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Biological De-Nitrification Process in Waste Water Treatment System

By: Haseeb Jamal / On: Dec 12, 2017 / Waste Water


  • Biological reduction of nitrate to nitric oxide, nitrousoxide, and nitrogen gas
  • Involves both nitrification and denitrification
  • Biological nitrogen removal (BNR) is more cost effective and used more often as compared to ammonia stripping, breakpoint chlorination and ion exchange;
  • BNR is used in wastewater treatment where
    • there are concerns for eutrophication;
    • where groundwater must be protected against elevated NO3‐N concentration;
    • where WWTP effluent is used for groundwater recharge and other reclaimed water applications

Process Description

Two modes of nitrate removal can occur in biological processes:

  1. Assimilating and
  2. Dissimilating nitrate reduction

Assimilating nitrate reduction

  • Involves reduction of nitrate to ammonia for use in cell synthesis;
  • Occurs when NH4‐N is not available and is independent of DO concentration

Dissimilating nitrate reduction

  • Nitrate or nitrite is used as electron acceptor for oxidation of variety of organic or inorganic electron donors

Substrate driven (preanoxic denitrification)

  • Figure 7‐21 (a) most common process used for biological nitrogen removal (BNR) in municipal WWT;
  • Process consists of anoxic tank followed by aeration tank;
  • Nitrate produced in aeration tank is recycled back to anoxic tank;
  • Organic substrate in influent WW provides electron donor for oxidation reduction reactions using nitrate; Process is termed substrate denitrification;
  • Furthermore, process is known as preanoxic denitrification because anoxic process precedes aeration tank

Endogenous driven (postanoxic denitrification)

  • Figure 7‐21 (b), denitrification occurs after nitrification
  • and electron donor source is from endogenous decay;
  • Process is termed as postanoxic denitrification as BOD removal has occurred first and is not available to drive nitrate reduction reaction
  • Depends on endogenous respiration for energy
  • Much slower rate of reaction than preanoxic processes
  • Exogenous carbon source such as methanol or acetate is added to provide sufficient BOD for nitrate reduction and to increase rate of denitrification
  • Include suspended and attached growth systems

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