparison of Field Measurements to Methane Emissions Models at a New Landfill. Environmental Science \& Technology 2016.
  15. Zhao, R.; Novak, J.T.; Goldsmith, C.D. Evaluation of on-site biological treatment for landfill leachates and its impact: A size distribution study. Water Res. 2012, 46 (12), 3837-3848.
  16. Zhao, R.; Gupta, A.; Novak, J.T.; Goldsmith, C.D.; Driskill, N. Characterization and treatment of organic constituents in landfill leachates that influence the UV disinfection in the publicly owned treatment works (POTWs). J. Hazard. Mater. 2013, 258–259, 1-9;
  17. Eleazer, W.E.; Odle, W.S.; Wang, Y.S.; Barlaz, M.A. Biodegradability of municipal solid waste components in laboratory-scale landfills. Environ. Sci. Technol. 1997, 31 (3), 911-917.
  18. Barlaz, M.A. Forest products decomposition in municipal solid waste landfills. Waste Manage. 2006, 26 (4), 321-333.
  19. World Population Prospects: The 2010 Revision; United Nations: New York; http://www.un.org/en/development/desa/population/publications/pdf/trends/WPP2010/WPP2010_Volume-I_Comprehensive-Tables.pdf. (accessed 1/27/18).