Industrial Compost Biodegradation Testing

The biodegradation of the compostable materials was tested in a controlled experimental environment. The experimental setup for the laboratory experiment is based upon procedures outlined in ASTM D5338. The procedures to measure the gases were done with detectors as allowed in the ASTM standards. Each of the compostable materials was added to compost soil in a 5-liter glass-canning jar and placed in an oven maintained at 58°C. The room temperature was between 22 C and 2TC during the course of the experiment. The jar containers have a rubber seal on the top. 

The samples were prepared by adding 100 grams of plastic sample to 600 grams of mature soil compost in a 5-liter glass jar. The mature compost, 2-3 months old, had a pH of 8.7, ash content of 35%, and Carbon/Nitrogen (C/N) ratio of 10. The C/N ratio was calculated based upon carbon dioxide and ammonia measurements taken with the Sol vita instrument on the compost at the beginning of the test. Solvita is an easy-to-use test that measures both carbon dioxide (CO2) and ammonia (NH3) levels in the soil and also indicates a Maturity Index value. The index is useful for maturity level of the compost soil (Solvita Test Kit 2013). The blank compost had a Solvita overall maturity index of 7 

Sustainable Plastics Environmental Assessments of Biobased, Biodegradable, and Recycled Plastics, First Edition. Joseph P. Greene. 

Avicell microcellulose was used as a positive control material. Polyethylene plastic sheet, called Clingwrap, from Glad was used as a negative control as required in the ASTM standard. Polylactic acid (PLA) and polyhydroxyalkanoate (PHA) materials were cut into small pieces and then ground into powder. The materials are added to a 5-liter vessel, which was filled with 600 grams of compost and 100 grams of test sample. The sample materials occupied 1.5 liters of the vessel and left 3.5 liters of open volume for the gas to occupy. Our experiment met the ASTM D5338 specification that a maximum of 75% of the container can be filled with the test sample and compost. 

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Q.8.6 ASTMD5338 is the test method for industrial compost biodegradation and requires that 100 grams of plastic pieces be added to 600 grams... 

Nevertheless, field trials in natural environments are still used to extrapolate results acquired in laboratory tests to biodegradation behaviour under realistic outdoor conditions " Recent German regulations for the assessment of compostability of plastics even impose exposure of the product to a full scale industrial composting process to ensure that total disintegration will occur in real-life waste-processing". ... 

Solid waste disposal environments for plastic materials can include industrial compost, home compost, anaerobic digestion, landfill, litter, and ocean water. Only two disposal environments have both biodegradation standards for test methods and biodegradation performance standards, for example, industrial compost and marine biodegradation environments. Test method standards are available for anaerobic digestion, home compost, and landfill environments. The second necessary performance specification standard for biodegradation performance is not available for anaerobic digestion, home compost, or landfill... 

Summary This American specification standard establishes the performance requirements for biodegradation of compostable plastic materials that are designed to biodegrade into CO2, water, and biomass in an industrial compost environment. The industrial compost environment is one that maintains a temperature above 40° C and results in thermophilic conditions. The performance specification standard requires the use of ASTM D5338-05 test method to measure the amount of CO2 that is emitted from the degrading plastic sample. 

Biodegradation Greater than 90% of the carbon in the original plastic sample is converted into CO2 after 180 days of exposure to industrial composting conditions specified in ASTM D5338 test method standard. 

Biodegradation standards for industrial compost environment require a biodegradation specification standard and a biodegradation test method standard. The specification standards in Europe are for plastics and for packaging. Both specification standards require the use of the same test method. 

The second test procedure for EN 13432 standard specifies that a satisfactory rate of biodegradation of the plastic material is under industrial composting conditions of at least 58°C and 50% moisture for 26 weeks, that is, more than 90% of the carbon in the original plastic sample is converted into CO2 as measured by a CO2 respirometer or wet chemistry methods. The details of the test procedures are listed in EN 14046 or ISO 14855 test method. 

Q.8.10 Plastic pellets can be tested for biodegradation under industrial composting conditions. T or F ... 

The test materials used are all commercially available plastics that are made from corn, namely, polylactic acid (PLA) and polyhydroxyalka-noate (PHA). PLA and PHA materials have passed the ASTM D6400 compostability standard and biodegraded in a simulated industrial compost environment in 180 days. ASTM standards are applicable for plastic molded products and not plastic pellets. The samples for the ASTM D6691 test included the following ... 

An alternative is to use a biopolymer. In a similar film application for example, an option would be to use one that is starch-based and derived from corn (PCL, PVA or PLA). These biodegradable films, dependent on thickness, would meet the ASTM standard (American Standard for Testing Materials) and European [EN13432] for composting. However these materials require a controlled microbial environment such as an industrial compost facility before they will degrade. 

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