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Using digested sludge with a total solids concentration of 1 g/L to 3 g/L and incubated at 35 ± 2°C in sealed vessels with the test substance normally at 20-200 mg C/L for up to 90 days. The activity of the sludge is measured by running parallel blank and reference controls. At least triplicate test vessels for each group are prepared. The increase in headspace pressure in the vessels or volume of biogas production is measured. The inorganic carbon is measured at the end of the test.
The amount of carbon (inorganic plus methane) resulting from the biodegradation of the test substance, is calculated from the net gas production and net inorganic carbon formation in the liquid phase, in excess of blank control values. The extent of biodegradation is calculated from total inorganic carbon and methane-C produced as a percentage of the measured or calculated amount of carbon added as test substance.
▶ Materials that can be tested:
➢ Natural and/or synthetic polymers, copolymers or mixtures of these;
➢ 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;
▶ Inoculum information:
➢ Digested sludge derived from a digester at a wastewater treatment plant which treats predominantly domestic sewage;
➢ 1 – 3 g/L of total suspended solids;
➢ May be pre-digested for up to 7 days to reduce the organic content in the inoculum;
▶ Inoculum dosage: 1 – 3 g/L of total suspended solids;
▶ Test substance dosage: 20-200 mg/L organic carbon;
▶ Reference substance: well-defined anaerobically biodegradable polymer (e.g., cellulose, poly-β-hydroxybutyrate, or polyethylene glycol 400);
▶ Reactor: normally 0.1-1 L pressure-resistant glass test vessels; headspace being 10-30% of the total volume;
▶ Number of reactors: 3 for each test substance, plus 3 for blank control, and 3 for reference control;
▶ Testing conditions:
➢ Temperature: 35 ± 2°C;
➢ pH: 7 ± 0.2;
▶ Duration: normally up to 90 days;
➢ Pressure increase in the headspace for calculating the total amount of methane (CH4) and carbon dioxide (CO2);
➢ Inorganic carbon in the test solution at the end of the tests;
▶ Test validity criteria:
➢ Over 70 % of degradation for reference within 60 days and the difference between the percentage biodegradation of the reference in different vessels is less than 20% of the mean value；
➢ No oxygen present in the reactors；
➢ pH should not exceed the range 7 ± 1 if insufficient biodegradation has taken place.
Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 14853. 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 14853||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