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ISO 11733: Biodegradability Test - Activated Sludge Simulation

ISO 11733 is an aqueous aerobic biodegradability test that determines the biodegradability of a material by measuring dissolved organic carbon or chemical oxygen demand under a simulated activated sludge condition. The test normally lasts for 12 weeks.


Similar to OECD 303A, ISO 11733 is designed to evaluate the primary and/or ultimate biodegradation of water soluble organic materials 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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ISO 11733 Key Summary

The ISO 11733 Activated Sludge Simulation test 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. 

▶ Measurement: DOC (or COD) and/or substance itself;
▶ Carbon source: easily biodegradable organic medium (synthetic sewage) and test compound;
▶ Duration: normally 12 weeks;
▶ Two systems: one test, one blank control (to determine the degradation of organic medium);
▶ Blank control is not required if the substance itself can be measured;
▶ Reference control is not required but the reference (e.g., adipic acid, 2-phenyl phenol, 1-naphthol, diphenic acid, and 1-naphthoic acid) may be added occasionally together with the test substance;
▶ Mean hydraulic retention time: 6 h;
▶ Mean sludge age (retention time): 6-10 day;
▶ Test substance dosage: 10-20 mg/L of DOC;
▶ Initial activated sludge dosage: 2.5 g/L suspended solids;
▶ Distinguish from bioadsorption: by examining the elimination-time curve, and confirming with ready biodegradation test using an acclimatized inoculum from the unit;
▶ Sampling: filtration with membrane filters (0.45 μm) or centrifugation (40,000 m/s2);
▶ Test substance requirement: normally involatile and soluble, able to calculate DOC or COD;
▶ Reproducibility: errors usually within 10-15% for substances degraded more than 80%. Lower degradation, larger error.

ISO 11733 Requirement and Applicability

Different testing methods are applicable for materials with different properties. Below is a summary of the applicability of ISO 11733. Find the applicability for all other methods on Aropha Resource Center

TestAnalytical methodSample info required *Poorly solubleVolatileAdsorbing
ISO 11733 (Activated sludge simulation)
DOC and/or COD
Organic carbon content* and/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, 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.

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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