Parameter & design criteria*

Equation* & obtained value

BOD₅/BOD_u = 0.666%

BOD_u/X_b = 1.42%

Desired effluent SS = 25 mg/l

Biodegradable fraction (generating solids) = 0.65

Desired effluent BOD = 20mg/l

$S_{ss}=\frac{{\text{BOD}}_{\text{5}}}{{\text{BOD}}_{\text{u}}}\ast \left[\frac{{\text{BOD}}_{\text{u}}}{X_b}*S{S}_b/S{S}_e\right]=15.4\text{mg/l}$

$S_{\text{sol}}=S_{\text{total}}-S_{\text{ss}}=4.6\text{mg/l}$

Sludge age, θ_c = 10 days

S₀ = 212.8 mg/l

Yield coefficient, Y = 0.5

MLVSS concentration = 3500 mg/l

Endogenous respiration coefficient,

K_d = 0.057d⁻¹ at (15˚C)

$V=\frac{Y{\theta }_c{Q}_{ave}\left(S_o-S_{sol}\right)}{\text{MLVSS}\left(1+K_d{\theta }_c\right)}=5,684{\text{m}}^3$

Return sludge ratio Q_r/Q = 0.8

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

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

$\to \text{sludgewasterate},Q_W=174{\text{m}}^{\text{3}}\text{/}d$

Hydraulic detention time, $\text{HRT}=V/\left(Q\right)=0.19d$

$\frac{F}{M}=\frac{S_0}{\text{HRT}\ast \text{MLVSS}}=0.32d^{-1}$