Surrey, UK July 2015

Department of Chemical Engineering

Direct gas emissions in urban sewer networks

Case study of two climatic regions

Elena Eijo-Ríoa,b, Gara Villalbaa,b, María Eugenia Suárez-Ojedac, Desirée Marínd, Maria José Amoresd, Xavier Gabarrella,b

aSostenipra (ICTA-IRTA-Inèdit) 2014 SGR 1412 Institute of Environmental Science and Technology (ICTA), Universitat Autònoma de Barcelona (UAB), Edifici ICTA-ICP, Carrer de les Columnes, 08193 Bellaterra, Barcelona, Spain.

bDepartment of Chemical Engineering, Xarxa de Referència en Biotecnologia (XRB). School of Engineering (ETSE), Universitat Autònoma de Barcelona (UAB), Campus of the UAB, Bellaterra (Cerdanyola del Vallès), 08193 Barcelona, Catalonia, Spain.

cGENOCOV research group, Department of Chemical Engineering. School of Engineering, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain.

dCETaqua, Water Technology Centre, Carretera d’Esplugues 75, 08940 Cornellà de Llobregat, Barcelona, Spain

INDEX

1. INTRODUCTION

2. CASE STUDIES

3. CONCLUSIONS

4. FUTURE WORK

2/14

1. INTRODUCTION

i. The Sewers The sewer network as a biological reactor:

Enough hydraulic retention time (HRT)

Different environmental conditions

Aerobic: Gravity sewers, manholes, wet wells

Anaerobic: Rising mains

Most attention has been placed on gas emissions from Wastewater Treatment Plants (WWTP).

Main objectives:

Quantify gas concentrations in sewers

Establish emission factors in sewers

Identify key parameters in gas formation

3/14

iii. Literature review: Main Findings

High temperatures favour gas emissions

Raising pH reduces H2S and CH4 formation

Longer HRT increases CH4 production

High dissolved oxygen levels prevent H2S and CH4 generation

High nitrite and nitrate concentration inhibit H2S and CH4 formation but increase N2O concentration

The bigger the headspace in a gravity sewer, the higher amount of N2O

1. INTRODUCTION

Image source: http://iraos.org/EN/img/research-icon.jpg

4/14

iii. Literature review: Research Gaps

None include all three gases

Focus on rising sewers, little attention to gravity sewers and combined sewer networks

Most results based on the dissolved gas concentration in the liquid phase

Emission factor calculation methodology not standardized: liquid phase or gas phase results presented

Differences in sampling methodology (in terms of duration and frequency)

Authors infrequently report other parameters such as dissolved oxygen

Little data about climate region or the season of the sampling campaign

Most of the studies performed in Australia

1. INTRODUCTION

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5/14

i. Project framework and Selected Cities

2

1

AQUAENVEC LIFE10 ENV/ES/000520

Life+ financial instrument of the European Commission

Project Title:

“Assessment and Improvement of the Urban Water Cycle Eco-Efficiency using LCA and LCC”

Ga

Betanzos, Galicia

• Oceanic climate, few dry periods

• Average rainfall: 1890 mm/year

• Population density: 94 inhab/km2

• Mostly rain-fed agriculture

• Household water consumption: 146L/cap/day

1

Ga

• Mediterranean climate, water stress

• Average rainfall: 640 mm/year

• Population density: 234 inhab/km2

• Mostly irrigated agriculture

• Household water consumption: 139 L/cap/day

Calafell, Catalonia 2

2. CASE STUDIES

6/14

CALAFELL

1. Wet well of a pumping station

2. Manhole in a centric street

3. Wet well of a pumping station

4. Wet well of the pumping station previous to the WWTP

5. Influent of the WWTP

BETANZOS

1. Wet well of a pumping station

2. Manhole near a pumping station

3. Manhole in a centric street

4. Wet well of the pumping station previous to the WWTP

5. Influent of the WWTP

2. CASE STUDIES

ii. Sampling Sites

GRAVITY SEWER

1 2 3 4

5 WWTP

Figure 1. Schematic representation of a combined sewer network 7/14

Continuous field sampling (1 hour) in five points of the network: CH4 and N2O gas concentration

Discontinuous H2S gas concentration by colorimetry

Discontinuous water sampling for water quality

Summer campaign in July 2013

Winter campaign in January and February 2014

2. CASE STUDIES

iii. Methodology

8/14 Figure 2. a) Hydrogen sulphide measurement. b) GHG analyzer

SERVOMEX 4900

Gas conditioner JCT model

JCC-P114111

Videoregistrator EUROTHERM

6100E

2. CASE STUDIES

iv. Results

BETANZOS

1 As Cascas

PS 2 As Cascas

MH 3 Marina St.

MH 4 Main

PS 5 WWTP influent

CH4 (µg/L) Winter 161.1 87.8 8.7 15.1 80.9

Summer 1109 27.8 20.2 42.4 192.6

N2O (µg/L) Winter 0.0 0.0 0.0 0.0 0.0

Summer 0.0 0.0 0.0 0.0 4.2

H2S (µg/L) Winter 0.0 0.0 0.0 0.0 0.0

Summer 0.0 0.0 0.0 0.0 0.0

CALAFELL

1 Baixador

PS 2 Victor Català St.

MH 3 Mas Mel

PS 4 Creu Roja

PS 5 WWTP influent

CH4 (µg/L) Winter n/m 10.0 32.3 89.4 31.8

Summer 1.8 125.9 226.9 316.7 150.4

N2O (µg/L) Winter n/m 0 0 6.8 0

Summer 0 5.9 8.1 18.3 0

H2S (µg/L) Winter n/m 0 0 0 4.3

Summer 0 0.7 3.4 1.4 2.7 9/14

2. CASE STUDIES

iv. Results

1109

30000

3100

CH4

18.3

298.3

9.8

N2O

Gas concentrations (mg/m3) compared to other studies

4.3

200

1.5

H2S

2. CASE STUDIES

Emission factors in Calafell and Betanzos with different calculation approaches:

iv. Results

11/14

Emission factor - air

(kg CO2 /year)

Emission factor - water

(kg CO2 /year)

Calafell Summer 18.6 494

Winter 3.84 66.5

Betanzos Summer 24.6 263

Winter 10.0 71.2

Contribution of the direct emissions to the total emissions of sewers in the operation stage:

Related to a volume of wastewater ≤ 30%

Related to a volume of air ≤ 4%

3. CONCLUSIONS

In general, higher gas concentrations were found in summer

Higher concentrations of CH4 than other gases were detected

Higher gas concentrations in Calafell than in Betanzos

Higher gas concentrations in wet wells than other appurtenances

Direct emissions of only one point of the network can represent up to 30%

Temperature is a key parameter favoring gas production

Turbulence contributes to a higher gas release The entire sewer network may represent a higher contribution to the total emissions

Gas emissions in sewers

are not irrelevant 12/14

4. FUTURE WORK

The sampling was carried out for one hour, and does not represent the fluctuations during the entire day

Other parameters such as redox potential, dissolved oxygen and water temperature should be measured in order to account cause-effect relationships between gas formation and water species

The entire network should be considered and characterized

13/14

Thank you

for your attention!

Surrey, UK July 2015

Department of Chemical Engineering

1. INTRODUCTION

i. The Sewers

Reactions leading to gas production:

CH4

Fermentation of readily biodegradable organic matter

Methanogenic Bacteria in anaerobic conditions

H2S

Fermentation of readily biodegradable organic matter

Sulphate-reducing bacteria in anaerobic conditions

N2O

Incomplete denitrification under anaerobic conditions

Nitrifier Denitrification under anoxic conditions

1. INTRODUCTION

DQO fermentable

CH4

WASTEWATER

AIR

N2O

H2S

N2O

H2S

CH4

Sulfuric Acid

Production

Meth

an

e

Pro

du

cti

on

H2SO4

H2S

Hy

dro

gen

Su

lph

ide

Pro

du

cti

on

SO42-

HS-

NO2-

NO

N2O

NO3-

NH4+

NH2OH

NH4+

NH2OH

ANAEROBIC

AEROBIC/

ANOXIC

AEROBIC/

ANOXIC

Den

itrif

icati

on

HD

N

MB SRB

SOB

N2O

N2O H2S

CH4

N2O

VFAs

HDN: Heterotrophic Denitrifying Bacteria

AOB: Ammonia-oxidizing Bacteria

AOA: Ammonia-oxidizing Archaea

MB: Methanogenic Bacteria

SRB: Sulfate-Reducing Bacteria

SOB: Sulfide-Oxidizing Bacteria

i. The Sewers

Figure x. Biological reactions in a gravity sewer. (Adapted from Hvitved-Jacobsen, 2002 )

CH4 N2O H2S

Cal

afel

l B

etan

zos

0

200

400

600

800

1000

1200

Gas

co

nce

ntr

atio

n (

µg/

L)

Winter

Summer

0

2

4

6

8

10

12

14

16

18

20

Gas

co

nce

ntr

atio

n (

µg/

L)

Winter

Summer

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Gas

co

nce

ntr

atio

n (

µg/

L)

Winter

Summer

0

200

400

600

800

1000

1200

Gas

co

nce

ntr

atio

n (

µg/

L) Winter

Summer

0

2

4

6

8

10

12

14

16

18

20

Gas

co

nce

ntr

atio

n (

µg/

L)

Winter

Summer

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Gas

co

nce

ntr

atio

n (

µg/

L)

Winter

Summer

iv. Results

2. CASE STUDIES