ISO 14855: Composting of Plastics - CO₂ Evolution

ISO 14855 Key Summary

The ISO 14855-2 uses respirometry to determine the biodegradability by measuring the CO₂ formation during the biodegradation process up to 6 months. As the plastic material decomposition process primarily result in the formation of CO₂ and H₂O, the measurement of generated CO₂ can well reflect the biodegradation of the test material. With the measured and the theoretical CO₂ amount, one can easily calculate the degradation percentages over a specified incubation time.

This method is designed to yield the optimum rate of biodegradation of a plastic material in mature compost by controlling the humidity, aeration ratio and temperature in the composting vessel. It also aims to determine the ultimate biodegradability of the test material by using a small-scale reactor. The degradation rate is periodically measured by determining the mass of the evolved CO₂ using an absorption column filled with soda lime and soda talc on an electronic balance. The test material is mixed with an inoculum derived from mature compost and with an inert material such as sea sand.

▶ Materials that can be tested:
     ➢ Natural and/or synthetic polymers, copolymers or mixtures of these;
     ➢ Plastic materials that contain additives such as plasticizers or colorants;
     ➢ Water-soluble polymers;
     ➢ Materials that, under the test conditions, do not inhibit the microorganisms present in the inoculum.
▶ Test substance requirement:
     ➢ Organic carbon content is required in order to calculate the ThCO₂;
     ➢ Preferably in powder form with maximum size of 250 um diameter;
▶ Measurement: CO₂ evolution;
▶ Temperature: 58 °C;
▶ Reference: a well-defined biodegradable polymer (e.g., thin-layer chromatography (TLC) grade microcrystalline cellulose with a particle size of less than 20 µm);
▶ Reactor size: preferred at 500 mL;
▶ Test substance dosage: normally a minimum of 10 g of total dry solids containing 4 g of TOC is required per 500 mL-vessel;
▶ Inoculum: well-aerated compost from a properly operating aerobic composting plant;
▶ Inoculum dosage: 60 g of total dry solids;
▶ Ammonia is absorbed by a bottle filled with 1 M sulfuric acid before CO₂ absorption;
▶ Stir the compost weekly to prevent extensive channelling and to ensure uniform attack by the microorganisms on the test material.
▶ Number of reactors: 3 for blank control, 3 for reference control, and 3 for test substance;
▶ Duration: normally 45 days, but can be continued for up to 6 months.

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