ENHANCED MICROBIAL METHANE OXIDATION IN LANDFILL COVER SOILSErin 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

Landfill Gas Generation & Greenhouse Gas Emissions Biochar-Amended Biocovers for Landfill Methane

Mitigation

• Experimental studies at UIC (Poupak Yaghoubi, PhD) Long-term Column Incubation Study Batch Experiments: Kinetics of Methane Oxidation

• Conclusions & Future Work Ongoing studies at UIC

Problem StatementGHG 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

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

 

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 MossSewage Sludge Yard wasteMulch Corn StoverActivated Carbon Wheat strawWood/bark chips Earthworm cast

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

Need a superior material to sustain CH4 oxidation for longer periods

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.

EXPERIMENTAL STUDY:PhD Dissertation, Poupak Yaghoubi Long-term Column Incubation Experiments

Isotopic Analyses

Molecular Analyses – qPCR for pmoA gene

Batch Experiments – Kinetic Parameters of Microbial CH4 Oxidation

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

Preliminary Research: Materials Used

• 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

Column Incubation Study

Gas Cylinder

Flow Meter

Cover Material

Sampling Points

Plexiglass Column

Gravel

Air

Inlet gas (CH4 and CO2)

Thermo Meter

Flow Meter

E-2

H

H

Humidifier

Humidifier

Column 1 Soil Only

Column 2 20% biochar amendment

Column Incubation Study

Column 1 Column 2

% Biochar 0 20Initial moisture

content (%) 15 15

Column size Inside diameter: 9 cm; height: 90 cmSampling ports 9, located at 5-cm or 10-cm intervalsSynthetic gas

composition (%)CH4: 25; CO2: 25; and N2: 50

Influx rate 0.038~0.055 ml cm-2 min-1

Experimental Setup & Design

- Testing after steady state oxidation reached

- Adsorption assumed negligible

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

0.038 0.041 0.0490

5

10

15

20

25Column 1 Column 2

CH4 Influx (ml cm-2 min-1)

Fra

ctio

nal

Oxi

dat

ion

of

CH

4 (%

)

Effect of CH4 influx on Oxidation Efficiency

• Lower efficiency at higher CH4 influx rates

• Consistent with other landfill biocover studies with different substrates (e.g. Abichou et al. 2008)

Effect of CH4 Influx on Gas Profiles

• More oxidation (lower CH4 concentrations) at lower flow rates

• Effect negligible past oxidation horizon (~30 cm depth in column 2)

8 10 12 14 16 18 20 22 24 26 280

10

20

30

40

50

60

70

80

I-0.038 I-0.041 I-0.049 I-0.055 II-0.038 II-0.041II-0.049 II-0.055

CH4 Concentration (%)

Col

um

n H

eigh

t (c

m)

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.

Gas Profiles: Effect of Moisture Addition

).

8 10 12 14 16 18 20 22 24 26 280

10

20

30

40

50

60

70

80

Bef-0.049 Aft-0.049 Bef-0.055

Aft-0.055

CH4 Concentration (%)

Col

um

n H

eigh

t (c

m)

8 10 12 14 16 18 20 22 24 260

10

20

30

40

50

60

70

80

Bef-0.049 Aft-0.049 Bef-0.055

Aft-0.055CH4 Concentration (%)

Col

umn

Hei

ght

(cm

)

Column 2• CH4 concentration increases after water addition

highest increase (decrease in oxidation) at 10 cm zone (oxidation horizon)

Column 1• Overall higher CH4 concentration (less

oxidation)

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)

SEM Images

Isotopic Analyses

-38 -36 -34 -32 -30 -28 -26 -24 -22 -20

9111315171921232527

0

10

20

30

40

50

60

70

80

Column 1 δ13C

Column 2 δ13C

Column 1 CH4 Profile

Column 2 CH4 Profile

δ 13C (‰)

Col

um

n H

eigh

t (c

m)

CH4 Concentration (%)

• Increasingly positive (less negative δ13C values towards top of column

• Indicates microbial oxidation enrichment in 13CH4 in unoxidized CH4

• Differences near bottom of column not significant

where :Rsam = 13C/12C of the sample Rstd = 13C/12C for standard Vienna Peedee Belemnite (0.01124)

Molecular Analyses: qPCR targeting pmoA

Depth below surface (cm)

0 5 10 15 20 25 30 35 40 45 50 55 60Ave

rag

e pmoA

Gen

e A

bu

nda

nce

per

gram

sed

imen

t

105

106

107

108

Column 1Column 2

Higher pmoA copies in biochar-amended soil More in upper

depths Higher

methanotrophic activity

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 CH4 every 2-4 hours until CH4 < 0.5%

• Concentrations monitored over time & oxidation rate and Michaelis-Menten kinetic parameters determined

C

KVV

M1

1max

whereV is the actual rate of the reaction (m3m-3s-1)Vmax is the maximum reaction rate (m3m-3s-1) KM is the Michaelis-Menten constant (m3m-3) C is the CH4 concentration (m3m-3).

Batch Experiments: Results

Column Position Temp (oC)Vmax (nmol s-1 g dry

soil-1)KM

(mol/m3)

1(Soil only)

Top 22 0.18 0.83Top 35 0.16 0.27

Middle 22 0.19 1.21Bottom 22 0.17 0.86

2(Biochar:

20%)

Top 22 0.38 0.89Top 35 1.35 2.57

Middle 22 0.28 1.27Bottom 22 0.24 0.52

Michaelis-Menten parameters from batch testing

• 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

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

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

Conclusions & Future Work• Biochar affords higher porosity & more habitable sites for methanotrophic

bacteria in landfill coversSupports higher overall CH4 oxidation Steady state oxidation rates higher than those in soil landfill coversBiochar 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 layersThickness and number of gas distribution layers (GDLs)

Acknowledgements• Poupak Yaghoubi, PhD• Dongbei Yue – Visiting Scholar

Thanks to the Illinois Biochar Group

and all attendees for listening!