Overview
SIST EN ISO 9887:1998 is an international standard developed by CEN for assessing the aerobic biodegradability of organic compounds in aqueous media using the Semi-Continuous Activated Sludge (SCAS) method. This method is designed for organic compounds that are soluble, non-volatile or have negligible vapor pressure, do not foam off or adsorb significantly on glass or sludge, and are not toxic to microorganisms. It offers a reliable technique for evaluating how effectively organic substances degrade under aerobic conditions typical of wastewater treatment processes.
Key Topics
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Scope and Applicability
The SCAS method applies to organic compounds that meet specific solubility and volatility criteria, ensuring the test results reflect microbial degradation rather than losses by evaporation or adsorption. The test excludes compounds that inhibit the activated sludge microorganisms.
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Principle of the Method
The evaluation is based on measuring the difference in dissolved organic carbon (DOC) concentration between the effluent of a control sludge unit (with sewage only) and a sludge unit dosed with the test compound. This difference indicates the level of organic compound breakdown.
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Test Conditions and Procedure
- Use of high microbial density activated sludge (1-4 g/L suspended solids) maintained in aerated SCAS units.
- Daily dosing of the test compound mixed with domestic or synthetic sewage.
- Aeration, settling, and removal of supernatant at fixed intervals (usually 23 hours aeration followed by settling).
- Regular sampling of effluent for DOC analysis via filtering or centrifugation.
- Monitoring continues for 12 to 26 weeks until consistent biodegradation measurement is achieved.
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Safety and Precautions
The standard includes warnings about the potential pathogenicity of activated sludge and toxicity of test compounds, recommending appropriate handling and safety measures.
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Reagents and Apparatus
Recommendations include the use of tap water with low DOC, domestic or synthetic sewage prepared with defined nutrient content, and lab equipment for DOC measurement including SCAS units, filtration devices, pH meters, and centrifuges.
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Evaluation and Reporting
The standard defines both ultimate biodegradation (complete mineralization) and primary biodegradation (structural changes without complete breakdown). The percentage elimination of the test compound or DOC is calculated from the stable differences in effluent concentrations over multiple measurements.
Applications
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Environmental Testing
The SCAS method provides key data for environmental safety assessments regarding the persistence and degradation of organic chemicals in aquatic ecosystems.
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Wastewater Treatment Optimization
Results can guide improvements in biological treatment design by identifying compounds that readily biodegrade under aerobic conditions.
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Regulatory Compliance
Used by industries and regulatory bodies to verify that organic substances meet biodegradability criteria required by environmental standards and legislation.
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Research and Development
Facilitates screening of novel organic compounds and formulations for environmental impact before commercial release.
Related Standards
- ISO 7827:1984 – Evaluation of ultimate aerobic biodegradability by DOC analysis
- ISO 9408:1991 – Biodegradability assessment via oxygen demand in a respirometer
- ISO 9439:1990 – Biodegradability evaluation by measuring released carbon dioxide
- ISO 8192:1986 – Test method for inhibition of oxygen consumption by activated sludge
- ISO 8245:1987 – Guidelines for total organic carbon (TOC) determination
Using SIST EN ISO 9887:1998 in conjunction with these related standards ensures comprehensive assessment of biodegradability for organic compounds critical to water quality management and environmental protection.