Activated sludge: secondary clarifier (solids flux)

Description

Secondary clarifier sized by the limiting solids flux theory. Zone settling velocity by the Vesilind equation:

$v = v_0 e^{-K C}$

$v_0$ and $K$ are taken from the settleability class (von Sperling and Fröes) unless given:

Class	SVI (mL/g)	$v_0$ (m/h)	$K$ (m³/kg)
Very good	0-50	10.0	0.27
Good	50-100	9.0	0.35
Medium	100-200	8.6	0.50
Poor	200-300	6.2	0.67
Very poor	300-400	5.6	0.73

Area for clarification:

$A_{cl} = \frac{Q_{max}}{v_0 e^{-K X}}$

Area for thickening, where $u$ is the underflow velocity at which the limiting flux carries the applied load $(Q + Q_r) X$ to the bottom:

$A_{ad} = \frac{Q_r}{u}$

The design area is the larger of the two, checked at average and peak flow with the return flow constant at $Q_r = R Q$ .

The return sludge ratio $R$ is either given or obtained from the return sludge concentration $X_r$ :

$R = \frac{X}{X_r - X}$

Results include the hydraulic and solids loading rates, the return sludge concentration by mass balance and the limiting underflow concentration for the design area.

Reference

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

Calculations

Activated sludge: secondary clarifier (solids flux)

Select calculation method

Input data

Average influent flow

Peak influent flow

Mixed liquor TSS (MLSS)

Return sludge ratio R

Settleability (SVI class)

Number of clarifiers

v0 (blank = settleability class)

K (blank = settleability class)

Output data

Return sludge ratio R

Return sludge flow

Total surface area

Area of each clarifier

Diameter of each clarifier

Hydraulic loading rate (average)

Hydraulic loading rate (peak)

Solids loading rate (average)

Solids loading rate (peak)

Return sludge TSS (mass balance)

Underflow TSS the clarifier can reach

Description

Reference