Calculating the Carbon Footprint of Various Municipal Waste Management Practices Allan Yee, CD, M.Sc., P.Eng. Senior Engineer Organics Processing 5 February 2013 Waste Management Services

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

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Waste Management Hierarchy: the 4 Rs

Reuse Recycle

Recover

Higher Preference

Reduce

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. Waste Management Services

Landfill Gas Generation

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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. Waste Management Services

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 MCF DOC DOCf F 16/12

= CH4 generation potential, kgs/tonne of waste = CH4 correction factor, fraction = degradable organic carbon, t C/t of waste = fraction of DOC that dissimilates under landfill conditions = fraction of CH4 in landfill gas = stoichiometric factor for conversion of CH4 to carbon Waste Management Services

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. Waste Management Services

Summation of Individual FOD Curves Over Time Time period of active landfilling

CH4 Emissions (Q)

Individual first order decay (FOD) time distribution curve for methane generation

0 1 2

Time (Yrs)

100

∞

Numerical Approximation of FOD Model Equation n

Qt ∑ 2k L

-kti M e o i

=

i=1

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 Management Services

Waste Recovery Example: Landfill Gas Collection

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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. Waste Management Services

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.* Waste Management Services *Using a GWP of 21 for CH4

Waste Recycling/Reuse Example: Composting

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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. Waste Management Services

Basic Composting System Boundary, Inputs and Outputs Waste Production (households, commercial)

Waste collection, sorting, transportation

Sorting

Landfill)

Recycle Aerobic Conversion

Compost

On site use of electricity

On site use by equipment

System Boundary Limit End User

Adapted from CDM (2005)

Electricity from grid

Fuel (Diesel)

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

FCO2

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

= 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

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Collected Mixed Residential MSW

Edmonton Composting Facility System Boundary, Inputs and Outputs Residues to landfill w/ no LFG Collection

Primary Residuals 14,000 tonnes, 13.4%organic

Secondary Residuals 15,000 tonnes, 45.3%organic Pre-processing (sorting)

110,000 tonnes

ECF – mechanical plant

Compost curing

10,000 tonnes Collected waste wood

Dewatered municipal biosolids

On-site waste wood chipping

Biosolids/wood chip mixing

On-site power use

Electricity from grid

14,000,000 kWh

On-site natural gas use

Natural gas

29,600 GJ

On-site diesel use

Diesel fuel

483,900 L

On-site gasoline use

Gasoline

1,280 L

On-site propane use

Propane

1,740 m3

Screening cured compost

Tertiary Residuals 2,000 tonnes, 45.3%organic

Biosolids/wood chip composting

System Boundary

Compost sales to end users

Residues to landfill w/ LFG collection

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. Waste Management Services *2007 IPCC GWP = 25 for CH4, 298 for N2O

Residential Recycling Discussion

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Residential Recycling

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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. Waste Management Services

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 Management Services

Waste Reduction Example: Grasscycling

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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. Waste Management Services

The Residential Grass Cultivation System System Boundary Water

Sunlight

Fertilizer

Grow Grass

Lawnmower Energy

Option 3: Grasscycling Cut Grass

Grass Clippings

Energy Inputs into Landfilling Operation

Option (Baseline) 1: Landfilling Grass Clippings

Option (Baseline) 2: Composting Grass Clippings

Landfill w/o LFG Collection

Composting Operation

Energy Inputs into Composting Operation

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.

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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. Waste Management Services

Alternative Baseline 2: Central Composting Residential collection as per landfilling baseline. Gross emission factors for centralized composting as per City of Edmonton operation.

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Relative GHG Emissions for Residential Grass Management in Edmonton 140000 129,037 tonnes CO2-e

120000

Metric Tonnes CO2

100000

80000

60000

40000 20,777 tonnes CO2-e

20000 1,758 tonnes CO2-e

0 Grasscycling

Composting

Disposal to Landfill

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 Waste Management Services

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.

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Questions???

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