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Edelstahl-Rohrleitungssystem zur chemischen Phosphorfällung in einer Kläranlage

Phosphorus Removal in Wastewater Treatment

Achieving ultra-low total phosphorus through chemical, biological, and physical processes.

Phosphorus removal targets in the EU are tightening to ≤ 0.5 mg/L TP for large plants (>150,000 PE) and ≤ 1.0 mg/L for plants >10,000 PE. Achieving these levels typically requires chemical precipitation (iron or aluminum salts) combined with tertiary filtration. Biological P removal (EBPR) can reduce chemical consumption but rarely achieves ultra-low limits alone.

Key Numbers

0.0
mg/L
TP limit >150,000 PE
0.0
mg/L
TP limit >10,000 PE
0%
%
Required removal (large plants)
0.0
Typical Fe:P molar ratio

Technical Overview

Phosphorus in wastewater exists as orthophosphate (PO4-P), polyphosphate, and organic phosphorus. Removal strategies target all three forms:

Chemical precipitation: Metal salts (Fe3+, Al3+) react with orthophosphate to form insoluble precipitates. Pre-precipitation, simultaneous precipitation, or post-precipitation can be applied depending on the target and plant configuration.

Biological phosphorus removal (EBPR): Polyphosphate-accumulating organisms (PAOs) take up excess phosphorus under alternating anaerobic-aerobic conditions. Requires adequate VFA supply in the anaerobic zone.

Tertiary filtration: Essential for removing particulate-bound phosphorus below 1.0 mg/L. Disc filters, sand filters, or membrane systems capture phosphorus-containing flocs.

Engineering Insight: Chemical Costs

Chemical P removal with FeCl3 typically costs €2–4 per kg P removed. For a 50,000 PE plant removing 5 mg/L TP, this translates to €50,000–100,000/year in chemical costs alone. EBPR integration can reduce chemical consumption by 40–60%.

Technology Comparison

Chemical Precipitation (FeCl3)

high

Simultaneous or post-precipitation using iron (III) chloride.

Energy: Low
Advantages
  • Reliable and proven
  • Easy to control
  • Achieves very low TP
  • Simple retrofit
Limitations
  • Ongoing chemical costs
  • Increased sludge volume
  • Possible color in effluent

EBPR

medium

Enhanced biological phosphorus removal using PAO organisms.

Energy: Low
Advantages
  • Reduces chemical use
  • Lower sludge production
  • P recovery potential
  • Sustainable
Limitations
  • Requires VFA/carbon
  • Less reliable alone
  • Needs anaerobic zone
  • Temperature sensitive

Tertiary Filtration + Coagulant

high

Post-precipitation with tertiary disc or sand filtration.

Footprint: Small
Energy: Low
Advantages
  • Achieves < 0.3 mg/L TP
  • Removes particulate P
  • Polishes effluent
  • Compact add-on
Limitations
  • Additional infrastructure
  • Backwash management
  • Coagulant costs

Adsorption Media

low

Reactive filter media (iron-based) for phosphorus adsorption.

Footprint: Small
Energy: Very low
Advantages
  • Very low TP achievable
  • No chemicals needed
  • Simple operation
  • Passive system
Limitations
  • Media replacement cost
  • Limited capacity
  • Not for high loads
  • Disposal of spent media

For Existing Plants

The most cost-effective retrofit for phosphorus removal is adding chemical dosing to the existing process (simultaneous precipitation) combined with a compact tertiary filter. This can typically achieve TP < 0.5 mg/L without major civil works.

EU Phosphorus Limits

Directive (EU) 2024/3019, Article 7: Total Phosphorus ≤ 1.0 mg/L for plants 10,000-150,000 PE, ≤ 0.5 mg/L for plants >150,000 PE. Minimum 87.5% removal or 90% for larger plants. Many member states already enforce stricter limits in sensitive catchments.
Source: Directive (EU) 2024/3019, Article 7

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Last reviewed: August 2026. Regulatory requirements may vary by national implementation. This content is for informational purposes and does not constitute legal or engineering advice.