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ISO 9888: Ultimate Biodegradability Test - Static Test (Zahn-Wellens Method)

ISO 9888 is an aqueous aerobic biodegradability test that determines the ultimate aerobic biodegradability of organic compounds in aqueous medium by measuring dissolved organic carbon or chemical oxygen demand. The conditions with a high inoculum concentration is optimal for allowing the maximum value of biodegradation. The test normally lasts for 28 days.


Similar to OECD 302B, The ISO 9888 Zahn-Wellens test measures the removal of dissolved organic carbon (DOC) or chemical oxygen demand (COD) during biodegradation and the degradation percentage is calculated as the ratio of DOC removal to original DOC loaded (or COD removal to original COD dosed). 

The carbon content of the test substance and its purity may be known to calculate the DOC, or otherwise the COD may be measured. 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 capable of testing samples that are highly soluble (> 50 mg DOC/L), non-volatile, and non-adsorbing

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ISO 9888

ISO 9888 Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 9888. You can find the applicability for many other methods on Aropha Resource Center

TestAnalytical methodSample info required *Poorly solubleVolatileAdsorbing
ISO 9888 (Zahn-Wellens)
DOC or CODOrganic carbon content * or COD *+/---

*"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, organic 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).
*"COD": we provide COD analysis at Aropha.

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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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