1 of 20

Nitrogen Removal

Nitrification and Denitrification

2 of 20

Key ideas

  • Nitrification is an aerobic process that requires a long SRT and HRT
  • The length of the SRT is affected by temp, DO, pH, and ammonia concentration
  • Denitrification is an anoxic process that requires very low DO with a carbon source

​

3 of 20

Nitrogen cycle

Organic matter

Ammonia nitrogen

Nitrite nitrogen

Nitrate nitrogen

Plant protein

Animal protein

Ammonification

Nitrification

Oxidation

Waste products/ death

Plant life

Animal life

N2 gas

Denitrification

4 of 20

Biological nitrogen removal

Assimilation nitrogen required for cell growth

Ammonification conversion of organic nitrogen to ammonia

Nitrification conversion of ammonia to nitrate

Denitrification conversion of nitrate to nitrogen gas

5 of 20

Nitrification

Ammonia + Oxygen + Alkalinity + Nitrosomonas �(NH3) (O2)

​

= Nitrite �(NO2)

​

Nitrite + Oxygen + Alkalinity + Nitrobacter � (NO2) (O2)

​

= Nitrate (NO3)

6 of 20

The ‘bugs’

Nitrosomonas europaea

Nitrobacter

7 of 20

Nitrification

  • SRT long enough to allow stable population of nitrifiers to be maintained
  • HRT long enough to allow biomass sufficient time to react with ammonia
    • Assume well mixed conditions with no short circuiting
    • Short HRT can see season nitrification

​

8 of 20

Target SRT varies

With:

  • Temperature – 7oC
  • Dissolved oxygen – 2 mg/L
  • pH – 6.8-8.0
  • Ammonia concentration

9 of 20

Sensitive

  • Organic
  • Inorganic
  • Heavy metals

​

10 of 20

Single sludge nitrification

Aeration tank

Clarifier

Influent

Effluent

Waste sludge

Return activated sludge

11 of 20

Separate sludge nitrification

Aeration tank

Clarifier

Influent

RAS nitrification

RAS BOD removal

Aeration tank

Clarifier

12 of 20

Denitrification

Nitrates (NO3) + Organics + heterotrophic bacteria =

​

Nitrogen gas + Alkalinity (carbon dioxide)

​

  • 2.86 mg CBOD/mg of nitrate
  • Anoxic zone less than 0.1 mg/L
  • Produces 3.57 mg of alkalinity

​

13 of 20

Basic removal of nitrogen in a wastewater facility�

Nitrification

Denitrification

Anoxic

​

🡺 Nitrogen gas

(N2)

Ammonia (NH3)

Aerobic

​

Nitrite 🡺 Nitrate

(NO2) (NO3)

14 of 20

Denitrification

Wuhrmann process

Anoxic tank

Clarifier

Aeration tank

Return activated sludge

15 of 20

Denitrification

Ludzack-Ettinger process

Aeration tank

Anoxic tank

Clarifier

Return activated sludge

16 of 20

Denitrification

Modified Ludzack-Ettinger process

Aeration tank

Anoxic tank

Clarifier

Return activated sludge

Nitrified recycle

17 of 20

Denitrification

Anoxic

Influent

Secondary clarifier

Effluent

Waste sludge

Return activated sludge

Oxic

(aeration)

NO3

Anoxic

Oxic

(aeration)

Four-stage Bardenpho process

18 of 20

Denitrification

Oxidation ditch

Clarifier

Waste

sludge

Oxic

Anoxic

19 of 20

Denitrification

Fill �phase

React phase

Settle phase

Decant phase

Sequencing batch reactors (SBR)

20 of 20

Key ideas

  • Nitrification is an aerobic process that requires a long SRT and HRT
  • The length of the SRT is affected by
    • temperature
    • DO
    • pH
    • ammonia concentration
  • Denitrification is an anoxic process that requires very low DO with a carbon source

​