ASTM D 7475 : 2020

1.1This test method is used to determine the degree and rate of aerobic degradation (as indicated by loss of tensile strength, molecular weight, possibly resulting in disintegration and fragmentation) and anaerobic biodegradation of plastic materials in an accelerated aerobic-anaerobic bioreactor landfill test environment. It can simulate the change from aerobic to anaerobic environments over time as landfill depth increases. In Tier 1, the test plastic material is mixed with household waste, then pretreated and stabilized aerobically in the presence of air, in a sealed vessel in a temperature range that is consistent with the average temperature range of those recorded for landfills. The tier is an accelerated simulation of degradation with concomitant oxygen consumption and depletion with time as if oxidative degradation proceeds. In Tier 2 samples of the plastic materials pretreated aerobically as described in Tier 1, are exposed to a methanogenic inoculum derived from anaerobic digesters operating only on pretreated household waste. The anaerobic decomposition and biodegradation occur under dry (more than 30 % total solids) and static non-mixed conditions.

1.2This test method generates comparative data for several materials and must not be used to make claims regarding benefits of placing degradable or biodegradable plastics in landfills. Claims must be limited to and dependent on the results obtained from each tier.

1.3Tier 1 of this test method is designed to estimate the aerobic degradation of plastics, that is disintegration and fragmentation, only, by measuring the loss of physical and chemical properties of said plastics. The test environment is then changed to that of Tier 2, an anaerobic condition, and biodegradation is measured by a combination of evolved carbon dioxide and methane gases as a percentage of the conversion of carbon in the plastic sample to carbon in the gaseous form under conditions that resemble landfill conditions. This test method does not simulate all conditions found in landfills, especially those found in biologically inactive landfills. This test method more closely resembles those types of bioreactor landfills in which the gas generated is recovered or even actively promoted, or both, for example, by inoculation (co-deposition of anaerobic sewage sludge and anaerobic leachate recirculation), moisture control in the landfill (leachate recirculation), and temperature control (short-term injection of oxygen and heating of re-circulated leachate) (1-7).2

1.4This test method produces partially degraded mixtures of municipal solid waste and plastics that, where required, are used to assess the ecotoxicological risks associated with the degradation of plastics after various stages of aerobic degradation and anaerobic biodegradation in a landfill.

1.5The intended use of this method is for a comparison and ranking of aerobic degradation and anaerobic biodegradation of plastics after disposal in a bioreactor landfill. It is not designed or intended to be used to support claims recommending the value of plastic degradation in full-scale landfills. This simulation of an active landfill allows measurement of the percentage of aerobic degradation and anaerobic biodegradation (biogas evolution) in specified time periods, only.

1.6Though the test method is in two tiers, they are meant to simulate a real world cycle of degradation in a landfill and are most preferably run consecutively and not independently or separately.

1.7It is cautioned that the results of any laboratory landfill simulation cannot be directly extrapolated to actual disposal environments: confirmation to real world exposure is ultimately required as with all ASTM Standards. This confirmation is essential for landfill as the types of landfills vary widely, some are even heavily lined, tombs, and these will limit degradation severely.

1.8The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.9This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.10This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.