Wastewater Technology – Part 1 - Universität Stuttgart

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UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

1

Iosif Mariakakis

(adopted from the lecture of

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



Exercise: Basic calculations of loads,
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
and for design inflow


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



UNIVERSITÄT

STUTTGART

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

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

4

Design inflow of a WWTP

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)








(about

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

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

7

Design inflow of a WWTP

Inf
h
WW
d
Q
Q
Q



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

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

8

Specific Loads and Concentrations per Inhabitant

Spe
c
ifi
c

Load

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

UNIVERSITÄT

STUTTGART

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
process (without addition of excess
sludge)

6

15

1.5

PS combined with activated sludge
process (with addition of excess
sludge)

2


3

45

2.0

PS combined with trickling filter or
rotating contactors (with/without
addition of excess sludge)

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


UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

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

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

11

Activated Sludge Process (scheme)

Influent

Effluent

Excess
sludge


Return sludge

Aeration tank

Final sedimentation

Aeration

Gujer, 1999

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

12

Parameters of Activated Sludge System


Sludge Loading (kg
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)


Volumetric Loading (kg
BOD
/(m³*d))

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

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

UNIVERSITÄT

STUTTGART

Wastewater Technology


Part 1: Urban Drainage

Exercise
-

Wastewater Quantity

14

Sludge Loading B
X

B
SS


= Sludge Loading kgBOD
5
/(kgSS*d)

B
d,BOD

=
Daily BOD
5

load

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

Sludge Loading B
SS
and Treatment Efficiency

100

80

60

40

20

> 13
°
C

< 11
°
C

Sludge Loading B
SS

BOD
-

Elimination [%]

1,0

10

0,1

0,2

Gujer, 1999

UNIVERSITÄT

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

UNIVERSITÄT

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

UNIVERSITÄT

STUTTGART

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

UNIVERSITÄT

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

Sludge Loading

Biomass Conc.

SS
AT

Sludge Age
SRT

kg/(kg

d)

kg/m³

d

Part Treatment

High
Loaded



1.0

1.5


2.0



1

BOD
5
-
Removal

Medium
Loaded

0.25


0.50

2.0


3.0

2
-

4

Nitrification

Low
Loaded

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


Surface loading important


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