Overview
ISO 9784:2024 - Guidelines for biological filtration of secondary effluent for water reuse - provides practical, stakeholder-oriented guidance for using biological filtration to upgrade secondary effluent for reuse. The standard covers general recommendations, process components, technical requirements for each component (biofilter, mixing, backwashing, control), post‑treatment, and water‑reuse applications. It supports the “fit for purpose” approach to reusing treated municipal and similar industrial effluents for nonpotable and industrial uses.
Key technical topics and requirements
- Process components
- Biofilter unit (BAF / DNF): configuration options (upflow/downflow), influent distribution, graded gravel layer, filter bed, aeration and backwash drainage, outlet and control systems.
- Mixing unit: dosing and mixing of external carbon sources where heterotrophic denitrification is required.
- Backwashing unit: pumps and blowers; recommendations on backwash mode and equipment sizing.
- Controlling unit: on‑site PLC and central control room architectures for centralized or decentralized control.
- Filter media: acceptable materials include graded mineral media (sand, gravel), granular activated carbon, ceramsite, foamed ceramics, engineered plastics, and particulate media containing reduced sulfur/iron for autotrophic or combined denitrification.
- Treatment targets and terminology
- Removal of organics (carbon), ammonium (NH4+-N), nitrate and total nitrogen via combined BAF and denitrification filter (DNF) configurations.
- Performance metrics referenced include backwash rate (commonly expressed as m3/(m2·h)) and volumetric nitrogen loading rate (kg N/(m3·d)).
- Monitoring and control
- Instrumentation, monitoring systems and control logic to ensure stable biological performance, manage backwashing cycles, and protect environmental and operational safety.
- Annexes
- Annex A: example structure diagrams for BAF and DNF.
- Annex B: case studies of reuse applications.
- Annex C: information on autotrophic denitrification.
Practical applications and users
ISO 9784:2024 is intended for:
- Municipal wastewater utilities and operators upgrading secondary effluent for urban reuse (irrigation, cooling, nonpotable supply).
- Water reuse planners, process designers and engineering consultants specifying BAF/DNF systems.
- Equipment manufacturers (media, aeration, backwash, control systems).
- Regulators and asset owners setting technical guidance for advanced treatment trains.
The standard helps select appropriate configurations (single/two‑stage BAF, DNF), choose filter media, size backwash and aeration equipment, and integrate monitoring and post‑treatment to meet reuse objectives.
Related standards
- This document contains no normative references. Terminology draws on ISO 6107:2021 and ISO 6707‑1:2020. For implementation, consult local water reuse regulations and applicable national standards.