ISO 20480-4:2021

Overview

ISO 20480-4:2021 - part of the ISO 20480 fine bubble technology series - is an international terminology standard that defines terms related to dissolved air flotation (DAF) bubble beds and their characteristics. Published in 2021 by ISO/TC 281, this document clarifies vocabulary used when describing DAF tanks, microbubble beds, and allied parameters to reduce ambiguity in research, measurement and full‑scale operations.

Key topics and technical content

This part is a terminology standard (no normative references) and focuses on precise definitions of DAF-related concepts, including:

• Flotation process and dissolved air flotation (DAF) - fundamentals of using fine bubbles to separate low‑density particles from water.
• DAF tank, contact zone, separation zone - distinctions between tank compartments and process stages.
• Treatment capacity and hydraulic loading rate - performance indices linked to flow and tank surface area.
• Recycle water and recycle ratio - role of recycled saturated water in bubble generation.
• Saturation pressure - internal pressure of the saturator used to generate bubbles.
• DAF bubble bed and effective depth - the bubble layer in the separation zone and its equilibrium thickness.
• Bubble number concentration - number of bubbles per unit volume of water.
• DAF bubble bed compactness - index expressing how saturated the bubble bed is with bubbles; defined as the ratio of total bubble volume to the DAF bubble bed volume (expressed as a percentage).
• Total bubble volume and bubble volume concentration index - metrics for the volume of air in bubbles and bubble volume per unit water volume.

The standard includes illustrative material (e.g., a figure for effective depth) and a formula for computing bubble bed compactness.

Applications and who uses it

ISO 20480-4:2021 is valuable for:

• Water and wastewater treatment engineers designing or operating DAF systems (potable and industrial wastewater).
• Researchers and instrumentation developers working on microbubble measurement methods and full‑scale bubble bed monitoring.
• Manufacturers of DAF equipment, consultants, and utility operators who need consistent terminology for specifications, testing, reporting and regulatory compliance.
• Standard writers preparing measurement or evaluation standards for bubble beds - the document reduces confusion ahead of method standards.

Practical uses include improving DAF design decisions (e.g., basin depth, recycle rates), comparing test results across studies, and ensuring consistent reporting of bubble metrics like compactness and number concentration.

Related standards

• ISO 20480-1: General terminology for fine bubble technology
• ISO 20480-2: Categorization of attributes of fine bubbles
• ISO 20480-3: (Related methods for bubble generation and measurement referenced in the series)

Keywords: ISO 20480-4:2021, fine bubble technology, dissolved air flotation, DAF bubble bed, bubble bed compactness, microbubble beds, bubble number concentration, effective depth.