Activated sludge: nitrification

Input data

Average influent flow

Influent TKN

Effluent TKN

Design effluent ammonia

Sludge production (VSS)

Sludge age

Liquid temperature

Dissolved oxygen

pH

Influent alkalinity as CaCO3 (optional)

Max. growth rate at 20 °C

Temperature coefficient θ

Ammonia half-saturation Kn

Oxygen half-saturation Ko

Nitrifier yield Yn (g VSS/g N)

Nitrifier decay bn

N in excess sludge Fa (g N/g VSS)

O2 for nitrification (g O2/g N)

Alkalinity consumed (g CaCO3/g N)

Output data

Nitrifier growth rate

Minimum sludge age

Safety factor on sludge age

Effluent ammonia at the sludge age

Nitrate produced (N nitrified)

Nitrified load

Oxygen demand, nitrification

Nitrifier production

Alkalinity after nitrification

Description

Nitrification in the aerobic volume of an activated sludge system.

Nitrifier growth rate corrected for temperature, dissolved oxygen and pH:

$\mu' = \mu_{max,20} \, \theta^{(T-20)} \, \frac{OD}{K_o + OD} \, f_{pH}$

$f_{pH} = 1 - 0.833 (7.2 - pH) \quad \text{for } pH < 7.2$

Growth rate at the design effluent ammonia $N$ and minimum sludge age:

$\mu_n = \mu' \frac{N}{K_n + N}$

$\theta_{c,min} = \frac{1}{\mu_n - b_n}$

Effluent ammonia at the adopted sludge age, with safety factor $\theta_c / \theta_{c,min}$ :

$N = \frac{K_n (1 + b_n \theta_c)}{\theta_c (\mu' - b_n) - 1}$

Nitrogen balance, discounting the nitrogen incorporated into the excess sludge:

$N_{ox} = NTK_0 - NTK_e - \frac{F_a P_{xv}}{Q}$

Oxygen demand of 4.57 g O₂/g N and alkalinity consumption of 7.14 g CaCO₃/g N nitrified. The nitrifier decay coefficient $b_n$ is zero by default.

Reference

VON SPERLING, M. Lodos ativados. Princípios do tratamento biológico de águas residuárias, v. 4. Belo Horizonte: DESA/UFMG.

Calculations