Wastewater Technology – Part 1 - Universität Stuttgart

Mécanique

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UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

1

Iosif Mariakakis

Prof. Dr.
-
Ing. Heidrun Steinmetz)

Institute of Sanitary Engineering,

Water Quality and Solid Waste Management

-

Sanitary Engineering and Water Recycling
-

Wastewater Technology

Part 2: Wastewater treatment

wastewater streams and tank dimensions

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

2

Contents

Calculation of wastewater inflow into a WWTP

Calculation of wastewater load into a WWTP for dry weather conditions

Dimensioning principles of primary sedimentation

Short description of the Activated Sludge biological treatment

Fundamental parameters of the Activated Sludge biological treatment

Dimensioning principles of the aeration tank of the Activated Sludge
system

Dimensioning principles of the sedimentation tank (secondary
sedimentation) of the Activated Sludge system

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Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

3

Basic Flow Scheme of a WWTP

Secondary sludge

= Excess sludge

Dewatering and

-
agricultural use

-
landfill

-
incineration

Primary treatment

Biological treatment

Return sludge

Screenings

Sand

Influent

Effluent

Grease

Primary

sludge

Aeration

tank

Secondary

sediment.

Raw sludge

Digester

35
°
C

Thickener and

storage tank

Biogas

Gas storage

Thickener

Screening

Grit

rem.

Grease

rem.

Primary

sediment.

Supernatant

Sludge treatment

Gujer, 1999

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STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

4

Gujer, 1999

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

5

Definitions

Wastewater (Sewage)

Dry weather flow (DWF)

Combined wastewater flow (CWF)

100

times the dry weather flow)

Q
ww

= Q
d

+ Q
i

+ Q
i

Q
DW

= Q
WW

+ Q
inf

Q
comb

= Q
DW

+ Q
R

Source: ATV
-
DVWK
-
A 198E

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

6

Daily Variations of Wastewater Flow

Determination of yearly wastewater flow (sewage flow on all days)

Determination of yearly dry weather flow (dry weather flow on days without rain)

Determination of peak flow during dry weather

i
q
C,i
A
WW,d
w
P
WW,aM
Q

86400
Inf,aM
Q
WW,aM
Q
DW,aM
Q

Inf,aM
Q
Q
x
WW,aM
Q
DW,
Q

max
24
max
Source: ATV
-
DVWK
-
Arbeitsblatt A 198 (April 2003)

[ l/s ]

Source: ATV
-
DVWK
-
A 198E

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STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

7

Inf
h
WW
d
Q
Q
Q

max
,
,
3
2
Source: ATV
-
DVWK
-
A 198E

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STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

8

Specific Loads and Concentrations per Inhabitant

Spe
c
ifi
c

W
astewater concentration
[mg/l]
for a wastewater production of

Parameter

g/
C

d

150 l/
C

d

200 l/
C

d

250 l/
C

d

B
OD
5

60

400

300

240

C
OD

120

800

600

480

N

11

73

55

44

P

1
.
8

12

9

7

TS

70

470

350

280

< 15 mg/l

< 75 mg/l

< 13 mg/l

< 1 mg/l

< 20 mg/l

Typical effluent
values of a
WWTP with

100,000 EW

e.g.

L
mg
d
C
L
d
C
g
C
BOD
/
300
200
60000
200
60
5

Source: ATV
-
DVWK
-
A 131E

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Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

9

Primary sedimentation
-

dimensioning

Treatment method

q
A

[m/h]

t

[min]

T

[m]

PS combined with activated sludge
sludge)

6

15

1.5

PS combined with activated sludge
sludge)

2

3

45

2.0

PS combined with trickling filter or
rotating contactors (with/without

3

30

1.5

(m/h)

q
(m³/h)

Q

(m²)

A

Surface
Tank
A
d
min

(h)
t

(m³/h)

Q

(m³)

V

Volume
Tank
d
min

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Wastewater Technology

Part 1: Urban Drainage

Exercise
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Wastewater Quantity

10

Efficiency of Primary Sedimentation

0
10
20
30
40
50
60
70
80
90
100
0
0,5
1
1,5
2
2,5
3
3,5
4
Retention Time [h]
Elimination [%]
Settleable Solids

Filterable Solids

BOD
5

and COD

Nitrogen

Source: ATV
-
Handbuch, 1997a

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Wastewater Technology

Part 1: Urban Drainage

Exercise
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Wastewater Quantity

11

Activated Sludge Process (scheme)

Influent

Effluent

Excess
sludge

Return sludge

Aeration tank

Final sedimentation

Aeration

Gujer, 1999

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Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

12

Parameters of Activated Sludge System

BOD
/(kg
TSS
*d)

Sludge Age, Sludge retention time; Mean Cell Residence
Time (d)

Biomass Concentration = Total suspended solids (TSS)

MLSS = Mixed Liquor Suspended Solids (kg/m³)

SV = Sludge Volume (mL/L)

SVI = Sludge Volume Index (mL/g)

Return Sludge Ratio (%)

Excess Sludge Production (kg
TSS
/d)

Oxygen Concentration and

Consumption (mg/L)

BOD
/(m³*d))

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Wastewater Technology

Part 1: Urban Drainage

Exercise
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Wastewater Quantity

13

Sludge Volume Index

In this Example

Sludge Volume Index

SVI = 110 ml/g or l/kg

(Diluted) Sludge Volume

SV=330 ml/l or l/m³

800

600

200

400

1000

800

600

1000

400

200

Start of Test

After 30 min

1 liter of Act. Sludge

SS
AT
=3.0 g/l

Volume: 330 ml/l

SVI=330/3.0

=110 ml/g

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Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

14

X

B
SS

5
/(kgSS*d)

B
d,BOD

=
Daily BOD
5

in influent kg/(m
3
*d)

V
AT

= Volume of aeration tank m
3

SS
AT

= Dry solids in aeration tank kg SS/m
3

M
F
isms
Microorgan
Food
SS
V
B
B
AT
AT
BOD
,
d
SS

5
Source: ATV
-
DVWK
-
A 131E

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

15

SS
and Treatment Efficiency

100

80

60

40

20

> 13
°
C

< 11
°
C

SS

BOD
-

Elimination [%]

1,0

10

0,1

0,2

Gujer, 1999

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STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

16

Sludge Retention Time SRT / Sludge Age t
SS

Sludge Retention Time (
SRT
) = Sludge Age = Mean Cell
Residence Time (
MCRT
)

The
SRT

is the average retention time of every sludge floc in the
system

The
SRT

controls the microbial population in the activated sludge

High SRT

slowly growing organisms can stay in the system (e.g. nitrifying
bacteria)

The
SRT

is difficult to measure, but it can be calculated as:

Mass of TSS in the aeration tank/daily sludge production

]
[
]
/
[
³]
[
³]
/
[
,
d
d
solids
kg
ES
m
V
m
kg
X
SRT
d
AT
AT
TSS

Source: ATV
-
DVWK
-
A 131E

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STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

17

Sludge Age t
SS
(SRT)

Size of the plant

< 20.000
PE

> 100.000
PE

Dimensioning temperature

Treatment target

10° C

12° C

10° C

12° C

W
ithout

n
itrifi
c
ation

5,0

4,0

W
ith n
itrifi
c
ation

10,0

8,2

8,0

6,6

W
ith nitrogen removal

V
D
/V
BB
= 0,2

12,5

10,3

10,0

8,3

V
D
/V
BB
= 0,3

14,3

11,7

11,4

9,4

V
D
/V
BB
= 0,4

16,7

13,7

13,3

11,0

V
D
/V
BB
= 0,5

20,0

16,4

16,0

13,2

Sludge
stabilization

incl. nitrogen removal

25,0

not
recommended

Selection of sludge age according to treatment purpose

Source: ATV
-
DVWK
-
A 131E

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Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

18

With return sludge, thickened activated sludge is pumped back
into the aeration reactor

RS = Return Sludge Ratio Q
RS
/Q

SS
RS

= Suspended Solids Concentration in Return Sludge

SS
AT

= Suspended Solids Concentration in the Aeration Tank

Return Sludge

RS
SS
RS
SS
RS
AT

1
Source: ATV
-
DVWK
-
A 131E

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

19

Sludge
Age [
days]
X/C
4
8
10
15
20
25
0,4
0,79
0,69
0,65
0,59
0,56
0,53
0,6
0,91
0,81
0,77
0,71
0,68
0,65
0,8
1,03
0,93
0,89
0,83
0,80
0,77
1,0
1,15
1,05
1,01
0,95
0,92
0,89
1,2
1,27
1,17
1,13
1,07
1,04
1,01

Specific excess sludge production (kg SS/kg BOD
5
)

Excess Sludge Production

X/C = Suspended solids / BOD
5

in the influent

Source: ATV
-
DVWK
-
A 131E

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STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

20

Required mass of suspended solids in the biological reactor (kg)

Volume of aeration tank

d
Dim
AT
SS
ES
SRT
M

,

V
olume of the biological reactor
(m³)

AT
AT
SS
AT
SS
M
V
,

Source: ATV
-
DVWK
-
A 131E

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

21

Main Parameter of Activated Sludge Processes

Treatment Target

Type of
System

Biomass Conc.

SS
AT

Sludge Age
SRT

kg/(kg

d)

kg/m³

d

Part Treatment

High

1.0

1.5

2.0

1

BOD
5
-
Removal

Medium

0.25

0.50

2.0

3.0

2
-

4

Nitrification

Low

0.10

0.15

3.0

5.0

7
-

12

Nitrification and
Denitrification

N
-
Eli
-
mination

0.07

0.09

3.0

5.0

12
-

15

Aerobic
Stabilization

Extended
Aeration

0.04

0.07

3.0

5.0

15
-

30

DIN EN 12255
-
6 (4/2002)

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Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

22

Secondary settling tank

Dependant from the sludge characteristics (SVI)

Calculation of the tank surface

[m²]

]
[
]
[
)]
[
3
2
,
kg
L
g
mL
m
kg
L
g
h
m
L
SVI
X
q
SV
q
q
AT
TSS
SV
SV
A

A
d
SST
q
Q
A

[m/h]

Source: ATV
-
DVWK
-
A 131E

UNIVERSITÄT

STUTTGART

Wastewater Technology

Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

23

Secondary settling tank

Depth of the sedimentation tank

Dependant from the sludge characteristics (SVI)

Dimensioning of the different zones according DWA A
-

131

Sludge level
Compression,
Consolidation
Removal of sludge
Outflow
Solids concentration
DS
o
DS
RS
Water zone
h
1
Thickening zone
Removal zone
h
4
Separation zone
h
3
Storage zone
h
2
Water level
Settling (hindered)
o
h
1
h
4
h
3
h
2
Inflow
Sludge level
Compression,
Consolidation
Removal of sludge
Outflow
Solids concentration
DS
o
DS
RS
Water zone
h
1
Thickening zone
Removal zone
h
4
Separation zone
h
3
Storage zone
h
2
Water level
Settling (hindered)
o
h
1
h
4
h
3
h
2
Inflow

h
1

= 0.5 m (min. for safety reasons)

h
2

= [0.5

q
A

(1 + RS)] / (1
-
SV / 1000)

h
3

= 0.45

q
SV

(1 + RS) / 500

h
4

= [X
TSS,AT

q
A

(1 + RS)

t
Th
] / X
TSS,SST

Source: ATV
-
DVWK
-
A 131E