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ISO 15985 specifies a method for the evaluation of the ultimate anaerobic biodegradability of plastics under high-solids anaerobic-digestion conditions by measurement of biogas formation including carbon dioxide and methane. ISO 15985 is equivalent to ASTM D5511.
ISO 15985 is designed to simulate typical anaerobic digestion conditions for the organic fraction of mixed municipal solid waste. The test material is exposed in a laboratory test to a methanogenic inoculum derived from anaerobic digesters operating only on pretreated household waste.
The anaerobic decomposition takes place under high-solids (more than 20% total solids) and static non-mixed conditions for normally 15 days at 52 °C (thermophilic conditions). The test method is designed to yield the percentage of carbon in the test material and its rate of conversion to evolved carbon dioxide and methane (biogas).
▶ Materials that can be tested:
➢ Plastics and many other types of materials;
▶ Inoculum information:
➢ Derived from a properly operating anaerobic digester functioning with a pretreated household waste as a sole substrate; ➢ Over 20% of dry solids;
➢ Post-fermentation for 7 days to reduce the organic content in the inoculum;
➢ pH between 7.5 and 8.5;
➢ Volatile Fatty Acids —Below 1 g/kg wet weight;
➢ NH4 -N—Between 0.5 and 2 g/kg wet weight;
▶ Inoculum dosage: a minimum of 500 g of wet inoculum per vessel;
▶ Test substance dosage: 15-20 g of volatile solids per 1000 g of wet inoculum (at least 20% dry solids). Normally, a minimum of 20 g of total dry solids containing 8 g of TOC is required per vessel;
▶ Positive control substance: analytical-grade cellulose;
▶ Reactor size: minimum volume of 750 mL;
▶ Number of reactors: 3 for each test substance, plus 3 for blank control, and 3 for reference control;
▶ Test conditions: in the dark or in diffused light at 52 °C (thermophilic conditions);
▶ Measurement:
➢ Biogas volume using inverted graduated cylinders;
➢ Room temperature and atmospheric pressure;
▶ Test duration: normally 15 days, but the incubation can be extended until the plateau phase is reached;
▶ Test validity criteria:
➢ Over 70% of degradation for cellulose (reference) after 15 days;
➢ The deviation among the cellulose replicates is less than 20% of the mean.
Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 15985. Please check our Method Selection Guide to select the most appropriate method for your materials. You can also find the applicability for many other methods on Aropha Resource Center
.
| Test | Analytical method | Sample info required * | Poorly soluble | Volatile | Adsorbing |
|---|---|---|---|---|---|
| ISO 15985 | CO2 and CH4 evolution | Organic carbon content * | + | +/- | + |
*"Sample info required" is the information needed to calculate the biodegradation percentages. This must be available for a selected method.
*"Organic carbon content" is the ratio of the organic carbon weight to the weight of the sample. It can be calculated by the sample formula (e.g., acetic acid C2H4O2, carbon content is 12*2/(12*2+1*4+16*2)=40%). Try our Online C% Calculator. If the formula is unknown, we can send the sample out to a third party lab for you for analysis (normally $110 with a 10-day turnaround time).
To learn more about different types of biodegradation tests, their applicability, biodegradation mechanisms, and many other information such as case studies, publications, and blogs, please check our Aropha Resource Center
.