Calculating the Carbon Footprint of Various Municipal Waste

Waste Management Services

Calculating the Carbon Footprint

of Various Municipal

Waste Management Practices

Allan Yee, CD, M.Sc., P.Eng.

Senior Engineer Organics Processing

5 February 2013


Outline Municipal Waste Management Decision Making IAW the 4 Rs

Waste Management Carbon Emission Effects

Carbon Footprint of Landfill Disposal

Waste Recovery Example: LFG Capture

Waste Recycling/Reuse Example: Composting

Residential Recycling Discussion

Waste Reduction Example: Grasscycling

Summary and Conclusions

Waste Management Hierarchy: the 4 Rs

Reduce

Reuse

Recycle

Recover

Hig

her

Pre

fere

nce


Carbon Emission Effects of Waste

Management Practices Every activity/process has a carbon footprint that can

be measured and/or calculated.

The carbon footprint (GHG emissions) of waste

management activities comes from:

Activity/process energy inputs;

Degradation of organic materials during activity;

Production of energy/energy containing substances.

Comparison of carbon footprints of alternative waste

practices.


Landfill Gas Generation


Landfill Gas Emissions Disposal and degradation of organic materials in a landfill under anaerobic conditions will generate GHGs.

CH4 is main GHG of concern as CO2 is biogenic.

Landfill emissions are the biggest contributor to the carbon footprint of most municipal waste management systems. Emissions from upstream extraction and consumption of fossil fuels in collecting waste plus energy inputs into landfilling efforts are relatively minor in comparison.

6% of total CH4 emissions worldwide are attributed to landfills.


Methane Generation Potential, Lo

Lo = amount of CH4 that can theoretically be produced from landfilling one tonne of waste

Lo = MCF x DOC x DOCf x F x (16/12) x 1000 kgs

CH4/tonne waste

Where Lo = CH4 generation potential, kgs/tonne of waste

MCF = CH4 correction factor, fraction

DOC = degradable organic carbon, t C/t of waste

DOCf = fraction of DOC that dissimilates under landfill conditions

F = fraction of CH4 in landfill gas

16/12 = stoichiometric factor for conversion of CH4 to carbon


Time Distribution of Lo

Mass of material landfilled M, times Lo yields the maximum amount of methane that can be generated from that material.

Applying a first order decay function (e-kt) to M x Lo will give a time distribution to the emissions.

Resulting relationship commonly known as Scholl Canyon Model.

Summation of Individual FOD Curves Over Time

CH4

Emissions

(Q)

Time (Yrs) ∞ 0 1 2

Time period of

active landfilling

100

Individual first order decay

(FOD) time distribution

curve for methane

generation


Numerical Approximation of FOD

Model Equation

Qt = ∑ 2k Lo Mi e-kti

i=1

n

Where Qt = total LFG emission rate, volume/time

n = total time periods of waste placement

k = methane generation rate constant, time-1

Lo = methane generation potential, volume/mass of waste

ti = age of the ith section of waste, time

Mi = mass of wet waste, placed at time i


Waste Recovery Example:

Landfill Gas Collection


Landfill Gas Collection Systems

Network of interconnected gas extraction wells installed in capped portions of landfill site.

Suction blowers capture and transport LFG from wells to a central point where gas is processed for straight combustion (flaring) or energy recovery (power, CHP, CNG, etc.).

Typical 75% capture efficiency for collection systems: comparisons of CH4 captured vs. generated.

Further 10% oxidation of CH4 emissions through the cover system of a landfill.


Edmonton’s LFG Capture System

In operation at Clover Bar Landfill since 1992,

current LFG flow is about 65,000 standard m3/day,

with average CH4 content of 52%.

2011 data:

City Scholl Canyon model calculated 8,122 tonnes CH4

generated.

Capital Power recorded 6,384 tonnes CH4 captured.

Net emissions difference, counting flaring/power

generation and cover oxidation = 32,848 tonnes CO2-e.*

*Using a GWP of 21 for CH4


Waste Recycling/Reuse Example:

Composting


Carbon Footprint of Composting Carbon footprint = emissions from:

Process of composting [mass of material composted x

composting emission factors];

Upstream extraction and consumption of the energy inputs into

the operation [quantities of fuel used x respective emission

factors]; and

Landfilling of residuals from process [mass of residuals x Lo].

Differences between above and emissions from a

baseline [landfilling of materials composted] are the

emission reductions [offsets] from the operation.

Basic Composting System Boundary, Inputs

and Outputs

Fuel (Diesel)

Waste collection,

sorting,

transportation

Sorting

Aerobic Conversion

Compost

End User

On site use of

electricity

On site use by

equipment

Electricity from grid

Landfill)

Recycle

Waste Production

(households,

commercial)

System Boundary Limit

Adapted from CDM (2005)

Windrow Composting

Baseline Emissions Ebaseline = [Mdelivered x (MCF)(DOC)(DOCF)(F)(16/12) –R][1-OX][GWPmethane]

Where Ebaseline = CH4 emissions from landfilled waste in CO2 equivalent (tonnes)

Mdelivered = waste delivered to composting facility (tonnes)

MCF = methane correction factor

= 1 for managed landfills (IPCC default)

DOC = degradable organic fraction of waste (tonne C/tonne waste)

= 0.19 for Alberta (calculated using Environment Canada data)

DOCF = fraction of degradable organic carbon dissimilated

= 0.77 (IPCC default)

F = fraction of LFG that is CH4, assumed to be 0.5

16/12 = stoichiometric factor (molecular weight fraction of CH4/C)

R = recovered landfill gas at baseline landfill (measured)

OX = landfill oxidation factor

= 0.1 for landfills with soil or compost covers (IPCC default)

GWPmethane = global warming potential of methane of 25 (IPCC default)

Diesel Usage Emissions Ediesel = (FCO2)(Vdiesel) + (FCH4)(Vdiesel)(GWPCH4) + (FN2O)(Vdiesel)(GWPN2O)

Where Ediesel = direct GHG emissions from diesel combusion, kg CO2-e

FCO2 = emission factor for CO2 emissions from diesel combustion

= 2.730 kg CO2 per m3 (CAPP value)

Vdiesel = volume of diesel gas consumed (m3)

FCH4 = emission factor for CH4 emissions from diesel combustion

= 0.000133 kg CH4 per m3 (CAPP value)

GWPCH4 = global warming potential for CH4 of 21 (IPCC default)

FN2O = emission factor for N2O emissions from diesel combustion

= 0.0004 kg N2O per m3 (CAPP value)

GWPN2O = global warming potential for N2O of 310 (IPCC default)

Diesel Production Emissions Ediesel,p = (FCO2,p)(Vdiesel) + (FCH4,p)(Vdiesel)(GWPCH4) + (FN2O,p)(Vdiesel)(GWPN2O)

Where Ediesel,p = upstream GHG emissions from diesel production, kg CO2-e

FCO2,p = emission factor for CO2 emissions from diesel combustion

= 0.138 kg CO2 per m3 (CAPP value)

Vdiesel = volume of diesel gas consumed (m3)

FCH4 = emission factor for CH4 emissions from diesel production

= 0.0109 kg CH4 per m3 (CAPP value)

GWPCH4 = global warming potential for CH4 of 21 (IPCC default)

FN2O = emission factor for N2O emissions from diesel production

= 0.000004 kg N2O per m3 (CAPP value)

GWPN2O = global warming potential for N2O of 310 (IPCC default)


ECF Example

Edmonton Composting Facility System

Boundary, Inputs and Outputs Collected

Mixed

Residential

MSW

Pre-processing

(sorting)

ECF –

mechanical

plant

Residues to

landfill w/ no

LFG

Collection

Compost curing

Collected waste

wood

On-site waste

wood chipping

Dewatered

municipal

biosolids

Biosolids/wood

chip composting

Screening cured

compost

Residues to

landfill w/ LFG

collection

Biosolids/wood

chip mixing

On-site power

use

On-site natural

gas use

On-site diesel

use

On-site

gasoline use

On-site

propane use

Electricity from

grid

Natural gas

Diesel fuel

Gasoline

Propane

Compost sales

to end users System Boundary

10,000 tonnes

110,000 tonnes

Primary Residuals 14,000 tonnes, 13.4%organic

Secondary Residuals 15,000 tonnes, 45.3%organic

14,000,000 kWh

29,600 GJ

483,900 L

1,280 L

1,740 m3

Tertiary Residuals 2,000 tonnes, 45.3%organic


Calculation of Emissions and Offsets

for the ECF*

Baseline emissions from landfilling feedstock = 263,340 tonnes CO2-e.

Project Emissions of 50,123 tonnes CO2-e:

Composting = 12,900 tonnes CO2-e;

On-site combustion and upstream processing/extraction for power/diesel/natural gas/propane/gasoline = 16,206 tonnes CO2-e; and

Landfill disposal of residuals = 21,017 tonnes CO2-e.

Net calculated offsets = 213,217 tonnes CO2-e.

*2007 IPCC GWP = 25 for CH4, 298 for N2O


Residential Recycling

Discussion

Residential Recycling




Complexities of Carbon

Accounting in Recycling Cannot assume away transportation component emissions.

Carbon footprint of end use of recycled materials must be compared against:

Avoided emissions from landfilling of organic materials; and

Carbon footprint for displacement of virgin materials in end manufacturing.

Municipalities only play small part in the long recycling chain.

Long chain of custody for diversity and grades of recycled materials from initial separation to final recycled use means no one player will likely have all info necessary for calculation.

Fast moving/changing markets for recyclable materials.

What proportion of the carbon footprint of collection and sorting is assigned to what commodities?


Newsprint Recycling Example

ONP6 vs. ONP8:

Less “outthrows” in ONP8, but greater effort required.

ONP8 however, can likely go to regional/NA mills vs.

overseas where it may be economical to re-sort the paper.

MRF operator’s incentives likely only returns vs. cost

(sorting and transportation), not carbon footprint.

Transportation costs disproportionate to actual GHG

emissions generated.

Downstream processing/manufacturing emission factors

(e.g., power) likely unknown to MRF operator.


Waste Reduction Example:

Grasscycling


Carbon Footprint of Grasscycling

Carbon footprint of grasscycling is due to

emissions from:

Production of potable water and chemical fertilizers

applied to a lawn to grow grass; and

Use and production of any fuels consumed in cutting

grass.

Carbon footprint of grasscycling can be compared

to carbon footprint of its alternatives.

The Residential Grass Cultivation System

Grow Grass

Cut Grass

Grass Clippings

Fertilizer

Water

Lawnmower

Energy

Landfill w/o LFG

Collection

Composting

Operation

Energy Inputs into Composting

Operation

Option (Baseline) 1: Landfilling Grass

Clippings

Option 3: Grasscycling

Option (Baseline) 2: Composting Grass

Clippings

System Boundary

Energy Inputs into Landfilling Operation

Sunlight


Numbers for Comparative Calculation

180,000 single family households @ 250 m2 lawn

size, 354 kgs yearly production of clippings.

Average cutting every 2 weeks April-October w/

gasoline powered mowers, 0.2 L gasoline/cutting.

No watering of lawns, displacement of 25%

fertilizer (28-4-8) requirements on 50% of lawns.


Alternative Baseline Scenario 1:

Landfill Disposal

Residential collection of clippings in 6.5 tonne payload vehicles, round trip distance of 80 kms to transfer station, 3.5 L diesel/km.

Transfer haul to landfill w/o LFG collection in 20 tonne payload long haul vehicles, round trip distance of 180 kms, 0.6 L diesel/km.

Pro-rated energy inputs (power, natural gas, diesel) into landfill operation.

GHG emissions from landfilling of grass.


Alternative Baseline 2:

Central Composting

Residential collection as per landfilling

baseline.

Gross emission factors for centralized

composting as per City of Edmonton

operation.

Relative GHG Emissions for Residential Grass

Management in Edmonton

0

20000

40000

60000

80000

100000

120000

140000

Grasscycling Composting Disposal to Landfill

Metr

ic T

on

nes C

O2

129,037 tonnes CO2-e

20,777 tonnes CO2-e

1,758 tonnes CO2-e


Hierarchy Comparison for

Residential Grass Management If the right-most bar on the graph (129,037 tonnes

CO2-e) indicates methane emissions that would result

from landfilling 63,270 tonnes of waste of grass

clippings, then emissions could be reduced by:

96,777 tonnes CO2-e with a 75% efficient LFG capture

system, a waste recovery activity

108,260 tonnes CO2-e by composting, a waste recycling

activity

127,279 tonnes CO2-e by grasscycling, a waste reduction

activity


Summary and Conclusions

As per the grasscycling example, in general, the higher a practice is in the waste management hierarchy, the lower the carbon footprint.

Logical and accepted methodologies for determining carbon footprint of various waste management practices.

Difficult to accurately quantify emission reductions from residential recycling.

Numbers used in carbon footprint calculations (emission factors, GWP values) will change, more important is the chain of logic used to determine how to do the calculation.


Questions???

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Calculating the Carbon Footprint of Various Municipal Waste

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