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Enhanced MicrObial Methane Oxidation in Landfill Cover Soils

Enhanced MicrObial Methane Oxidation in Landfill Cover Soils. Erin Yargicoglu, Krishna Reddy Department of Civil & Materials Engineering University of Illinois at Chicago Midwest Biochar Conference Friday, June 14, 2013. Overview. Problem Statement & Objectives of Study

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Enhanced MicrObial Methane Oxidation in Landfill Cover Soils

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  1. Enhanced MicrObial Methane Oxidation in Landfill Cover Soils Erin Yargicoglu, Krishna Reddy Department of Civil & Materials Engineering University of Illinois at Chicago Midwest Biochar Conference Friday, June 14, 2013

  2. Overview • Problem Statement & Objectives of Study • Landfill Gas Generation & Greenhouse Gas Emissions • Biochar-Amended Biocovers for Landfill Methane Mitigation • Experimental studies at UIC (PoupakYaghoubi, PhD) • Long-term Column Incubation Study • Batch Experiments: Kinetics of Methane Oxidation • Conclusions & Future Work • Ongoing studies at UIC

  3. Problem Statement GHG emissions from landfills = 3rd largest source of anthropogenic CH4 in the U.S. • CO2 and CH4 generated during waste degradation • Estimated 500-800 Mt CO2-equivalent per year globally • Waste generation expected to continue increasing with population • LFG recovery systems mitigate GHGs from newer landfills; not efficient or cost-effective for older landfills • CH4 mitigation during construction of new landfills also needs to be addressed (i.e. use of engineered daily cover) Biocovers identified as a key mitigation strategy for landfill CH4 by the IPCC (Bogner et al., 2007) Need a practical, economic & effective long-term solution to reduce landfill GHG emissions

  4. Fig. 1 from Huber-Humer et al. (2008) “Biotic Systems to Mitigate Landfill Methane Emissions” Waste Management 26:33-46.

  5. Current Biocover Technologies: • Materials used must be sustainable, readily available, cost-effective & easy to apply • Current biocovers employ a variety of materials: • Oxidation efficiencies limited by several factors: Compost Peat Moss Sewage Sludge Yard waste Mulch Corn Stover Activated Carbon Wheat straw Wood/bark chips Earthworm cast Need a superior material to sustain CH4 oxidation for longer periods • Material degradation, especially in labile C sources • Methane generation (rather than oxidation) in fresh compost or labile OM • Formation of EPS that reduces vertical gas transport • Inhibition of methanotrophic activity due to NH4+ or competition with heterotrophic bacteria

  6. Biochar-amended soil cover Biofilters, biocovers & biowindow designs • Include gas distribution layer at base • Low permeability cover above waste layer • Biochar can be mixed into soil or spread across in a layer Scheutz et al. (2011) “Mitigation of methane emission from Fakse landfill using a biowindow system” Waste Management 31:1018-1028.

  7. Experimental Study:PhD Dissertation, PoupakYaghoubi Long-term Column Incubation Experiments Isotopic Analyses Molecular Analyses – qPCR for pmoAgene Batch Experiments – Kinetic Parameters of Microbial CH4 Oxidation

  8. Preliminary Research: Materials Used • Biochar- Produced by Chip Energy Inc. (Goodfield, Illinois) by gasification process (520°C) using hard wood pellets • Soil - Silty clay soil used in Carlinville Landfill Cap • Sieved through sieve #10 (<2 mm) before using

  9. Column Incubation Study • 4 month duration • Steady state reached within 1 month • Daily measurement of headspace concentration & concentration along depth profile • Column extruded after 4 months: • DNA extraction from top, middle & bottom • Batch testing to determine kinetic parameters • Isotopic analysis for 13CH4 in headspace and at each depth

  10. Column Incubation Study • Experimental Setup & Design • Testing after steady state oxidation reached • Adsorption assumed negligible Column 2 20% biochar amendment Column 1 Soil Only

  11. Calculation of Methane Oxidation Efficiency • Fractional conversion of CH4 used to estimate oxidation: where CCO2 = Concentration of CO2 in headspace CCH4 = Concentration of CH4 in headspace -Allows estimation of oxidation rates without O2 concentration data - Ignores losses due to sorption and dilution

  12. Effect of CH4 influx on Oxidation Efficiency • Lower efficiency at higher CH4influx rates • Consistent with other landfill biocover studies with different substrates (e.g. Abichou et al. 2008)

  13. Effect of CH4Influx on Gas Profiles • More oxidation (lower CH4 concentrations) at lower flow rates • Effect negligible past oxidation horizon (~30 cm depth in column 2) Experimental conditions are identified in legend by column number (I for Column 1 [closed markers] and II for Column 2 [open markers]) and CH4 influx rate in units of ml cm-2min-1.

  14. ). Gas Profiles: Effect of Moisture Addition Column 2 • CH4concentration increases after water addition  highest increase (decrease in oxidation) at 10 cm zone (oxidation horizon) • Column 1 • Overall higher CH4 concentration (less oxidation) (a) Column 1 (b) Column 2 Figure 6. CH4 concentration profile along depth before and after adding water to (a) Column 1 and (b) Column 2. “Bef” and “Aft” in Legends Indicate “before” and “after” Adding Water, respectively. Figures in Legends Indicate CH4 Influx Rate in Unit of ml/cm2.min

  15. SEM Images a) Soil before column 1 (50 μm) b) Soil after column 1 (50 μm) C) 20% biochar before column 2 (100 μm) d) 20% biochar (w/w) after column 2 (100 μm)

  16. Isotopic Analyses • Increasingly positive (less negative δ13C values towards top of column • Indicates microbial oxidation  enrichment in 13CH4 in unoxidizedCH4 • Differences near bottom of column not significant where : Rsam = 13C/12C of the sample Rstd= 13C/12C for standard Vienna Peedee Belemnite (0.01124)

  17. Molecular Analyses: qPCR targeting pmoA • Higher pmoA copies in biochar-amended soil • More in upper depths • Higher methanotrophic activity

  18. Batch Experiments: Determination of Kinetic Parameters of Microbial CH4 Oxidation • Soils from upper, middle & bottom portions isolated • Sealed contained with known volume of CH4 added (5% v/v) • Gas samples analyzed for CO2 and CH4every 2-4 hours until CH4< 0.5% • Concentrations monitored over time & oxidation rate and Michaelis-Mentenkinetic parameters determined where V is the actual rate of the reaction (m3m-3s-1) Vmaxis the maximum reaction rate (m3m-3s-1) KM is the Michaelis-Menten constant (m3m-3) C is the CH4 concentration (m3m-3).

  19. Batch Experiments: Results • Higher Max Oxidation rate (Vmax) in biochar-amended cover soil • Greatest in upper portion (oxic layer) of soil • Some oxidative activity in unamended soil; lower rates and activities • Effect of increased temperature elevated in biochar-amended soil  greater microbial abundance in column 2 Michaelis-Menten parameters from batch testing

  20. Summary • Evidence for enhanced methane oxidation in biochar-amended soil • Higher fractional conversion of CH4 • Higher Vmax (max. oxidation rate) in biochar-amended soil  greatest near oxic zones • Greater abundance of pmoA genes in biochar-amended soil (except at lowest depth) • Increasing enrichment in 13CH4 in upper depths of biochar-amended soil vs. unamended soil • SEM images of bacterial biofilm material (Exopolymeric substances, EPS) deposited within soil pores in oxidation zone of column 2

  21. Summary (2) • Biochar-amendment increased depth of oxidation zone from 10 cm to ~30 cm • Oxidation kinetics significantly increased in oxic zone • EPS production likely reason for decline in CH4 oxidation efficiency over time • More EPS observed in layer of active oxidation • Consistent with results of prior column incubation studies • May be an effect of uniformly high & continuous CH4 fluxes used • EPS clogging less prominent in field-scale biofilters • More variable methane fluxes  shorter periods of exposure to high fluxes & excess C

  22. Conclusions & Future Work • Biochar affords higher porosity & more habitable sites for methanotrophic bacteria in landfill covers • Supports higher overall CH4 oxidation • Steady state oxidation rates higher than those in soil landfill covers • Biochar amendment effective & inexpensive strategy to improve oxidation capacity of soils Ongoing field-scale & laboratory studies will investigate the impact of biochar type and landfill cover design on oxidation rates & long-term performance (>1yr) • Effect of seasonal variations in temperature, moisture & CH4 loading • Identification of factors limiting methane oxidation efficiency in the field • Effect of amendment strategy & biocover design on microbial community development and oxidation rates & kinetics: • Biochar mixed into soil vs. applied in thin layers • Thickness and number of gas distribution layers (GDLs)

  23. Acknowledgements • PoupakYaghoubi, PhD • DongbeiYue – Visiting Scholar Thanks to the Illinois Biochar Group and all attendees for listening!

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