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Third tier of tests in OECD standard methods aiming at evaluating the biodegradability under environmentally realistic conditions.

Less commonly used than OECD 301 and 302, this test is designed to evaluate the primary and/or ultimate biodegradation of water soluble organic compounds in a continuously operated activated sludge system simulating the realistic wastewater treatment process. The dosage of the test compound is generally between 10 and 20 mg DOC/L, and the biodegradation percentage is calculated based on the DOC/COD removal.

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OECD 303A system setup scheme

OECD 303A Activated Sludge Units

The OECD 303A Activated Sludge Unit measures the DOC/COD removal during biodegradation. Two parallel units are generally used, one containing organic medium only as a blank control, while the other containing both organic medium and the test compound. The difference of the DOC removal between the two units is believed to be the contribution of the test compound. 

This method cannot be used for testing insoluble or volatile materials. 

No specific pass levels have been defined for this tier of tests. It would have to be related to the specific operating conditions and system design.

OECD 303A simulated biodegradation test system setup scheme


Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of OECD 303A. Find the applicability for all other methods on Aropha Resource Center

Test Analytical method Poorly soluble Volatile Adsorbing
303A (Activated sludge unit)
DOC and/or COD
- - -/+

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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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