• Unites States student, Arynn Rogers - composter, not waster
Hello everyone.
My name is Arynn Rogers, and I am about to start my senior year at Arizona State University (ASU). I am studying sustainability with a focus in ecosystems and completing a certificate in food system sustainability. I have spent part of this summer researching how the United States and Australia deal with food waste, and how they might be fixing this issue.
During my time at ASU, I have learned about food waste and how a lot of it goes straight to the landfill.
Americans, on average, waste about 1 pound (0.45kg) of food each day per person and the average Australian household throws away about 1.8 pounds (0.82kg) of food each day.
All this rotting food waste in a landfill generates methane which is a harmful greenhouse gas. Greenhouse gases trap heat in the atmosphere and warm the earth. According to the Food and Agricultural Organization (FAO) of the United Nations, a specialized agency that is working to defeat international hunger, food waste accounts for approximately 8% of all greenhouse gas (GHG) emissions globally. As seen in the graph below, food waste is the third largest contributor to GHG emissions worldwide.
• This graph shows that if food waste were a country, it would be the third largest emitting country in the world.
This got me thinking about what my food waste looks like, what happens to our food waste, and how it is being addressed across the globe. In my home city of Lexington, Kentucky, our food waste is tossed in the garbage and sent straight to the landfill where it releases these harmful greenhouse gases.
• A map of the United States with a pinpoint on my home town of Lexington, Kentucky (image provided by google earth)
My neighborhood has limited options of waste disposal due to our location. The city government does not service our area, even though we are within the city limits. In my neighborhood, we use a private company called Rumpke to pick up our garbage and recyclables. Rumpke does not readily provide customers with detailed information about their waste disposal process. However, Rumpke is known for owning the sixth largest landfill within the United States, locally known as Rumpke Mountain.
• Aerial view of the Rumpke Waste and Recycling landfill. This landfill covers 344 acres (139 ha) of a 800-acre (324 ha) tract of land that the company owns
This large landfill is located approximately 110 miles (177km) from my home. Though this is their largest, our garbage is most likely dumped at one of their smaller landfills approximately 30 miles (48km) away.
• The photo on the left shows a picture of the truck that picks up solid waste. The photo on the right shows my recycle bin (green bin on the left) and my garbage bin (brown on the right)
Rumpke, the garbage pick-up service, uses more than 1,700 trucks to collect trash from 4 different states within the United States. Each day, one driver of one truck stops at an average of 500 households a day. Each of those 500 houses produces around 50 pounds (22.7kgs) of trash a week. If this truck hauled nothing but food waste, that would be a collection of 25,000 pounds (11,339.8 kg) of food waste per day. This food waste sits in our landfills, rots, and releases harmful gases into our atmosphere.
There are many ways to avoid food waste, such as buying only what you know you will consume, donating to an organization, or composting it. In my city, we have limited organic waste options, one being Treehouse Compost, which will come and pick up your food waste to make compost. There are many cities such as Sydney, New South Wales, Australia, that have organic waste bins which are picked up for anaerobic digestion.
Anaerobic digestion collects food waste from individual households and businesses and digests the food to create materials which are then used to generate electricity. I have provided a diagram of an anaerobic digestion system and how the process works.
• This is an image provided by Earthpower technology of the process of anaerobic digestion
Step one of this process is weighing the waste on the weighbridge. The full truck is weighed and then the truck is weighed again when it is empty.
Step two is where all the waste is dumped and separated into solid waste and liquid waste. It is then tested for contamination.
During step 3 all solid waste is agitated down to a pulp.
Step 4 is where the pulp and liquid waste is fed into the digester where bugs eat the waste producing methane also known as biogas.
The methane rises and is transferred to the cogeneration engine in step 5. During cogeneration (step 5), biogas is fed into the engine to create ‘Green Electricity’. The ‘Green Electricity’ is then transferred to the energy grid. The cogenerator also produces heat some of which is used in the making of fertilizer.
The remaining waste in step 4 is withdrawn from the digester and makes its way to step 6 to be de-watered into sludge.
At step 7 the solid waste is fed to the dryer which is heated from the exhaust of the cogeneration process therefore creating fertilizer.
The water from step 6, is sent to step 8 which is the water treatment segment. This treated water is then discharged to the trade waste sewer. See more of what the company say about its biodigestion, here.
This alternative to dumping food waste into the landfill is marketed as a ‘green energy’ solution as it produces electricity which is returned to the energy grid. According to a study by environmental researcher Suraj Opatokun and her colleagues, they found that every 1kg of food waste used for anaerobic digestion would produce 0.240 kWh of energy, 0.369 kWh of heat, and 0.030 kg of fertilizer.
Using Opatokun’s results from the anaerobic digestion system they evaluated, this could produce 2,721.6 kWh of energy, 4,184.4 kWh of heat, and 340.2 kgs of fertilizer per truck per day.
The average U.S. residential utility customer uses an average of 877kWh per month in their home. This is enough energy to power one average American household for 3 months.
While this seems like a great alternative, there are still harmful aspects to anaerobic digestion that need to be considered such as water and air pollution. According to an article in Environmental Science and Technology, 2-3% of methane is leaked during anaerobic digestion. This seems like a very small percentage but methane is 86 times worse than CO2 (the most commonly known GHG) for the climate over a 20 - year time frame. Learn more here.
Earthpower is one anaerobic digestion and energy generation company located on the Parramatta River in Camellia, New South Wales, Australia.
• This photo shows an aerial view of Earthpower Technologies located on the Paramatta river. (Image provided by google earth)
Earthpower technologies has disclosed some of their environmental reports of emissions on their website.
They test the exhaust from their co-generation exhaust stacks once a year.
The stacks release volatile organic compounds, nitrogen oxides, and sulfuric acid mist and sulfur trioxide. Volatile organic compounds are man made chemicals that are often found in petroleum fuels, hydraulic fluids, and even in paint thinners. These chemicals are harmful to our health causing problems such as shortness of breath, nausea, dizziness, among other health issues.
Nitrogen oxides, when released into the atmosphere, interact with oxygen, water, and other chemicals to create acid rain. Not only does nitrogen oxide affect the environment, but they are also particularly harsh on the respiratory system in humans.
Finally, sulfuric acid mist and sulfur trioxide also presents issues for the respiratory tract in addition to being a main component in acid rain.
According to Earthpower technology data, their release of nitrogen oxides has decreased within the last two years. However, the release of volatile organic compounds, sulfuric acid mist, and sulfur trioxides have increased within the last two years.
• The orange line is the limit of volatile organic compounds that are allowed to be released during a test period by the EPA. The blue line is the actual emissions that Earthpower Technologies had when they were testing their exhaust stacks. As shown here, the volatile organic compounds being released fluctuate from year to year but are still well under the EPA’s limit.
• The orange line is the limit of nitrogen oxides that are allowed to be released during a test period by the EPA. The blue line is the actual emissions that Earthpower Technologies had when they were testing their exhaust stacks. It seems that their nitrogen oxide emissions have decreased within the last two years.
The orange line is the limit of sulfuric acid mist and sulfur trioxide that are allowed to be released during a test period by the EPA. The blue line is the actual emissions that Earthpower Technologies had when they were testing their exhaust stacks. While their emissions are well under the EPA limit, their emissions rose significantly in 2019. Earthpower technologies does not provide reports for 2020 so it is unknown if this is a developing trend.
While anaerobic digestion has what appears to be many great benefits, there is research needed to verify the environmental impacts as we must ensure that we are not creating another environmental problem. For example; where does the sludge and trade waste go - into the river? How much energy is lost as waste heat during the process? How much energy is used by the process? What is the embodied energy in the truck movements to and from the facility both by the garbage trucks and by the fertilizer trucks?
One way I know I can help is by buying food I know I will eat as well as composting any food scraps or waste at my own home. If i can easily compost you can, too, and affordably at your own home too.
Read my other blog post where I show you how I made my own and how you can make your own compost bin and the steps to produce nutrient soil with food scraps allowing you to help keep food waste out of the landfills and places that burn food waste.
Anaerobic digestion sources:
https://www.theguardian.com/environment/2018/apr/18/americans-waste-food-fruit-vegetables-study
https://www.environment.gov.au/protection/waste/food-waste#:~:text=Food%20waste%20is%20also%20a,in%20five%20bags%20of%20groceries.
https://www.epa.gov/ghgemissions/overview-greenhouse-gases
https://www.un.org/en/ccoi/fao-food-and-agriculture-organization-united-nations
https://www.rumpke.com/newsroom/blog-post/thoughts/2013/08/24/rollin-with-rumpke-rear-load-trucks
https://www.treehousecompost.com/
https://earthpower.com.au/the-technology/
https://www.mdpi.com/2071-1050/9/10/1804
https://www.eia.gov/tools/faqs/faq.php?id=97&t=3
https://www.energyjustice.net/digesters#leakage
https://www.epa.gov/indoor-air-quality-iaq/what-are-volatile-organic-compounds-vocs
https://www.healthlinkbc.ca/healthlinkbc-files/air-quality-VOCs#:~:text=VOCs%20include%20a%20variety%20of,kidney%2C%20or%20central%20nervous%20system.
https://www.sciencedirect.com/topics/engineering/acid-mist
https://www.epa.gov/no2-pollution/basic-information-about-no2