Managing Food Waste for Sustainability: Landfills versus Composting
Food waste are problems with our food system that require sustainable solutions. One means to address the problem is composting this organic waste. This is becoming a popular means to manage food waste and offset the amount of organic waste sent to landfills. The historical approach to managing food waste, landfilling , will not be sustainable in years to come. According to the U.S. EPA, organic waste sent to landfills decomposes and produces 18% of U.S. methane 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 difference. While we initially sought to determine this specifically for Dane County, WI, data were lacking so a national perspective.
- We set out to determine the social and environmental consequences of poor food waste management.
- First we reviewed conducted general research to review the literature for existing studies of the sustainability of landfills and studies that investigated if diversion of food waste and composting reduces Greenhouse Gas (GHG) emissions from landfill.
- In order to be able to provide a better perspective on general food waste management strategies we decided to change our scope to Dane County as a whole from our original focus on the UW.
- We then scheduled interviews:
First at the West Madison Agricultural Research Station where we met and talked to Superintendent Tom Wright about the composting operation. We discovered that the UW campus diverts a portion of their waste stream from landfilling that is composted in windrows at the station.
Next we scheduled another interview with the John Welch the supervisor at the Dane County Landfill and met him at Dane County's landfilling facility to gather more information. We learned that Dane County’s landfilling operation is more sustainable than we initially thought due to the makeup of the landfill itself which generates electricity by through its methane capture system. We also learned that the only things being composted was yard waste which began with Wisconsin's state-wide ban on landfilling yard waste in 1994.
- We realized we needed to expand our question to how can we get more food waste to be composted and how can we reduce the amount of food being wasted in the first place to best improve the Dane County waste management system.
|Food Loss||the edible amount of food, postharvest, that is available for human consumption but is not consumed for any reason. It includes cooking loss and natural shrinkage (for example, moisture loss); loss from mold, pests, or inadequate climate control; and food waste|
|Food Waste||a component of food loss and occurs when an edible item goes unconsumed, as in food discarded by retailers due to color or appearance and plate waste by consumer|
|Source: USDA Economic Research Service (2014)|
According to the EPA as of 2012 the U.S. produces:
|Source: U.S. EPA Facts and Figures 2012|
Food waste is a inevitable outcome of human consumption in modern society. Home food waste results from preparation of meals and plate waste. Pre-consumer food waste, food wasted in its production, harvest, processing and storage, along with post-consumer waste resulting from over preperation of meals and partial consumption (plate waste) contributes to a total of 31% or 66 million tons of food wasted in 2010, of this food waste, only 3 % was composted while the other 97% went to a landfill resulting in 23% of methane emissions in the U.S., which has a global warming potential 25 times more powerful as carbon dioxide (Gunders 2012).
As such food waste is a problem of significant concern among many sectors in the U.S. 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 various 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 (see table 1 above). 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.The amount of food loss produced on a daily basis requires a management plan that will mitigate the environmental impact from disposal of the waste in landfills. While the means of disposal in many municipalities calls for waste to be sent it to a nearby landfill, this practice has been found to shorten the life of landfills and lead to the production of potent greenhouse gases such as methane and carbon dioxide. 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 possible 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 taking into account factors regarding environmental degradation and/or economic benefits or harms.
|Source: Natural Resource Defense Council (2012)|
|Redirecting lost food from regulations to fertilizer, feedstock, and charities||Adopting new technologies with food utilization in mind||Analyzing sales at supermarkets making inventory is calculated based on passed sales|
|Providing tax credits for redirection of otherwise unused but edible food
||Secondary uses for trimmings||Limiting menu options, planning for food re-purposing|
|Revision food standards allowing for wider array of food appearances||Training for proper handling and storage of food||Education on food quality and expiration|
|Source:Natural Resource Defense Council|
Net Source Reduction = Process Energy + Transportation Energy + Process Non-Energy
|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|
|Process Non-Energy||non-energy GHG emissions (i.e. methane) resulting from production processes and refrigeration|
|Source: U.S. EPA WARM: Food Waste (2014)|
|Material||Process Energy||Transportation Energy||Process Non-Energy||Net Emissions|
|Source: U.S. EPA WARM: Food Waste (2014)|
*95% of waste is deposited via landfill*
Background on Landfills
The GHG emissions by MSW landfills depends are determined by two general factors:
Environmental Hazards of Landfilling
One of the main benefits of landfilling is the optional gas capture and energy reuse system. Methane and carbon dioxide capture has the ability to be compressed to produced natural gas and electricity that can power buildings and motor vehicles as well (Welch 2015).
MSW Landfills with recommended precautionary measures-The Example of Dane County
The landfill is following regulations which we verified according to:
RCRA Subtitle D along with
- Collection wells: methane and carbon dioxide emissions are used to generate electricity and natural gas
- Pipes directly towards the sewer, for leachate leaks or overflow
- Adequacy of monitoring
Only those with capacities greater than 2.5 million m3 are required to install a gas collection system to reduce methane emissions. Otherwise, it is currently up to the individual states to decide in this investment (Brown et al, 2007).
However, according to G. Fred Lee, PhD et al, the mandates by Subtitle D are unreliable; the different capping and layering systems are bound to fail. Gases and leachate will, over time, be able to leak through the liner and the gas detection system. 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. Pivato in 2011 calculated the estimated “failure time” of different clay and geomembrane liners for used in 30 different countries. The estimated failure time for clay liner mandated within the United States is five years.
Greenhouse Gas Emissions from Landfilling Foodwaste
To determine the environmental impacts of landfilling food waste in Dane County we sought to determine what percentage of total MSW food waste occupies. While the WI DNR has conducted a waste audit of the Dane County Landfill MSW to determine its composition, this study has yet to be made public. Without this data the environmental impacts of food waste in Dane county could not be estimated. As an alternative we turned to the EPA for national statistics on the composition of MSW.
These national statistics were also used to provide a comparison between the greenhouse gas emissions from landfilling and from composting. As illustrated in the figures below landfills produce an abundance of GHG, 18% of total U.S. GHG in fact. In contrast, composting results in net negative emissions largely as a result of the credit of carbon sequestration.
|Source: U.S. EPA WARM: Food Waste (2014)|
The Art and Science of Composting
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 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 different 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 largely 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 as a result 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 relatively 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 generally 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 through the use of 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.
Greenhouse Gas Emissions from Composting
This project began as a means to mitigate greenhouse emissions that result from current food waste management, i.e. landfilling. It found the amount of GHG emissions will largely 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 took into account 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 roughly 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 (mainly CH4 and N2O), and carbon sequestration after compost is applied to soil. Figures 7 above 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 largely 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 carbon dioxide that has been captured by photosynthesis is naturally added to the soil and becomes part of the organic C pool. That is to say carbon sequestration has occurred. When crop products are harvested less C goes into the pool. This C is lost, or returned back to the atmosphere, when food waste is sent to landfills. This is a result of the anaerobic processes that convert it into volatile methane as described above. As mentioned methane is a GHG with a global warming potential 21 times that of carbon dioxide. While the concentration of atmospheric carbon dioxide is initially reduced by photosynthesis, the resultant production of methane landfills from decomposing food waste exacerbates the problem of greenhouse gases. Figure 8 at right illustrates how composting food waste adds C to the soil.
|Adapted from R. Lal (2004)|
There are many ways to encourage Dane County to move towards a sustainable food waste management system. 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. The table at right lists ways compost can be marketed and the ways it can be utilized. As depicted there are many uses of compost in a variety of sectors. This added value of compost could potentially provide a revenue stream from food waste management which is typically a cost.
Dane county currently does not have a comprehensive residential food waste composting program nor do they require large food waste generators such as farms, restaurants, and/or grocery stores to compost their food waste. While there have been pilot studies to determine the feasibility of a composting program, the majority of Dane County's food waste is sent to landfills. The landfill described above is only one of the landfills that receives food waste from the county.In this way Dane County is similar to other counties in Wisconsin that have yet to comprehensively address the unsustainable approach the current food waste management, which largely involves landfilling.
While Wisconsin has banned yard waste from landfills other states have taken measures to reduce food waste sent to landfills by requiring restaurants to compost. One such instance is the State of Massachusetts which requires restaurants that generate more than one ton of food waste a week to compost. Similarly, Connecticut and Vermont require restaurants that generate more than two tons of food waste a week to compost.
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 looked into 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 looked into the different ways that people all over the United States and we found that the vast majority 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 greatly outweighs the food that we consume resulting in large amounts of food going to waste. If we are able to 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 greatly. 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 possible emissions from landfilling we found a number of 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 taken into account 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 were able to provide will help Dane County take all of 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.
1. Brown S, Kruger C, Subler S. Greenhouse gas balance for composting operations. J Environ Qual 2008;37:1396.
2. Cooperband L. The art and science of composting: A resource for farmers and compost producers. University of Wisconsin-Madsion. Center for Integrated Agriculture Systems 2002.
3. El-Fadel M, Findikakis AN, Leckie JO. Environmental impacts of solid waste landfilling. Journal of Environmental Management 1997;50:1.
4. Platt B, Goldstein N, Coker C. The state of composting in the US: What, why, where, & how. Institute for Local Self-Reliance 2014.
5. U.S. Environmental Protection Agency. Solid waste management and greenhouse gases: A life-cycle assessment of emissions and sinks report.3rd ed.2006.
6. U.S. Environmental Protection Agency. Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures 2012.
7. Lee, PhD, G.Fred, Anne Jones-Lee, PhD, and G. Fred Lee and Associates. Flawed Technology of Subtitle D Landfilling of Municipal Solid Waste. (2015)
Tim Allen (middle) is a graduate student in the Nelson Institute for Environmental Studies. His hometown is Milwaukee, WI. He is an educator and lifelong learner interested in urban agriculture, composting, and sustainability.
Nicole Cancel is a senior studying Biology and Chican@ and Latin@ studies. She grew up in Marshfield, WI and plans on teaching high school Biology in Chicago after graduation. She is new to the study of sustainability, but is interested in food system management on a local and global scale.
Gabe Orduna is an undergraduate Community and Environmental Sociology major getting a certificate in Environmental Science. He grew up in Lexington, Massachusetts and is interested in community leadership and sustainability.