Modelling greenhouse gas emissions for municipal solid waste management strategies in Ottawa, Ontario, Canada

Modelling greenhouse gas emissions for municipal solid waste management strategies in Ottawa, Ontario, Canada

Resources, Conservation and Recycling 52 (2008) 1241–1251 Contents lists available at ScienceDirect Resources, Conservation and Recycling journal ho...

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Resources, Conservation and Recycling 52 (2008) 1241–1251

Contents lists available at ScienceDirect

Resources, Conservation and Recycling journal homepage:

Modelling greenhouse gas emissions for municipal solid waste management strategies in Ottawa, Ontario, Canada Adrian K. Mohareb a , Mostafa A. Warith b,∗ , Rodrigo Diaz b a b

Technology Early Action Measures (TEAM) Office, 55 Murray Street, Suite 230, Ottawa, ON, Canada K1A 0E4 Department of Civil Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, Canada M5B 2K3

a r t i c l e

i n f o

Article history: Received 20 April 2006 Received in revised form 7 June 2008 Accepted 17 June 2008 Available online 11 September 2008 Keywords: Municipal solid waste Emissions modelling Greenhouse gases Source reduction Recycling Composting Anaerobic digestion Incineration

a b s t r a c t Human-induced climate change, through the emission of greenhouse gases, may result in a significant negative impact on Earth. Canada is one of the largest per capita emitters of greenhouse gas, generating 720 megatonnes (Mt) carbon dioxide equivalents (CO2 e), or per capita emissions of 23.2 t CO2 e. The solid waste sector in Canada was directly responsible for 25 Mt CO2 e in 2001, of which 23 Mt CO2 e were produced by landfill gas (LFG). A modelling exercise was undertaken to determine greenhouse gas (GHG) emissions from the waste sector using the waste disposal, recycling, and composting data from Ottawa, Ontario, Canada for the year 2003, as well as the results of an audit of residential units performed in the same year. This evaluation determined that, among the options examined, waste incineration, further source separation of recyclables, and anaerobic digestion of an organic wastes have the greatest benefits for reducing GHG emissions in the City of Ottawa’s waste sector. Challenges surrounding the installation of incineration facilities in Canada suggest that improved diversion of recyclable materials and anaerobic digestion of organic materials are the optimal options for the City of Ottawa to pursue. © 2008 Elsevier B.V. All rights reserved.

1. Introduction 1.1. The climate change threat Human-induced climate change, brought about by the increased release of greenhouse gases (GHGs) to the atmosphere, is a phenomenon that is currently threatening and will continue to threaten the quality of life for humanity and ecosystems. The current trend of climate change is warming the planet towards its highest temperatures in the last 1–40 million years (Thomas et al., 2004). The Intergovernmental Panel on Climate Change (IPCC) projects a minimum temperature increase of 1.4 ◦ C and projected sea level increase of 0.2 m by 2100 resulting from anthropogenic climate change (Albritton and Meira Filho, 2001). This increase will pose a threat to about 18% of the species in regions of study, spanning 20% of the Earth’s terrestrial surface (Thomas et al., 2004). On a per capita basis, Canada is a large generator of GHGs. The most recent version of Canada’s Greenhouse Gas Inventory (Olsen et al., 2003) contains data on GHG emissions in Canada between 1990 and 2001. Canada’s GHG emissions increased from 608 mega-

∗ Corresponding author. Tel.: +1 416 979 5000x6459; fax: +1 416 979 5122. E-mail address: [email protected] (M.A. Warith). 0921-3449/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2008.06.006

tonnes (Mt) carbon dioxide equivalents (CO2 e) to 720 Mt CO2 e, an 18.4% increase in emissions. With Canada’s 2001 population of 31.021 million (Statistics Canada, 2004), this translates to 23.2 t CO2 e per capita emissions annually. For comparison, among other developed nations, the United States generates GHG emissions of 25.4 t CO2 e per capita annually, while Germany, the United Kingdom and France emit 12.1, 11.1 and 9.2 t CO2 e, respectively (OECD, 2002; OECD, 2004).

1.2. Greenhouse gas emissions from waste in Canada Of the emissions generated in Canada in 2001, the year of the most recent national GHG inventory, 24.8 Mt CO2 e are generated by the waste sector (Olsen et al., 2003) (Table 1). However, this sector has a very narrow definition, as it includes only the emissions generated by the treatment and disposal of waste, including emissions generated at municipal solid waste (MSW) landfills and wood waste landfills, emissions from handling wastewater, and emissions from the incineration of MSW and sewage sludge. It does not include emissions generated in the transportation of waste, nor does it consider the life-cycle emissions of waste. Landfill gas (LFG) emissions are the greatest source of solid waste emissions in Canada, as given by the national GHG inventory (Olsen et al., 2003). Diverting solid waste, particularly organic


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Table 1 GHG emissions from the waste sector in Canada, 2001 (adapted from Olsen et al., 2003) Greenhouse gas

CO2 (1)a (kt)

CH4 (kt)

Solid waste disposal on land Wastewater handling Waste incineration

– – 284

1100 19 –

23,100 400 7

– 3 –

– 970 60

23,100 1,370 350

2001 waste total








CH4 (21)a (kt CO2 e)

N2 O (kt)

N2 O (310)a (kt CO2 e)

Total (kt CO2 e)

Relative global warming potential (CO2 = 1).

wastes, from ultimate disposal in landfills will result in significant GHG emission reductions. Some waste management options that offer direct emissions reductions from the point of disposal include LFG recovery and utilization and waste incineration. Waste management strategies such as source reduction, recycling, composting and anaerobic digestion of waste can reduce emissions throughout a product’s life-cycle. This report will analyse the life-cycle GHG emissions from the management of MSW in Ottawa, Ontario, Canada. It will use a life-cycle model to determine the emissions generated by several waste management strategies. Before describing the GHG emissions resultant from different waste management strategies, it will be useful to describe the life-cycle assessment concept, as well as the modelling tool used in this analysis. 1.3. Life-cycle assessments of municipal solid waste A conventional life-cycle assessment (LCA) analyses the item under scrutiny on a “cradle-to-grave” basis. In general, LCA systems are modeled so that inputs and outputs are followed from raw material acquisition to the point where the material is discarded to the environment without further human transformation. However, life-cycle assessments of MSW exhibit certain differences compared to LCA. As described by Finnveden (1999), the LCA for waste management often starts when the solid waste is generated, with emissions being counted from the point that the discarded material reaches the curb or waste collection bin. This difference does not have an effect given the general premises of a LCA, but does require modifications for different aspects of the analysis. These aspects include system boundaries, recycling, multi-input processes, and time-frame considerations. With regard to municipal solid wastes, LCAs have been used only (relatively) recently; several models have been developed to quantify the impacts of MSW management decisions on life-cycle emissions. 1.4. Choice of integrated waste management model There are several models available to help determine the best options for reducing GHG emissions from waste in the City of Ottawa. This report used the Integrated Waste Management Model (IWM) for municipalities, produced by Corporations Supporting Recycling (CSR) and the Environment and Plastics Industry Council (EPIC), and offered through the University of Waterloo (EPIC and CSR, 2004). The model is a Microsoft Excel spreadsheet with macros designed for inputting data based on the municipality in question. This model was chosen among three models (the WARM model of the EPA; the Canadian Cities Greenhouse Gas Emissions Strategy Software of Torrie-Smith Associates; and the IWM model of EPIC and CSR) because of its dedication to the waste sector, its consideration for Canadian emissions factors, and the flexibility of this model for data inputs (i.e. emission factor and operations data can be input in some cases, or left at the default values). The model has been analyzed by Torrie-Smith Associates and has been accepted by Environment Canada as valid.

The potential for different waste management strategies to reduce GHG emissions can be determined through modelling. This report models GHG emissions generated through several waste management scenarios, using the City of Ottawa, Ontario, Canada as the example for the modelling exercise. The model used for this exercise is the Integrated Waste Management Model (IWM) produced by the Environment and Plastics Industry Council (EPIC) and Corporations Supporting Recycling (CSR) (EPIC and CSR, 2004). The IWM model is currently administrated through the University of Waterloo. The objective of this model is to “provide Canadian municipalities with tools that will enable them to evaluate the environmental and economic performance of the various elements of their existing or proposed waste management systems” (Haight, 2004). IWM is a spreadsheet-based model that consists of several input screens. Each screen covers different aspects of the management of municipal solid waste (e.g. landfilling, transportation, recycling, etc.). The model’s outputs are in the form of Excel spreadsheets, and include a summary of the input data, a summary of the outputs, including the total life-cycle emissions of GHGs and criteria pollutants, an output table that breaks down the burdens from each waste management process, and a table that presents the inventory results in terms of “everyday” equivalents, such as energy consumption per household and greenhouse gases produced by car use. In order to model the GHG emissions from the solid waste sector using the IWM model, a set of inputs is required. These include: 1. Categorization of the waste stream (how much waste is generated, how much of each category of waste is sent for landfilling, recycling, etc.); 2. Knowledge of the destination of the wastes, i.e. how much of each component of the waste stream is recycled, composted, incinerated, digested anaerobically, or landfilled; 3. For recyclables, the distance from materials recovery facilities to markets; 4. For landfilled/incinerated wastes/digested wastes, the average distance travelled to the site of waste treatment and disposal; 5. For a landfill, the extent of LFG capture and ultimate use of LFG (flaring, conversion to energy); 6. For compostable materials, their distance to the composting site. 2. Waste management in Ottawa, Ontario, Canada The City of Ottawa, Ontario, is Canada’s capital, located at the confluence of the Gatineau River, the Rideau River and the Ottawa River, on the south shore of the Ottawa River (latitude 45◦ 20 N; longitude 75◦ 40 W). On 1 January 2001, the amalgamated 11 former municipalities, including the former City of Ottawa, as well as the municipalities of Nepean, Gloucester, Cumberland, Kanata, Rockcliffe Park, Vanier, Osgoode, Rideau, Goulbourn and West Carleton, combined to create the City of Ottawa. Prior to this, these municipalities were linked through the Regional Municipality of Ottawa-Carleton. Waste generation rates have been collected for 2003, and a waste audit was also performed towards the end of 2003.

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The City of Ottawa had a population of 774,000 in 2001, and is growing rapidly; the population is projected to be greater than 1 million by 2011 (City of Ottawa, 2003). There are three landfills in the region that received residential MSW—the Trail Road Landfill, the Carp Road landfill in West Carleton and the Springhill Landfill. There are also two other landfills in the region: Huneault Landfill, which receives construction and demolition and dry commercial waste, and the Howie Road Landfill, which receives residential waste from Almonte, located about 50 km WSW of downtown Ottawa. In the City of Ottawa, waste collection is performed on a weekly basis. Recyclable materials are also collected weekly. The “blue box” is the container designated for glass, metals and plastics, and is collected bi-weekly. The “black box” is the assigned for collecting paper wastes, and is collected bi-weekly on the alternating weeks. This program commenced in 1999, and generated savings of around $1 million/year while improving residential recycling participation rates, from 77% prior to the switch to 79% for blue boxes and 84% for black boxes (Solid Waste Division, 2000). The participation rates have since increased, to 90% for black boxes and 91% for blue boxes (IEWS, 2004). There are two materials recovery facilities (MRFs) in Ottawa, one for the paper stream, one for the plastic, glass and metal stream. Starting in 1999, and continuing to the present time, black box materials were sent to the Waste Recycling Inc., MRF. Halton Recycling Inc. handles blue box materials at their MRF. Both MRFs are located in an industrial area of Ottawa, in the east end of the city, within 10 km of downtown Ottawa. These facilities are responsible for marketing the recycled materials to material reprocessors. The markets, the challenges surrounding these markets and the distances to these markets from Ottawa will be discussed later this chapter. Leaf and yard wastes are collected bi-weekly in the spring and summer, weekly in autumn, once in January (collection of Christmas trees). Presently, these materials are collected and unloaded at Trail Road landfill, and then sent by transfer trucks to l’AngeGardien, Québec, a 70 km one-way trip from the Trail Road landfill, for composting (Wood, 2003). Contractors undertake residential waste collection in four of the city’s five zones, and for multi-unit (i.e. buildings with greater than six units) residential buildings. However, the city collects waste in one zone, in order to generate competition with private companies, with the aim of reducing collection costs (Solid Waste Division, 2000). For some materials that are not within the boundaries of regular household pick-up, Ottawa operates a return program (called Take It Back!) and also collects household hazardous waste (HHW) at depots four times a year within the city. The City of Ottawa also accepts HHW at the Trail Road Landfill every Saturday from May to December (City of Ottawa, 2004). The Take It Back! program, which started in 1997 with 16 retail partners accepting 3 products, increased to 259 partners accepting 61 different products by 1999 (Solid Waste Division, 2000). Diversion rates through this program had not been measured before 2002, the last date for which data is available (Solid Waste Services Division, 2002). In 2002, the HHW collection at Trail Road Landfill and at the mobile depots received 62.9 t of solid material (including batteries, pharmaceuticals, aerosols and propane cylinders) and 405,000 L of liquid materials such as paints, antifreeze, pesticides and oils. In 2003, 513 t of HHW was collected (Harris, 2004). The Solid Waste Services Division also measures the amount of non-hazardous MSW disposed by landfilling, recycling and composting (Table 2). These statistics concern residential wastes only. Of the greater than 308,000 t of waste generated, 67% of this waste was sent directly for landfilling. At the Trail Road landfill, there is


Table 2 Waste disposal statistics for the City of Ottawa, 2003 (Harris, 2004) Amount generated (t) Residential solid waste Sent for disposal to landfill Waste sent for recycling Sent from MRF to market Sent from MRF to disposal Leaf and yard waste sent for composting Food waste sent for composting Compost produced Organic waste diverted by backyard composting (estimated)

308,609 206,307 68,835 66,799 2,036 31,452 2,015 20,080 7,400

a LFG collection system. Leachate is recirculated into the landfill to encourage degradation of organic materials, in order to reduce the volume of the waste in the landfill. This increases the rate of LFG generation by providing sufficient amounts of water for anaerobic decomposition. In 1999, the LFG system captured 57,000 m3 /day, with a gas composition of 45% CH4 . This LFG is flared at the present time (Solid Waste Division, 2000); there are efforts underway to upgrade the LFG capture infrastructure at Trail Road and to install facilities to convert LFG to electricity. It is estimated that only 40% of the LFG generated at Trail Road is being captured due to leaks in the system (Filipowich, 2003). Of the 33% of waste that was diverted from the MSW stream, 22% of the total material was sent for recycling, and the remaining 11% was organic waste sent for composting. The City of Ottawa estimates that of the material sent for composting, 60% becomes compost product, while the other 40% is lost as moisture and CO2 (Solid Waste Services Division, 2002). There were 74,000 backyard composters in the City of Ottawa in 2003, and the city estimates that these composters divert an average of 100 kg/(unit year). If this is achieved, the composters reduce the amount of organic waste sent for disposal by 7400 t (Harris, 2004). In order to determine waste composition and how the waste is being disposed, the City of Ottawa retained Integrated Environmental Waste Services to perform a waste audit in the fall and winter of 2003 (IEWS, 2004). IWES analyzed the wastes of 10 households on each of 11 streets (for a total of 110 households), with each street being located in a different part of town. This analysis was performed over 2 weeks in the fall (22 September 2003 to 3 October 2003) and in the winter (1 December 2003 to 12 December 2003). The waste and recyclable materials were collected and transported to Trail Road Landfill for sorting, with the materials being sorted into 6 main classes and 46 specific categories (Table 3) (IEWS, 2004). It should be noted that the waste diversion rate in the audit was 47.2%, higher than the city’s average diversion rate of 33%. This is because this audit was performed on single-family households; among residential units in the City of Ottawa, diversion rates are much greater in single-family households. An audit of apartment waste showed that paper made up twice as much of the material sent for landfill compared to single-family waste (28–14%). The capture rate in apartments is 33% for paper, and 31% for containers (Solid Waste Services Division, 2002). For comparison, among the single-family households audited, the capture rates were 75% for paper and 61% for blue box materials (85% for glass, 65% for metals and 33% for plastics) (IEWS, 2004). One of the required inputs for the model is the amount of waste generated in each specific category. The statistics in Table 3 had to be scaled up to match the results of the audit to the totals demonstrated in Table 1. The ratios of each category captured to the total amount captured were determined. These ratios were then multiplied by the total amount of waste recycled to determine how much


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Table 3 Results of a waste audit performed in Ottawa during the autumn and winter of 2003 (IEWS, 2004) Materials

Total refuse collected (kg) (1)

Gross recyclables (and compostables) total (kg) (2)

Total MRF contamination (kg) (3)

Net recyclables and compostables total (kg) [(4) = (2) − (3)]

Total waste generation (kg) [(5) = (1) + (4)]

Paper Old newspaper Magazines and catalogues Old corrugated cardboard Boxboard Telephone books Mixed residential fibre Polycoat Tissue Molded pulp Tetrapack Spiral wound Non-recyclable paper

551.29 60.91 22.05 14.24 69.60 3.30 142.80 9.86 174.80 3.82 4.43 9.88 35.60

1784.55 1009.50 195.70 200.60 149.21 2.30 185.17 22.03 1.77 9.65 1.60 3.01 4.01

25.77 4.30 0.00 1.30 2.16 0.00 5.12 6.23 1.77 0.07 0.36 0.45 4.01

1758.78 1005.20 195.70 199.30 147.05 2.30 180.05 15.80 0.00 9.58 1.24 2.56 0.00

4120.39 2079.91 413.45 415.44 368.02 7.90 513.14 53.92 178.34 23.12 7.63 15.90 43.62

Glass LCBO clear containers LCBO coloured containers Clear containers Coloured containers Other glass

70.07 6.60 9.55 27.95 0.91 25.06

413.78 63.00 197.40 125.30 26.10 1.98

2.18 0.00 0.00 0.20 0.00 1.98

411.60 63.00 197.40 125.10 26.10 0.00

897.63 132.60 404.35 278.55 53.11 29.02

Metal Steel food and beverage containers ferrous Steel food and beverage containers non-ferrous Aluminum food and beverage containers Aluminum foil and trays Aerosol cans Paint cans White goods Other metal

63.38 18.08 2.38 6.56 8.00 5.30 1.50 0.00 21.56

117.57 79.00 2.86 27.52 1.52 1.27 0.00 0.00 5.40

5.43 0.00 0.01 0.02 0.00 0.00 0.00 0.00 5.40

112.14 79.00 2.85 27.50 1.52 1.27 0.00 0.00 0.00

298.52 176.08 8.10 61.60 11.04 7.84 1.50 0.00 32.36

257.57 5.52 7.86 7.35 0.53 0.92 1.50 25.85 0.45 14.32 66.40 126.87

174.18 36.85 18.95 24.45 1.52 0.18 4.92 11.36 1.70 16.80 28.82 28.63

30.41 0.05 0.00 0.10 0.00 0.00 0.00 0.71 0.00 0.00 0.92 28.63

143.77 36.80 18.95 24.35 1.52 0.18 4.92 10.65 1.70 16.80 27.90 0.00

605.93 79.22 45.76 56.25 3.57 1.28 11.34 48.57 3.85 47.92 124.04 184.13

Organics Kitchen organics (food prep.) Leaf and yard waste Pet waste Other materials Disposable diapers/sanitary products Electronics/appliances Tires Textiles Construction and demolition Household special waste Unclassifiable items

1882.71 1418.26 68.40 396.05 659.64 227.17 31.30 0.00 101.20 124.50 17.93 157.54

627.45 53.25 571.70 2.50 2.70 0.00 0.10 0.00 1.00 0.30 0.00 1.30

3.95 1.45 0.00 2.50 2.70 0.00 0.10 0.00 1.00 0.30 0.00 1.30

623.50 51.80 571.70 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

3137.61 1524.76 1211.80 401.05 665.04 227.17 31.50 0.00 103.20 125.10 17.93 160.14

Total Total recycled Total composted




3049.79 2426.29 623.50


Plastics PET (#1)-polyethylene terephthalate—bottles PET (#1)-polyethylene terephthalate—other HDPE (#2)-high density polyethylene PVC (#3)-polyvinylchloride LDPE (#4)-low density polyethylene PP (#5)-polypropylene PS (#6)-polystyrene Other (#7) Wide mouth tubs and lids (# 2,4,5,7) Recyclable film Waste plastic

waste was recycled. This was also done for the waste that was sent to landfill and for the contamination at the two MRFs. The distance that recycled materials travel from MRFs to markets is a required input for the model. It is important to know the locations of the companies to which recyclables are marketed. Paper is typically marketed locally to the Cascades group; this paper is reused within an 80 km radius of Ottawa. An average of 50 km to market will be used. Glass was initially marketed to manufacturers in Montréal, 160 km east of Ottawa (Solid Waste Division, 2000; Solid Waste Services Division, 2002). Starting in 2003, how-

ever, recycled glass began to be used locally in a pilot project that diverts crushed glass to be used in aggregates (Harris, 2003). Steel is usually marketed to companies in Hamilton, ON (550 km from Ottawa), including Poscor and Waxman and Sons (Solid Waste Division, 2000). Aluminum is marketed to Camco Recycling Inc. in Dillonville, Ohio (a distance of 970 km from Ottawa) and Montréal, Alcan in Hamilton, as well as a remanufacturer in New Hampshire (Wood, 2003). An average distance of 600 km is assumed for aluminum. Plastics are sold to a variety of markets. High-density polyethylene (HDPE) is currently being marketed to through Hay-

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Table 4 Distance to markets for recyclable materials from City of Ottawa

Table 6 Estimated distances travelled by all waste handling vehicles, City of Ottawa


Distance to market (km)

Material handled

Paper Glass Ferrous materials Aluminium Plastics

50 0 550 800 500

Garbage Blue box Black box Leaf and yard waste

core, a materials reseller in Russell, ON (30 km southeast of Ottawa), to Solplast and Polychem in Montréal. Polyethylene terephthalate (PET) is marketed to Wellman Inc. in Shrewsbury, NJ (700 km south of Ottawa) (Wood, 2003). Polystyrene (PS) has been marketed to the Canadian Polystyrene Recycling Association (CPRA) in Mississauga, ON, 500 km southwest of Ottawa (Solid Waste Division, 2000; Solid Waste Services Division, 2002). Increasingly, however, plastics #3–7 (refer to Table 3) are being delivered by ocean freight to China for recycling, due to poor markets for these plastics in North America (Wood, 2003). By mass, PET and HDPE comprise 60% of Ottawa’s plastics sent for recycling. An estimate of 500 km travelled for recyclable plastics to markets will be used (Table 4). Finally, the emissions from the transport of waste to the MRFs and the landfill are necessary inputs for the model. Both the Trail Road landfill (in the southwest end of Ottawa) and the MRFs (in the southeast) are easily accessible and in close proximity to the city, reducing the travel distances compared to other major metropolitan centres. The collection in one region of Ottawa is performed by the city, and this region has data that is available. Thus, the data from this region will be used to determine standards for the city. The city’s fleet averaged 8 garbage trucks, 5.2 blue box trucks, 6.2 black box trucks, and between 1.4 and 3.5 leaf and yard waste trucks, depending on time of year and volume of material. The city’s fleet of collection vehicles travelled a combined 600,000 km in 1999 (Solid Waste Division, 2000). For these distances travelled, fuel consumption was 450,000 L in 2002, and it has been assumed that fuel consumption was constant between 1999 and 2002 (Villeneuve, 2003). Thus, fuel efficiency of the truck fleet is 1.3 km/L. The City of Ottawa’s waste collection fleet operates 260 days/year (5 days/week for 52 weeks). Table 5 displays the fleet’s characteristics. The city’s fleet serves only residences with six residential units or less; it does not service institutions or apartment buildings. All of the city’s trucks are used interchangeably; a truck that may be used for garbage 1 week may be used for recyclables the next week (Villeneuve, 2003). It is assumed that the average distance travelled for loads of garbage and leaf and yard waste (as both are processed at Trail Road) is 30 km (one-way), and 21 km (one-way) for all recyclable materials (the MRFs are located 5 km away from each other, and are easily accessible from Highway 417, Ottawa’s main eastwest artery). These statistics, combined with the annual number of trips (Table 5) equal 600,000 km travelled in a year, consistent with the Region of Ottawa-Carleton’s report on their fleet’s distance travelled (Solid Waste Division, 2000).

Distance travelled by vehicles handling residues (km) 1,500,100 668,700 796,200 542,200

Distance traveled per tonne of waste (km/t) 7.2 38.7 16.7 16.2

Knowing the fraction of the City of Ottawa’s waste that is dealt with by the City’s own fleet (Table 5), the total km travelled by all garbage, recycling and organic collection vehicles in the City of Ottawa (both public vehicles and private vehicles) can be determined (Table 6). All of the required information is now available to model the GHG emissions generated by waste in the City of Ottawa/Region of Ottawa-Carleton, and to model the potential of reducing emissions in Ottawa. 2.1. Modelling GHG emissions from the waste sector in the City of Ottawa There are several scenarios that can be considered for modelling, to determine the impact of different waste management decisions and strategies. Initially, the modelling exercise considered eight scenarios: 1. The “landfill everything” approach (all waste is sent to landfill, no recycling occurs, no LFG capture occurs—this is the baseline condition for waste management prior to the 1970s); 2. The usual approach of the City of Ottawa (LFG is captured and flared, recycling and composting occur at rates given in the waste audit)—the base case 1; 3. LFG capture system upgrade (LFG capture rate increases to 50%, energy conversion facilities are installed, at 30% energy conversion efficiency); 4. Improved diversion rates of materials currently being recycled, without improvements at any other point in the system (capturing 50% of the recyclable/compostable material that are currently not being captured); 5. Diversion of food waste (30% capture rate), with organics diverted sent for composting; 6. Diversion of food waste (30% capture rate), with organics diverted sent for anaerobic digestion; 7. Source reduction of recyclable materials by 10%; 8. Incineration of materials being sent to landfill, with energy recovery. For the organics diversion cases, the diversion rate was chosen to be 30%, as this figure is consistent with the results of the Compost Plus pilot program operated in the City of Ottawa, beginning in 2001 (Solid Waste Services Division, 2002). The IWM

Table 5 Region of Ottawa-Carleton’s waste collection fleet characteristics (adapted from Solid Waste Division, 2000) Material being disposed

Number of trucks

Garbage Blue box Black box Leaf and yard waste

8 5.2 6.2 1.4–3.5

a b

Number of daily loads/truck 2 2 2 1–4

Average daily loads

Amount dumped yearly (t)a

Annual trips to landfill

Fraction of Ottawa waste handled (%)

16 10.4 12.4 6.1

35,200 2,900 8,100 6,000b

4160 2704 3224 1593

19 24 18 25

Statistics for 2002 (Villeneuve, 2003). Waste disposed is for organic pilot project as well as leaf and yard waste.


A.K. Mohareb et al. / Resources, Conservation and Recycling 52 (2008) 1241–1251 Table 7 (Continued)

Table 7 Inputs for IWM model for the City of Ottawa, case 2 Quantity and composition of waste Quantity of waste Composition of waste Paper

Glass Ferrous metals Aluminium Plastics


Newspaper OCC Telephone directories Boxboard Mixed paper

PET HDPE LDPE PP PS PVC Food waste Yard waste Other waste

Waste flow Recycling Composting Landfill Waste collection Distance driven by collection trucks annually

Transfer and transportation Energy consumed in transfer station operations

Transfer station

Transportation distances Electricity—provincial grid selected Coal Natural gas Diesel and light fuel oil Heavy fuel oil Hydro Nuclear Materials recovery facility Energy consumption Residue Residue management Distance to markets

Distance from MRF to landfill/incinerator Composting Composting Breakdown

31,489 t 5446 t 780 t 6797 t 24,888 t 10,522 t 5348 t 1454 t 1504 t 1331 t 2701 t 712 t 1077 t 182 t 90,092 t 30,864 t 46,973 t 56,840 t 23,687 t 181,633 t

Garbage trucks

Recycling trucks Yard waste trucks Type of fuel Fuel efficiency

262,160 t

1,309,300 km

Collection trucks Transport trucks

1,216,000 km 383,100 km Diesel 1.3 km/L 2.5 km/L


0.5 L/t

Electricity Recyclable Yard waste Garbage to incineration Garbage to landfill From transfer station to composting facility

0 kWh/t No Yes No No 70 km

Composition of yard waste

Electricity Natural gas

Paper Glass Ferrous Aluminum Plastics

Paper Food waste Yard waste

25 kWh/t 0.264 m3 /t 2.7% Landfilled 50 km 0 km 550 km 800 km 500 km 39 km

23,687 t 0t 0t 23687 t

9500 t

Grass Yard material

7100 t 7087 t 0.3 km

Distance residue transported Residue Energy consumption Electricity Diesel Landfilling Carbon sequestration Gas recovery Gas recovery efficiency Energy recovery Energy recovery efficiency Annual precipitation Landfill lined, with leachate collection Landfill not lined, with leachate collection Landfill not lined, leachate not collected Leachate collection efficiency Energy consumed by landfilling

Recycling Waste sent for recycling Recovery ratesa Paper

Ferrous metals Aluminum Glass Plastics

Ontario 21% 10% 0% 0% 24% 45%


Forest sequestration

5% Windrow 0 kWh/t 1 L/t No Yes 40% No 0% 943 Mm Yes No No 90% Diesel

1.5 L/t

Natural gas Electricity

0 M3 /t 0 kWh/t 56,840 t

Newspaper OCC Telephone directories Boxboard Mixed paper


89.2% 84.4% 50.1% 46.6% 34.2% 37.5% 52.4% 64.2% 50.1% 39.3% 9.9% 22.9% 17% 28% No


Recovery rates are the proportion of the waste generated that is diverted for recycling.

model (EPIC and CSR, 2004) requires that the composition of leaf and yard waste be inputted. The Region of Ottawa-Carleton has not collected separate data on leaf and yard waste composition in its previous analyses of the composition of waste. However, the average composition of leaf and yard waste is roughly 40% leaves, 30% grass and 30% yard materials, such as tree prunings (Oshins and Block, 2000). For the base case of 31,452 t of yard waste generated in 1999, it has been estimated that 12,600 t are leaves, 9452 t are grass, and 9400 t are yard materials. Table 7 displays the inputs for the current scenario (base case) (case 2). Data on incineration (including waste composition for incineration and emissions from incineration), anaerobic digestion (digestion process and feed) and land application of yard waste can also be added. These considerations will not be displayed in Table 7, though they are necessary for other cases.

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Table 8 GHG emissions from the base case (case 2) scenario Scenario

Management option

Mass of waste managed (t)

CO2 emissions (t)

2. Current case

Collection Landfill Recycling Composting/anaerobic digestion Energy from waste (incineration) Gross emissions Virgin material displacement credit Net emissions

262,160 182,255 56,218 23,687 0 262,160 n/a 262,160

7,687 1,221 14,516 0 0 23,424 −45,622 −22,198

CH4 emissions (t CO2 e) 173 90,993 33 0 0 91,199 −1,153 90,047

N2 O emissions (t CO2 e) 2,085 384 6,062 0 0 8,531 −11,507 −2,975

GHG emissions (t CO2 e) 9,946 92,598 20,611 0 0 123,155 −58,282 64,873

Table 9 Gross and net GHG emissions from scenarios run in IWM model Scenario

Mass handled differently from case 2 (t)

1. Landfill all waste 2. Current case 3. Upgrade LFG capture system 4. Increase diversion of manufactured goods by 50% 5. Diversion of organic waste (30%)—composting 6. Diversion of organic waste (30%)—anaerobic digestion 7. Source reduction of manufactured goods (10%) 8. Incineration of waste

79,905 0 182,255 22,611 27,028 27,028 8,495 182,255

Gross GHG emissions (t CO2 e) 212,517 123,155 106,268 116,695 102,606 107,454 118,137 103,337

2.2. Results from the modelling experiments The results displayed in this section are indicative of the GHG emissions and energy consumption statistics that may be possible through the nine scenarios analyzed. They should not be assumed to be exact, due to the assumptions necessary in the model and the actual conditions that are present in waste management in Ottawa. The emissions generated from the base case (the current state of waste management in the City of Ottawa, for which the inputs are shown in Table 7) are displayed in Table 8. A summary of the emissions calculated from IWM is demonstrated in Table 9. The emissions have been categorized as collection (or transport) emissions, landfilling emissions (note that the landfill CH4 emissions are those that are not captured by the LFG recovery system at Trail Road landfill), recycling emissions (this category includes emissions from reprocessing recycled materials), composting or anaerobic digestion emissions (these two categories are combined as there are no cases where both composting and anaerobic digestion occur) and energy from waste emissions. Table 10 demonstrates the energy consumption of the eight scenarios. Table 11 displays the changes in energy consumed and GHGs emitted between scenario 2 and the other seven scenarios.

Virgin materials displacement credit (t CO2 e)

Net GHG emissions (t CO2 e)

0 −58,282 −58,282 −83,689 −58,282 −58,282 −55,444 −58,281

212,517 64,873 47,987 33,006 44,324 49,173 62,693 45,056

The gross emissions given by the IWM model shown in Tables 9–11 are the sum of emissions from waste collection and transportation, landfill operations (including LFG generation) and reprocessing of recycled materials. The virgin materials displacement credit refers to emissions reduced and energy saved by reprocessing the recycled materials, as opposed using virgin materials. These credits are subtracted from the gross emissions to give the net emissions statistics. One of the peculiarities of the model is that, in its calculations of GHG emissions and global warming potentials of the gases considered, all NOx emissions are considered to be N2 O emissions. This is erroneous; NOx , as defined, is a combination of all nitrogen oxides, including nitrogen oxide (NO) and nitrogen dioxide (NO2 ) (Killeen, 1995). It has been estimated that the N2 O emissions are about 10% of total NOx emissions (EIOLCA, 2003). Thus, the N2 O emission data shown in Table 8 are 10% of the results given by the IWM model. The model also considers that the global warming potential of N2 O is 331. It is generally considered now that the global warming potential of N2 O is 296 (Ramaswamy et al., 2001), though for all accounting of emissions through to the end of the Kyoto Protocol commitment period, a global warming potential of 310 will be used for N2 O (Olsen et al., 2003). Prior to the regular

Table 10 Energy consumed in the eight waste management scenarios considered for the City of Ottawa Scenario

1. Landfill all waste 2. Current case 3. Upgrade LFG capture system 4. Increase diversion of manufactured goods by 50% 5. Diversion of organic waste (30%)—composting 6. Diversion of organic waste (30%)—anaerobic digestion 7. Source reduction of manufactured goods (10%) 8. Incineration of waste

Difference in mass landfilled from case 2 (t)

Waste management energy consumption (GJ)

Energy consumed in reprocessing recycled materials (GJ)

Gross energy consumption (GJ)

Virgin material energy displacement credit (GJ)

Net energy consumption (GJ)

79,905 0 0 −22,611

90,398 143,963 78,724 159,979

0 815,855 815,855 1,044,480

90,398 959,817 894,578 1,204,458

0 −1,929,652 −1,929,652 −2,661,709

90,398 −969,835 −1,035,074 −1,457,251


























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Table 11 Reductions in GHG emissions and energy consumption for eight scenarios compared with case 2 (base case) Scenario

Mass handled differently from case 2 (t)

Gross energy consumption Net energy consumption reduction compared to reduction compared to base case (GJ) base case (GJ)

1. Landfill all waste 2. Current case 3. Upgrade LFG capture system 4. Increase diversion of manufactured goods by 50% 5. Diversion of organic waste (30%)—composting 6. Diversion of organic waste (30%)—anaerobic digestion 7. Source reduction of manufactured goods (10%) 8. Incineration of waste

262,160 0 182,255

869,420 0 65,239

−1,060,232 0 65,239

−89,362 0 16,886

−147,644 0 16,886


























Gross GHG emissions reductions compared to base case (t CO2 e)

Net GHG emissions reductions compared to base case (t CO2 e)

not demonstrate lower emissions than the composting scenario (emissions are 49.2 kt CO2 e), though displacing fossil fuel generated power, as would be the case in anaerobic digestion, should reduce emissions. This will be examined in the discussion on energy consumption of different waste management strategies. The fossil fuel emissions that are displaced by the generation of power associated with some of the waste handling methods, such as incineration, LFG capture for energy and anaerobic digestion, are not incorporated into the figure. The net GHG emissions (waste emissions less emissions offset through recycling) from each scenario are demonstrated in Fig. 3. Fig. 1. Gross GHG emissions from the City of Ottawa’s waste sector for the eight waste management scenarios proposed, by greenhouse gas.

use of 310 as the global warming potential of N2 O, the potential was assumed to be 331 (Torrie, 2004). The data for N2 O forcing has been edited to reflect a radiative forcing of 310 rather than 331. The forcing for CH4 is assumed to be 21 by the model, a reasonable assumption given that the global warming potential of CH4 is usually given as 21 (Olsen et al., 2002). The greenhouse impact of black carbon is not considered in this model, although the combustion of diesel fuel, as is common in the collection of MSW, is a significant source of black carbon (Jacobson, 2002). This is to be expected, as it is still difficult to quantify the impact of black carbon on warming. The results of the modelling are displayed in the following figures. Fig. 1 demonstrates the gross emissions from each case, by greenhouse gas, while Fig. 2 displays gross emissions from each case by emission source. Fig. 3 displays the net emissions, with the crosshatched section demonstrating the emissions reductions achieved by recycling and source reduction in each scenario. The cases that generate the fewest gross emissions are case 5 (diversion of food waste for composting) (102.6 kt CO2 e) and case 8 (incineration of refuse) (103.3 kt CO2 e), respectively. However, for net GHG emissions, the lowest amount was generated by scenario 4 (capturing 50% of the remaining recyclable material) (33 kt CO2 e), while scenario 5 (44.3 kt CO2 e) and scenario 8 (45 kt CO2 e) also emitting fewer GHGs than the other cases considered. It should be noted that these figures only consider the emissions from the generation of waste by consumers, handling of waste by collectors, and disposal of waste. The model does not consider all emissions throughout the life-cycle of the materials. Surprisingly, the anaerobic digestion scenario (case 6) does

Fig. 2. Emissions from the City of Ottawa’s waste sector for the eight waste management scenarios proposed, by emission source.

Fig. 3. Gross (full bar) and net emissions (in solid blue) from the City of Ottawa solid waste sector for the eight waste management scenarios proposed. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

A.K. Mohareb et al. / Resources, Conservation and Recycling 52 (2008) 1241–1251

Fig. 4. Net energy consumption for the City of Ottawa from the eight waste management strategies proposed, excluding energy consumed and avoided through the reprocessing of recycled materials.

Fig. 5. Net energy consumption for the City of Ottawa from the eight waste management strategies proposed.

It is also interesting to determine how much energy is being consumed in each of the scenarios, as energy consumption is linked to greenhouse gas emissions. Most emissions recognized by the model result from energy consumption, including CO2 , CH4 and N2 O emission. The exceptions to this are LFG emissions. Fig. 4 demonstrates the energy consumed through the waste management cycle excluding energy consumed by material recycling and energy displaced by avoiding the use of virgin materials through recycling. Fig. 5 displays the energy consumed by waste management, including the energy consumed by processing recycled materials and the energy displaced by avoiding the production of virgin materials. The consideration of energy consumed through the reprocessing of recycled materials account for the much higher positive energy consumption totals in Fig. 5. The energy consumed through reprocessing recycled materials was between 5 and 10 times greater than the energy consumed in waste management for scenarios 2–7, though this energy consumption is more than compensated for by avoided energy consumption through the production of materials from virgin feedstocks.


As expected, the lowest levels of gross energy consumption occur in case 3 (LFG capture for energy) (78,700 GJ), case 6 (anaerobic digestion of waste) (117,000 GJ) and case 8 (incineration of waste) (−1,242,000 GJ). In case 8, the incineration of 182 kt of waste (the remaining 80 kt of waste is assumed to be diverted through recycling and composting) generates 1.323 PJ. With this, it can be estimated that the rate of energy production is 7.3 MJ/kg of solid waste. At 75% energy conversion efficiency (for a co-generation plant), as assumed in the inputs into the model, the energy content of the waste is 9.7 MJ/kg, consistent with the lower range of MSW energy content given by Tchobanoglous et al. (1993) of 9.3–14.0 MJ/kg. It is surprising that, while there is an output of energy in the incineration scenario, there is an input of energy into the scenarios analyzing LFG capture for energy recovery (78.7 GJ) and anaerobic digestion (117.1 GJ), before recycling is taken into consideration. The model does not take the energy generated by the anaerobic digestion case into full consideration; there is a reduction in energy consumption from scenario 5 (composting: 19,800 GJ) to scenario 6 (anaerobic digestion: 3800 GJ). This is partially due to the transport of the compost. The organic materials being sent for composting would be transported 70 km to the composting site, while materials sent for anaerobic digestion would be transported directly to the digestion facility. It would be expected that there would be an overall output of energy for the cases where energy is generated. As for net energy consumption, recycling has an evident impact on reducing energy consumption (Fig. 5 and Table 10). With the exception of the incineration case, scenario 4 (greater diversion of manufactured goods) displaces the greatest amount of energy consumption. From an emissions and energy consumption standpoint, it is evident that the incineration case reduces emissions to a greater extent than any other case. However, the negative aspects of incineration of waste, especially air pollution and cost, as well as the attendant difficulty of siting an incinerator in the City of Ottawa, make this option unattractive. The costs of these options are beyond the scope of this project. Composting, improved LFG capture, improved diversion and anaerobic digestion also offer reduced energy consumption and emissions. Using what was shown above and the information contained in the IWM model (EPIC and CSR, 2004), the amount of CH4 generated (with an energy content of 49.5 MJ/kg (AFDC, 2002)) in the anaerobic digester in scenario 6 can also determined. In this scenario, 50,715 t of organic material (27,028 t of food wastes, 9500 t of leaves, 7100 t of grass and 7087 t of yard materials) sent for degradation. The biogas generation rates for these materials are shown in Table 12. Assuming that the biogas generated in the digester has a volumetric ratio of 55% CH4 , 45% CO2 , then 7.6 million m3 of CH4 is generated, with a mass of 5450 t. Due to the heating value of CH4 of 49.5 MJ/kg, 270,000 GJ of energy is available in the gas. At 75% co-generation efficiency, 202,000 GJ of the energy in the fuel will be converted to heat. Assuming that the cogeneration system uses a steam backpressure turbine, the ratio of power to heat from the system will be 0.3; that is, for every 10 J of heat produced by the system, 3 J of electricity will be produced (i.e., electricity will account

Table 12 Biogas generation rates of organic materials in anaerobic digesters (EPIC and CSR, 2004; Tchobanoglous et al., 1993) Material

Food wastes



Yard wastes


Mass of material sent for anaerobic digestion (t) Moisture content (%) Biogas generation rate (m3 /kg) Amount of biogas generated (m3 )

27,028 70 0.365 9,872,000

9500 60 0.079 750,310

7100 60 0.289 2,052,000

7087 60 0.162 1,145,000

50,715 N/A 0.273 13,820,000


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for 23% of the energy produced, while heat will account for the remaining 77% of energy produced) (Roca, 2003). Thus, 47,000 GJ (13 million kWh) of electricity and 155,000 GJ of heat will be produced by anaerobic digestion. If instead the system produced only power at a conversion efficiency of 30% (as was the case in scenario 3), 81,000 GJ of power would be generated. The anaerobic digestion scenario is capable of generating more power than the LFG capture scenario, even if power production occurred at the same efficiency in both instances. Comparing the results of the calculations in Table 12 (i.e. for scenario 6, anaerobic digestion) to those of LFG capture and conversion to energy (scenario 3 in Table 10), it can be observed that the model has not adequately considered the energy generated in scenario 6. The difference in energy consumption between the composting case (scenario 5) and the anaerobic digestion case (scenario 6) is about 16,000 GJ. As seen in the previous paragraph, the conditions for anaerobic digestion that were inputted into the model would result in 202,000 GJ of energy being produced. Thus, it is evident that the model results have not incorporated the energy production from anaerobic digestion. The IWM model has a module that allows for anaerobic digestion analysis alone. When case 6 is analyzed in the anaerobic digestion module, there are no net reductions in either GHG emissions or energy consumption, nor is there any virgin material displacement credit. This demonstrates further that the IWM model (EPIC and CSR, 2004) has not fully incorporated the benefits of anaerobic digestion. It is worth noting that the net energy consumption difference between case 6, without taking into consideration the energy displacement of anaerobic digestion, and case 8 (incineration) is 1.38 million GJ. The energy produced by anaerobic digestion, even at 75% efficiency, as would be achieved by a cogeneration system that is operating properly, would be 202,000 GJ. In scenario 8, all food wastes as well as paper and plastic wastes (with a total waste mass of 181,600 Mt) are combusted. In scenario 6, only 50,700 t of organic material is fed to the digester. The CH4 generated in case 6 has a mass of 5450 t, which is about 15% of the mass of the organic materials being fed to the digester. There are several reasons for this. The given mass of the feed to the anaerobic digester is the wet mass of the waste, and the water, though it may give some hydrogen to produce CH4 (Kaluzhnyi, 2001), does not contribute greatly. CH4 is a light molecule, with a density of 0.717 kg/m3 ; comparatively, CO2 has a density of 1.977 kg/m3 (O’Leary, 2000). If the composition of the biogas produced is 55% CH4 :45% CO2 , as is assumed in this exercise, the mass of CH4 will be 31% of the total mass of the biogas. Thus, the low amount of biogas produced will limit the energy produced from biogas, producing less energy from anaerobic digestion in scenario 6 than from the incineration of refuse in scenario 8. The benefits of recycling on emissions and energy consumption are very evident in this model. Recycling 50% of the recyclable material that is currently not being captured (about 19,000 t of paper, metal and plastic) would reduce emissions by 32,000 t CO2 e. The current rates of diversion of recyclable materials reduce energy consumption by 1.11 million MJ (gross energy consumption displaced minus reprocessing energy requirements) through avoiding the processing of virgin materials. Recycling a further 19,000 t of recyclable material, as suggested in scenario 4, would reduce net energy consumption by a further 500,000 GJ, more than twice the energy produced in the anaerobic digestion scenario. 2.3. Conclusions from modelling scenarios The modelling scenarios analyzed in this paper indicate that emissions are reduced the most through diverting 50% more of the waste that is currently recycled. Though this may seem a challenge, there already has been a noticeable increase in diversion rates

among single-unit residences in Ottawa between 1997 and 1999; paper diversion increased from 67% to 81% (capturing 42% of what was being discarded) while container diversion increased from 51% to 65% (capturing 29% of what was being discarded) (Solid Waste Division, 2000). Minimum recycled content legislation will further promote material recycling, encouraging greater GHG emissions reductions. Incineration offers significant emissions reductions, but the political cost of this option may be too great. Source reduction reduced net emissions by only about 0.25 t CO2 e/T waste reduced, but this was partially because of the assumption in that scenario that only manufactured materials would be source reduced. Most LFG emissions come from the degradation of food and yard wastes; paper diversion has been successful in Ottawa, with 64% of paper being diverted at present. Since it was assumed that the capture rates of recyclable materials would remain consistent, this scenario witnessed a reduction in the amount of material being recycled. Source reduction has perhaps a much greater benefit that the IWM model predicts. Anaerobic digestion has potential to reduce the emissions from the sector, but its greatest potential lies in reducing net energy consumption. A law banning the landfilling of organic material, such as the one implemented in Nova Scotia in 2000 (Nova Scotia Environment and Labour, 2003), would increase the amount of organic material being diverted, making anaerobic digestion a more feasible emissions and energy consumption reduction strategy. The benefits of composting lie in the low per-tonne cost for GHG reductions. Improved LFG capture reduced GHG emissions by 17,000 t CO2 e, as well as exporting energy. It appears that recycling and anaerobic digestion each offer significant GHG emissions and energy consumption reductions. 3. Conclusions and recommendations Canada’s waste sector generated 24.8 Mt CO2 e in 2001, of which 23 Mt CO2 e were produced by the decomposition of organic wastes in landfills. The main options for Canada’s solid waste sector to contribute to reducing emissions are through source reduction, recycling, LFG capture, composting, anaerobic digestion, and incineration. LFG capture, composting, anaerobic digestion and incineration will directly reduce emission from landfills, while source reduction and recycling will indirectly reduce emissions, perhaps to a greater measure, through displacing the processing of virgin materials. The IWM model was used to analyze the emissions from the waste sector. It indicated that further diversion of materials through recycling has the greatest effect on reducing GHG emissions, mostly through reducing production emissions through feeding recycled material instead of virgin material to production processes. Incineration follows with the next highest levels of GHG emissions reductions, followed by composting. Energy consumption is reduced the most through incineration with energy recovery, followed by recycling and improved LFG capture. The IWM underestimates the GHG emissions and energy consumption reductions on anaerobic digestion. It is possible that anaerobic digestion will reduce emissions and energy consumption significantly, but at 30% diversion of food wastes as well as current diversion rates of yard wastes, the emissions reductions will still rank behind diversion of an additional 50% of the recyclable material and incineration. Furthering efforts to divert recyclable materials will achieve the greatest amounts of emissions reductions in the Canadian solid waste sector. Acknowledgements The authors wish to thank Ralph Torrie of Torrie-Smith Associates and the City of Ottawa’s Solid Waste Services Division,

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