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Environmental sustainability assessment of a microalgae raceway pond treating wastewater

4th International Congress on Sustainability Science & Engineering
26-29 May 2015

Environmental Sustainability Assessment of a Microalgae
Raceway Pond Treating Wastewater from a Recirculating
Aquaculture System
From Upscaling to System Integration
Sophie Sfez(a), Sofie Van Den Hende(b), Sue Ellen Taelman(a), Steven De
Meester(a), Jo Dewulf(a)
(a) Department of Sustainable Organic Chemistry and Technology, Ghent University, Coupure Links 653, B9000 Ghent, Belgium
(b) Laboratory for Industrial Water and Eco-Technology (LIWET), Faculty of Bioscience Engineering, Ghent
University, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium

Sustainable Pathways for Algal Bioenergy


Introduction
EnAlgae: INTERREG IVB North West Strategic Initiative
(03/2011 – 06/2015)
9 pilot scale algae cultivation sites (micro- and macroalgae)
• In Roeselare, Belgium: Algae-based wastewater treatment plant,

treating wastewater from a pikeperch recirculating aquaculture
systems (RAS)

Sustainable Pathways for Algal Bioenergy


Introduction
Aquaculture: fast growing sector competing for freshwater resources
RASs: promising option to mitigate the environmental footprint of
aquaculture systems
Recirculating aquaculture system
O2

UV

Backwash
Biofilters

Fish ponds

Drum
filters

wastewater

Backwash
supernatant

Algae-based
wastewater
treatment
system

Fish sludge

Anaerobic
digestion

Settling
tank

Water

The MaB-floc technology tested in 2013 in Belgium at pilot scale to treat
pikeperch aquaculture wastewater from the Aquaculture Research Center
of Inagro (Belgium)
Sustainable Pathways for Algal Bioenergy


Introduction
MaB-flocs: bioflocculating consortium of bacteria and
microalgae
As they grow, MaB-flocs need to be harvested, delivering a new source
of biomass: valorisation as shrimp feed and anaerobic digestion were
tested at pilot scale
Industry needs insights to know which direction to take

Goal of the study
Goal 1: Assess the environmental footprint of a pilot MaB-floc SBR treating
pikeperch culture WW and identify its improvement potential
Goal 2: Forecast the most sustainable valorisation pathway for MaB-flocs in the
framework of an integrated aquaculture waste treatment system at industrial scale

Sustainable Pathways for Algal Bioenergy


Studied MaB-floc based WWT plants
Pilot MaB-floc SBR treating pikeperch wastewater (real case)
Electricity
Sunlight Land

Flue
gas

Natural
gas
Heat

MaB-floc
raceway pond

To stirring pumps

Backwash
supernatant

Electricity

MaB-floc
liquor

1 pond
Area: 12 m2
Volume: 28 m3
Flow: 2.59 m3 day-1

Settling
tank

Supernatant

MaB-floc
liquor

Effluent
water

Van Den Hende 2014

Sustainable Pathways for Algal Bioenergy


Studied MaB-floc based WWT plants
Pilot MaB-floc SBR treating pikeperch wastewater (real case)
Hypothetical up-scaled cases (1000 m3 of WW treated per day):
L: linearly up-scaled MaB-floc plant
Natural gas
Flue gas

Heat

5m
Blower

To stirring
pumps

Electricity
50 m

MaB-floc
raceway
pond

Supernatant
Sunlight
Effluent
Water

Land

41 ponds
Area: 245 m2 pond-1
Volume: 98 m3 pond-1
Flow: 24.5 m3 day-1 pond-1

Electricity
Settling
tank

41 reactors
=
1ha of
cultivation

MaB-floc
liquor

Sustainable Pathways for Algal Bioenergy


Studied MaB-floc based WWT plants
Pilot MaB-floc SBR treating pikeperch wastewater (real case)
Hypothetical up-scaled cases (1000 m3 of WW treated per day):
L: linearly up-scaled MaB-floc plant
S: linearly up-scaled MaB-floc plant with improved stirring system

Propeller pump
22 W m-2

Paddle wheel
5.1 W m-2

Sustainable Pathways for Algal Bioenergy


Studied MaB-floc based WWT plants
Pilot MaB-floc SBR treating pikeperch wastewater (real case)
Hypothetical up-scaled cases (1000 m3 of WW treated per day):
L: linearly up-scaled MaB-floc plant
S: linearly up-scaled MaB-floc plant with improved stirring system
E: linearly up-scaled MaB-floc plant with Belgian electricity mix
replaced by 100% wind energy

Sustainable Pathways for Algal Bioenergy


Studied MaB-floc based WWT plants
Pilot MaB-floc SBR treating pikeperch wastewater (real case)
Hypothetical up-scaled cases (1000 m3 of WW treated per day):
L: linearly up-scaled MaB-floc plant
S: linearly up-scaled MaB-floc plant with improved stirring system
E: linearly up-scaled MaB-floc plant with Belgian electricity mix
replaced by 100% wind energy
M: linearly up-scaled MaB-floc plant with MaB-floc productivity
improved by 30%

Sustainable Pathways for Algal Bioenergy


Studied integrated system
Three scenarios are compared:
Valorisation of MaB-flocs as shrimp feed
Treated backwash supernatant
released in the sewage system

Pikeperch Backwash
Settling
RAS
wastewater

Fish sludge
Maize silage

MaB-floc
liquor

Raceway
ponds

Digester

Valorisation as shrimp feed

Dewatering
Heat
Biogas
CHP

Drying

Electricity

Digestate

Heat

Milling

Shrimp
feed

Electricity to
the grid
Soil conditioner

Valorisation of MaB-flocs as biogas
Treated backwash supernatant
released in the sewage system

Pikeperch Backwash
RAS

wastewater

Settling

Raceway
ponds

MaB-floc
liquor

Soil conditioner
Valorisation as biogas
Digestate

Dewatering

Digester
Biogas

Fish sludge
CHP

Maize silage
Heat

Electricity
to the grid

Sustainable Pathways for Algal Bioenergy


Studied integrated system
Three scenarios are compared:
Valorisation of MaB-flocs as shrimp feed
Valorisation of MaB-flocs as biogas
Baseline scenario
Backwash supernatant released in
the sewage system

Pikeperch Backwash Settling
wastewater
RAS

Electricity to the
grid

Fish sludge
Heat

Heat

Digester

Maize silage

Biogas

CHP

Electricity

Digestate

2 MaB-flocs plants are integrated:

Natural gas
Flue gas

Heat

Soil conditioner

5m
Blower

To stirring
pumps
Electricity

Plant L (linearly up-scaled plant)

50 m

MaB-floc
raceway
pond

Supernatant
Sunlight
Effluent
Water

Land
Electricity
Settling
tank

41 reactors
=
1ha of
cultivation

MaB-floc
liquor

Plant SEM (plant L with the 3 improvements implemented
Natural gas
Flue gas

Heat

5m
Blower

To stirring
pumps

Electricity
50 m

MaB-floc
raceway
pond

Supernatant
Sunlight
Effluent
Water

Land
Electricity
Settling
tank

41 reactors
=
1ha of
cultivation

+

+

+

MaB-floc
liquor

Sustainable Pathways for Algal Bioenergy


Env. Sustainability Analysis
Life Cycle Assessment (LCA), ISO standards 14040 & 14044

Functional
unit
Syst.
boundaries

Production of 1 kg
TSS MaB-floc
liquor

Goal 2: SA of the integration
of MaB-floc based WWTP in
an aquaculture system

Treatment of 1 m3
of wastewater

Goal and scope
definition

Cradle-to-gate

Foreground Pilot: site data
Data from up-scaled
system Up-scaled: pilot data + plant + ecoinvent v 2.2
literature
+ literature

Inventory
analysis

Background ecoinvent v 2.2 +
system literature
Resource consumption (CEENE 2013)
resource efficiency analysis

Global warming potential (IPCC 2007)
air emission efficiency analysis

Marine and freshwater eutrophication (ReCiPe 2013)

Impact
assessment

water emission efficiency analysis

Sustainable Pathways for Algal Bioenergy

Interpretation

Goal 1: comparison
of the 4 MaB-floc
based WWTP


LCA results: environmental sustainability of the
MaB-floc based WWTP
Total CEENE:
848 MJ kg-1 MaB-floc TSS

Resource footprint (CEENE results)
450
350
300
250
200
150
100
50
0
S

E M P

Land resource

L

S

E M P

L

Fossil fuels

S

E M P

Metal ores

L

S

E M P

Minerals

L

S

E M P

Nuclear energy

L

S

E M P

L

S

E M

Water resources Abiotic renewable
resources

Electricity consumption - stirring pumps

Electricity consumption - other pumps

Electricity consumption - flue gas blower

Heating of the pond

M

L

S

P

Pilot

MJex,CEENE kg-1 MaB-floc TSS

400

Direct Land occupation

Infrastructure

Direct phosphorus emissions to water

Direct nitrogen emissions to water

Sustainable Pathways for Algal Bioenergy


LCA results: environmental sustainability of the
MaB-floc based WWTP
Total CEENE plant L:
278 MJ kg-1 MaB-floc TSS

Resource footprint (CEENE results)
450

-77%
-69%

350

300
250
200
150
100
50
0
S

E M P

Land resource

L

S

E M P

L

Fossil fuels

S

E M P

Metal ores

L

S

E M P

Minerals

L

S

E M P

Nuclear energy

L

S

E M P

L

S

E M

Water resources Abiotic renewable
resources

Electricity consumption - stirring pumps

Electricity consumption - other pumps

Electricity consumption - flue gas blower

Heating of the pond

M

L

S

P

Pilot

MJex,CEENE kg-1 MaB-floc TSS

400

Direct Land occupation

Infrastructure

Direct phosphorus emissions to water

Direct nitrogen emissions to water

Sustainable Pathways for Algal Bioenergy


LCA results: environmental sustainability of the
MaB-floc based WWTP
Re CiPe 2013 - Freshwater
eutrophication
1,E-02

Re CiPe 2013 - Marine
eutrophication
28% 34% 36%

1,E-02

kg Neq kg--1 MaB-floc TSS

8,E-03
6,E-03
4,E-03
2,E-03
0,E+00
S

1,E-02
8,E-03
6,E-03
4,E-03
2,E-03
0,E+00

E

Pilot

L

S

25
20
15
10
5
0

E

Pilot

L

S

Electricity consumption - other pumps

Electricity consumption - flue gas blower

Heating of the pond

M

Electricity consumption - stirring pumps

S

L

Pilot

Pilot

67% 90% 97% 75%
kg CO2 eq kg-1 MaB-floc TSS

1,E-02

1,E-02

kg Peq kg-1 MaB-floc TSS

30

2,E-02

67% 85% 91%

1,E-02

IPCC 2007 - Climate change

Direct Land occupation

Infrastructure

Direct phosphorus emissions to water

Direct nitrogen emissions to water

E

M

Sustainable Pathways for Algal Bioenergy


LCA results: environmental sustainability of the
Integrated systems
Baseline scenario
Pikeperch Backwash Settling
wastewater
RAS

Backwash supernatant released in
the sewage system

Electricity to the
grid

Fish sludge
Heat

Heat

Digester

Maize silage

Biogas

CHP

Electricity

Digestate

Soil conditioner

Scenario 1 - valorisation of MaB-flocs as shrimp feed
Treated backwash supernatant
released in the sewage system

Pikeperch Backwash
Settling
RAS
wastewater

Raceway
ponds

Fish sludge

MaB-floc
liquor

Digester

Maize silage

Valorisation as shrimp feed

Dewatering
Heat
Biogas
CHP

Drying

Electricity

Digestate

Heat

Shrimp
feed

Milling

Electricity to
the grid
Soil conditioner

Scenario 2 - valorisation of MaB-flocs as biogas
Treated backwash supernatant
released in the sewage system

Pikeperch Backwash
RAS

wastewater

Settling

Raceway
ponds

MaB-floc
liquor

Soil conditioner
Valorisation as biogas
Digestate

Dewatering

Digester
Biogas

Fish sludge
CHP

Maize silage
Heat

Electricity
to the grid

Sustainable Pathways for Algal Bioenergy


LCA results: environmental sustainability of the
Integrated systems
Resource footprint1

- 133%

- 101%

Left bar:

Right bar:

Avoided processes
1

CEENE results without abiotic
renewable resources

Sustainable Pathways for Algal Bioenergy


LCA results: environmental sustainability of the
Integrated systems
Freshwater
eutrophication

Marine
eutrophication

(ReCiPe 2013)

(ReCiPe 2013)

Left bar:

Carbon footprint
(IPCC 2007)

Right bar:

Avoided processes

Sustainable Pathways for Algal Bioenergy


Conclusion
MaB-floc technology: stirring has the highest contribution to most
impact categories
Integrated aquaculture waste treatment system:
• Potential to compete with the baseline scenario and contribute to a
sustainable connection of the water-food-energy nexus in the aquaculture
sector
• Valorizing MaB-flocs into shrimp feed: overall more sustainable than into
biogas
Bottleneck: EU legislation

Future research:
• Improvement of LCA with more complete data on nutrient cycle
(measurements needed)
• Focus on the improvement of the energy efficiency of the system, rather
than of MaB-flocs productivity
Sustainable Pathways for Algal Bioenergy


Thank you!
Sophie.Sfez@UGent.be
+32 (0) 9 264 99 27

Sustainable Pathways for Algal Bioenergy



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