Overview
ISO/TR 22707:2023 is a technical report that provides practical information on processes and technologies for inorganic substance and nutrient recovery from sludge. The document applies to sludge and products from urban wastewater collection systems, night soil, and wastewater treatment plants for urban and similar industrial waters. It excludes hazardous industrial sludge and dredged sludge. The report is published by ISO/TC 275 and focuses especially on phosphorus recovery while covering other nutrients and inorganic constituents.
Key topics
- Scope and definitions: Terms such as struvite, hydroxyapatite (HAP), centrate and incineration ash are defined to standardize terminology for nutrient recovery from sludge.
- Methods of nutrient recovery: Four principal approaches are described:
- Whole use - direct land application of treated sludge (compost, biosolids).
- Cleaning - removal of contaminants (plastics, heavy metals) by mechanical or chemical means prior to reuse.
- Separation - physical/chemical partitioning of sludge into fractions, enabling targeted utilization.
- Extraction - chemical recovery of specific elements (e.g., P, N) into stabilized compounds.
- Phosphorus recovery (detailed):
- Struvite recovery from anaerobic digested sludge or filtrate - chemical precipitation in crystallizers (air-fluidized or mechanically agitated), dosing of magnesium and pH control; recovered struvite is a slow-release fertilizer. The report notes that dissolved phosphorus recovery can exceed 80% under optimum conditions.
- Hydroxyapatite recovery, phosphorus recovery from incineration ash, sewage sludge slag, and other emerging technologies - principles, schematic diagrams, operating conditions and product characteristics are summarized.
- Other nutrients & inorganics: Guidance on nitrogen (e.g., ammonia stripping), sulfur, potassium and recovery of metals.
- Supporting material: Annex A (sewage sludge composition examples) and Annex B (case studies and practical implementations).
Applications and users
ISO/TR 22707:2023 is useful for:
- Wastewater treatment plant (WWTP) designers and operators planning phosphorus recovery or struvite control systems.
- Environmental and process engineers specifying nutrient recovery or sludge valorisation technologies.
- Technology developers and vendors of crystallizers, ash treatment systems and nutrient recovery units.
- Municipal authorities, regulators and agronomy stakeholders assessing reuse quality and fertilizer potential.
- Researchers and consultants evaluating feasibility, economics and environmental benefits of sludge recovery and recycling.
Related information
- The report references national standards and guidance and will be updated as technologies evolve. For practical examples consult Annex B case studies and Annex A composition tables. For broader context, refer to other ISO and national standards on wastewater treatment, sludge management and biosolids reuse.