ISO 11733:2004

Overview

ISO 11733:2004 - "Water quality - Determination of the elimination and biodegradability of organic compounds in an aqueous medium - Activated sludge simulation test" specifies a laboratory method to evaluate the elimination and biodegradability of organic compounds by aerobic microorganisms under conditions that simulate a wastewater treatment plant. The method uses parallel continuously operated test systems (activated sludge plants or porous pots) to quantify removal and, where possible, primary or ultimate biodegradation of soluble or suitably dispersible, non‑volatile, non‑inhibitory test compounds.

Key topics and requirements

• Test principle: Continuous-flow activated‑sludge simulation with a treated influent containing an organic medium plus the test compound in one unit and a control unit without the test compound. Effluent samples are analyzed to determine elimination.
• Analytical endpoints: DOC (dissolved organic carbon) or COD (chemical oxygen demand) are used to calculate degree of elimination; substance‑specific analysis can assess primary biodegradation.
• Test conditions:
  • Typical mean hydraulic retention time (HRT): about 6 h.
  • Typical sludge retention time (SRT): 6–10 days (sludge age).
  • Temperature control usually 20–25 °C (diffuse light or dark enclosure).
  • Influent DOC for test compound commonly targeted between 10–20 mg/L when added to organic medium.
• Applicability: Suitable for compounds that are water‑soluble at test concentration or satisfactorily dispersible, non‑volatile under test conditions, and not inhibitory to test microorganisms at the chosen concentration. Inhibitory compounds may be tested at lower concentrations or after acclimatization.
• Optional modes: Tests can be modified for nitrification/denitrification and for coupling of units (see annexes in the standard).
• Safety note: Activated sludge and sewage can contain pathogenic organisms; toxic test compounds require careful handling.

Applications and who uses it

• Environmental and analytical laboratories assessing biodegradability and removal efficiency of chemicals in simulated wastewater treatment.
• Wastewater engineers and treatment plant designers evaluating fate of organic micropollutants under activated‑sludge conditions.
• Chemical manufacturers and environmental compliance teams generating data for regulatory submissions and risk assessment.
• Researchers studying adaptation, pre‑exposure, and biodegradation kinetics in treatment systems.

Related standards

• ISO/TR 15462 - Selection of tests for biodegradability
• ISO 5667‑16 - Guidance on biotesting of samples
• ISO 10634 - Preparation of poorly water‑soluble compounds for biodegradability testing

Keywords: ISO 11733:2004, activated sludge simulation test, biodegradability, elimination, DOC, COD, wastewater treatment simulation, nitrification, denitrification, HRT, SRT.