University of Wisconsin

Managing Food Waste for

Sustainability

Composting versus Landfilling

Timothy O. Allen Jr, toallen@wisc.edu, Nicole Cancel, Gabe Orduna

5/14/2015

Food loss and food waste are problems with our food system that require sustainable solutions. Both pre-consumer stages of the food system including production, processing, and distribution as well as post-

consumer waste by households and retail providers combines to around 35% of the food produced being

wasted. Composting this organic waste is becoming a popular means of managing it, helping offset the

amount of organic waste sent to landfills. This preserves landfill space and therein the need to create

new ones. Organic waste sent to landfills decomposes and produces methane, a potent greenhouse gas.

This contributes to total U.S. greenhouse gas emissions. Composting the organic waste instead is

purported to reduce the amount of methane gas emissions in addition to leading to carbon sequestration

as the finished compost product can be used as a soil amendment. This project outlines the respective

decomposition processes that occur in landfills and composting. In so doing, we demonstrate the

greenhouse gas emissions from composting food waste are less than if it were landfilled by quantifying

the amount of gases generated. While we initially sought to determine this specifically for Dane County,

WI, data were lacking so a national perspective was taken.

Keywords: Food waste, Composting, Sustainability, Greenhouse Gases, Landfilling

1. INTRODUCTION

Food waste in our country is a problem of significant concern among many sectors in the U.S. One of the

most often cited studies Kantor et al (1997) put food waste at 40 percent of edible food, or 49 million short tons

per year. More recently, the United States Environmental Protection Agency (EPA) released its report, “Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures 2012” which describes

the quantity of municipal solid waste (MSW) produced over the course of a year in the U.S. The report provides

figures for several types of MSW, of the most interest for this paper are the waste streams which can be disposed

of by an alternative means to a landfill, such as feedstock for composting projects. This project will seek to

determine if the alternative food waste management practice of composting is more environmentally sustainable

than landfilling in terms of the amount of greenhouse gas (GHG) emissions produced in each practice.

According to the EPA report, as of 2012 14.5%, or 36.5 tons, of the total MSW was food waste. Of the

food wasted less than 3 % was composted while the other 97% went to a landfill resulting in what the EPA cites as 18% of all methane emissions in the U.S., which has a global warming potential 21 times more intense than

carbon dioxide. With this abundance of food waste alone, without considering the other streams of organic waste,

there is ample opportunity to consider more sustainable practices. Across the U.S., cities regularly include

organic wastes with other MSW collection and disposal in landfills. Brenda Platt of the Institute for Local Self-

Reliant Cities (ILSRC) created the report; "The State of Composting in the U.S.: What, why, where, and how"

which estimated that the total organic wastes taken to landfills nationwide is 62 million tons annually. This

practice contributes to the growing concern over landfill capacity and the need for new landfill sites as well as

U.S. GHG emissions as detailed below. This study will look to examine the question: what is the most sustainable

way to manage food waste with respect to climate change? To answer this question, we will first consider source

reduction options as a sustainable means to decrease the amount of food waste and thereby the associated

emissions. Next, the GHG emissions from common landfilling and composting systems will be compared to assess which is the more sustainable option. Additionally, other points of environmental degradation that result

from each will be considered as well as possible social or economic benefits or downfalls of the respective

systems. To guide our study, we are defining sustainability to mean both least possible GHG emissions while also

considering factors regarding environmental degradation and/or economic benefits or harms.

2. METHODS

The initial means of examining the above-mentioned aspects of sustainability for composting and

landfilling was to review relevant articles on the topics of food waste, landfilling, and composting. Though our

findings were shared within the group, these reviews were divided among our three group members and provided

a working knowledge of the problem of food waste, current landfill practices, and current composting practices.

The next step was to explore the sources for each to contribute to climate change through GHG emissions. This

process also entailed reviewing articles as well as referring to authorities on these topics which primarily meant

the EPA to utilize their Waste Reduction Model (WARM) study to analyze GHG emissions from food production

and disposal. A report by the Natural Resource Defense Council (NRDC) was also oft referenced. As a result, we

were able to obtain estimates of the amount of food waste nationwide and the greenhouse gases that are associated

with food production and food waste decomposition in landfills and composting. In addition, we contacted

individuals who work directly with managing food waste which included Frank Kooistra formerly of the University of Wisconsin-Madison’s Office of Sustainability, who oversaw establishing the campus composting

program, Tom Wright, Superintendent of the West Madison Agricultural Field Station, and John Welch, Dane

County Solid Waste Manager. Through email and in person interviews at composting and landfill sites we could

obtain firsthand accounts of the food waste management practices that occur in Dane County.

3. RESULTS

The first section of the results will analyze reductions in GHG emissions from balancing our food

production with our food consumption, principally referencing WARM to “estimate streamlined life-cycle

greenhouse gas emission factors for food waste” including: beef, poultry, grains, bread, fruits and vegetables, and

dairy products (EPA, 2015). The second and third sections of our results will analyze the emissions those food

materials will produce in landfill and compost facilities (as the emissions from the food groups are averaged

together in landfills and compost sites, there will be no differentiation made in food material type once it enters

the landfill/compost site).

3.1. Source Reduction

The WARM study looks at annual emissions produced in the production, processing, and transportation

of the food products to the retail or commercial outlet (transportation from retail to consumer site are not

included) of several food materials with the most recent study being conducted in March of 2015. The study

provides average estimates of GHG emissions at each stage in the supply chain. Some of the solutions provided to

remedy some of these factors come from an NRDC (2012) study titled “Wasted: How America is Wasting up to 40 Percent of its Food from Farm to Fork to Landfill”. The WARM study operates on the premise that not only

does the food that we waste result in 18% of all methane emissions in the U.S. when landfilled (along with other

organic waste), but it also results in unnecessary GHGs being emitted from its overproduction, processing, and

transportation for consumer and retail use.

Before a food waste management system deals with the wasted food in either a landfill or composting

facility, a significant portion of GHGs associated with food waste are generated during production, processing,

and transportation of the six major food materials that make up most of the food waste stream: beef, poultry,

grains, bread, fruits and vegetables, and dairy products. The potential for GHG reduction involved in these food material’s overproduction is listed in Table 1 below in MTCO2E/short ton, as cited by the EPA. MTCO2E/short

ton is a measure of the global warming potential of GHGs that are equivalent to the emissions of a metric ton of

carbon dioxide. This unit provides a standard means measure the total emissions of all greenhouse gases.

Table 1. Net Emissions for Food Waste under Material Management Option (MTCO2E/Short ton)

Materials Net Source Reduction Emissions Net Landfilling Emissions Net Composting Emissions

Beef -30.05 0.71 -0.15

Poultry -2.47 0.71 -0.15

Grains -0.62 0.71 -0.15

Fruits and Veg -0.44 0.71 -0.15

Dairy Products -1.74 0.71 -0.15

Table from U.S. EPA WARM: Food Waste

To get the measurements for net source reduction emissions, the WARM study combined the appropriate sources of greenhouse gas emissions for the particular food material; process energy (GHG emissions from energy

used during the acquisition and manufacturing of one short ton of food material), transportation energy (GHG

emissions from energy used to transport one short ton of food material), and process non-energy (non-energy

GHG emissions resulting from production processes), and non-energy GHG emissions resulting from refrigerated

transportation and storage (usually combined with process non-energy). Net Source Reduction

Emissions=Process Energy + Transportation Energy + Process Non-Energy. The EPA cites what is

represented in the various stages of GHG emissions from food production where “process non-energy GHG

emissions occur during the manufacture and application of agricultural fertilizers, from the management of

livestock manure, and from enteric fermentation [while] transportation and storage non-energy emissions result

from the fugitive emission of refrigerants” as well as fossil fuel combustion usually in the form of diesel emitting

CO2 and lesser amounts of N2O. While WARM does not take all food waste into account, it provides a detailed

life cycle assessment of emissions for a very significant portion of total food waste. The distribution of food

materials covered in the study is exemplified in Table 2 from the EPA below.

Table 2. Relative Shares of Food Materials Modeled in WARM Relative to Total Waste Stream

Material Modeled in WARM % of Total Food Waste Generation* Weighted Percentage in WARM

Beef 5.50% 9.30%

Poultry 6.50% 11.00%

Grains 7.80% 13.10%

Fruits and Vegetables 29.30% 49.10%

Dairy Products 10.30% 17.70%

Total Modeled in Warm 59.40% 100%

Table compiled from U.S. EPA WARM: Food Waste

3.1.1. Beef

The first and largest potential for GHG reduction from source reduction as shown in Table 1, is beef.

With a loss rate, according to the EPA, of 12,777 million pounds of lost beef per year (or 6,388,500 short tons),

and a high potential for GHG reduction from lessening its volume, monitoring and refining our procedures for

production, storage, and transportation. The process energy in the production of beef consists of a combination of

most aspects of its production including “livestock feed, cattle raising, enteric fermentation from cattle, and the

processing of the beef to prepare for retail sale.” The first major overall stage with resulting emissions from beef

production came from calculating the cumulative energy demand to produce a single short ton of beef. Once converted to MTCO2E/short ton from energy per short ton in million Btu, it was found that 3.85 MTCO2E of

process energy per one short ton of beef is produced. This number was then combined with CH4 and N2O

emissions (26.09 MTCO2E/short ton) resulting from enteric fermentation and fertilizer for feed

production/application and diesel fuel from transportation (.12 MTCO2E/short ton) totaling 30.05 MTCO2E being

produced per one short ton of beef. By reducing the amount of beef, we produce, thus reducing the amount we

waste, we could decrease the 30.05 MTCO2E/short of beef GHG emissions.

3.1.2. Poultry

The data for poultry was taken from raw material and acquisition statistics including impacts of producing

broiler chicken, representing 83.6% of the poultry products in US (USDA, 2010) and the majority of the 15,134

million pounds of poultry lost per year (or 7,567,000 short tons). The poultry stages included in the WARM study

consisted of:” production of poultry feed, poultry production on a broiler farm (including energy use and emissions

for milling feed and housing poultry), poultry processing, and transportation.

Energy is used during the production of poultry feed, poultry processing and retail transport. The EPA cited

the calculation for the process energy from poultry feed production (the production of the various ingredients of

which the feed consists) and the emissions emitted during poultry production. The process non-energy emissions

from poultry production consisted of the fertilizers used in poultry feed production – resulting in CO2, CH4, and N2O

- emissions of N2O from poultry litter application as a fertilizer, and emissions avoided by replacing synthetic

fertilizer with poultry litter (EPA, 2015). The final aspect of GHG emissions to be saved from reducing poultry

production comes from the transportation and storage consisting of both the GHG emissions associated with diesel

consumed for vehicle operation and the GHG impact of refrigerants. If the poultry industry could better manage their

production to match consumption, they could save 0.26 MTCO2E per ton of poultry they produced.

3.1.3. Grains and Bread

The emission factor for bread was included for that of grains by including the additional energy used to

manufacture wheat flour into bread, which together resulted 18,761 million pounds (or 9,380,500 short tons) of all

grains being lost annually along the food production chain. This loss results in immense excess of this food waste

material producing GHGs both from its production and then again in its disposal.

The GHG emissions from the production of grains and bread is majorly produced from the combustion of

fossil fuels during harvest and production where CO2 and small amount of N2O are emitted. While the diverse types

of grains require different material and energy inputs the for the WARM study the EPA created a weighted average

of the grain types used to create a single emission factor for grains. The information was compounded to provide the process energy of grains and breads using SimaPro to calculate the Btu required to produce one unit of wheat, corn,

and rice, and then were combined to create an average Btu output for grains.

The non-energy emissions in the system looked at fertilizer production resulting in non-GHG emissions and

fertilizer application. Using the IPCC Tier 1 method for managed soils, the EPA calculated the total amount of N2O

and CO2 released from fertilizer application again by averaging the numbers for different types of grain. The study

then found the process energy storage from bread production in terms of million Btu per short ton of wheat flour

production and bread baking, then combined the two. Once the numbers for grains and breads were combined, the

EPA utilized the Bureau of Transportation Statistics to get an average emission per mile and average miles traveled for transportation to retail of combined grains and breads, to quantify their net emission factor of 1.29 MTCO2E

produced for every short ton of grains/bread produced (EPA, 2015).

3.1.4. Fruits and Vegetables

While the fruits and vegetables that are wasted do not have the highest possible averted emissions from

managing production, the vast volume of fruits and vegetables makes the possibility of GHG aversion significant.

While the fruits and vegetables modeled in WARM were not comprehensive (including only potatoes, tomatoes,

citrus, melons, apples, and bananas) the significant percentage covered of 59.6% (representing 67,737 million pounds

or 33,868,500 short tons annually) is a representation of the larger picture of produce waste.

As is the case with the food materials so far mentioned, the bulk of the GHGs being emitted are from

combustion of fossil fuels from the acquisition of raw materials and the food production process, which was the

process energy, and measured in millions of Btu per short ton. These numbers combined to form an average Btu per short ton of fruit and vegetable produced, which was then combined with the non-energy GHG emissions from

harvesting and fertilizer production/application (which also was a combined number). The transportation energy the

again resulted from fossil fuel consumption and fugitive refrigerants for shipping (EPA, 2015).

3.1.5. Dairy Products

The dairy products that WARM covers in its study represents 97% of the total dairy products on the

market where around 76.97 pounds are lost per year per capita. Most of the process energy emissions from dairy

production again comes from the combustion of fossil fuels during the farming process or the electricity grid.

Process non-energy emissions for dairy production present a higher risk than other food materials as CH4 is

produced from enteric fermentation, as well as CO2, N2O, and refrigerant emissions from transportation. The net

source reduction emissions were 1.74 MTCO2E/short ton of dairy produced (EPA, 2015).

Table 3. Raw Material Acquisition and Manufacturing Emission Factor for Production of Food Material (MTCO2E/Short Ton)

Material Process Energy + Tran Transportation Energy + Process Non-Energy = = Net Emissions

Beef 3.85 0.12 26.09 30.05

Poultry 1.34 0.27 0.87 2.47

Grains/Bread 0.66 0.03 0.58 1.29

Fruits/Veg 0.2 0.17 0.07 0.44

Dairy Products 0.8 0.05 0.89 1.74

Table compiled from: U.S. EPA WARM: Food Waste

3.1.6. Potential Remedies

The NRDC cites a plethora of remedies farmers, processors, and consumers can implement to reduce the

extent to which they waste food. On the production level, extending the secondary markets for the food that

farmers produce could allow extra food to go into the hands of those who need it at homeless shelters and nearby

soup kitchens. Some states, including California, have recently set up pilot programs to connect farmers with

shelters and are providing farmers with tax credits for the food they redirect from the waste stream (NRDC, 2012).

On the consumer level, educating the people around us about what a food label means when it gives a sell by date

versus its expiration date, as well as reducing consumer expectations of perfect looking food and overflowing

grocery stores could reduce the expectations of consumers that end up requiring grocery stores to either not accept

shipments from farmers, or waste food that has been sitting on the shelf for too long.

If municipalities could align food production with actual food consumption even a little more than we do

today, the municipality would be able to make their food system significantly more sustainable with all of the

respective food materials represented, as shown by the vast amount of each food material wasted, and the

potential GHG avoidance by not producing what was wasted altogether. Once there is no longer an option to avert

food from being disposed in the first place, there are many methods of disposal. What follows will focus on this

aspect of food waste comparing landfilling and composting.

3.2. Landfilling

Landfills are one of the main operations in the United States to manage waste. There are four types of

landfills, depending on the waste received: hazardous waste, MSW, industrial, construction & demolition landfills

(Waste Management Options 2014). According to Title 40 of the Environmental Protection Agency, hazardous

waste exhibits clear characteristics of ignitability, corrosivity, reactivity, and toxicity, such as hospital or laboratory waste. Industrial landfills consist of waste from manufacturing or industrial operations (Ohio EPA).

Waste from construction & demolition landfills are from the building or demolition of infrastructure, such as

buildings bridges, etc. (EPA 2014). MSW consists of household waste, which includes food waste, although it

may consist of lesser amounts of industrial waste (EPA 2014). For the purposes of reporting the GHGs emitted by

landfills because of food waste, only MSW landfills will be considered. The greenhouse gases emitted by MSW

landfills are determined by two factors: structural design and decomposition of waste.

3.2.1 Structural design

The structure of the MSW landfill is determined by subtitle D of the Resource Conservation and

Recovery Act (RCRA), which provides the mandates each type of landfill must legally abide by. Design criteria

describes the landfill as an empty tomb, starting with a composite liner of compacted clay at least two feet thick,

followed polyethylene plastic liner. This liner is described as “strong” and “resistant to chemicals” and

“impermeable to water” and must be sixty millimeters thick. Topping this plastic layer is a compacted soil layer, with a leachate (liquid residue from garbage) drainage system within its structure. However, this drainage system

is susceptible to clogging, which can reduce the effectiveness of leachate protection. It is meant to ensure that

leachate never reaches a level of more than one foot (EPA 2001).

The landfill structure determines the amount of GHGs emitted. If there are no cracking or tears within the

plastic liners or layers of clay, GHGs should not be emitted. That said, subtitle D is limited in its regulation of gas

emissions; the mandates available are meant to prevent gas explosions and reduce fire hazards so that “the

concentration of methane gas generated by the facility does not exceed 25 percent of the lower explosive limit for

methane in facility structures (excluding gas control or recovery system components)”, rather than regulating based on GHG emissions (EPA 2001). It is unclear, however, what this number may be, and it is dependent on the

facility.

3.2.2 Decomposition

The amount of GHG emissions produced within a landfill directly depends on the contents and the four stages of decomposition. Regarding contents, bacteria will produce more methane and carbon dioxide in more

organically rich waste. The first stage of decomposition in an MSW landfill is aerobic, where bacteria break down

carbohydrates, proteins and lipids in an oxygen-filled environment. Nitrogen, hydrogen, and carbon dioxide gases

result from stage one. Stage two starts when oxygen runs out; the bacteria continue to break down the products

from stage one to produce “acetic, lactic and formic acids and alcohols such as methanol and ethanol” (EPA

2015). Nitrogen, hydrogen, and carbon dioxide gases are the result once again. Stage three is unstable

decomposition where most landfill gases are produced because bacteria break down acids from stage three to

acetate. Methane producing bacteria begins to consume carbon dioxide and acetate in this stage. It continues until

decomposition becomes more stable, which is when stage four starts (the same as stage three but more stable)

(ATSDR 2001). From MSW decomposition, carbon dioxide and methane are the two main GHGs produced by

bacteria, with methane being between 45-60% and carbon dioxide between 40-60% of emissions. Nitrogen is 2-5% and oxygen is 0.01%-1% of emissions as it is mostly absent (ATSDR 2001). There are four ways that

decomposition can be indirectly influenced, thus changing GHG production: waste age, oxygen within the

landfill, moisture, and temperature. Since the most gas is produced between years 5 and 7 of being dumped, newer

waste will produce more emissions than older waste. If there is oxygen within the landfill, decomposition will not

become methanogenic, and the moisture content assists in GHG production because it supports both bacteria and

the chemical reactions that result in emissions. The bacteria involved in decomposition thrive better in warmer

conditions, so warmer temperatures will only encourage the production of gases (ATSDR 2001).

3.2.3 Emissions Data for Landfilling

Regarding total emissions

in the U.S, from landfilling, a 2015

study reported 0.71 MTCO2E/short

ton of food waste and 0.29

MTCO2E/short ton of mixed organics

(EPA 2015). These included both

transportation to the landfill, methane emissions, and carbon dioxide

recovery as described in the figure

below. Carbon dioxide emissions are

not included in this data; according to

the EPA’s WARM responsible for

measuring this data, it is assumed that

the carbon dioxide produced in the

landfill is “offset by CO2 captured by

regrowth of the plant sources of the

Figure 1. Greenhouse Gas Emissions from Landfill

material.” The EPA categorized three landfills types those without gas collection systems, those with a collecting

and flaring management system, and with a recover and energy use system. Regarding methane emissions solely,

landfills without collection systems, on average, result in 1.57 MTCO2/short tons of food waste. For those with

collection systems, flaring results in 0.68 MTCO2/short ton, and those with recover and energy use is 0.46

MTCO2/short ton. There is a 1.11 MTCO2E difference per short ton of food waste between MSW landfills without collection and those with energy reuse systems, thus making it the most sustainable landfilling option, regarding

reducing GHGs (EPA 2015).

3.2.4 Benefits and Downfalls

One of the main benefits of landfilling is the optional gas capture and energy reuse system. Methane and carbon dioxide capture can be compressed to produced natural gas and electricity that can power buildings and

motor vehicles as well. The MSW landfill of Dane County, Wisconsin, supervised by John Welch, currently uses

this system to power two buildings within the landfill, heat them, sell natural gas, and power several vehicles.

According to Mr. Welch, this system saves the county thousands of dollars. However, this energy reuse system is

state mandated within Wisconsin, but not nationally via subtitle D. Subtitle D currently does not require gas

collection or recovery and use systems for all MSW landfills. Only those with capacities greater than 2.5 million

cubic meters are required to install a gas collection system. Otherwise, it is currently up to the individual states to

invest in gas capture systems (Brown et al, 2007). When emissions are collected they can either be combusted

(where methane there converted into carbon dioxide) or then utilized for energy, which would reduce methane by

sixty to ninety percent and carbon dioxide by (EPA, 2012). Overall, regarding the soundness of the required MSW

landfill designs within subtitle D, the EPA says,

“RCRA, Subtitle D regulates the management of nonhazardous solid waste. It establishes minimum

federal technical standards and guidelines for state solid waste plans in order to promote environmentally

sound management of solid waste. RCRA Section 4001 of subtitle D outlines primary goals of the Act,

which are: promote environmentally sound disposal methods, maximize the reuse of recoverable

resources, and foster resource conservation.” (EPA, 2013)

However, a few decades of research suggest that the reliability and long-term sustainability of MSW

landfills, according to subtitle D, are uncertain. When a landfill is capped and closed, if the biochemical contents

of the landfill are unstable, further decomposition will continue, thus creating more GHGs within the landfill

(Laner 2011). Also, if at any point, there were to be a malfunction in landfill design (via hole or stress in a liner),

that would imply that from decades to centuries worth of emissions would diffuse into the atmosphere.

Researchers G. Fred Lee and Amy Jones-Lee agree with the possibility of liner failure through its referral of

previous EPA acknowledgement of eventual liner decay (EPA Federal Registrar, 1981). Thirty years later,

research still supports this.

3.3. Composting

While composting is neither a new idea nor practice, interest is growing because of the growth of urban

agriculture, green infrastructure, and sustainability initiatives. There has been an increase in composting efforts in

locales across the country at both the community and the municipal levels. As is the case in the State of

Wisconsin, many states require yard waste to be composted. In some cities, individuals are leading composting

efforts, for example, to create soil that can be used for community gardening. Additionally, many community

gardens have their own composting bins they maintain (KompostKids.org, 2015). While these efforts should be applauded there are still ample opportunities to divert organic waste from landfills and compost it into a

sustainable soil amendment. This is especially true considering the estimated organic waste currently sent to

landfills nationwide could generate 21 million tons of additional compost (Platt 2012). As described above,

landfilling food waste generates GHGs, and most commonly, methane, which has a global warming potential 21

times that of carbon dioxide. While composting food waste can also generate GHGs, in comparison to landfills

there is an avoidance of emissions and can result in net negative emissions when carbon sequestration is

considered.

3.3.1. The Art and Science of Compost

Composting has been called both an art and a science. This is due to the complicated factors involved in

the composting process that determine the time the process requires, the amount of GHGs generated, and the

quality of the finished compost product. A general definition of composting is the biological decomposition of

organic material into humus, the most basic compound of soil. Here composting is used as the controlled

decomposition of organic material. Decomposition occurs by microorganisms that secrete hydrolytic enzymes that

break down organic material and produce heat. As determined by MacCready et al (2013) at least 40 distinct

species of bacteria can be present in a compost pile including aerobic and anaerobic bacteria, along with fungi and

insects. The ideal composting process differs from the decomposition that takes place in landfills due to the

presence of oxygen which makes the process aerobic and therefore methane is minimally produced. There is a

possibility of methane production in composting, though, which depends on the method used. In general, methane

production is reduced if aerobic conditions in the pile are maintained.

As Cooperband (2002) explains, the composting process consists of two general phases; the active phase

and the curing phase. During the active phase, thermophilic microorganisms dominate the compost pile and

temperatures can rise to 150 °F, this phase is important as it kills pathogens and weed seeds that can reduce the

quality of the final product. The second general phase is the curing phase. Here mesophilic microorganisms re-

enter the pile and continue the decomposition process. The temperature of the pile resides around 100 °F and

bacteria continue to break down any remaining organic matter. The curing process can take one to four months

and is important for the quality of the final product which contains stable humic acid compounds.

The aerobic decomposition of food waste produces carbon dioxide. These emissions are considered

biogenic (part of the short-term carbon cycle) and not typically used in calculations of GHG emissions as mentioned in the

landfilling section. Methane is produced because of anaerobic conditions which can result from too much moisture

which prevents oxygen circulation through the material. Anaerobic pockets can also form, typically at the bottom

of the pile. While these anaerobic pockets may form, the methane produced is typically oxidized by other

microbes before it leaves the pile. Anaerobic pockets do not typically form near the top or sides of a pile as air can

penetrate easily (EPA 2015). In addition, methanogenic bacteria are typically inhibited by high ammonia

concentrations in compost piles (Brown 2008). Nitrous oxide can also be produced under anaerobic conditions,

which will occur during the mesophilic finishing stage when temperatures are cooler and denitrifying bacteria can

enter the pile. This is dependent on the amount of nitrogen as well as the presence of oxygen and results from

nitrogen oxides’ denitrification (EPA 2015).

As mentioned above, the method of composting is important to controlling the conditions within the pile

as well as the final product. Windrows, static pile, and mechanical (in-vessel) are the three categories within

which most methods fall. Within these categories there are variations for scale and duration of the process. In the

windrow method, feedstock is piled up between 3 and 12 feet high and 9 and 20 feet wide and the pile is extended

into a narrow row as new feedstock is added. The pile height and width depends on the type of turner used to

aerate the pile. In the static pile, a height of between 3 and 6 feet is obtained and between 10 and 12 feet in width.

A static pile may be passively aerated in which perforated tubes are placed under and/or within the pile so air can

flow through. A static pile may also be forcibly aerated in which an electric blower is used to ‘force’ the air through the tubes to aerate the pile. In mechanical composting methods feedstock are typically in-vessel, as

opposed to a pile. The feedstock is added to the vessel and aeration occurs within it, typically by mechanically

turning the vessel, or internal mixing of the feedstock.

According to Brown (2008) to ensure aerobic conditions for decomposer bacteria and to minimize the

production of methane the compost pile should be properly turned regularly. If properly managed, the main source

of GHG in composting systems is using electricity and petrol fuels to run equipment and machinery. Emissions

from these sources will vary by site depending on the type of energy generation, i.e. coal-fired power plant or

wind turbines which have obvious differences in emissions. Additionally, the type of fuel and machinery will have

different emission coefficients.

3.3.2. Emissions Data for Composting

The amount of GHG emissions will vary depending on the scale of the compost operation and the

method of composting used. The amount of GHG emissions produced from a windrow composting operation was

found to be 0.1 MT CO2 per MT of material composted according to Brown (2011) citing a 2002 study by the

EPA. This considered transportation of the feedstock and use of electricity and machinery. In an aerated static pile

energy is used to force air through the pile. The amount of GHG emissions produced can vary depending on the

operation but can be calculated using the carbon equivalent of 0.66 kg CO2 kWh-1 of electricity used. An aerated

static pile will also require that materials be transported and machinery will be used to set up the pile. In a mechanical system, again the emissions

will depend on the electricity source and

the machinery used but one estimation is

60 kg CO2 per metric ton of material

(Brown 2011).

The method widely used for

composting yard trimmings and MSW

and recently used by the EPA to model waste reduction in WARM, was the

windrow method in large scale

composting facilities. The major points

that affect GHG emissions were found to

result from collection and transportation

of materials to compost site, mechanical

turning of compost pile, non-CO2

emissions during composting (CH4 and

N2O), and carbon sequestration after

compost is applied to soil. Figures 2

summarizes the amount of GHG emissions generated in in a composting facility. Transportation of the materials resulted in 0.04 MTCO2E/short

ton of food waste. Emissions from the composting process which included CH4 and N2O were 0.05. As illustrated

on the whole composting of food waste results in net negative GHG emissions. This is the result of carbon

sequestration, referred to soil carbon storage in the table above as -0.24 MTCO2E/short ton of food waste.

Carbon sequestration results when the finished compost which consists of organic carbon (C) is added

back to the soil. Photosynthesis is the primary process through which carbon dioxide is removed from the

atmosphere. If plant residues are left on the field the C that has been captured from the atmosphere by

photosynthesis is naturally added to the soil and becomes part of the organic C pool, carbon sequestration has occurred. When crops are harvested less C goes into the pool. This C is lost, or returned to the atmosphere, when

food waste is sent to landfills. This is a result of the anaerobic processes that convert it into methane as described

above. While the release of carbon dioxide is negligible as plants can use it in photosynthesis, the production of

methane in landfills exacerbates the problem of GHGs in the atmosphere and can be avoided.

3.3.3. Benefits and Downfalls

While the need to preserve landfill, space is one aspect of the need to do so, highlighting the benefits of

composting food waste may be the most effective means to drive the change. In another report by ILSRC

“Growing Local Fertility: A Guide to Community Composting” different models of community composting

operations are detailed and 29 existing composting ventures are highlighted. These ventures range from collection

entrepreneurs who charge to pick up organic waste and in turn drop it off where it will be composted to schools

with on-site composting. In many cities individuals are acting to divert organic waste and make a profit at the

same time. Compared to landfill tipping fees (the fee charged to dump waste), which are lower in Wisconsin than

some other states, composting tipping fees are typically lower which offer both municipalities and for-profit

businesses savings; especially in the long run. On a smaller scale, composting may take the form of biking organic

waste or using a small truck to transport the waste to a community composting site, where there are no tipping

fees, with individuals charging different fees for the service.

The finished compost also has considerable value for operations when the finished compost is sold. Table

6, below, lists the many different markets for finished compost. This prospect encourages entrepreneurial ventures

with many examples currently up and running across the U.S. (Platt 2014). BioCycle magazine has featured

several articles on composting at correctional institutions. Institutional composting, these programs serve as

Figure 2. Greenhouse Gas Emissions from Composting

models of how to divert food waste. The table at right lists ways compost can be marketed and the ways it can be

utilized.

Table 4. Compost Uses

Market Compost Use

Agronomic Soil amendment

Horticultural Seed starter, soil amendment, mulch, container mix, natural fertilizer

Urban/Suburban landscaping Soil amendment, mulch

Turf Seed starter, soil amendment, topsoil, natural fertilizer, mulch

Forestry Seed starter, soil amendment, topsoil, mulch

Land reclamation/Landfill

cover/Bioremediation

Soil amendment, mulch

While there are many benefits there are also some potential downfalls of composting. These downfalls mostly

result from the contact with rotting organic waste and the decomposition process which produces leachate. The

WI state legislature set requirements on temperature in a compost pile to 55℃ for 16 days during the thermophilic

phase to effectively kills pathogens (and weed seeds) using the windrow composting method.

While most states have similar regulations to prevent health hazards there is a chance of compost facility

workers meeting the pathogens. The is also the possibility of leakage of leachate from the compost pile if

windrows are not placed on concrete pads. WI statutes also address this potential environmental effect in the

regulation of compost facilities.

4. CONCLUSION

After agreeing to Dane County’s request to find the most sustainable way to manage their food waste

system with regards to climate change we first considered the literature to determine where the waste they manage

comes from and what the waste consists of. Once we knew how much food was being wasted, we considered the

diverse ways that people all over the United States and we found that most of the food that municipalities dispose

of goes into landfills with a small portion being composted. With an outline of these findings we found three

approaches to creating a more sustainable food waste system within Dane County.

The first approach considered source reduction or reducing the volume of the food that is produced and

goes into the landfill. The volume of the food that we produce outweighs the food that we consume resulting in

copious amounts of food going to waste. If we can lower the production of food materials to align better with our

consumption rates we would be able to reduce total greenhouse gas emissions from production of those foods. We

can also look to smarter practices in production, processing, transportation, and consumption of food that would

lead to a reduction in volume of food wasted. Combing net emissions from the food materials covered, the

WARM study shows that 35.99 MTCO2 could be saved for every short ton of food material wasted. With up to

40% of our entire food supply going to waste, there is ample opportunity to reduce GHG from better food supply

management (NRDC, 2012).

In our second and third approach, we considered food waste disposal. Landfilling food waste results in

0.71 MTCO2E/short ton. After looking at the information about the emissions from landfilling we found many

options to make the systems more sustainable, such as adopting gas capture methods which brought the emissions

down to 0.46 MTCO2E per short ton of food material put into the landfill. However, the emissions from

composting food waste were -0.24 MTCO2E/short ton when carbon sequestration is considered and 0.11

MTCO2E/short ton when it is not. Therefore, we can conclude that on a per ton basis, the amount of greenhouse

gas emissions from composting food waste is lower than if it is landfilled. While each option has additional associated environmental impacts that must be taken into consideration, we find that composting is the most

environmentally sustainable food waste management approach.

With these findings, we advise Dane County on the most sustainable food waste management approach.

This study did not consider how to move forward and implement such a project. Our hope is that the information

we could provide will help Dane County take all the factors of waste management, including the possibilities for

management both before the product reaches the consumer, and once the product enters the ground. The County

should also take possible economic and social benefits of the respective systems such as uses for compost and

possible economic gains from gas capture in existing landfills.

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