Case study: Design of VEAS Wastewater Treatment Works

at Oslo of Norway and other Norwegian plants built underground

Prof. em. Hallvard Ø degaard

NTNU/SET AShallvard.odegaard@ntnu.no

Where is Norway, Oslo and VEAS WWTP

VEAS - the history

• 1970'ies - Discussions on location and process for VEAS WWTP for prevention of eutrophication of the Oslo fjord

• 1982 – 1995 Direct precipitation plant (CEPT) built inside rock caverns• 1989 – Nitrification required and retrofit with new compact CEPT settling

tanks • 1990 – New standard : N-removal required• 1991 – 1995 Retrofitting planned and executed, targeting N- removal, without

footprint expansion. • 1993 - Digestors in operation • 1996 – N-removal in operation

– Wastewater process:• CEPT• Nitrification/post-denitrification in biofilters

– New sludge treatment facilities:• Mechanical thickeners installed• Ammonium stripping on sludge water (1997)

• 2003 Filterpress retrofitted for thermal vacuum drying• 2008 – New stormwater-plant based on Actiflo in operation

The rock cavern system

• Plant designed for 4.8 m3/sec

• 8 parallel lines

• 6 lines of N-removal in BAF's• 2.6 – 2.8 m3/sec

• 2 lines of CEPT (stormwater)Deep sludge blanket lamellasettling tanks

• New stormwater plant (RVR)based on Actiflo

• The tunnel represents a reservoir of 150-200.000 m3

Flow sheet of existing plant

Coagulant

Inlet

Screens

Washwater

Polymer

Gritremoval

SettlingTank

SieveNitrification

filterDenitrification

filterOutlet

Washwater tankTrash picker

Internal recycles

Polymer

Sludgethickener

Sludgeholding

tank

Lime

Vacuumfilterpress/dryer

Ammonium stripperMethanol

HNO3

NH4NO3

Air

SludgeWater

Constructed soil

Trashpicker

Air

SludgeWater

07.05.2004

K

u

n

kj

e

m

i

K

u

n

kj

e

m

i

Prøvetaking

innløp 2 st

Prøvetaking utløp, 8 st

Prøvetaking

RVR, 3 st

Overview of basin halls and flow path

Overview – Flows at VEAS, 2008-2012

2012:• Treated water : 105.106 m3

(99,2 %)

• In main plant : 99.106 m3

(94,0 %)o Biol/chem : 90,3 .106 m3

(86,0 %)o Chem (CEPT): 8,7.106 m3

(8,2 %)

• In RVR : 5,6 .106 m3

(86,0 %)o Chemical : 4,2.106 m3

(4,0 %)o Mechanical : 1,4.106 m3

(rist) (1,3 %)

• Untreated overfl. 0,93 .106 m3

(in tunnel system) (0,9 %)

Main plant

RW plant Overflow

Supplied and treated wastewater flows

Q50% = 2,8 m3/sec , Q90% = 5,9 m3/sec, Q95% = 7,3 m3/sec, Q99% = 9,0 m3/sec

l/sec

50 % 90 % 99 %

Max. cap.bio- step

Max. cap.main plant

Max. cap.incl. RVR

Absolute max. cap. at rainstorm

Supplied 2011 Sum treated 2011

Overall treatment results 2011

SS mg/l

BOD mg/l

TOCmg/l

Tot Pmg/l

Tot Nmg/l

NH4-Nmg/l

TOFdypv

mg O2/l

VEAS, 2011 10,5 8,4 15 0,26 7,7 4,4 39,5

VEAS, 2030 5 4 8 0,10 3,0 1,0 15,3

% reduksjon 2011-2030 52 52 40 61 61 75 58

Planning for 2030

Screening

Coagulant addition

A = 278 m2

D = 10,5 mA = 4 x 87 = 348 m2

D = 5 m (til filterbunn)

6,0 m

15,7 m

Sed

N1

N4N2

N3

14,7 m17,7 m 4,4 m 14,7 m 12,7 m

Maskin rom

3,7 m

DN1

DN2

DN3

DN3

10,75 m

Rentvannsbass.

10,75 m

A = 4 x 65 = 260 m2

D = 4,4 m til filterbunn)A = 200 m2

D = 6 m

The deep CEPT settling tank

Number of tanks: 6 Brutto area: • Per tank: 278 m2 (15,7 m x 17,7 m) • Total: 1668 m2

Depth: 10,5 m (12 m fra center bottom to surface)

Lamellas:• Length: 71,5 cm• Distance between: 12,5 cm• Angle: 60°Surface overflow rate• Daily operation : 4.5 – 7 m/h• Peak flow: max 12 m/hSludge conc. Out : 3.5 % DS

Similar tank at Høvringen WWTP, Trondheim

Number of tanks: 4

Size: • Area : 225 m2

• Volume: 2025 m3• B/W: 15 x 15 m • Depth: 9 m

Overflow rate, • 5,0 m/h at Qdim

• 7,8 m/h at Qmaksdim

Overflow rate on projectd area • 0,6 m/h at Qdim• 0,9 m/h at Qmaksdim

• Submerged overflow pipes

• Bottom scraper

SS versus turbidity – VEAS Sed8To

tal s

usp

eb

de

dso

lids

(TSS

), m

g/l

Turbidity, FTU

Separation performance

Surface overflow rate, m/h

Turb

idit

y, F

TU

Sludge surface rate, kg TSS/m2d

TSS

in e

fflu

en

t, m

g/l

NH4-N in effluent, mg N/l

Turb

idit

y, F

TU

TSS in inlet water, mg/l

TSS

in e

fflu

en

t, m

g/l

• Upflow BAF

• Co-current, intermittent backwash

• Expanded clay or expanded shale media– 3.5 or 4.5 mm round– 2.7 mm angular

• Even water and air distribution

• High velocities

• Need good screening upstream

The nitrification filters - BIOFOR

The nitrification filters

Number of filter cells: 24 (4 x 6)Each filter• Area : 87 m2 (14,7m x 6 m)• Filter volume: 330 m3

Water depth: 6,6 m• Depth above filter bottom: 5,2 m• Gravel depth: 0,3 m• Filter depth: 3,8 m• Depth above filter: 1,1 m

Biofilter loading rate vs temperatureLo

adin

gra

te g

NH

4-N

/m3d

Temperature, oC

Nitrification removal vs loading rateN

itri

fica

tio

nra

te,

g N

H4-N

/m3d

Ammonium load , g NH4-N/m3d

Nitrification rate vs temperature

Ѳ = 1.035

Nit

rifi

cati

on

rate

, g

NH

4-N

/m3d

Temperature, oC

Influence of particle loading

Nit

rifi

cati

on

rate

, g

NH

4-N

/m3d

Particle loading, gTSS/m3d N

itri

fica

tio

nra

te,

g N

H4-N

/m3d

Particle loading, g TSS/g NH4-N

Diurnal variations

DO out of filters vs temperatureD

O o

ut

of

filt

er,

g O

2/m

3

Temperature, oC

The denitrification filters

Number of filter cells: 24 (4 x 6)Each filter• Area : 65 m2 (10,8m x 6 m)• Filtervolume: 195 m3

Water depth: 5,5 m• Depth above filter bottom: 4,4 m• Gravel depth: 0,3 m• Filter depth: 3,0 m• Depth above filter: 1,1 m

Methanol addition:

Phosphorous addition when: PO4-P < 0,2 mg/l

3,0

1,1

0,3

1,4

Denitrification rate vs temperature - all filtersD

en

itri

fica

tio

nra

te,

g N

Ox

-N/m

3d

Temperature, oC

Denitrification rate vs temperature

Ѳ = 1.01 based onNOx- Nequiv.

Ѳ = 1.01 based onNOxN

Temperature, oC

De

nit

rifi

cati

on

rate

, g

NO

x –N

equ

iv./

m3d

o

r g

NO

x -N

/m3d

DN-rate versus NOx-N loading rate

Average denitrification rate (1.3.2010 – 1.7. 2011): 715 g NOx-N/m3filter

. d

De

nit

rifi

cati

on

rate

, g

NO

x -N

/m3d

Loading rate, g NOx -N/m3d

Methanol dosage – as C/N values

How it looks inside the rock cavern

Using lining fabrics to make work-placepleasant – from RVR

The plant positioning inside caverns

Future expansions

Høvringen WWTP, Trondheim

- Qave = 96. 000 m3/d

- Qdim = 4 500 m3/h

- Qmaksdim= 7 000 m3/h

- Qmaks = 15 000 m3/h

- Max observed = 17 000 m3/h

Number of tanks: 4

Size: • Area : 225 m2

• Volume: 2025 m3• B/W: 15 x 15 m • Depth: 9 m

Overflow rate, • 5,0 m/h at Qdim

• 7,8 m/h at Qmaksdim

Overflow rate on projected area • 0,6 m/h at Qdim• 0,9 m/h at Qmaksdim

• Submerged overflow pipes

• Bottom scraper

Deep CEPT settling tank at Høvringen WWTP, Trondheim

NRA WWTP (outside Oslo, Norway)

Inlet

Screens

Sand and fat removal

Pre-settling

Post-settling

Biological treatment

Sludge treatment

Sludge storage

The Moving Bed Biofilm Reactor (MBBR) in practice

MBBR in glasfiber re-inforced plastic

Bucher filter press

NRA WWTP

- Qave = 45. 000 m3/d

- Qdim = 2.000 m3/h

- Qmaksdim= 5. 000 m3/h

- Max observed = 8.000 m3/h

• 35-40% of all wastewater from Oslo, treated at Bekkelaget WWTP

• Plant put in operation in 2000

• Owned by the City of Oslo, operated by the private company Bekkelaget Water inc. (BEVAS)

• Approximate 280.000 pe

• Average daily flow ~100.000 m3/d

• Average design flow: 125.000 m3/d

• Outlet requirements:P-removal > 90%N-removal > 70%(including overflow)

• Sludge production ~5.800 tons DS/year

BEVAS WWTP, Oslo, Norway

VEAS

BEVAS

Rock caverns

Admin. building

Water and sludge treatment process

Buffertank

BufferSilo

Silo

Dewatering

Thickener

DigesterDigester

OverflowMagasin~35.000m3

4000 l/s < Q < 6000 l/s

Sand, grit and screenings FeSO4

PAX-18

Activated sludgeClarifierPrimary Filter

Primary sludge

Bio sludge

PrecipitationPrimary

1900 l/s<Q< 4000 l/s

Q=1900 l/s

PAX-18

Q<1900 l/s

Overview of underground plantWater treatment

1. Inlet tunnel

2. Screens, sand and grit removal

3. Primary settling/ direct precipitation

4. Bio step, activated sludge

5. Clarifiers

6. deAmmon®

7. Sand filters

Sludge treatment

8. Digesters

9. Sludge treatment

10. Sludge treatment

11. Ventilated air treatment – odor control

212 m

Bakgrunn og rammer

Overview of plantExpansion in yellow

Underground area: 40.000 m2 todayLength of rock cavern: 212 mWidth of rock cavern: 22 m