Composting & Anaerobic Digestion Facilities

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Introduction

When considering recovery solutions for foodservice packaging, composting and anaerobic digestion (AD) facilities may offer a suitable processing option for some foodservice packaging (FSP) items.

Hundreds of communities now have residential access to food scrap composting in the U.S., and of the larger cities on this list (>50k population), twenty-two are within 40 miles of at least one composter that accepts food service packaging. The opportunity for growth in residential settings is immense, but the number of collection programs for commercial venues is sizeable as well. Over 300 large (>50k population) communities that do not currently have residential programs are located within 40 miles of a composter that accept food service packaging.

As with recycling, there are many variables that determine successful recovery of FSP in these environments, both in terms of the actual foodservice packaging type as well as a specific facility's operating parameters. Factors that will determine compatibility include specific technology, processes used, which feedstocks are accepted, and the ultimate end product being produced. For example, materials may compost differently in windrows than in covered aerated static pile (CASP) systems, and performance will vary with temperature and moisture conditions, cycle time and accompanying composting materials. Many materials that would be considered contaminants in low-solids digesters are frequently accepted in dry, batch-fed anaerobic digesters. These considerations all help determine whether FSP is a good candidate for this form of recovery.

In terms of which kinds of FSP may be viable feedstocks for composting or AD facilities, there are a variety of different types of paper and plastic foodservice packaging which are compatible with these end-of-life solutions. For paper products, these typically include bags, cups, boxes, containers, napkins, etc. that have either no coating at all, a clay coating or a compostable polymer coating (such as PLA). In the same arena, molded fiber and bagasse packaging may be an option. On the plastics side, bags, cups, containers, cutlery, etc. can be made from compostable materials and are excellent candidates for those composting facilities throughout North America that operate under suitable conditions. Keep in mind, however, that it’s not just the core material type, but also chemical factors (like inks and adhesives), and physical factors including the thickness of the material that can impact acceptance at composting and AD facilities.

The quantity of foodservice packaging available for recovery in a composting or AD facility is difficult to determine, since use of these materials vary widely across large and small foodservice operations and acceptance by composters and AD facilities also varies.

What is not so tricky is recognizing the mounting interest in diverting food scraps away from landfills and sending them instead to composting or AD facilities. Increasingly, communities and organizations (including foodservice operations) are implementing organics collection programs in an effort to achieve zero waste and meet sustainability goals. At the same time – and for similar reasons – use of compostable foodservice packaging is growing. For composters and AD facility operators interested in potentially adding these materials, this raises questions.

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FAQ for Compost Facilities

  • Compostable foodservice packaging can contribute valuable carbon nutrients to a composter’s “recipe” and bring with it additional nitrogen-rich food scraps. Compostables can also help reduce contamination from non-compostable packaging which may otherwise come along with the food scraps.

  • Special permits are not required to accept compostable foodservice packaging, but composters may need additional permitting in order to process food scraps. Composting regulations  vary in terms of specific requirements and complexity. For more information about permitting, please check out  US Composting Council’s map of state compost regulations.

  • The Foodservice Packaging Institute surveyed food waste composters across North America and Canada in 2017 and found that there is not a clearly defined set of operating parameters that is required for success with foodservice items. Research found that composters of many different scales, geographic regions, climates, and technologies are successfully processing cups, containers, boxes, and paper bags. These composters generally accept both pre-consumer and post-consumer food scraps, and the amount of compostable packaging is very small, in fact less than 2% of total incoming material. Greater than half of facilities which accept foodservice packaging operate windrows, while roughly a quarter use aerated static piles; other technologies include in-vessel or mass bed.

    At the same time, several factors will contribute to successful composting of these items. Generally speaking, a starting carbon-to-nitrogen recipe of 30:1, size reduction, longer residence times (the ASTM specification is 84 days for disintegration), thermophilic (50°-55°C or 122°-131°F) temperatures and maintenance of optimal operating conditions (such as sufficient aeration, moisture, pile porosity) increase the ability of a facility to process compostable packaging.

    Another consideration is the ultimate end product being manufactured by the composter. If a composter sells a “certified organic” product in the U.S., compostable plastics are not currently an allowable feedstock (this would also apply to paper FSP that has a compostable polymer coating), based on the current USDA National Organic Program guidelines. .

  • There are numerous ways to identify which foodservice packaging products are suitable for composting:

    • Check with the FSP manufacturer to determine whether the item has been tested to meet appropriate standards, such as ASTM D6400 (for compostable plastics) or ASTM D6868 (for compostable polymer coated-items like paper) in the U.S., or CAN/BNQ 0017-088 (for compostable plastics) in Canada.

    • Research whether the item has been certified by the Biodegradable Products Institute as meeting the above standards. If so, the item can display the BPI certification logo to show that it has been independently tested and verified. A searchable database of BPI-certified products may be found here.

    • Look to see whether the product is accepted by other composters. Many composters turn to Cedar Grove's list of accepted items.

    • Last, many composters prefer to test products directly within their own facility to ensure they are a good fit. Most likely, if the FSP meets applicable standards, is BPI certified and/or is accepted by other composters, it will compost successfully in your facility. But because the operational aspects of facilities do vary so widely, field testing should be done to confirm. One best practice for pre-processing involves shredding materials to decrease particle size and increase surface area. This is particularly helpful for thicker or denser materials, both fiber-based and compostable plastic and will contribute to faster decomposition.

  • That depends. Most compostable foodservice packaging is designed for commercial scale/industrial compost facilities because higher temperatures (~130°F) need to be reached for a certain amount of time to kill pathogens and ensure a safe finished product (compost). Achieving and maintaining the necessary temperatures can be difficult in backyard and some community-scale operations. Having said that, some FSP may successfully compost in these smaller facilities. It may be necessary to process for a longer period or shred the materials into smaller pieces to help the decomposition process along.

  • ​Once you determine which foodservice packaging will successfully compost in your facilities, it’s important to work with various stakeholders to make sure you get the materials you want – and limit the materials you do not want. After all, contamination is one of the biggest challenges for composters accepting these items.

    • If you plan to accept food scraps and compostable foodservice packaging from residential collection programs, work with the municipality or county’s program coordinator to review the list of acceptable materials. If possible, provide input into the educational materials for and outreach to residents. It is advisable to launch resident education and collection of these new materials on a pilot basis (e.g. certain routes or neighborhoods) to manage the change in the stream. During the pilot phase, communicate your observations back to the program coordinator and identify any areas that need to be improved before a broad roll-out.

    • If you plan to accept food scraps and compostable foodservice packaging from commercial collection programs (i.e. restaurants and other foodservice establishments), work with these operators and/or their haulers to review the list of acceptable materials. Enquire whether the foodservice operator will use only compostable packaging (which will help reduce contamination), or a combination of recyclable and compostable packaging. Beyond managing the packaging assortment at the outset, check whether they will be taking the appropriate steps to further minimize contamination by educating both staff and customers to put only compostable items in the compost bins. You may want to discuss ramifications (if any) of loads contaminated with non-compostable materials. You may even offer them a tour of your facility, so they understand the process and value the end-product – compost.

FAQ for Anaerobic Digestion Facilities

  • Both paper and bioplastic foodservice packaging, and the food scraps associated with it, contain valuable carbon which is needed to produce biogas. In addition, the digestate resulting from the AD process can be used as feedstock for a composting facility.

  • Each digester and each waste stream is unique, yet three basic AD technologies are predominant in the market: Wet (low-solids) AD, dry (high solids) plug-flow AD, and dry (high solids) batch fermentation AD. Typically, in wet systems, a pre-treatment step sorts out packaging materials, and it may be possible for screened compostable packaging to be sent directly to composting. Dry plug flow systems also require that feedstocks undergo pre-treatment such as shredding/pulping, and packaging materials can enter the digester without significant impact to digester operation.  Lastly, dry fermentation digesters are best suited to handle larger items like packaging and don’t generally require pretreatment. Any undigested fractions of compostable materials can be sent to composting along with the digestate solid fraction.

    Other factors that may influence the performance of foodservice packaging in a digester include residence time, temperature and digester size. Many digesters run for roughly 28 days, and additional retention time and/or a composting phase may be needed to completely break down compostable packaging. Thermophilic digesters, which run at higher temperatures (above 50°-55°C, or 122°-131°F) may be able to biodegrade compostable packaging more readily than mesophilic digesters, which operate at lower temperatures (typically 30°C, or 86°F). However, this may not always be the case. Today, some mesophilic digesters are processing FSP without issue.

    Small AD facilities are frequently built for very specific feedstock recipes and cannot handle much variability that may drastically disturb the microbial balance of the digester. These small systems would most likely not be good candidates for significant quantities of foodservice packaging. Large scale systems often co-digest food scraps with animal waste and sewage sludge, and these may be a better option for FSP. Again, because of different variables, this may not always be the case, and therefore small AD facilities shouldn’t be ruled out.

  • Paper items typically digest more readily under anaerobic conditions than bio-based plastics, however different bio-based plastic resins also behave differently. Other factors such as how the incoming feedstocks (including FSP) are pre-processed have an impact as well. If the digestate exiting a digester is ultimately going to be used as a compost product, further processing the digestate solid fraction at a composting facility is recommended. This will provide greater opportunity for the materials, both the compostable FSP and other organics, to fully biodegrade and be incorporated into the final product.

  • There are a couple of options to identify which foodservice packaging products are suitable for an AD facility:​

    • Most facilities require digestate solids be subsequently sent to anaerobic composting, so check with the foodservice packaging manufacturer to determine whether the item meets appropriate compostability standards or whether it’s been certified compostable by BPI. If the digestate is not being composted, check to see whether testing has been done according to ASTM D5511, the “Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic Digestion Conditions.” 

    • Test the product in your facility. Anaerobic conditions in an AD facility are quite different from aerobic conditions in a composting facility, so it should not be assumed that compostable items will process well in your AD facility.

  • Once you determine which foodservice packaging will process successfully in your facilities, it’s important to work with various stakeholders to make sure you get the materials you want – and limit the materials you do not want. 

    • If you plan to accept food scraps and compostable packaging from residential collection programs, work with the municipality or county’s program coordinator to review the list of acceptable materials. If possible, provide input into the educational materials for and outreach to residents. It is advisable to launch resident education and collection of these new materials on a pilot basis (e.g. certain routes or neighborhoods) in order to manage the change in the stream. During the pilot phase, communicate your observations back to the program coordinator and identify any areas that need to be improved before a broad roll-out.

    • If you plan to accept food scraps and compostable packaging from commercial collection programs (i.e. restaurants and other foodservice establishments), work with these operators and/or their haulers to review the list of acceptable materials. Check whether they will be taking the appropriate steps to minimize contamination by using clearly-labeled compostable items and educating both staff and customers to put only compostable items in the compost bins. You may want to educate them on the importance of receiving only compostable materials and discuss ramifications (if any) of loads contaminated with non-compostable materials.

  • Not necessarily. Some large AD operations may screen the incoming feedstock by pulping and separating into fractions according to the natural tendency of the pulped materials to float or become sediment when centrifuged. If appropriate, foodservice packaging may be removed at this stage and sent directly to the subsequent aerobic composting finishing stage.