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
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UNIVERSITÄTSTUTTGART
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 TechnologyPart 2: Wastewater treatment
Exercise: Basic calculations of loads,
wastewater streams and tank dimensions
UNIVERSITÄTSTUTTGART
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
UNIVERSITÄTSTUTTGART
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
GreasePrimary
sludge
Aeration
tank
Secondary
sediment.
Raw sludge
Digester
35°C
Thickener and
storage tank
BiogasGas storage
Thickener
Screening Grit
rem.
Grease
rem.
Primary
sediment.
Supernatant
Sludge treatment Guje
r, 1
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
4
Design inflow of a WWTP
Guje
r, 1
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UNIVERSITÄTSTUTTGART
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)
Qww = Qd + Qi + Qi
QDW = QWW + Qinf
Qcomb = QDW + QR
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UNIVERSITÄTSTUTTGART
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
iq
C,iA
WW,dwP
WW,aMQ
86400
Inf,aMQ
WW,aMQ
DW,aMQ
Inf,aMQ
Qx
WW,aMQ
DW,Q
max
24
max
Sourc
e: A
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WK
-Arb
eitsbla
tt A
198 (
April 2003)
[ l/s ]
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
7
Design inflow of a WWTP
InfhW Wd QQQ max,,32
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
8
Specific Loads and Concentrations per Inhabitant
Specific Load
Wastewater concentration [mg/l] for a wastewater production of Parameter
g/C·d 150 l/ C·d 200 l/ C·d 250 l/ C·d
BOD5 60 400 300 240
COD 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. Lmg
dC
LdC
g
CBOD /300200
60000
200
60
5
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
9
Primary sedimentation - dimensioning
Treatment methodqA
[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 SurfaceTank
A
dmin
(h)t (m³/h) Q (m³) V VolumeTank dmin
UNIVERSITÄTSTUTTGART
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 1 2 3 4
Eli
min
ati
on
[%
]
Retention Time [h]
Settleable Solids
Filterable Solids
BOD5 and COD
Nitrogen
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UNIVERSITÄTSTUTTGART
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
Guje
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
12
Parameters of Activated Sludge System
Sludge Loading (kgBOD/(kgTSS*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 (kgTSS/d)
Oxygen Concentration and –Consumption (mg/L)
Volumetric Loading (kgBOD/(m³*d))
UNIVERSITÄTSTUTTGART
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
SSAT =3.0 g/l
Volume: 330 ml/l
SVI=330/3.0
=110 ml/g
UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
14
Sludge Loading BX
BSS = Sludge Loading kgBOD5/(kgSS*d)
Bd,BOD = Daily BOD5 load in influent kg/(m3*d)
VAT = Volume of aeration tank m3
SSAT = Dry solids in aeration tank kg SS/m3
M
F
ismsMicroorgan
Food
SSV
BB
ATAT
BOD,d
SS
5
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
15
Sludge Loading BSS and Treatment Efficiency
100
80
60
40
20
> 13°C
< 11°C
Sludge Loading BSS
BO
D -
Elim
ina
tio
n [%
]
1,0 100,1 0,2
Guje
r, 1
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
16
Sludge Retention Time SRT / Sludge Age tSS
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]/[, ddsolidskgES
mVmkgXSRT
d
ATATTSS
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
17
Sludge Age tSS (SRT)
Size of the plant
< 20.000 PE > 100.000 PE
Dimensioning temperature Treatment target
10° C 12° C 10° C 12° C
Without nitrification 5,0 4,0
With nitrification 10,0 8,2 8,0 6,6
With nitrogen removal
VD/VBB = 0,2 12,5 10,3 10,0 8,3
VD/VBB = 0,3 14,3 11,7 11,4 9,4
VD/VBB = 0,4 16,7 13,7 13,3 11,0
VD/VBB = 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
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UNIVERSITÄTSTUTTGART
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 QRS/Q
SSRS = Suspended Solids Concentration in Return Sludge
SSAT = Suspended Solids Concentration in the Aeration Tank
Return Sludge
RS
SSRSSS RS
AT
1
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UNIVERSITÄTSTUTTGART
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 BOD5)
Excess Sludge Production
X/C = Suspended solids / BOD5 in the influent
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
20
Required mass of suspended solids in the biological reactor (kg)
Volume of aeration tank
dDimATSS ESSRTM ,
Volume of the biological reactor (m³)
AT
ATSSAT
SS
MV
,
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UNIVERSITÄTSTUTTGART
Wastewater Technology – Part 1: Urban Drainage
Exercise - Wastewater Quantity
21
Main Parameter of Activated Sludge Processes
Treatment TargetType of
System
Sludge LoadingBiomass Conc.
SSAT
Sludge Age
SRT
kg/(kg•d) kg/m³ d
Part TreatmentHigh
Loaded 1.0 1.5 – 2.0 1
BOD5-RemovalMedium
Loaded0.25 – 0.50 2.0 – 3.0 2 - 4
NitrificationLow
Loaded0.10 – 0.15 3.0 – 5.0 7 - 12
Nitrification and
Denitrification
N-Eli-
mination0.07 – 0.09 3.0 – 5.0 12 - 15
Aerobic
Stabilization
Extended
Aeration0.04 – 0.07 3.0 – 5.0 15 - 30 D
IN E
N 1
22
55
-6 (
4/2
002)
UNIVERSITÄTSTUTTGART
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
ghm
L
SVIX
q
SV
qq
ATTSS
SVSVA
A
dSST
q
QA
[m/h]
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UNIVERSITÄTSTUTTGART
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