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ISO 14851- Ultimate Biodegradability of Plastics - Oxygen Consumption

ISO 14851 is an aqueous aerobic biodegradability test that determines the ultimate aerobic biodegradability of plastic materials in aqueous medium by measuring oxygen demand during biodegradation in a closed respirometer. The test normally lasts for 2 months, but can be extended up to 6 months.


ISO 14851 determines the biodegradability of a plastic material by measuring oxygen consumption during the biodegradation process in a period of 2-6 months in a closed bottle setup (with head space). The degradation percentage is calculated as the ratio of oxygen consumption to the theoretical oxygen demand (ThOD).

The oxygen consumption is usually determined by measuring the quantity of oxygen (produced electrolytically) required to compensate the consumed one to maintain a constant gas volume/pressure in the respirometer flask, or from the change in the volume or pressure in the flask without compensating the consumed oxygen. The evolved CO2 is absorbed by sodium hydroxide solution present in a tube in the flask.

The formula of the test substance and its purity may be known to calculate the ThOD. The material is preferably in powder form with a maximum size of 250 um in diameter to provide better bioavailability for faster biodegradation.

Information on the toxicity of the test substance is helpful in determining the appropriate dosage so that the material does not inhibit bacteria at the concentration tested.

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ISO test overview

Key Point Summary

▶ Materials that can be tested:
     ➢ Natural and/or synthetic polymers, copolymers or mixtures thereof;
     ➢ Plastic materials which contain additives such as plasticizers, colorants or other compounds;
     ➢ Water-soluble polymers;
     ➢ Materials which, under the test conditions, do not inhibit the microorganisms present in the inoculum.
▶ Test substance requirement:
     ➢ Formula needs to be known in order to calculate the ThOD;
     ➢ Preferably in powder form with maximum size of 250 um diameter;
     ➢ Similar shapes of different substances should be used if they are to be compared;
     ➢ Preferably, plastic materials without additives such as plasticizers should be tested;
     ➢ Do not inhibit bacteria at the concentration tested.
▶ Measurement: oxygen consumption (any type of respirometer is fine as long as the measurement is accurate);
▶ Temperature: 20-25°C;
▶ Reference: aniline and/or a well-defined biodegradable polymer (e.g., microcrystalline cellulose powder, ashless cellulose filters or poly-β-hydroxybutyrate);
▶ Test substance dosage: at least 100 mg/L of the substance, or 170 mg/L of ThOD. Lower concentration can be used if the sensitivity of the respirometer is adequate;
▶ High mineral medium concentration should be used if the test substance dosage is high;
▶ Inoculum: activated sludge, use preferably on the same day of collection, or within 72 hours;
▶ Inoculum dosage: 30 – 1000 mg/L of TSS;
▶ Pre-exposed inoculum is generally not used, but could also be used depending on the purpose of the test;
▶ Number of reactors: 3 for blank control, 2 for reference control, and 3 for test substance;
▶ Duration: normally up to 2 months; prolong the test up to 6 months if significant biodegradation is still observed after 2 months;
▶ Upon termination, determine pH, nitrate and nitrite to correct the calculated degree of biodegradation for nitrification; ▶ Nitrification inhibitor (allylthiourea) is not recommended for long term test. However, nitrification generally does not occur with low inoculum concentration (about a volume fraction of 1%).

Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 14851. 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 14851
Oxygen consumption
ThOD *
+ +/- +

*"Sample info required" is the information needed to calculate the biodegradation percentages. This must be available for a selected method.
*"ThOD" can be easily calculated based on the formula of the sample. Try our Online ThOD Calculator.

Aropha Resource Center

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

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