Overview
EN ISO 9408:1999 - Water quality specifies a laboratory method for evaluating the ultimate aerobic biodegradability of organic compounds (including wastewaters) in aqueous media by measuring oxygen demand in a closed respirometer. The standard describes a static test system in which a test substance is the sole carbon/energy source, oxygen consumption is monitored, and evolved CO2 is absorbed. Results are reported as percent biodegradation relative to theoretical oxygen demand (ThOD) or chemical oxygen demand (COD). Typical test conditions include 28 days (or longer where necessary), incubation at 20–25 °C in the dark, and a nominal test concentration of 100 mg/L (or equivalent to ≥100 mg/L ThOD).
Key topics and technical requirements
- Test principle: Closed respirometric measurement of O2 uptake with CO2 absorption; oxygen change expressed as % of ThOD or COD.
- Test concentration: Normally 100 mg/L test compound (or ≥100 mg/L ThOD); adjustments allowed for low-solubility or toxic substances.
- Temperature & lighting: Incubate at 20–25 °C (±1 °C) in dark or diffuse light.
- Duration: Follow biodegradation for 28 days or longer when required.
- Inoculum: Mixed microbial inoculum (commonly activated sludge); preconditioning allowed but pre‑exposure generally avoided unless stated.
- Corrections & controls: Blanks and reference compounds (e.g., aniline or sodium benzoate) to verify inoculum activity; optional inhibition check combining test + reference compound.
- Measurements (optional): Dissolved organic carbon (DOC) removal, COD where relevant.
- Apparatus & reagents: Closed respirometer, CO2 absorbent (KOH or soda lime), test medium, pH meter, centrifuge/filtration for DOC, and standard reagents specified in the method.
- Reporting & validity: Calculation methods, validity criteria, and reporting requirements detailed (see clauses on calculation, validity, and test report).
Applications and practical value
- Environmental fate testing for regulatory submissions and chemical safety assessments.
- Biodegradability screening in research labs and environmental testing laboratories.
- Process evaluation for wastewater treatment operations (assessment of treatability).
- Product stewardship and eco-design decisions for chemical and pharmaceutical manufacturers.
The method provides quantitative, comparable data on ultimate biodegradability, useful for risk assessment, classification, and treatment process design.
Who should use this standard
- Environmental testing laboratories and contract research organizations (CROs)
- Wastewater treatment engineers and plant operators
- Chemical manufacturers, formulators, and regulatory affairs specialists
- Environmental regulators and consultants assessing biodegradability
Related standards
- ISO 10634 (handling poorly soluble compounds)
- ISO 15462 (alternative biodegradation methods)
- ISO 8192 (toxicity testing methods)
- ISO 6060 (COD determination)
- ISO 9887 / ISO 9888 (pre‑exposure / biodegradation tests)
Keywords: EN ISO 9408:1999, biodegradability test, closed respirometer, oxygen demand, water quality, ThOD, DOC, activated sludge.