Overview
EN ISO 8192:2007 - Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation (ISO 8192:2007) specifies a laboratory method to assess how a test material affects the oxygen uptake of activated sludge microorganisms. The method is designed to represent conditions in biological wastewater treatment plants and reports short-term inhibitory or stimulatory effects after exposures typically from 30 min to 180 min (or longer). It applies to waters, wastewaters, soluble chemicals and chemical mixtures, with caveats for low-solubility, highly volatile, or abiotic oxygen-consuming/producing materials.
Key topics and requirements
- Principle: Measure oxygen consumption rates of activated sludge (using an oxygen electrode) in the presence and absence of a test material; calculate percentage inhibition by comparison with blank controls.
- Scope of measurement: Total oxygen uptake (carbonaceous oxidation + nitrification) or separated components by using a nitrification inhibitor.
- Nitrification discrimination: Use N‑allylthiourea (ATU) to inhibit ammonia-oxidizing bacteria and separate heterotrophic (carbonaceous) and nitrifying oxygen consumption.
- Endpoints and units: Inhibition expressed as percentage; EC50 (effective concentration causing 50% inhibition) and the toxic range (concentration span from 0% to 100% inhibition). Oxygen consumption rates typically in mg/(l·h) and specific rates in mg/(g·h).
- Reagents and controls: Grade 1 water (ISO 3696), ATU, reference substances (e.g., 3,5‑dichlorophenol or N‑methylaniline), antifoam, synthetic sewage medium. Abiotic controls may be required; mercury(II) chloride can be used but poses significant safety and disposal concerns.
- Apparatus & procedure elements: Oxygen electrode, cultured activated sludge inoculum, controlled test environment, calculation and validity checks. Tests must be performed by trained personnel following laboratory safety practices.
Practical applications and users
- Environmental laboratories assessing toxicity of industrial effluents, chemicals and wastewater on biological treatment systems.
- Wastewater treatment plant operators and process engineers evaluating the risk of process inhibition (especially nitrification inhibition).
- Regulatory agencies and consultants performing environmental impact assessments or compliance testing.
- Chemical manufacturers and formulators conducting ecotoxicity testing to derive safe discharge limits and EC50 data.
Related standards
- ISO 3696 - Water for analytical laboratory use (referenced for reagent water quality).
- ISO 9509 - Additional methods for investigating nitrification (referenced for deeper nitrification assessment).
EN ISO 8192:2007 is a practical, standardised test for predicting short-term impacts of substances on activated sludge respiration and the performance of aerobic biological wastewater treatment processes.
