ASTM International

Standard Test Method for Determining the Aerobic Degradation and Anaerobic Biodegradation of Plastic Materials under Accelerated Bioreactor Landfill Conditions
 N D7475

Annotation

This modification of Test Method D5526, which only considered anaerobic degradation, 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 bioreactor landfill test environment. It simulates the change from aerobic to anaerobic environments over time as landfill depth increases. Plastic materials found in landfills include discarded plastic products such as bags and wrappers and also deliberately applied plastic covers as inter-layer sealers between daily refuse fills to prevent windblown scatter of garbage overnight or at other down times. This modification is a two-tiered test method in which the two tiers, which address aerobic degradation and anaerobic biodegradation, are most preferably run sequentially to more closely resemble the real world condition of a biologically active landfill, or a bioreactor landfill, but are functional independently and separately depending on the plastic under evaluation and the information sought: either aerobic degradation or anaerobic biodegradation or both. The tiered system approach is shown schematically in Fig. 1. 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 for a time period of four weeks. 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. If it is desired to only assess anaerobic biodegradation of a plastic material, Tier 2 is run using preconditioned household waste, as described in Tier 1 but without the added plastic. The mixtures obtained from Tier 1 and Tier 2 in this test method are sampled and used to assess the environmental and health risks of plastic materials that are degraded in a landfill under aerobic and anaerobic conditions