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FNR Process

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FNR Process

FNR (Ferrous Nutrient Removal) process is de-nitrogen and removal of phosphorus process. This process first starts de-nitrogen in biological treatment process, then the process removes phosphorus by using direct current adaptor on iron ion extract equipment. In this process, iron ions are produced by decomposed iron molecules, and these ions combine with oxygen iron, while phosphorus irons forms phosphate acid.

Schematic Diagram

FNR Process
Unit Description Remark
Anoxic Tank De-nitrification -
Aerobic Tank Removal of Organic substance
Reaction between iron ion and phosphorus
Ferrator Precipitate iron ions to remove phosphorus Electrolysis using S.P module
Final sedimentation Separate of Suspend solid from water Sludge return Excess sludge transfers to drying bed Advantage in dehydration of Sludge


  • High phosphate removal efficiency even in low organic loading.
  • Removal of both phosphorus and nitrogen without anaerobic process.
  • Effective due to generating chemical bond.
  • Time and cost effective (no needs of anaerobic tank)
  • Removal of phosphate without concerning the rate of phosphorus.

Principles of the FNR process

  • N2 gas is formed by denitrifying accumulating organisms and released into the air.
  • Removes phosphorus in the water by combining Iron ion with dissolved phosphorus in the water.
  • Educed iron ion combined with oxygen, and it attaches to phosphorus on iron plate. In this process, phosphorus in the water is removed and crystalized.
FNR process
Detail picture of the FNR plate
Qualification Certificate of Excellent Technology No. 120
Certificate of Excellent Technology No. 183
Certificate of Excellent Technology No. 95
Maximum Contaminant Level BOD(mg/ℓ) <5
Patent No. 0490310 SS(mg/ℓ) <5
Patent No. 0490307 T-N(mg/ℓ) <20
Patent No. 0657850 T-P(mg/ℓ) <2

Contrast Table

Contrast between A2/O process and FNR
Classification A2/O Process FNR Process Remark
Design And Operational Parameter MLSS 1,500-3,500 ㎎/ℓ 2,000-4,000 ㎎/ℓ -
HRT 7-8 hr 5-6 hr Doesn't require anoxic tank
SRT 6-15 days 6-20 days Reduces HRT
Internal Return Rate 100-300 % 6-20 days Reduces HRT
External Return Rate 30-50 % 30-50 % -
Benefits Agitator for
Anoxin tank
Necessary Not required Reduces Cost for equipment and maintenance
Anoxic tank Necessary Not required Reduces cost for site and construction
Flow meter for
Anoxin tank
Necessary Not required Reduces cost for construction and equipment