Effects of Organics Diversion on Landfill Gas Generation and Comparison of

Landfills and WTE

Morton A. BarlazNorth Carolina State University

• Prediction of landfill gas production and collection is critical• Financial viability of gas recovery projects• Estimates of landfill carbon footprint

• Landfill gas and carbon storage dominate other aspects of landfill operation (construction, operation, closure, leachate management)

• Life Cycle Analysis• Landfills vs. WTE• Yard waste composting vs. daily cover

Introduction

Relative Contributions to Landfill Carbon Footprint

2.12 5.75 2.53 0.45

411.50

-535.00

0.25

-600.0

-400.0

-200.0

0.0

200.0

400.0

600.0

Constru

ction

Operat

ion

Closure

Post-C

losure

Leac

hate Gas

Carbon S

torag

e

CO

2-e

(kg)

per

Mg

Derived for a landfill that received 2 million Mg over 20 years

• How does methane production change with changing waste composition?

• Yard waste diversion• Increasing diversion of food waste

• We need to consider both k and L0

Introduction

Landfill Gas Modeling

• Qn is annual methane generation for a specific year t (ft3CH4/yr);

• k is first order decay rate constant (1/yr)• L0 is total methane potential (ft3 CH4/ton of waste);• Mi is the annual burial rate (tons)• t is time after initial waste placement (yr);• J is the deci-year time increment

Landfill Gas Emissions Model (LandGem)http://www.epa.gov/ttn/catc/products.html#software

∑∑= =

⋅−⋅⋅⋅=n

i j

tkin

jieM

LkQ0

9.0

0.00

,

10

Methane Production Rate Curve for Five Years Waste

0.00E+00

3.00E+06

6.00E+06

9.00E+06

1.20E+07

1.50E+07

0 10 20 30 40 50Time (Yr)

Met

hane

Rat

e (m

3/yr

)

Year 1Year 2Year 3Year 4Year 5total

Effect of Decay Rate (k) on Methane Production

Based on 286,000 short tons of refuse annually for 20 years and Lo = 1.5 ft3/wet lb (93.5 m3/wet Mg)

0.00E+00

2.00E+06

4.00E+06

6.00E+06

8.00E+06

1.00E+07

1.20E+07

0 10 20 30 40 50

Year

Met

hane

Pro

duct

ion

(m3

per y

ear)

0.02 0.04

0.08 0.12

0.16

Effect of Decay Rate (k) on Methane Production

Based on 286,000 short tons of refuse annually for 20 years and Lo = 1.5 ft3/wet lb (93.5 m3/wet Mg)

0

10

20

30

40

50

60

70

80

1 1.5 2 2.5 3 3.5 4 4.5 5

Year

% o

f Cum

ulat

ive

Met

hane

0.02 0.04

0.07 0.1

0.15 0.2

0.25 0.3

0.00E+00

2.00E+06

4.00E+06

6.00E+06

8.00E+06

0 5 10 15 20

Time (Yr)

Met

hane

Rat

e (m

3/yr

)

MethaneProductionMethanecollection

k = 0.04Collection Efficiency = 69.6%

0.00E+00

2.00E+06

4.00E+06

6.00E+06

8.00E+06

0 5 10 15 20 25

Time (Yr)

Met

hane

Rat

e (m

3/yr

)

MethaneProductionMethanecollection

k = 0.12Collection Efficiency = 60.6%

Effect of Decay Rate on Gas Collection

Temporally Averaged Collection Efficiencies (Barlaz et al., 2009)

Case 1:Phased in collection

Years 1-2: 0%Year 3: 50%Year 4: 70%Years 5-100: 75%

Case 2:Phased in collection with improved cover

Years 1-2: 0%Year 3: 50%Year 4: 70%Years 5-10: 75%Years 11-100: 95%

Case 3:Aggressive Gas Collection; Bioreactor Operation

Years 1-2: 25%Year 3: 50%Year 4: 70%Years 5-10: 75%Years 11-100: 95%

0

10

20

30

40

50

60

70

80

90

100

Case 1 Case 2 Case 3

Col

lect

ion

Effic

ienc

y (%

)

0.02 0.04 0.07 0.1 0.15

Derivation of Decay Rates for Individual Waste Components

• The decay rate has a significant influence on the amount of gas that can be collected for a given gas collection scenario

Lab-Scale Data

Conversion of Lab Rate to Field Rate

• Klab,i is the average decay rate from the lab reactors

• Wt. fraction is the composition• kMSW (0.04) is the assumed decay rate in a landfill

and will vary for different scenarios• f is a fitting factor and the only unknown

MSW

n

iiilab kfractionwtkf =××∑

=1, ) .(

Conversion of Lab Rate to Field Rate

• Once f is determined, Kfield,i is determined as:

MSWkfractionwtkfn

iiilab =××∑

=1, ) .(

ilabifield kfk ,, ×=

• Kfield,i is specific to an assumed bulk MSW decay rate (e.g., 0.04)

Calculated Field-Scale Decay Rates for Waste Components

00.10.20.30.40.50.60.70.80.9

1

Food W

aste

Leave

sGras

s

Branch

es

Newsp

aper

Office P

aper

Glossy P

aper

OCC

Dec

ay R

ate k = 0.02

k = 0.04

k = 0.12

Bulk MSW Decay Rate

Decay Rate Observations

• Food waste, grass and leaves are the highest• Decay rates were calculated for multiple waste

compositions. The standard deviation (normalized by the mean) was ~ 27%.

• Uncertainty in the assumed bulk MSW decay rate remains

Requires knowledge of both k and L0

0

50

100

150

200

250

300

350

Newsp

rint

Office

OCC

Coated

Paper

Branch

esGras

s

Leav

esFoo

d

Hardwoo

d

Softwoo

d

Plywoo

d (so

ft)

Oriente

d Stra

ndbo

ard (h

ard)

Particle

board

Medium

-dens

ity Fibe

rboard

CH

4 Yi

eld

(m3 C

H4/d

ry M

g)

Ongoing

Estimate of Bulk MSW L0 from Waste Composition Data

0102030405060708090

100

USEPA

Califor

nia

Delaware

Florida

Georgia

Iowa

Kansa

s

Minneso

ta

Missou

ri

Oregon

Penns

ylvan

ia

Wiscon

sin

Lo (m

3 CH

4 M

g w

et re

fuse

-1) AP-42

Effect of Assumed L0 on Estimate of k from Methane Collection Data

Explore the Effect of Waste Diversion on Methane Production

Case 1: Base Case (1 million metric tons/yr for 20 years)

Case 2: 100% diversion of yard waste (930,000 ton/yr)

Case 3: 100% diversion of yard waste and food waste (800,000 ton/yr)

Case 4: 90% diversion of yard waste and 50% diversion of food waste (870,000 ton/yr)

Case 5: 50% of office and mixed paper (942,000)

Comparison of Landgem and Multiphase Model with Calculated L0 = 48 m3/ton

Remove 90% YW + 50% FW

0.0E+00

1.0E+07

2.0E+07

3.0E+07

4.0E+07

5.0E+07

6.0E+07

0 20 40 60 80 100

Year

CH4

Prod

uctio

n (m

3/yr

)

LANDGEM Predicted

Mutiphase Predicted Production

Mass reduction is 13%

Comparison of Landgem and Multiphase Model with Calculated L0 = 48 m3/ton

Remove 90% YW + 50% FW

0.0E+00

1.0E+07

2.0E+07

3.0E+07

4.0E+07

5.0E+07

6.0E+07

0 20 40 60 80 100

Year

CH4

Prod

uctio

n (m

3/yr

)

LANDGEM Predicted

Mutiphase Predicted Production

Mutiphase Predicted Collection

Collection ScenarioYears 1-2: 0Year 3: 50%Year 4: 70%Years 5-10: 75%Years 11-100: 95%

Effect of Diversion on Methane Production Rate

0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

3.0E+07

3.5E+07

0 20 40 60 80 100

Year

CH4 P

rodu

ctio

n (m

3 /yr)

Remove 50% OFF + 50% Mixed Paper

Base Case

Remove all YWRemove all YW + FW

Remove 90% YW + 50% FW

100%93%

75%

55%

86%

production vs. collection

convergence

Effect of Diversion on Cumulative Methane Production

0

20

40

60

80

100

100-yearProduction

100-yearCollection

CollectionRate at year

10

CollectionRate at year

20

CollectionRate at year

40

Pece

nt o

f Bas

e Ca

se (%

) Base Case

Remove allYW

Remove allYW + FW

Remove 90%YW + 50%FWRemove 50%OFF + 50%Mixed Paper

Conclusions and Implications

• Waste composition has a significant effect on gas collection

• Changing only the mass buried does not lead to good estimates of future gas production and collection

• Component specific decay rates allow better assessment of future gas production and collection

De la Cruz, F. B. and M. A. Barlaz, 2010, "Estimation of Waste Component Specific Landfill Decay Rates Using Laboratory-Scale Decomposition Data,” Env. Sci. Technol., 44, 4722 – 28.

Life-Cycle Comparison of Landfills and WTE

• Review of 8 studies conducted in the US and Europe was uniform in showing that WTE is preferable to a landfill in consideration of:– Fugitive emissions from landfills– Avoided emissions associated with energy recovery

from combustion• Report is available on WTERT web site.

• Benefits of ADC:– Sequestered CO2 (153 kg C per wet Mg

of waste)– LFG collection (15.7 scm/Mg)– Avoided soil excavation (3 m3/Mg)

• Windrow composting drawbacks:– High ammonia emissions (2.5 kg/Mg)– Little benefit from avoided production of

fertilizer (3.5kg-N/Mg)

What to do with Yard Waste?A Life-Cycle Comparison of Windrow Composting and

the Use of Yard Waste as Alternative Daily Cover (ADC)

Results

• Results of study show ADC method to be more ‘Eco-efficient’ than windrow composting: lower cost and better for the environment.

– MS Thesis and journal article

van Haaren, R., Themelis, N. J. and M. A. Barlaz, 2010, “LCA Comparison of Windrow Composting of Yard Wastes with use as Alternative Daily Cover (ADC),” accepted, Waste Management.

Questions

Morton Barlazbarlaz@ncsu.edu

http://people.engr.ncsu.edu/barlaz/