Characteristics of depackaged food waste: Challenges and opportunities in circular economies

Poster 173 – Click on poster below to view presentation from author.

Click on poster to view presentation from author.

Katherine Porterfield

University of Vermont

Co-Authors: Matthew Scarborough, Eric Roy

Food waste diversion programs are becoming increasingly common at state and local levels as a means to reduce landfill methane emissions and recover organic resources. Anaerobic digestion can be used to convert food waste to valuable coproducts (i.e. biogas and digestate fertilizers), however many pre- and post-consumer food waste streams are mixed with plastics and other packaging materials that would disrupt the digestion process. Mechanical depackaging systems separate food waste into an organic and non-organic stream, creating opportunities to divert additional organic waste streams to anaerobic digestion. However, there are potential challenges associated with microplastics formation that remain largely unquantified. We evaluated biochemical methane potential (BMP) and other key anaerobic digestion parameters (TS, TVS, COD, N, P, S, pH) as well as microplastics (>500 um) content for organic slurry produced at a full-scale depackaging installation located in Williston, VT. In order to capture the variability in waste stream composition, we collected organic slurry samples on five separate days from a relatively homogenous pre-consumer waste stream (off-spec Ben & Jerry’s pints) as well as a more heterogeneous post-consumer waste stream (commercial food scraps). Collectively, these metrics will indicate the suitability of the two waste streams for anaerobic digestion, and help determine if additional processing steps are needed to reduce microplastics contamination levels.

Post comments and questions for author below.

All posts are publicly visible after review by site administrator. Students’ responses to posted questions is factored into scoring for the poster competition. Finalists announced May 25 and awards presented May 26, 2021.

2 thoughts on “Characteristics of depackaged food waste: Challenges and opportunities in circular economies

  1. Hello Kate – Thank you for presenting this poster. We have a food waste digestion system at UC Davis as well with capacity of 50 ton/d and we are working towards ammonium recovery for the digestate; we also see many microplastic particles in the digester. I have a few questions on your depackaging research:
    How does the type of depackaging technology/system impact the occurrence of microplastics?
    How do microplastics in digestate impact digestate management options?
    What level of microplastics is acceptable for land application or other digestate management option?
    What type of plastics compose the microplastic that you are finding? Is there potential for source control?
    What type of technologies are needed to remove microplastics to a suitable level?
    Is there any concern about plastic particles smaller than 500 micron?
    Thanks in advance for your response.

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    1. Hi Dr. Leverenz,

      Those are all great questions, and I think that each could be the subject of an entire investigation. I’ll take a shot at addressing each.

      Q: How does the type of depackaging technology/system impact the occurrence of microplastics?

      A: We are only looking at one type of depackaging technology in this study, the THOR turbor separator.

      Q: How do microplastics in digestate impact digestate management options?

      A: I think this will depend in a large degree on how state and local governments decide to regulate micropalstics in organic fertilizers. I know it’s an ongoing conversation here in the state of Vermont. We’re hoping to generate some data with this project that could help to inform those decisions. I think many people are concerned about adding a lot of microplastics to the soils, but I’m not sure how much consensus there is yet on what the actual impacts of microplastics are on human and soil health.

      Q: What level of microplastics is acceptable for land application or other digestate management option?

      A: We’re currently focusing on trying to quantify the extent of microplastics presence in depackaged food waste. When paired with a better understanding of the human and environmental health effects of microplastics, perhaps we could ultimately arrive at some sort of “acceptable level” of microplastics contamination in organic fertilizers.

      Q: What type of plastics compose the microplastic that you are finding? Is there potential for source control?

      A: A next step of our study will be to use FTIR spectroscopy to identify the types of plastics present in our depackaged food waste samples. We are certainly interested in determining if there are specific types of plastic that are particularly problematic, which might suggest that waste streams using those types of packaging are less suitable for mechanical depackaging.

      Q: What type of technologies are needed to remove microplastics to a suitable level?

      A: Different sized screens and sieves have typically been used to remove plastics, but smaller particles can pass through these. I think a more efficient strategy would be to work further upstream to make food packaging more compatible with organics recovery in the first place.

      Q: Is there any concern about plastic particles smaller than 500 micron?

      Yes– 500 um is just the limit of our resolving power in this particular study.

      Thank you for your thoughtful questions. I would love to continue the conversation and hear about your experience with the UC Davis system. Please feel free to reach out during one of the live sessions.

      Thank you,

      Kate

      Like

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