Parameter & design criteria*

Equation* & obtained value

Sludge age, θc = 10 days

Half-saturation coefficient: Ks = 20 mg/l

maximum specific growth rate, m = 4.28 d⁻¹

Endogenous respiration coefficient,

Kd = 0.1 d⁻¹ at (15˚C)

$\begin{array}{l}\text{EffluentCOD},S=\frac{K_S\left(1+K_d\text{SRT}\right)}{\text{SRT}\left(m-K_d\right)-1}\\ =1mg\text{COD}/l\end{array}$

Design flow, Qave = 30,000 m³/day

biodegradable COD, bCOD = 1.6 × BOD = 340 mg/l

oxidizable ammonia concentration, NO_x = 49.3 mg/l

yield coefficient, Y = 0.5

growth yield of nitrifying bacteria, yn = 0.12 decay constant of nitrifying bacteria,

Kdn (15˚C) = 0.065 d⁻¹

fraction of biomass accumulated during decay, fd = 0.15

inert material in influent wastewater,

$X_{o,i}=21.5mg/l$

solids production,

$p_{x,bio}\frac{QY(S_o-S)}{1+\left(k_d\right)\text{SRT}}+\frac{Q{y}_{n}N{O}_x}{1+\left(k_{dn}\right)\text{SRT}}+f_d{k}_d$ $\frac{QY(S_o-S)}{1+\left(k_d\right)\text{SRT}}\text{SRT}=2443.5\text{kg}/\text{d}$

total solids, P_x,T

$P_{x,T}=p_{x,bio}+Q{X}_{o,i}=3088.5\text{kg}/\text{d}$

MLVSS concentration =3500 mg/l

$V=\frac{P_{x,T}}{\text{MLVSS}}=8824{\text{m}}^3$

H.D.T = 2 h

$V_{anox}=\text{H}\text{.D}\text{.T}\ast Q_{ave}/24=2500{\text{m}}^3$

Effluent nitrate concentration, $N{O}_e=25\text{mg}/\text{l}$

recycle nitrate = $N{O}_x-N{O}_e=24.3\text{mg/}l$

$IR=NOx/NOr-1=1.03$

based on Metcalf & Eddy SDNR = 0.35 g/g∙d (15˚) = 0.31

$\begin{array}{l}{X}_{anox}=\frac{Q\ast SRT}{V_{era}}\ast \frac{Y\left(S_o-S\right)}{1+\left(k_d\right)SRT}\\ \ast \frac{IR}{IR+1}=1170\text{mg/l}\end{array}$

$\frac{F}{M_{anox}}=\frac{Q{S}_o}{V_{anox}{X}_{anox}}=3.5{\text{d}}^{-1}$

$\text{Noxfeed}=Q\ast IR\ast N{O}_r=751\text{kg}/\text{d}$

$\begin{array}{l}\text{NOrreduce}=V_{anox}\ast \text{SDNR}\ast X_{anox}\\ =907\text{kg}/\text{d}\end{array}$

$\text{Capacityratio}=\frac{\text{NOreduce}}{\text{Noxfeed}}=1.2$

Return sludge ratio Q_r/Q = 0.8

concentration of recycle sludge, Xr = 10,000 mg/l

${\theta }_c=\frac{V\ast X}{\left(Q_W\ast X_r\right)+\left(Q_e\ast X_e\right)}$

$\text{sludgewasterate},Q_W=311{\text{m}}^{\text{3}}/\text{d}$