ISO 8192:2007

Overview

ISO 8192:2007 - Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation - specifies a laboratory method to assess how a test material affects oxygen uptake by activated sludge microorganisms. The test is designed to represent conditions in aerobic biological wastewater treatment plants and reports short-term inhibitory or stimulatory effects after exposure (typically 30–180 minutes or longer). It applies to waters, wastewaters, soluble chemicals and chemical mixtures, with caveats for low-solubility or highly volatile materials and those that abiotically consume or produce oxygen.

Key topics and technical requirements

• Principle: measure oxygen consumption rates with an oxygen electrode; compare test mixtures to control mixtures to calculate percent inhibition and EC50 (effective concentration causing 50% inhibition).
• Carbonaceous vs. nitrification effects: separate heterotrophic (carbonaceous) and autotrophic (nitrifying) contributions by using a nitrification inhibitor (N‑allylthiourea, ATU) or by selecting nitrifying sludge.
• Reagents & media: specifies high-purity water (ISO 3696 grade 1), ATU stock, optional mercuric chloride for abiotic controls, antifoam, and reference substances (3,5‑dichlorophenol or N‑methylaniline). A synthetic sewage (100-fold OECD medium) with pH 7.5 ± 0.5 is defined.
• Inoculum: activated sludge from the aeration tank of a domestic wastewater treatment plant is recommended; typical suspended-solids guidance (e.g., ~2–4 g/L) is given.
• Apparatus & conditions: BOD bottles or Erlenmeyer flasks, oxygen electrode and recorder, magnetic stirrer, aeration devices, pH meter and centrifuge. Test environment: (22 ± 2) °C, dust- and toxic-vapour-free.
• Controls & validity: include blank controls, abiotic controls where necessary, and reference‑substance checks; Annexes provide measuring units, nitrifying-sludge culture apparatus and procedure overviews.
• Reporting: calculate inhibition curves, toxic range, EC50, and document test conditions and sludge characteristics.

Applications and who uses it

ISO 8192:2007 is used for:

• Toxicity screening of industrial chemicals, effluents and wastewater to predict impacts on biological wastewater treatment performance.
• Regulatory compliance and environmental risk assessment where effects on activated sludge respiration and nitrification must be quantified.
• Process troubleshooting in wastewater plants to identify inhibitory discharges.

Typical users: environmental laboratories, wastewater treatment operators, chemical manufacturers, consultants and regulatory agencies focused on water quality, activated sludge testing, nitrification inhibition and EC50 determination.

Related standards

• ISO 3696 (water for analytical use)
• ISO 9509 (nitrification testing reference)
• ISO 10634 (handling insoluble materials)
• ISO 9888 (suspended solids definitions)

Keywords: ISO 8192:2007, water quality, activated sludge, oxygen consumption, inhibition test, nitrification, EC50, biological wastewater treatment, toxicity assessment.