ISO 14852 Key Summary
The ISO 14852 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.
The aeration of the working solution requires the use of CO2-free air, which can be easily obtained by using a few NaOH washing bottles to remove all the CO2 present in the air. After that, CO2-free air can be sent to aerate the working solution.
During the aeration, CO2 is generated as a result of test substance biodegradation. Such CO2 can be easily stripped off the working solution during the aeration process. To capture it, three absorption bottles are usually used containing known amount of Ba(OH)2 to convert CO2 to BaCO3 precipitation. An afterwards acid-base titration using HCl as the titrant can determine the amount of the residual Ba(OH)2, which can be used to back calculate the amount of CO2 generated during the 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.
This method is appropriate for highly soluble, poorly soluble (or even insoluble) and/or absorbing materials. However, since aeration is performed throughout the incubation process, the test substance should not be volatile.
▶ 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:
➢ Carbon content is required in order to calculate the ThCO2;
➢ 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;
➢ Do not inhibit bacteria at the concentration tested.
▶ Measurement: CO2 evolution;
▶ Temperature: 20-25°C;
▶ Reference: a well-defined biodegradable polymer (e.g., microcrystalline cellulose powder, ashless cellulose filters or poly-β-hydroxybutyrate);
▶ Test substance dosage: normally at least 30 mg/L of organic carbon, preferably 100 mg/L;
▶ 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, 3 for reference control, and 3 for test substance;
▶ Duration: normally up to 6 months;
▶ On the last day of the test, measure the pH and acidify all the bottles in order to measure any of the carbonates and bicarbonates.
