Overview
ISO 19658:2025 specifies a protocol for validating methods used to determine the physical properties of sludges. It defines procedures for interlaboratory validation applicable to sludges and suspensions from storm water handling, urban wastewater collection and treatment, similarly treated industrial wastewater, water supply plants and related products (excluding hazardous industrial and dredged sludge). The standard addresses practical challenges of working with fresh sludge, offers alternatives such as synthetic sludge, and sets out three validation routes: Conventional Round Robin Tests (C-RRT), Modified Round Robin Tests (M-RRT) and Confidence Level Evaluation (CLE).
Key topics and requirements
- Scope and applicability: urban and similar industrial sludges, night soil and stormwater sludges; hazardous and dredged sludges excluded.
- Preliminary arrangements: selection of at least nine participating laboratories across a minimum of three countries; experienced analysts and computer-based statistical tools required.
- Conventional Round Robin Tests (C-RRT):
- Organizer circulates real or synthetic reference samples or recipe/ingredients for on-site preparation.
- Minimum of three concentration levels per parameter; an additional 20% of samples held in reserve.
- Sample handling rules: half-filled containers, tolerances for inner pressure, cooling to +4 °C for biodegradable sludge; freezing prohibited.
- Measurement window: analyses within 1 week, starting within 24 h after receipt.
- Modified Round Robin Tests (M-RRT):
- “Circulation of analysts” to a central site near sample origin; participants use their own apparatus.
- Same sample-count and storage precautions as C-RRT.
- Confidence Level Evaluation (CLE):
- Statistical evaluation of field samples analyzed in laboratories near their collection sites when sample circulation is impractical.
- Statistical requirements:
- Check for normal distribution; if non-normal, apply robust statistics.
- Follow ISO 5725 series for repeatability and reproducibility calculations.
- Outlier handling: Type B (reproducibility) outliers eliminated; Type C (repeatability) included; Type D removals documented.
Practical applications and users
- Who uses ISO 19658: municipalities, wastewater treatment operators, water utilities, environmental laboratories, method developers, and standards bodies validating analytical methods for sludge characterization.
- Use cases include validation of methods for solids content, settling behavior, rheology, and other physical sludge properties needed for sludge recovery, treatment design, process control, regulatory reporting and product valorisation.
- Enables consistent interlaboratory comparisons and supports reliable method adoption across regions.
Related standards
- ISO 5725 (statistical methods for repeatability and reproducibility) - referenced for statistical calculations.
- ISO 6707-1 - terminology (definition of “sludge”).
- Aligned with the scope of ISO/TC 275 (sludge recovery, recycling, treatment and disposal).
Keywords: ISO 19658, sludge validation protocol, sludge physical properties, round robin tests, interlaboratory validation, synthetic sludge, fresh sludge, repeatability, reproducibility.