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OECD 311: Anaerobic Biodegradability of Organic Compounds

OECD 311 specifies a method of determining the anaerobic biodegradability of organic materials under anaerobic conditions. OECD 311 is similar to ISO 11734 and ISO 14853.

OECD 311 is designed to yield a percentage of conversion of carbon in the sample to carbon in the gaseous form (CO2 and CH4) under conditions found in anaerobic digesters. Incubation is usually performed for 15 to 30 days at 37 °C.

OECD 311 Key Summary

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 at 20 to 100 mg C/L for up to 60 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 resulting from the production of carbon dioxide and methane 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:
     ➢ Water soluble or insoluble organic compounds;
▶ Test substance dosage: 20-100 mg/L organic carbon;
▶ Reference substance: phenol, sodium benzoate, or polyethylene glycol 400;
▶ Inoculum information:
     ➢ Digested sludge derived from a digester at a wastewater treatment plant which treats predominantly domestic sewage;
     ➢ 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;
▶ 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 60 days;
▶ Measurement: 
     ➢ 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 60 % of degradation for reference within 60 days;
     ➢ No oxygen present in the reactors;
     ➢ pH should not exceed the range 7 ± 1 if insufficient biodegradation has taken place.

OECD 311 Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of OECD 311. 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

TestAnalytical methodSample info required *Poorly solubleVolatileAdsorbing
OECD 311CO2 and CH4 evolutionOrganic 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).

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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