The Problem

Annually 2.01 billion tonnes (World Bank) of municipal solid waste (MSW) is produced worldwide. Previous methods of disposal of contaminated MSW in the United States included shipment to other countries such as China. However, recent regulation has criminalized importation of MSW into China, making the issue much more present in the United States. A large portion of this waste is plastic products, which are non-biodegradable and could sit in landfills for hundreds of years. However, technology has allowed for a new way to give this waste a second life, waste to energy conversion. Plastics can be broken down to oil and gas products through pyrolysis. This not only serves as a clean energy source, but it can cut down on the greenhouse emissions created by plastics in landfills.

Current Methods

Researchers at Idaho National Laboratory are involved in a project aimed at creating techniques for converting nonrecyclable municipal solid waste (MSW) into biofuel. The end product is a liquid oil that can be produced through pyrolysis, or high temperature conversion. Some steps of the working process include sorting, size reducing, and washing MSW materials for preparation for conversion. Decontamination is important for this project because contaminants such dirt and particulates in plastic fractions are hypothesized to decrease yields. Contaminants can significantly decrease the efficiency of the process, as well as gum up and damage equipment. In order for this process to be feasible on a large scale, it must be economical, efficient, and replicable. The researchers have experimented with several different techniques for size reduction and several different washers, each with their own pros and cons. Researchers test the use of alkaline, acid, and dimethyl ether washes, all which target different contaminants, but none of which can eliminate all contaminants. These methods have led to fairly satisfactory biochemical yield rates thus far.

Efficient comminution, or the reduction of material down to small particles, can result in improved material recovery (Jekel & Tam, 2007). Generally, commonly used size reduction techniques include using granulators, swing hammer shredders, alligator shears, hammer mills, ring mills, shear shredders and impact crushers .Bulk waste is pulverized using forces that are produced by high pressure, high impact, cutting or abrasion to achieve comminution. These techniques combined with sieves, rotating drums or membranes separate the pulverized particles from contaminates and particles that require further size reduction(Gundupalli, Hait, & Thakur, 2017).

Currently, there is no single system to both reduce and clean the MSW. This is where our project comes in. Our task is to create an all-in-one type of device that can carry out the size reduction and decontamination of MSW in preparation for pyrolysis. Including a device like this could potentially cut down on manual work necessary for conversion and save on cost in the long run. The product must include optimal techniques for size reduction as well as a single decontamination method that allows for the most efficient yield.

Standards

To ensure the size reduction portion of the product meets the standardization of size reduction machinery, the standard test method for characterizing the performance of refuse size-reduction equipment will be followed. For safety and protection around the shredder, the standard provided by OSHA on the use of pulp, paper, and paperboard mills, will be used since it mentions safety precautions needed to use a shredder. The standard provided by ASABE on terminology and definitions associated with biomass production, conversion, and utilization can aid the design in using clear and concise wording that aligns with the industry standards. In addition, to ensure that the water exiting from the cleaning procedure is environmentally sound we will be following the “Policy Handbook Establishing A Standard Method Of Testing And Reporting Of Microplastics In Drinking Water”, developed by the California Water Boards. According to this standard we will be producing large microplastics, which we intend to treat with the proper care.

Problem Statement

Municipal solid waste (MSW) often derives from single-use products which flood landfills worldwide. After disposal, MSW decomposes and produces methane, a potent greenhouse gas. These products use nonrenewable resources and their potential value is depleted when discarded. To prolong the material’s life cycle and reduce emissions, size reduction combined with decontamination presents opportunities for alternative use. Currently, no single system efficiently integrates these operations.

References

American Society of Agricultural and Biological Engineers. (1970, January 1). Terminology and definitions for biomass production, harvesting and collection, storage, processing, conversion and utilization. ASABE Technical Information Library. Retrieved October 21, 2022, from https://elibrary.asabe.org/abstract.asp? aid=36432&redir=%5Bconfid&redirType=standards.asp&dabs=Y

California State Water Quality Control Board. (n.d.). Drinking water programs - certificates and licenses. SWRCB.gov. Retrieved October 21, 2022, from https://www.waterboards.ca.gov/drinking_water/certlic/

Department of Labor United States department of Labor. 1910.261 - Pulp, paper, and paperboard mills. | Occupational Safety and Health Administration. (n.d.). Retrieved October 21, 2022, from https://www.osha.gov/laws- regs/regulations/standardnumber/1910/1910.261

Gundupalli, S. P., Hait, S., & Thakur, A. (2017). A review on automated sorting of source-separated municipal solid waste for recycling. Waste Management, 60, 56–74. https://doi.org/10.1016/j.wasman.2016.09.015

Jekel, L. J., & Tam, E. K. (2007). Plastics Waste Processing: Comminution Size Distribution and Prediction. Journal of Environmental Engineering, 133(2), 245–254. https://doi.org/10.1061/(asce)0733-9372(2007)133:2(245)

Standard Test Method for Characterizing the Performance of Refuse Size-Reduction Equipment. ASTM compass. (n.d.). Retrieved October 21, 2022, from https://compass.astm.org/document/?contentCode=ASTM%7CE0959-83R18%7Cen-US

World Bank. (n.d.). What a waste 2.0. Trends in Solid Waste Management. Retrieved October 19, 2022, from https://datatopics.worldbank.org/what-a-waste/trends_in_solid_waste_management.html