Application of ASM

Grady et al. (1999) published some examples for applications of the ASM 1. It is necessary to first determine values for all 19 coefficients compiled in Table 11.5.

Some of them have been chosen from mean values from many kinetic measurements; some of them are still unreliable. The processes 6 (ammonification of soluble organic nitrogen) and 8 (hydrolysis of entrapped organic nitrogen) are neglected.

In addition to the parameters in Table 11.5, some characteristics of a domestic wastewater following primary sedimentation were considered (Table 11.6).

A large number of questions can be answered using this model. One interesting question is: what is the oxygen requirement QG Ac°2 in dependence on sludge retention time tRX? The model was calculated for a steady-state condition and XA + XH; and then XH and QG Ac°2 were both plotted versus sludge age (Fig. 11.3).

Table 11.5 Typical parameter values at neutral pH and 20 °C for domestic wastewater (Grady et al. 1999, p. 199).

Symbol

Units

Value

Stoichiometric coefficients

YXH/SS

mg biomass COD formed per mg COD removed

0.60

fp

mg debris COD (mg biomass COD)-1

0.08

Ixb

mg N (mg COD)-1 in active biomass

0.086

Ixp

mg N(mg COD)-1 in biomass debris

0.06

1 XA/NH4

mg biomass COD formed per mg N oxidized

0.24

Kinetic parameters

h-1

0.25

Ks

mg L-1 COD

20

KH

mg L-1 O2

0.10

Kno

mg L-1 N

0.20

kdH

h-1

0.017

n

Dimensionless

0.8

%

Dimensionless

0.4

ka

L (mg biomass COD h)-1

0.0067

kH

mg COD (mg biomass COD h)-1

0.092

Kx

mg COD (mg biomass COD)-1

0.15

Fmax,A

h-1

0.032

Kno

mg L-1 N

1.0

KA

mg L-1 O2

0.75

kdA

h-1

0.004

Table 11.6

Characteristics of a domestic wastewater of the USA after

primary sedimentation (Grady et al. 1999, p. 214; Bidstrup and Grady 1988).

Symbol

Component

Concentration

(mg L-1)

X,

Inert particulate organic matter (COD)

35.0

Xs

Slowly biodegradable substrate (COD)

150.0

Ss

Readily biodegradable substrate (COD)

115.0

c'

Oxygen (O2)

0.0

SNO

Soluble nitrate N

0.0

SNH

Soluble ammonia N

25.0

SNS

Soluble biodegradable organic N

6.5

XND

Particulate biodegradable organic N

8.5

Fig. 11.3 Effect of sludge age tRX on bacterial concentration XH and XH + XA as well as oxygen demand in a CSTR with tRX/tR = 20. Parameter values given in Tables 11.5 and 11.6. c' = 4.0 mg L-1 (Grady et al. 1999, p. 214).

11.3 Models for Optimizing the Activated Sludge Process 285 1-1-1-r

Fig. 11.3 Effect of sludge age tRX on bacterial concentration XH and XH + XA as well as oxygen demand in a CSTR with tRX/tR = 20. Parameter values given in Tables 11.5 and 11.6. c' = 4.0 mg L-1 (Grady et al. 1999, p. 214).

The sludge age can be calculated using: V(XA + XH)

QexXR V 1

where Qex is the excess sludge flow rate (m3 d-1) and XR is the concentration of excess sludge (kg m-3).

For a sludge age of tRX < 35 h, the nitrifiers are washed out. Their growth rate is too low compared with their dilution time in the system consisting of reactor and secondary clarifier. For tRX> 148 h = 7 d, the oxygen demand increases mainly as a result of endogenous respiration; nitrogen and carbon are removed to a greater extent.

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