Bioplastics are rolling to market fast, with biobased resin makers touting their wares as compost-facility ready.
But is it a given that these alternatives to conventional plastics will break down well and quickly under composters’ operating conditions? Part 1 of this two-part series broaches this question and others.
In Part 2, Emily McGill, manager of Research and Communications for BSIbio Packaging Solutions and founding partner of the Compostable Field Testing Program, discusses limitations of lab testing on bioplastics and other “compostables.” She describes how a program to test these products in real-world facilities is working with composters; what they are learning; who they’ll be sharing the data with; and when.
Emily McGill, manager of Research and Communications for BSIbio Packaging Solutions and founding partner of the Compostable Field Testing Program, shares in this Q&A work being done to bridge the gap between lab certification for compostability and real-world facility experiences.
Waste360: What is the difference between “compostable” and “biodegradable”?
McGill: “Biodegradable” just means an item can “degrade” (break down) “biologically” (through the action of living microbes.) It does not infer a timeline, nor that it’s compostable. “Compostable” has more prescribed conditions for biodegradation. It is generally defined as: “Can biodegrade completely, creating no toxic residues, under appropriate composting conditions”, where the conditions consider factors such as temperature, moisture, and feedstock.
It’s important to know that there are internationally recognized third-party certifications to confirm an item is compostable, but that the term biodegradable doesn’t have third-party certifications attached to it. It’s not that it’s a bad term, it’s just inexact. Calling an item biodegradable doesn’t give enough information to determine an appropriate end-of-life destination.
Waste360: What do you think about the research into whether bioplastics will biodegrade in the timeframe required to be classified as compostable?
McGill: On the biodegradability side, one has to be cautious when reviewing research that purports to increase resin’s biodegradability, without considering composting as an end-of-life. The publicity around such innovations can be misleading, where the base resins being tested are conventional plastics. For example, there are seemingly biodegradable additives for polyethylene terephthalate (PET) that can cause PET to disintegrate due to microbial action. But tiny fragments of PET stay intact and can essentially become microplastics in the environment.
Waste360: What are limitations of ASTM testing to confirm if a material will biodegrade in the timeframe that composters expect?
McGill: The ASTM standards which relate to testing the biodegradability of standalone polymers (D6400) and polymers as coatings, additives with paper, or other substrates (D6868) have similar limitations. The limitations include:
- The timeframe for the lab tests is longer than the typical residence time in a modern industrial composting facility. Many larger-scale facilities only have 4 to 6 weeks active composting, and many will screen the material before it goes to curing, at which point any material not sufficiently broken down is taken out.
- The “feedstock” must be consistent across lab tests, so a relatively mature material with an ideal carbon to nitrogen ratio (C:N) is used. But in real-world facilities there is a range of C:N in a mixed feedstock, and real-world feedstock is immature at the beginning of the composting process.
- The temperature and moisture are kept more constant in a lab test than might be expected in a real-world facility.
- The products are size-reduced in lab-tests, again for consistency. Relatedly, the reactors used in lab-scale testing are sized for the lab bench. They can’t accurately simulate the microbial and macrobial dynamics of a large compost pile.
Waste360: What does ASTM testing tell you about biobased compostable plastics?
McGill: The current certifications based on ASTM standardized testing can reassure a compost operator that any certified compostable plastic has been proven it is capable, when exposed to the conditions required for composting, of being fully broken down by microbes and not leave toxic residues in the resulting soil amendment. This is critical assurance that a material is not just fragmenting or disintegrating, but actually undergoing an important biochemical transformation.
As for whether this confirms the material will break down in the timeframe operators expect, not necessarily.
The ASTM biodegradability standards evaluate disintegration at 84 days and biodegradation at 180 days. The 84-day timeframe is longer than some composters’ active composting residence times. Aside from the duration, facilities also might have different operating conditions than certain certified compostable items require to fully biodegrade.
Waste360: Tell us about the Compostable Field Testing Program (CFTP) and its goal
McGill: CFTP is an international, non-profit research platform that helps facilitate field testing with composters across North America. It is a collaborative joint venture between the Compost Research and Education Foundation (CREF) and BSIbio Packaging Solutions.
The program’s goal is to collect and publish field test data gathered from a range of facilities to help understand what composting conditions are appropriate for certified compostable foodware and packaging, and which compostable items are a good fit for what kinds of facilities, or not.
Participating facilities share their data with CFTP to be aggregated and anonymized for public release. The audience for the data includes composters, the compostable product manufacturing industry, the public, policymakers, consultants, and academics.
Waste360: How does the CFTP work with composters, and what materials do you help them test?
McGill: CFTP provides a standard test kit and customizable protocol for the mesh bag method, where feedstock is contained in a bag, to test compostable product disintegration in real-world facilities, and provides remote support during testing. We’re also collaborating to develop a bulk-loading method where products are not contained in a bag during testing.
The baseline kit includes sugarcane-based, paper-based, polylactide (PLA), and PLA-lined paper, among items. Facilities can choose to add more test products. They often choose to include compostable bioplastics, such as cold cups, straws, cutlery, hot cups and lids, deli containers, etc.
Waste360: What have you learned from field testing so far?
McGill: We’ve learned that field testing is an inexact science. The results from one test in one season at one facility are not enough information to make year-round acceptance decisions for other facilities. Repeated testing with different feedstocks and variations in operating conditions are important.
As far as results on product testing, anecdotally, what we’ve learned is that, in a compost facility operating within the recommended operating ranges within the Compost Handbook guidelines, PLA items that don’t need to withstand heat during use, like cold cups and deli containers, break down within the first few weeks. Even heat-stable PLA structures that are very thin, like hot cup lids, can break down in a similar timeframe, as long as there’s sufficient heat and moisture and other conditions for healthy composting.
Heat-stable PLA items like cutlery require higher heat and moisture and will not break down completely without those conditions.
Fiber-based materials -- think fiber plates, bowls, clamshells -- generally take the longest to break down. But most composters will choose to accept these materials because they readily take on the appearance of the other compost substrate.
Waste360: What motivated the launch of CFTP? And what will you look to do next?
McGill: Our origins date back to 2013/14 when there was significant mistrust of compostable plastics on the market, despite widely known third-party compostability certifications based on lab testing.
BSIbio wanted to understand why composters had widely varying acceptance of compostable foodware and created a survey. Seventy percent of the composters surveyed said that they would be open to testing product disintegration in their facilities, if they just had a method. And so, the concept for the field testing program was born.
BSIbio partnered with the University of British Columbia to launch field tests with facilities in BC. The CREF and BSIbio joined forces in 2016 to expand the program because of a shared understanding of the need to bridge the gap between lab certification for compostability and real-world facility experiences.
Establishing a public database of field test results is the first step for the CFTP, so that everyone -- the public, academia, composters, product manufacturers -- has access to the same real-world disintegration data.
Our initial public data release is slated for this winter, and we’ll be sharing this at the COMPOST2024 conference.
We’re also looking to build a wider umbrella of research so we can really focus on finding out exactly which operating parameters have the biggest impact on disintegration, through both lab-based and in-field assessments.
We’ll be engaging more community composters, and looking to expand into research topics like monitoring contamination in both feedstock and overs, and assessing the microbial impacts of compostable packaging.