wama 3 wastewater treatment

Department of Hydro Sciences, Institute for Urban Water Management

UNEP Course CIPSEM Dresden, September 2014

Water Management and Climate Change Adaptation

3 Wastewater treatment

Peter Krebs

UNEP Water and Climate 3 Wastewater treatment PK, 2014 page 2

3 Wastewater Treatment

3.1 Boundary conditions

3.2 Layout of a wastewater treatment plant (WWTP)

3.3 Physical treatment

3.4 Biological treatment

3.5 Final clarification

3.6 Sludge treatment

Department of Hydro Science, Institute for Urban Water Management Peter Krebs

Environmental management


Goals of wastewater disposal

Hygiene

Flood protection

Water protection

Hygienic disposal

No backwater effects in and from sewers

Minimising of pollutants impact

Minimising oxygen depletion

Maintaining hygienic water quality


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Rain-runoff processSewage

retention tank

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Retention tank CSO structure

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Urban water system

Infiltration Overflow

Retention

Sedimentation

Sludge disposal

In-/Exfiltration

Clean water inflow

Treatment


The urban drainage system

Overflow structure

Receiving water

Overflow

Combined water storage

WWTP

WWTP effluent

Sewage retention


0

100

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300

400

0 4 8 12 16 20 24Time (h)

I

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Dry-weather flow Q tAverage inflow rate

Capacity of WWTPQ m = 2 Q S,max (85%) + Q f

Q s

Q f

WWTP capacityfor stormwater inflow

Q s,m

Capacity of WWTP

Extraneous water flow

Sewage flow


Extraneous water flow Qf

Groundwater infiltration

Drainage

Small rivers

Water from fountains

Cooling water

Excess water from drinking water reservoirs

Extraneous water flow is variable

sf QQ 5,0Average, if no data available lengthsewerfQ f Better: mechanistic reason


Load variation in WWTP inlet

0

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00:00 04:00 08:00 12:00 16:00 20:00 00:00

Time (hh:mm)

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Daily average COD and NH4

NH4-load

COD-load


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NH4 FrachtAbflussTSS Fracht

Wet-weather load of NH4+ and TSS from sewer N

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NH4+ load

Flow rate

TSS load


Effluent standards

Class COD (mg/l)

2 < 5000 PE 300 kg BOD5 / d

1 < 1000 PE 60 kg BOD5 / d

3 < 10000 PE 600 kg BOD5 / d

5 > 100000 PE 6000 kg BOD5 / d

4 < 100000 PE 6000 kg BOD5 / d

BOD5(mg/l)

NH4-N (mg/l)

N* (mg/l)

Ptot(mg/l)

150

110

90

90

75

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* N = Sum of NH4+, NO3-, und NO2-


Emission

Immission

Approach of Water Framework Directive


Screen Grid and fat chamber

Primary clarifier

Activated sludge tank Secondary

clarifier

MEST

Digester Storage

Return sludgePrimary sludge

Fresh sludge

Fat

Sand

Excess sludge

Biogas

Disposal and treatment with

solid waste

Washing, Disposal

fertiliser compost Drying Incineration

River, filtration

Mechanical treatment Biological treatment

Precipi-tation

Dewatering

Process-water

Process water

FHM

NitriDeni

Sludge treatment

Layout of a WWTP


Example: WWTP Chemnitz-Heinersdorf


Typical residence time in reactors

Mechanical pre-treatment

Primary clarifier

Activated sludge tank

Secondary clarifier

Sludge thickener

Digester

Wastewater HRT (h)

Sludge SRT (d)

0.2

1.5

10

5

0.01

1

10

2

2

20

< 1 d > 1 month


Automatically cleaned trash rack


L

H

U

VS

U

Q

Critical case

Settling condition

LU

HVS

SVH

UL

NBS A

QBLHBUV VS qA

Independent of H !

Sedimentation: hydraulic overflow rate qA = Q/A

(Hazen, 1904)


Grid chamber

In connection with combined systems Effects of non-organic particles:

Abrasion of steel (e.g. pumps)Clogging (Sludge hopper, pipes, Pumps)Sedimentation (activated sludge tank, digester) High maintenance requirements

Sludge in sand is hindering Sand in sludge is detrimental for operation !


Aerated grid chamber


Efficiency of primary clarifier

0102030405060708090

100

0 1 2 3 4 5

Residence time HRT (h)

E

f

f

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y

(

%

)

settleable solids

TSS

BOD5


Effects of primary clarifier on wastewater

Compound Unit Inlet Outlet*in

outin

CCC

TSS BOD5CODTKN NH4-N NO2-N NO3-N PtotAlkalinity

g TSS / m3

g O2 / m3

g O2 / m3

g N / m3

g N / m3

g N / m3

g N / m3

g P / m3

mol HCO3- / m3

360 30060060 4001

10= f(Drinking water) + NH4-N

180 23045056 4001 9

0.5 0.230.250.067 000 0.1

* Short residence time


Biological treatment

Suspended biomass Activated sludge system

Sessile biomass Biofilm system

suspended through turbulence sludge flocs with 0.1 1 mm diameter degradation related to biomass

biofilm on carrier little erosion degradation related to biofilm surface area

Increase suspended biomass concentration

Increase of specific surface area


Important micro-biological processes

Growth

Decay

Hydrolysis

Aerobic degradation Nitrification

Denitrification

Implementation of C, N, P in biomass

If external nutrients are rare

Heavily easily degradable substances, through encymes

organic compounds CH2O + O2 CO2 + H2O

NH4+ + 2 O2 NO3- + H2O + 2 H+

5 CH2O + 4 NO3- + 4 H+ 2 N2 + 5 CO2 + 7 H2O


Inlet


Secondary clarifier

Effluent

Return sludge Excesssludge

Nutrients

Bacteria

Air, O2 Sedimentation

Activated sludge system


Sludge inventory in activated sludge system


Secondary clarifier

Q Q + QRASXAST

XAST

Q

Xe

QRAS = RQXRAS

(QWAS)

(XWAS)

Sludge balance in equilibrium

RRXX ASTRAS

1Q

QR RASmit


Flow scheme of activated sludge system

Hydraulic wash-out of sludge to secondary clarifier sludge must be returned to activated sludge tank

Activated sludge is circled 20 to 50 times sludge concentration in activated sludge tank is maintained

Excess sludge is withdrawn from system equivalent to sludge production

Through increased hydraulic loading (wet-weather condition) sludge is shifted to secondary clarifier


Dynamic sludge shift

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Sludge bed


Dimensioning on sludge loading

Sludge loading ASTAST

in,

XVBODQ

M/F 5

dTSSkgBODkgin 5

F/M BOD5 loading related to dry sludge mass (Food/Microorganisms)

Q Inflow to WWTP (m3/d)

BOD5,in BOD5 concentration in inlet (kg BOD5 / m3)

VAST Volume of activated sludge tank (m3)

XAST Sludge concentration in activated sludge tank (kg TSS / m3)

BOD5 inlet load is related to sludge mass in activated sludge tank (AST)


Dimensioning on sludge age

Sludge age BODin,BOD

ASTASTASTAST

ESPM/FBODQESPXV

SPXVSRT

15

SRT Sludge age in (d), 3 15 d

SP Sludge production (kg TSS / d)

ESPBOD Specific excess sludge production per BOD5 converted (kg TSS / kg BOD5)

Sludge production is related to sludge mass in activated sludge tank

inBOD BODQESPSP ,5


Nutrients demand of micro-organisms

Nitrogen iN = 0.04 0.05 (g N / g BOD5) Phosphorous iP = 0.01 0.02 (g P / g BOD5)

Partial elimination of nutrientsWastewater composition in the inlet 300 (g BOD5/m3)

60 (g TKN/m3) 12 (g TP/m3)

Effluent concentrations after 100% BOD5 degradation

TKNeff = TKNin iNBOD5,in = 60 0.045300 = 46.5 (g N / m3)

TPeff = TPin iPBOD5,in = 12 0.015300 = 7.5 (g P / m3)

Enhanced nutrients removal is necessary!


Nitrification NH4+ NO3-Nitrifying organisms (autotrophic biomass XA) have a low growth rate A

high sludge age necessary to omit nitrifiers from being washed out of the system

ASTASTAAASTAA VXVrSP ,

AASTAST,AA

AST,AAST

A

AST,AAST SFVX

XVSF

SPXV

SFSRT

1

With production of autotrophic biomass

and a safety factor SF the necessary sludge age yields

Volume of activated sludge tank must be large


anoxic aerobic

aerobic

C-Elimination

Nitrification

De-nitrification

Bio-P

aerobic

anaerobic anoxic aerobicanoxic

Development of activated sludge system


Design rules

Type of biological reactor

Without nitrification

Nitrification >10C

Denitrifi-cation

Simultaneous aerobic sludge stabilisation

SRT < 20000 PE

> 100000 PE

ESPBOD

F/M

5

0.9 1.2

0.30

4

10

0.8 1.1

0.15

8

12 18

0.7 1.0

10 16

0.12

25

1.0

0.05 (kg BOD5 / (kg TS d))

(kg TS / kg BOD5)


Trickling filter

Primary clarification

Trickling filter

Secondary clarification

Recirculation

Return sludgeSludge

withdrawal

Biofilm grown on internal surface


Dimensioning of trickling filter

Surface loading TF

inSu Va

BODQB

,5

BSu Surface loading (g BOD5 / (m2d))

without nitrification 4 (g BOD5 / (m2d)), with nitrifi. 2 (g BOD5 / (m2d))

Q Inflow to trickling filter (m3/d)

BOD5,in BOD5 inlet concentration (kg BOD5 / m3)

VTF Volume of trickling filter (m3)

a Specific biofilm surface per volume of trickling filter (m2 / m3 TF)

100 140 180 (m2 / m3 TF)


Degradation in trickling filter

Concentration

BOD5

NH4+

N03-

Trickling filter

C-degradation and nitrification are separated in space


Functions of final clarifiers

Separation

Clarification

Storage

Thickening

of sludge and cleaned wastewater through Sedimentation

Low effluent concentrationof sludge shifted from actibated sludge tank, namely under wet-weather conditions

High return sludge concentration

Geometry Circular, flow from centre to periphery Rectangular, longitudinal flow Rectangular, lateral flow Vertical, upward flow


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Particle-Interaction

Thickening

Hindered settling

Flocculating settling

Free settling

none flocculatinghigh

low

Classification of sedimentation processes

Primary clarifier Final clarifier, separation zone

Final clarifier, sludge bed

Final clarifier, bottom


Sludge volume index SVI

SVI is an indicator for volume of sludge flocs and their settling characteristics

0.5 h

H

hS

X0

V

HhVSV S

0XSVSVI

Sludge volume

(ml/l)

(ml / g TSS)


Final clarifier, idealised functions

Clear water layer

Separation layer

Storage layer

Thickening layer

Inlet zone Effective zone

> 3 m

ATV A131 (2000)


Dimensioning of surface

Surface overflow rate SVIXq

SVq

AQq

AST

SVSV

FCA

Sludge overflow rate SVIXqq ASTASV

Limit values qA qSV

(m/h) (l/(m2h)

Horizontal flow tanks

Vertical flow tanks

1.6

2.0 650

500

ATV A131 (2000)


Dimensioning of water depth

Clear water layer

Separation layer

Storage layer

Thickening layer

m501 .h 10001150

2 SVRqh A

.

500

130513

Rqh SV ..

BS

thAAST

XtRqXh 14 311000 thBS tSVIX

XBS Sludge concentration at bottom

tth Thickening time 1.5 2.0 h without nitrification 1.0 1.5 h with nitrification 2.0 (2.5) h with denitrification ATV A131 (2000)


Circular tank

With scraper or suction removal device

Inlet

Flocculation chamber

Scum skimmer

Sludge scraper


Rectangular tank, longitudinal flow, flight scraper system

Sludge hopper

Inlet

Sludge

Chain motor Water level Effluent launder

Effluent


Rectangular sedimentation tank

Primary / secondary clarifier Flight scraper

Effluent weir

Inlet

Sludge withdrawal

Effluent to activated sludge tank or to receiving water

Surface:

Primary clarifier qA = 2 to 6 m/h

Secondary clarifier qA = 0.5 to 1.5 m/h


Rectangular tank, lateral flow, suction system

Removal bridge Inlet channel

Scum skimmer

Inlet baffle


Vertical flow tank

Effluent

Filter

Thickening

Inlet

Return sludge

Return sludge

Effluent launder

Pump


Composition of sludge

All non-degraded compounds removed from wastewater are in the sludge

Micro-organisms

Viruses, pathogens, germs

Inert and heavily bio-degradable organic particles energy

Nitrogen, renewable resource ev. use as fertiliser

Phosphorous, non-renewable resource recovery

Heavy metals, micro-pollutants

Predominantly water


Goals of sludge treatment

Volume reduction

Elimination of pathogenic germs

Stabilisation of organic substances

Recycling and use of substances

Thickening Dewatering

If used in agriculture as fertiliser or compost

Gas production Reduction of dry content Improvement of dewatering characteristics Reduction of odour

Nutrients, fertiliser Humus Biogas


Overview

Thickening

Thickening

Hygienisation

Stabilisation

Dewatering

Drying

Incineration

P

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Biogas

Energy

Agriculture

Disposal site

Atmosphere

Wastewater treatment

Primary, secondary, tertiary sludge

Construction industry

Gujer (1999)


Water content of stabilised sludge > 95% ! reduction of water content and volume

Sludge volume

SWDSWDSS VVVVV With water content S

WW V

V

DSW

S VV 11

non-linear relation!

Volume reduction

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Water content W

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S thickeningdewateringdrying


Anaerobic mesophilic sludge stabilisation

Content of digester is mixed Sludge and water obtain a similar residence time

Heated to 33 37C process rates are higher

34242275 HCO2NH2CO3CH5OH8NOHC2

Biogas production: 63% CH4 (Methane) 35% CO22% other gases (N2, H2, H2S)

electricity and heating

Organic nitrogen is converged to NH4+

N-loading of WWTP

Degradation of organic substances of app. 50%


Sketch of an anaerobic digester (egg shape)


Construction of a digester


Incineration

Use of energy content, and eventually of P

Mono incineration (sludge exclusively)

Co- incineration

In solid waste incinerators

In cement production, ash is bounded to cement

Calorific value of sludge high enough no biogas use before, no stabilisation Water content not minimised (no full drying)

Incineration at 800 950C in fluidised sand bed

Expensive!

In coal power station


Incineration: calorific value of sludge

-5

0

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0 10 20 30 40 50 60 70 80 90 100dry mass content [ % ]

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40% oTR 50% oTR

60% oTR 70% oTR

Stone cole

Waste Brown cole

but: Energy investment for dewatering and drying

wama 3 wastewater treatment

Documents

wastewater treatment

loadunep water

biological treatment

physical treatment

mechanistic reasonunep

wastewater treatment3

und no2unep water

climate change adaptation