The ASTM D5511 Test Method is a test used to determine the rate of biodegradation of plastic products in an anaerobic biodigester environment.
The method calls for plastic samples to be placed in sealed fermentation vessels filled with a required amount of inoculum derived from a mix of composted solids and active waste water treatment plant sludge. For each sample the test is run in triplicate and compared to a positive control, a negative control, and an inoculum control. The fermentation vessels are connected to collection devices that measure waste gas produced by bacterial metabolic processes.
This collected gas is regularly sampled and placed in a gas chromatograph instrument for highly accurate composition analysis. The test method calls for Methane (CH4) and Carbon Dioxide (CO2) levels to be carefully measured and recorded, as these are carbonaceous gasses commonly produced as waste by-products during the process of biodegradation. At the end of the test the exact carbon-weight of the gasses collected is calculated and recorded.
Accurately measuring biodegradation is an extremely difficult task. Biodegradation is a complex system of microbial metabolic processes that involve many species of bacteria producing many by-products which are in turn utilized by other bacteria involved in the system. Other ASTM tests, including the D5338, a composting test, use the same process of recovering carbonaceous gas to determine percent biodegradation of test samples. The D-5511 test was designed by the the American Society of Testing and Measurements (ASTM) and is widely utilized around the globe to detect evidence of the biodegradation of plastic substances.