Economically Viable Food-Waste-to-Compost Conversion Scaled to Urban Neighborhoods

Economically Viable Food-Waste-to-Compost Conversion Scaled to Urban Neighborhoods

Jordan Nehls

Biological Systems Engineering Department, University of Wisconsin-Madison

Date submitted: March 14, 2017

Table of Contents

Title page / 1
Table of Contents / 2
Keywords / 3
Statement of Need / 3
Project Goal / 6
Design Specification / 6
Project Output / 7
Annotated References / 7

Keywords

Food waste, windrow compost, in-vessel compost, methane, C/N ratio, Ohio University in-vessel composter, solid waste regulations

Statement of Need

According to the Environmental Protection Agency (EPA), in 2013, Americans generated about 254 million tons of municipal solid waste, and recycled and composted about 34.3 percent of it. The total municipal solid waste is separated by material type in Figure 1. Recycling and composting prevented 87.2 million tons of material away from being disposed in 2013 compared to about 15 million tons in 1980. Recycling is the recovery of useful materials, such as paper, glass, and plastic from the trash. These materials are used to make new products and reduces the need for raw materials. Composting involves collecting organic waste, such as food scraps and yard trimmings. The organic wasteis stored under conditions designed to help it break down naturally (Municipal Solid Waste, 2016). Compostable materials currently make up 20 to 30 percent of what we throw away but not all of this is actually composted (Composting At Home, 2016). Recycling and composting prevented the release of approximately 186 million metric tons of carbon dioxide equivalent into the air in 2013 (Municipal Solid Waste, 2016).

Figure 1: Total municipal solid waste by material type in 2013 totaling 254 million tons,according to the EPA(Municipal Solid Waste, 2016).

There are several benefits of composting.First, compost contains several macro and micronutrients for plant growth (Composting At Home, 2016).Second, itsupplies and encourages the production of beneficial microorganisms. Third, compost improves the soil structure, porosity, and density and creates a better plant root environment. Fourth, it reduces erosion and runoff.Fifth, compost reduces water loss and leaching in sandy soils by improving water holding capacity (USCC Factsheet: Compost and Its Benefits, 2008).Additionally, it reduces or eliminates the need for fertilizers(Composting At Home, 2016).Also, composting reduces methane emissions from landfills (Adhikari, 2010). Methane is a greenhouse gas and has an estimated Global Warming Potential (GWP) of 28–36 times greater than carbon dioxide over 100 years (Understanding Global Warming Potentials, 2017), (Levis, 2011). Next, it improves the soil’s ability to hold nutrients for plant use (USCC Factsheet: Compost and Its Benefits, 2008), (Singh, 2011).Finally, all of these benefits add togetherpromote a higher crop yield.

Five main areasneed to be controlled in a compost pile. First, the nutrient balance must be kept constant. Composting requires green and brown materials. Green materials like grass clippings or food scraps provide carbon to the compost. Brown material like dry leaves, woodchips, or branches provide the nitrogen to the compost. Maintaining a proper ratio of carbon to nitrogen is very important in producing high-quality compost (Kumar, 2010). Particle size is the second area that needs to be controlled. Smaller pieces of materials have more surface area that the microorganisms can live on. Also, the smaller pieces allow for a more homogeneous mixture. However, the pieces shouldn’t be too small that they prevent air from moving through the pile. Third, moisture content must be regulated because water allows for movement of key nutrients used by the microorganisms. Fourth, oxygen flow should be maintained by manually turning the pile, placing the pile on perforated pipes, or including bulking agent such as woodchips. Aerating the pile allows for faster decomposition. Finally, temperature must be monitored. Certain temperature ranges allow for rapid composting and destruction of pathogens (Types of Composting and Understanding the Process, 2016).

There are two ways of composting that have been suggested by Greg during our initial meeting (Lawless, G., & Tashjian, M., 2017). First, windrow composting is used for large volumes of diverse compostable wastelike those generated by communities.This type of composting piles the waste into rows of long piles, called windrows, and aerating them manually or mechanically by turning the piles. A typical pile is 4-8 feet high and 15 feet wide. This type of composting requires large amounts of land, equipment, and labor. It’s possible to use this type in changing climates but requires a lot of labor.Windrow composting produces leachate, a liquid released during composting that can contaminate water sources. It must be collected and treated. Odor is created by windrow composting but can be controlled, but might attract pests(Types of Composting and Understanding the Process, 2016).

Second, in-vessel composting can process large, diverse amounts of waste. This method involves feeding organic waste into a drum or silo and can vary in size. This allows good control of the environmental conditions such as moisture, airflow, and temperature. The material is mechanically turned to allow aeration. This method produces compost in a few weeks, but takes a few more months until it is ready to use.The moisture, airflow, and temperature can be controlled electronically. It can be used in varying climates.Very little odor or leachate is produced.This method is expensive and may require technical expertise to operate it properly, but it uses much less land and manual labor than windrow composting(Types of Composting and Understanding the Process, 2016).

Our customer needs a composting system that can transform variable quantities of food waste and carbon materials into high quality compost with minimal labor required. It should make no odor or noise, attract no pests, and create no runoff or emissions.We chose in-vessel composting as our suggested solution because it matches all the needs of the customer.

Ohio University has an in-vessel composter which is very similar to what we are designing(Lawless, G., 2017). Originally, Ohio University had a 2-ton in-vessel composter but upgraded to a 4-ton expandable in-vessel system in 2012, as depicted in Figure 2. The university uses solar panels to collect the energy used by the composter. They collect rainwater and use a solar thermal water heating system to heat it. The water is used by workers to clean the collection bins. The in-vessel system composts 100% of the university’s pre- and post-consumer dining waste collected six times per week. The system controls airflow, moisture levels, and temperatures with probes, fans, and an air circulation system. The material moves through a set of spinners that homogenize, agitate and stack it into the next zone. The composting material is moved through the composter in a plug flow fashion for a designated number of retention days. Leachate is controlled throughout the process and is either pumped back onto the material or released to the on-site septic system. Finally, the compost is cured for at least 90 days in windrows (Ohio University, n.d.). The Ohio University’s in-vessel composter is very similar to what we are designing and it has been a huge success.

Figure 2: A schematic of Ohio University’s in-vessel composter(Ohio University, n.d.).

Project Goal

We aim to design an economically viable, aerobic composting system that will accommodate 100 Milwaukee homes with the potential to be scalable, and will produce a high-quality compost at a proper carbon to nitrogen ratio while minimizing odor and pests, and creating no runoff or noise.

Design Specifications

The design specifications with (NR 502…) are found in the Wisconsin State Legislature, Department of Natural Resources’ Administrative Code: Chapter NR 502(United States, Wisconsin State Legislature, 2015).

  1. Meet the needs of 100 families currently, but should be scalable.
  2. Should have an minimum initial Carbon to Nitrogen ratio of 20:1 to create high-quality, low odor compost. (NR 502.12(10)(e))
  3. Must be an aerobic system.
  4. Must be an in-vessel compost system (United States, City of Milwaukee, n.d.).
  5. Each bin shall be no taller than 5 feet and the total volume of all bins on a property shall not exceed 125 cubic feet(United States, City of Milwaukee, n.d.).
  6. Must minimize odor produced in the compost bin(s).(NR 502.12(10)) (Beaulieu, 2002)
  7. Must not attract pests or insects(United States, City of Milwaukee, n.d.).
  8. Must create no runoff from the compost system. If run-off/leachate is produced, use it as a moisture addition or collect in basin.(NR 502.12(12)(a))
  9. Must make no noise. (NR 502.07(4)(u))
  10. Should require minimal labor.
  11. Compostable material coming in should not contain any physical contaminants and if it does, they must be separated before introduction to bin(s).(NR 502.12(10))
  12. Compostable material should be grinded or cut down to a small enough size to provide adequate surface area for effective composting. (NR 502.12(10))
  13. pH of compost system must be between 6 and 8 (Sundberg, 2013). (NR 502.12(13)(h))
  14. Moisture content should be around 30-50% by weight and wetted as needed, but should aim for low moisture content to decrease hauling costs.(NR 502.12(10)(g))
  15. Must cost about 5000$ per system that meets the needs of 100 families.
  16. Should be insulated to achieve high temperatures inside compost bin(s) and maintain an optimal temperature of 50-65 degrees Celsius. (NR 502.12(13)(h))
  17. Compost bin(s) should have an electronic monitoring system for temperature, moisture content, and/or aeration.
  18. Ideally, should not use any power from the grid.
  19. Bin(s) should use occasional mixing or perforated pipes to ensure adequate oxygen is available at all times (Standard Test Method for Determining, n.d.).(NR 502.12(10)(d))
  20. End produce shall be free of toxin and pathogens in amounts of concentrations that could cause detrimental impacts to public health or the environment. (NR 502.12(10)(h)3)
  21. For in-vessel or static aerated pile composting, the pile must be maintain at a continuous minimum temperature of 55°C, or 131°F, for a minimum of 3 consecutive days.(NR 502.12(10)(h)3)
  22. Finished product should be tested to see if it complies with chemical contaminant limits as set by the EPA.

Project Output

When our solution is finished in BSE 509, we plan to have a design on paper and SolidWorks that could be made into a working, small-scale prototype. However, we do not plan on making the prototype.

Annotated References

Books

Journal Articles

Kumar, M., Ou, Y., & Lin, J. (2010). Co-composting of green waste and food waste at low C/N ratio.Waste Management,30(4), 602-609. doi:10.1016/j.wasman.2009.11.023

-Carbon to nitrogen ratio is a very important part of the composting process and affects the properties of the end compost product. Studies have shown that composting can operate at low C/N ratios of ~15 which will reduce the carbon requirement (bulking agent). This paper looks at C/N ratios that you can compost at.

Sundberg, C., Yu, D., Franke-Whittle, I., Kauppi, S., Smårs, S., Insam, H., . . . Jönsson, H. (2013). Effects of pH and microbial composition on odour in food waste composting.Waste Management,33(1), 204-211. doi:10.1016/j.wasman.2012.09.017

-This article found that odor was much stronger when compost was acidic than when it was neutral or alkaline. One way to reduce odor is to quickly change the low pH to a more neutral one by using high aeration that allows for cooling. Also, additives like recycled compost could help.

Singh, R. P., Singh, P., Araujo, A. S., Ibrahim, M. H., & Sulaiman, O. (2011). Management of urban solid waste: Vermicomposting a sustainable option.Resources, Conservation and Recycling,55(7), 719-729. doi:10.1016/j.resconrec.2011.02.005

-This article looks at several options for disposing of municipal solid waste including landfilling, waste to energy, composting, and vermicomposting. They discuss the pros and cons of each and concluded that vermicomposting was the best option becausetheend product is pathogen free, odorless and rich in plant nutrients.

Adhikari, B. K., Tremier, A., Martinez, J., & Barrington, S. (2010). Home and community composting for on-site treatment of urban organic waste: perspective for Europe and Canada.Waste Management & Research,28(11), 1039-1053. doi:10.1177/0734242x10373801

-This article looks at the state of landfilling and makes recommendations about how the EU and Canada should decrease the amount of waste going to the landfill including implementing waste management legislation with emphasis on reduction, reuse, and recycling. They want the EU and Canada to encourage composting more because it diverts waste from landfills, reduces GHG emissions, creates high-quality soil, etc.

Levis, J. W., & Barlaz, M. A. (2011). What Is the Most Environmentally Beneficial Way to Treat Commercial Food Waste?Environmental Science & Technology,45(17), 7438-7444. doi:10.1021/es103556m

-This article discusses aerobic composting system of different complexity, anaerobic digestion, and landfills with and without gas collection and energy recovery and analyzed global warming potential, NOx and SO2 emissions, and total net energy use. All composting option gave lower GHG emissions than landfilling.

Government laws, Codes and Regulations

United States, Wisconsin State Legislature, Department of Natural Resources. (2015, July).SOLID WASTE STORAGE, TRANSPORTATION, TRANSFER, INCINERATION, AIR CURTAIN DESTRUCTORS, PROCESSING, WOOD BURNING, COMPOSTING AND MUNICIPAL SOLID WASTE COMBUSTORS. Retrieved March 12, 2017, from

-When establishing, constructing, operating, maintaining or permitting a composting facility, you must follow the rules listed in the Wisconsin State Legislature, Chapter NR 502. This is a good document when writing the design specifications.

Standards

Standard Test Method for Determining the Stability of Compost by Measuring Oxygen Consumption. (n.d.). Retrieved March 10, 2017, from 17088%3a2012&source=blog

-This standard measures the oxygen consumption after exposure of the compost to a well stabilized compost under controlled conditions on a laboratory scale while using active aerations. This method can be performed on different types of compostable materials like food wastes, municipal solids wastes, yard wastes, etc.

United States, City of Milwaukee. (n.d.).CHAPTER 79 SOLID WASTE REGULATIONS(pp. 221-228p). Milwaukee, WI.

-This standard is from the City of Milwaukee and has regulations on compost piles in the city.

Patents

Beaulieu, G. (2002). Odor-free composting method and installation: Google Patents.

-This composting method is done in a building held at negative pressure because the pressure will drive the odor to a biofilter where the odor is removed. This method is good for urban/community areas because it does not decrease the air quality. Also, this method is done with a small number of employees to keep the cost down.

Miscellaneous Technical Reports and Publications

Miscellaneous Publications - Websites

Municipal Solid Waste. (2016, March 29). Retrieved March 12, 2017, from

-This website discusses the data of municipal solid waste from 2013 and breaks it down by material type, recyclable and compostable, and also contains many helpful graph that can be used in the proposal.

Composting At Home. (2016, August 24). Retrieved March 13, 2017, from

-This website contains the basics of composting and some benefits of composting that I used in my proposal.

Understanding Global Warming Potentials. (2017, February 14). Retrieved March 13, 2017, from

-This website discusses global warming potential. I was especially interested in carbon dioxide and methane since these numbers and information can be used in the proposal.

USCC Factsheet: Compost and Its Benefits. (2008). Retrieved March 12, 2017, from

-This website article provided numerous benefits of composting that were used in the statement of need section. It talk about physical, chemical, and biological benefits.

Types of Composting and Understanding the Process. (2016, August 29). Retrieved March 13, 2017, from

-This website included a lot of useful information about the five main areas that need to be controlled when composting and different kinds of composting methods. Both were used in the statement of need.

Ohio University. (n.d.). Retrieved March 14, 2017, from

-This website provided a good example of an in-vessel composting system that runs off renewable energy and is very similar to what we are designing.

Personal Conversations

Lawless, G., & Tashjian, M. (2017, February 6). Initial Meeting via Webcam [Online interview].

-This initial meeting via webcam introduced us to Greg and Melissa and provided us information of the current state of Melissa’s composting business. Also, they made recommendation about what type of composting systems we should be researching.

Lawless, G. (2017, March 7). Interview in Class [Personal interview].

-This interview helped us get answers to lingering questions and clarify the project further. Greg gave us a few examples to research that are similar to what we are designing.

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