Overview
ISO 7027-1:2016 - "Water quality - Determination of turbidity - Part 1: Quantitative methods" - defines standard quantitative procedures for measuring turbidity in water using optical nephelometers and turbidimeters. The standard covers two measurement principles: nephelometry (diffuse-scattered light, for low turbidity like drinking water) and turbidimetry (attenuation of transmitted light, for highly turbid waters such as wastewaters). It specifies sample handling, reagents (notably formazin reference suspensions), calibration, measurement procedures and expression of results.
Key topics and technical requirements
- Measurement methods
- Nephelometry: measures diffuse radiation; results expressed in nephelometric turbidity units (NTU). Typical range: <0.05 NTU to 400 NTU (instrument dependent).
- Turbidimetry: measures attenuation of radiant flux; results expressed in formazin attenuation units (FAU). Typical range: 40 FAU to 4 000 FAU.
- Instrumentation: optical nephelometers and turbidimeters with defined geometry (measurement angle θ and aperture Ω affect readings).
- Calibration and standards:
- Use formazin stock suspensions (stock I = 4 000 FNU/NTU; stock II = 400 FNU) or approved commercial stabilised standards.
- Numerical equivalence of NTU and FNU holds for prepared formazin standards; traceability recommended via the same calibration suspension.
- Secondary polymer bead standards may be used for nephelometry after verification.
- Sampling and sample handling:
- Clean containers, avoid contamination and air bubbles.
- Analyze as soon as possible; if stored, keep cool/dark and measure within 24 hours (bring to room temperature before analysis).
- Interferences and measurement conditions:
- Dissolved coloured substances can affect turbidity - measurements at >800 nm reduce colour interference.
- Particle size, shape and optical properties influence readings; therefore instrument-to-instrument comparisons require using the same measurement principle and ISO conformity.
- Safety and reagents: preparation of formazin involves hydrazine sulfate - toxic; follow safety precautions.
Applications and users
ISO 7027-1:2016 is used by:
- Water utilities and laboratories for drinking water quality monitoring
- Wastewater treatment plants and effluent monitoring teams
- Environmental monitoring agencies and consultants
- Instrument manufacturers and calibration laboratories
- Research laboratories studying suspended solids and optical properties of water
Key applications: regulatory compliance, process control, environmental assessments, instrument calibration, and interlaboratory comparison.
Related standards
- ISO 7027-2 (semi-quantitative methods - under preparation)
- CIE Publication No. 17 (terms and definitions referenced)
- Developed by ISO/TC 147 (Water quality)
Keywords: ISO 7027-1:2016, turbidity measurement, nephelometry, turbidimetry, NTU, FAU, formazin standards, water quality, optical turbidimeter, nephelometer.
