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Issue 04/2019

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Highlights: Blowmoulding Composites Basics: Home Composting Cover Story: Cove PHA Bottles

Basics Compostable

Basics Compostable Plastics & Home Composting - Food for thought! By: Ramani Narayan University Distinguished Professor Michigan State University, USA Certified, verifiable compostable plastics is the “enabling technology” to efficiently and efficaciously divert food and other organic wastes from landfills & open dumps (mismanaged wastes in the emerging economy countries) to environmentally responsible end-of-life solutions like composting. Compostable defines boundary conditions under which complete biodegradation (microbial utilization) needs to be validated using ASTM/ISO International Standards. ASTM D6400 & D6868 is used for USA- BPI certifications. EN 13432, ISO 18606 are specifications for compostable packaging used in European certifications, and ISO 17088 is a specification standard for compostable plastics used in Asia. AS 4736 and 5810 is used in Australia. The fundamental requirements are the same in all these standards – 90%+ biodegradation as measured by the evolved carbon dioxide from microbial metabolism in 180 days or less; 90 % of the product passes through a 2 mm sieve after 12 weeks in active composting vessels, and show no eco or phyto toxicity as per the standards. The Composting Process Composting is a process in which microorganisms break down organic carbon substrates and produce carbon dioxide, water, heat, and a relatively stable organic product called humus. Composting proceeds through three phases: 1) the mesophilic, or moderate-temperature phase, which lasts for a couple of days, 2) the thermophilic, or hightemperature phase, which can last from a few days to several months, and finally, 3) a several-month cooling and maturation phase – see figure 1 for compost temperaturetime profile. Different communities of microorganisms predominate during the various composting phases. They utilize the substrates’ carbon as food/fuel for its life process. Mesophilic microorganisms biologically oxidize accessible carbon substrates to carbon dioxide (CO 2 ) inside the cell. This is a highly exothermic process and the heat generated causes the temperature of the compost to rise rapidly. As the temperature rises above 40°C, the mesophilic microorganisms become less competitive and are replaced by thermophiles. During the thermophilic phase, the higher temperatures accelerate the breakdown of proteins, fats, and complex carbohydrates like cellulose and hemicellulose, the major structural molecules in plants. Temperatures of 55°C and above destroy human or plant pathogens, ensuing a safer product. The U.S. EPA, and National Organics Standards Board (NOSB) mandate that compost must achieve a minimum temperature of at least 131ºF (55°C) and remain there for a minimum of 3 days for safety reasons. However, temperatures over 65°C kill many forms of microbes and limit the rate of decomposition, so aeration and mixing keep process temperatures below this temperature. As supply of the high-energy carbon compounds depletes, compost temperature gradually decreases and mesophilic microorganisms take over for the Figure 1. Compost pile temperature as a function of time in days 140 130 120 110 Temperature (°F) 100 90 80 70 60 50 40 Arrows indicate turning events 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Days 44 bioplastics MAGAZINE [04/19] Vol. 14

Basics final phase of “curing” or maturation of the organic matter. Figure 2 shows the growth of bacteria vs temperature regime. Therefore, whether composting is done at home, in a residential/community backyard, or in an industrial facility, the process must ensure a succession of microbial communities (mesophiles -- thermophiles -- mesophiles) and corresponding temperature regimes to operate. This ensures a safe and quality compost product and process. Most industrial composting systems operate within this regime and process parameters. Best practices for home or backyard composting teach operating the composting process similarly with the correct mix of feedstocks, humidity, aeration, and temperature. Home Composting There is currently no international standard specifying conditions for home composting of biodegradable plastics. However, there are several national standards, such as the Australian norm AS 5810 “Biodegradable plastics – biodegradable plastics suitable for home composting”. TÜV Austria developed the OK compost – home certification scheme, requiring at least 90 % degradation in 12 months at ambient temperature. The French standard NF T 51- 800 “Plastics — Specifications for plastics suitable for home composting” specifies the same requirements for certification. Italy has a national standard for composting at ambient temperature, UNI 11183:2006. These standards assess the biodegradability of the test plastics in a controlled laboratory protocol using the same or similar test matrix used in EN 13432 operating at ambient temperatures (20 30°C) for a one-year period. It is possible and very likely that homeowners do not follow the correct protocol and allow dissipation of heat resulting in much lower temperatures. They may choose not to use the proper mix of feedstocks (C/N ratio), aeration, moisture content, and the pile could have pockets of anaerobic activity. The process could operate for 2 months, 6 months or one year. Such uncontrolled, poorly managed operations are not representative of an acceptable “composting process”. The certification of home compostability using any of the above-mentioned standards does not guarantee complete biodegradability in each uncontrolled, poorly managed home composting operations. Therefore, it is imperative to clearly define and characterize home composting with respect to the compost matrix, time, temperature, moisture, and other operating parameters. ASTM committee D20.96 initiated a new work item on developing standards in the residential/ home composting space. The first one is “Standard practice for testing compostable plastics in residential or home composting. Given the wide variation of operating parameters possible, three residential/home composting best practices representing two extremes and one middle set of conditions will be included. The parameters will be identified based on learnings from meta-analysis of the literature papers and operating sites. Example for a (hopefully) properly managed home (backyard) compost as practised by your Editor: “This year” in compartment #1 organic waste such as kitchen residues, and yard-clippings are collected. The organic matter from the previous year is “maturing” in compartment #2. The mature compost (humus) from the year before that (from compartment #3) is being spread out in the garden. Then, with the beginning of a new garden-year, the collected organic matter in #1 and #2 will be turned upside down, #3 is now empty. The fresh organic waste will now be collected in #3. #1 from last year can “mature”, and the humus from #2 can now be spread out in the garden. And so on … The times for turning the heaps and changing compartments can vary. It could well be two or more times per year, depending e.g. on climate conditions (MT) Figure 2: Composting regime Composting regime thermophiles Growth rate of bacteria psychrophiles mesophiles hyperthermophiles -10 0 10 20 30 40 50 60 70 80 90 100 110 Temperature (°C) bioplastics MAGAZINE [04/19] Vol. 14 45

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