Bioflocculation of microalgae for wastewater treatment,
biogas and shrimp feed:
A pilot-scale study
Van Den Hende S., Beelen V., Vervaeren H.
Lab of Industrial Water and Ecotechnology, Ghent University, Campus Kortrijk
18th September 2014
Wastewater treatment
most used in NW Europe:
activated sludge system
Algal bacterial system
Wastewater
COD, N, P
CO2
Microalgae
Bacteria
O2
Photosynthetic aeration
CO2 scavenging
Solar energy into biomass
Nutrient recovery
Wastewater treatment
most used in NW Europe:
activated sludge system
Algal bacterial system
Wastewater
COD, N, P
Wastewater
COD, N, P
CO2
Bacteria
Discharge
norms for
effluent
Microalgae
Bacteria
O2
Nutrient removal
Photosynthetic aeration
CO2 scavenging
Solar energy into biomass
Nutrient recovery
Wastewater treatment
most used in NW Europe:
activated sludge system
Algal bacterial system
Wastewater
COD, N, P
Wastewater
COD, N, P
CO2
Discharge
norms for
effluent
Bacteria
O2
Microalgae
Bacteria
O2
Nutrient removal
Nitrification/denitrification
Mechanical aeration
~50 % of working costs
O2
Photosynthetic aeration
CO2 scavenging
Solar energy into biomass
Nutrient recovery
Wastewater treatment
most used in NW Europe:
activated sludge system
Algal bacterial system
Wastewater
COD, N, P
Wastewater
COD, N, P
CO2, N2
CO2,
N2
CO2
Discharge
norms for
effluent
Bacteria
O2
Microalgae
Bacteria
O2
Nutrient removal
Nitrification/denitrification
Mechanical aeration
~50 % of working costs
O2
Photosynthetic aeration
CO2 scavenging
Solar energy into biomass
Nutrient recovery
Needed: redesign of wastewater treatment
Activated sludge system
Algal bacterial system
Wastewater
COD, N, P
Wastewater
COD, N, P
CO2, N2
CO2,
N2
CO2
Discharge
norms for
effluent
Bacteria
O2
Microalgae
Bacteria
O2
Nutrient removal
Nitrification/denitrification
Mechanical aeration
~50 % of working costs
O2
Photosynthetic aeration
CO2 scavenging
Solar energy into biomass
Nutrient recovery
Needed: redesign of wastewater treatment
Activated sludge system
Microalgal bacterial system
Wastewater
COD, N, P
Bioresource water
COD, N, P
CO2, N2
CO2,
N2
CO2
Discharge
norms for
effluent
Bacteria
O2
Microalgae
Bacteria
O2
Nutrient removal
Nitrification/denitrification
Mechanical aeration
~50 % of working costs
O2
Nutrient recovery
CO2 scavenging
Photosynthetic aeration
Solar energy into biomass
Needed: cheap separation of algae & water
Problem
Microalgae are difficult to separate from
the treated wastewater
Microscopic small and don’t settle
Harvesting: up to 30 % of operational costs
0.1 mm
Microalgae
Bacteria
Solution @ Ghent University/Howest
Biomass-free effluent
200 µm
Bioflocculation of microalgae & bacteria
Microalgal bacterial flocs = MaB-flocs
Settle without flocculant addition
Van Den Hende S., 2014. Microalgal bacterial floc for wastewater treatment: from concept to pilot scale.
PhD dissertation, Ghent Univ., 324p. Promotors: Prof. dr. Nico Boon (LabMET), dr. Han Vervaeren (LIWET).
The secret recipe of making MaB-flocs
1. Collect a mix of microalgae outdoors
Water tank, Alpro
Sieve, Alpro
2. Collect wastewater
Wastewater, Alpro
The secret recipe of making MaB-flocs
3. Mix algae and wastewater in sequencing batch reactor (SBR)
Selection of fast-settling flocs in 1-2 weeks
Stirring of
MaB-flocs
and
wastewater
Add
wastewater
= influent
Settling of
MaB-flocs
Discharge
treated
wastewater
= effluent
Other advantages of the MaB-floc SBR concept
1. Costless separation of treated wastewater and MaB-flocs
MaB-flocs are present in the reactor and settle at night in the reactor
No additional settling tank is needed for effluent discharge
2. Hydraulic retention time can be decoupled from sludge retention time
Dilution rate ≠ algal growth rate
Possible: treatment of low-strength wastewaters & high algal biomass densities
3. Flocs are large (200-500 µm) and easily harvested
No flocculants needed: cost saving, no chemical contamination
Can be harvested by filter press (200 µm)
Which wastewaters?
Problem: wastewaters strongly differ
Nutrient composition, pH, toxic compounds, ….
Solution: screen various wastewaters
Aquaculture (Inagro)
Manure treatment (Innova Manure)
Food-processing industry (Alpro)
Chemical industry (BASF)
Van Den Hende et al., 2014b. Treatment of industrial wastewaters by microalgal bacterial flocs in
sequencing batch reactors. Bioresour. Technol. 161, 245-254.
Selection of suitable wastewaters
Removal efficiency (%)
100
75
50
25
0
Turb TCOD sCOD BOD
TIC
TOC
TC
TN
TP
Removal efficiencies vary amongst wastewaters
Aquaculture
:
Highest removals
Manure
:
Low COD & N removal; P limitation
Chemical
:
Toxicity to algae
Food
:
Second highest removals; high-strength wastewater
Selection of suitable wastewaters
Removal efficiency (%)
100
75
50
25
0
Turb TCOD sCOD BOD
TIC
TOC
TC
TN
TP
Removal efficiencies vary amongst wastewaters
Aquaculture
:
Highest removals
Manure
:
Low COD & N removal; PO43- limitation
Chemical
:
Toxicity to algae
Food
:
Second highest removals; high-strength wastewater
Selection of suitable wastewaters
Removal efficiency (%)
100
75
50
25
0
Turb TCOD sCOD BOD
TIC
TOC
TC
TN
TP
Removal efficiencies vary amongst wastewaters
Aquaculture
:
Highest removals
Manure
:
Low COD & N removal; PO43- limitation
Chemical
:
Toxicity to algae
Food
:
Second highest removals; high-strength wastewater
Selection of suitable wastewaters
Removal efficiency (%)
100
75
50
25
0
Turb TCOD sCOD BOD
TIC
TOC
TC
TN
TP
Removal efficiencies vary amongst wastewaters
Aquaculture
:
Highest removals
Manure
:
Low COD & N removal; P limitation
Chemical
:
Toxicity to algae
Food
:
Second highest removals; high-strength wastewater
Selection of suitable wastewaters
Removal efficiency (%)
100
75
50
25
0
Turb TCOD sCOD BOD
TIC
TOC
TC
TN
TP
Removal efficiencies vary amongst wastewaters
Aquaculture
:
Highest removals -> Best !
Manure
:
Low COD & N removal; P limitation
Chemical
:
Toxicity to algae
Food
:
Second highest removals; high-strength wastewater
From lab reactor to open pond
Lab PBR
160 ton
ha-1 y-1
Outdoor ponds
? ton
ha-1 y-1
Problem: lab data should not be extrapolated to
outdoor scale with conversion factor of 1
Different conditions lab & outdoors:
- Volume: from 4 L to 4.000 m3 (1 ha)
- Light and T
- Reactor dimensions
- ....
Solution: up-scaling to raceway algae pond
EnAlgae Pilot Reactor Network
Conversion factors from lab reactor to outdoors
EnAlgae research questions
Up-scaling to outdoor pond ?
1. Wastewater treatment
2. MaB-floc production and harvesting
Wastewater
Settling
Dewatering
Shrimp feed
Shrimp
MaB-floc SBR
Flue gas
Dischargeable
effluent
3. MaB-flocs
for biogas ?
Biogas
4. MaB-flocs as
shrimp feed ?
Outline
1. Wastewater treatment
2. Biomass production and harvesting
3. Biogas
4. Shrimp feed
20
Wastewater origin: pikeperch culture @ Inagro
Feed
MaB-floc
SBR
Pikeperch
Sander lucioperca L.
Fish tanks
Drum filter (30 µm)
Effluent
discharge
(10 % per day)
Biofilter
O2
UV
Water
Upscaling for aquaculture wastewater: reactors
4 L indoor
Kortrijk (Belgium)
40 L indoor
Kortrijk (Belgium)
20 L
day-1
20 L
day-1
D: 0.350 m
L: 0.351 m
B: 0.325 m
Upscaling for aquaculture wastewater: reactors
400 L indoor
Inagro, Roeselare (Belgium)
100 L
day-1
100 L
day-1
D: 0.356 m
L: 1.170 m
B: 0.960 m
Sludge
Settling tank
Sieve on settling tank
Influent tank
MaB-floc SBR
Upscaling for aquaculture wastewater: reactors
12 m3 outdoor
Inagro, Roeselare (Belgium)
Pilot construction by 2 SMEs: CATAEL bvba, Bebouwen & Bewaren nv
Settling tank
1.5-3 m3
day-1
Influent tank
1.5-3 m3
day-1
Sludge
Effluent tank
N
pH,T DO
MaB-flocs
Heater
CO2
PLC
MaB-floc SBR
D: 0.4 m
L: 11.7 m
B: 2.5 m
S
Propeller pump
for SBR stirring
Outdoor pond: effluent quality
Below effluent discharge norms for COD, BOD5, NH4+, TN, TP, PO43Low PO43- and TP concentrations in effluent (< 0.8 mg P L-1 ; as low as 0.1)
-> potential as P-polishing technology
Outdoor pond: effluent quality
Below effluent discharge norms for COD, BOD5, NH4+, TN, TP, PO43Low PO43- and TP concentrations in effluent (< 0.8 mg P L-1 ; as low as 0.1)
-> potential as P-polishing technology
Influent
Effluent
40 L indoor
400 L indoor
12 m3 outdoor pond
Outdoor pond: photosynthetic aeration is ok!
Photosynthetic aeration by
microalgae was sufficient
Dissolved oxygen production
in line with solar radiation
No mechanical aeration
needed: cost saving
More land area needed !
MaB-floc ponds: 0.4 m deep
<-> CAS :
4 m deep
Time
Problem 1: pH in outdoor pond
12
1
2
3
4
5
6
7
Diurnal pH fluctuations
8
Reactor pH
11
10
Photosynthesis
increases pH during day
Respiration
decreases pH during night
9
8
80
1
2
3
4
5
6
7
8
60
40
20
Time
2013-09-05
2013-08-08
2013-07-11
2013-06-13
2013-05-16
2013-04-18
2013-03-21
2013-02-21
0
2013-01-24
PPFD (mmol PAR/ Lreactor / SBR cycle)
7
Effluent discharge
after night to reach pH
discharge norm
-> this strategy is not
sufficient outdoors
Problem 1: pH in outdoor pond
12 m3 raceway pond
11
1
2
3
4 5
6
7
8
pH
10
Norm
9
Effluent
8
Influent
7
0
50
100
150
200
250
Time (days)
No flue gas
Outdoors, flue gas (5% CO2) was needed to lower pH
Flue gas injection = extra cost !
But, low flue gas flow rates: 0.00004 vvm, so low cost
Flue gas injection in open pond ≠ CO2 credits !
MaB-floc SBR is not a flue gas treatment systems -> needed area !
Problem 2: nitrite in outdoor pond
12 m3 outdoor pond
400 L
8
2
N-NO2- (mg/ L)
6
Discharge
Norm
Influent
Effluent
1
0
4
2
0
0
25
50
Time (days)
75
100
0
50
100
150
200
250
Time (days)
Indoors, nitrite in effluent was not a problem
Outdoors, nitrite was often above the norm for discharge (0.9 mg N-NO2- L-1)
for reuse (1.8 mg N-NO2- L-1)
Solution: avoid nitrite formation in the influent buffer tank?
Conclusions: upscaling
1. Need for flue gas outdoors -> small cost
Biggest costs is stirring by propellor pumps
2. Upscaling from indoors (4 to 40 to 400 L) to outdoors (12 m3)
Decreased the removal of COD, BOD5, TOC, TN, TP
Decreased the removal efficiencies of by a factor of 0.1 - 3.3
Decreased the removal rates by a factor of 0.1 - 46
Increased the removal of TIC and EC
Increased the TIC removal efficiency from –15 % to 60 %
Increased the EC removal efficiency to 27%
-> Removal as carbonate precipitates?
3. Effluent quality was ok, but …
Except for nitrite
1 m2 MaB-floc pond area per m3 pike perch fish tank <-> 0.05 m2 CAS pond area
Pond heating was needed -> waste heat?
Outline
1. Wastewater treatment
2. Biomass production and harvesting
3. Biogas
4. Shrimp feed
32
Effect of scale-up on MaB-flocs: settling
Settling of
MaB-flocs
Discharge of
treated
wastewater
= effluent
Importance of adequate settling:
safeguards biomass-free effluent
Sludge volume after settling
< reactor volume after effluent withdrawnal
dSVI (diluted sludge volume index)
Volume of 1 g of MaB-floc sludge
After 30 minutes of settling
Effect of scale-up on MaB-flocs: settling
750
dSVI (mL/ g TSS or VSS)
dSVI TSS
a
dSVI VSS
Scale-up enhanced the settling
dSVI decreased during pilot operation
500
250
Scale-up enhanced the ash content
Increased ash content during pilot operation
VSS:TSS from 79.1% in February
to 30.7 % in August
0
100
b
60
40
20
Correlation VSS:TSS and dSVI (rs = 0.93)
Reactor operation
12M_all
12M_08_T4_F5
12M_07_T4_F0
12M_06_T8_F0
12M_05_T8_F3
12M_04_T4_F3
12M_03_T4_F0
12M_02_T4_F0
12M_01_T8_F0
400L_T4_0.50
400L_T4_0.75
40L_T2
0
4L_T2
VSS/TSS (%)
80
Effect of scale-up on MaB-flocs: crystals
400 L indoor
Raceway outdoor
Up-scaling increased crystal content
Fluorescence microscopy: blue = crystals
Ash was up to 30% calcium -> CaCO3
Positive for wastewater treatment
Interesting for hardness removal
Negative for biomass valorisation?
Decreased energy content of biomass
Reactor scaling
Imbalanced Ca:P:K ratio
Effect of scale-up on MaB-flocs: species
400 L indoor
Up-scaling shifted the dominant algal sp.
Phormidium sp. indoor
(filamentous cyanobacteria)
to Ulothrix or Klebsormidum sp. outdoor
in raceway (filamentous microalgae)
Raceway outdoor
Monoculture of filamentous sp.
Filamentous: are suitable candidates for
wastewater treatment : harvesting
(Markous & Georgakis, 2011)
Ulothrix sp.: antibacterial activity
(J.P. Goud et al., 2007)
Effect of scale-up on MaB-flocs: productivity
Reactor
Productivity
(mg TSS
Lreactor day-1)
Productivity
(mg VSS
Lreactor day-1)
4L_T2
236 ± 73 (10)*
109 ± 30 (13)
40L_T2
65 ± 8 (2.9)
45 ± 6 (5.5)
400L_T4
16 ± 23 (0.6)
12 ± 17 (1.3)
12M_all
23 ± 54 (1.0)
8 ± 18 (1.0)
*Scale-up conversion factor
Scale-up decreased the biomass productivity
Per reactor volume: 10 times less TSS, 13 times less VSS
Pilot (January - September 2013): 33 ton TSS hapond-1 y-1 or 12 ton VSS hapond-1 y-1
1.5-4 times lower compared to www-fed HRAP in cold climate (Park et al., 2011)
Increased presence of predators
Tubifex sp. can increase palatability and appetites of fish (Lietz, 1988)
MaB-floc harvesting: 1. settling , 2. filtering
1.
Settling of
MaB-flocs
2.1.
Filtering by
gravity
MaB-floc pilot EnAlgae
2.2.
Filtering by
hydropress
MaB-floc cake
MaB-floc harvesting: 98% biomass recovery
1. Concentrating step: settling
Supernatant:
7.9 ± 5.7 % MaB-floc TSS loss,
pumped back into pond -> No loss!
MaB-flocs
In pond
Settled MaB-floc slurry 70 g TSS L-1
2. Dewatering step: filtering 150-250 µm
2.1. Gravity filtering
Gravity filtrate:
1.2 ± 0.9 % MaB-floc TSS loss
2.2. Hydropress filtering
MaB cake: 43 ± 8 % dry matter
Press filtrate:
0.05 ± 0.03 % MaB-floc TSS loss
Conclusions: biomass
Upscaling improved settling of MaB-flocs !
Proof-of-principle that bioflocculation outdoors in NWE can be successful
As for dominant algal species, lab results can not be extrapolated
Importance of outdoor pilot tests !
Low biomass productivity
Should only be improved if a lucrative valorisation pathway is found
Very efficient dewatering with filter press at large pore size (200 µm) !!
Water powered filter press: 0.16 € kg-1 dry MaB-flocs (4 bar water)
Electricity powered filter press: 0.04-0.07 kWhel kg-1 DM (Udom et al., 2013)
-> Dewatering: < 0.01 € kg-1 DM MaB-flocs !
Van Den Hende et al., 2014a. Up-scaling aquaculture treatment microalgal bacterial flocs in sequencing
batch reactors: From lab reactors to an outdoor raceway pond. Bioresour. Technol. 159, 342-354.
Outline
1. Wastewater treatment
2. Biomass production and harvesting
3. Biogas
4. Shrimp feed
41
Biogas resource: MaB-flocs?
Biomethane potential (BMP) of MaB-flocs
MaB-flocs from pilot: July - September 2013
Moderate MaB-floc BMP ~ activated sludge BMP
143-203 NL CH4 kg-1 MaB-flocs VS and 67 % CH4 in biogas
143-587 NL CH4 kg-1 algae VS (Ward et al., 2014)
Significant differences among harvesting dates
Low anaerobic digestion efficiency
ƞAD 27 - 34 %
Only 51-65 % of chlorophyll was removed during AD batch
Needed: pretreatment of MaB-flocs
Biogas resource: pretreated MaB-flocs?
Chlor. + sonication
Microwave
Autoclave
Freeze/thaw
Control
0
50
100 150 200
BMP (NL CH4 kg-1 VS)
0
20
ƞ AD (%)
40 0
0,5
khydrolysis (d-1)
Which pretreatment?
Only positive effect on BMP was microwave treatment (870 s, 700W)
9.4 ± 5.4 % increase of BMP with 2.3 MJ kg-1 MaB-floc TS
Compared to 27 % increase of BMP with > 20 MJ kg-1 TS (Passos et al., 2013)
-> Energetically not interesting
Biogas resource: pretreated MaB-flocs?
Chlor. + sonication
Microwave
Autoclave
Freeze/thaw
Control
0
50
100 150 200
BMP (NL CH4 kg-1 VS)
0
20
ƞ AD (%)
40 0
0,5
khydrolysis (d-1)
Which pretreatment?
Only positive effect on BMP was microwave treatment (870 s, 700W)
9.4 ± 5.4 % increase of BMP with 2.3 MJ kg-1 MaB-floc TS
Compared to 27 % increase of BMP with > 20 MJ kg-1 TS (Passos et al., 2013)
-> Energetically not interesting
No significant improvement of khydrolysis
Conclusions: biogas
AD to biogas seems not economical interesting
for MaB-flocs fed with wastewater of pikeperch culture in NWE
2500 Nm-3 CH4 hapond area-1 y-1 (= half of 1 ha of corn)
Biogas low price: 0.30 € kg-1 MaB-floc VS or < 0.01 € m-3 wastewater
Low compared to wastewater treatment cost of 0.30-0.60 € m-3 (Verstraete et al., 2009)
Practical constraints
Low VS:TS content of MaB-flocs ~ 25%
Scaling (CaCO3) of reactors due to high ash content of MaB-flocs
Needed: biomass valorisation pathways with €
If MaB-floc market price of 2.5 € kg-1 TS -> 0.32 € m-3 wastewater
Outline
1. Wastewater treatment
2. Biomass production and harvesting
3. Biogas
4. Shrimp feed
46
Need and research question
Problem:
Research question:
What to do with these
low-energy MaB-flocs ?
Can MaB-flocs be included in diets of
white Pacific shrimp?
Litopenaeus vannamei (Boone 1931)
Compound
0 - 2 - 4 - 6 - 8 % inclusion
Mainly wheat was replaced
Content
(%)
Ash
62
Calcium
17
Protein
21
Lipid
4
1. Shrimp growth?
2. Shrimp quality?
Shrimp production: no effect of diets
2-8 % MaB-floc inclusion did NOT lead to significant difference of
Shrimp quantity
Survival and growth
Feed conversion ratio
Shrimp quality
Proximate composition
Fatty acid profile
Reflectance of redness, yellowness of cooked shrimp
Shrimp colour: significant effect of diets
30
a
a
25
b b b
ba
a
b
a
ba ba b
cb
20
dc
d
15
10
5
0
0% MaB
a
Redness
2% MaB
b
Yellowness
4% MaB
6% MaB
L
8% MaB
MaB-flocs effect pigmentation of
cooked shrimp tails
Enhance redness and yellowness
MaB-flocs contain 0.25 % carotenoids
Increased market value of shrimp ?
EU feed marked legislation: is it legal?
Regulation EC No 767/2009: NO!
Restricts the use of waste from treatment of industrial wastewater in animal feed
Directive 91/271/EEC: BUT…
Industrial wastewater is ‘wastewater which is discharged’
e. g. aquaculture RAS = process water
Regulation EC No 767/2009: BUT…
Restricts the use of faeces and urine including of fish (aquaculture)
Opportunities: YES!
1. Don’t bring it on the market -> use it where it is produced -> integrated system!
2. Food company process water = bioresource water
MaB-floc pilot operation in 2014 by LIWET at food company Alpro
Conclusions: shrimp feed
High ash content of MaB-flocs from pikeperch wastewater treatment
8 % MaB-flocs can be included in shrimp diets and enhance pigmentation
Increased inclusion of MaB-flocs in diets: 0-50 %?
Replace more expensive ingredients of > 300 € ton-1
Dewatering, drying and grinding of MaB-flocs: 200-300 € ton-1 MaB-floc DM
Wheat ~200 € ton-1
Region specific applications
NWE Europe: process water which does not contain manure particles
Integrated systems
Tropical regions with large shrimp industry
Van Den Hende et al., 2014c. Microalgal bacterial flocs originating from aquaculture wastewater treatment as diet
ingredient for Litopenaeus vannamei. Aquacult. Res., DOI: 10.1111/are.12564.
MaB-floc pilot: current research
1. Economics
(E. Vulsteke, UGent)
3. Modelling
(Swansea University)
2. LCA
(S. Sfez, UGent)
Settling of
MaB-flocs
Wastewater
Dewatering of MaB-flocs
MaB-floc SBR
Flue gas
Dischargeable
effluent
4. Outdoor pilot at
food industry?
Shrimp
Biogas
5. MaB-flocs
for biogas?
Fertilizer
6. Fertilizer ?
(J. Coppens,
UGent)
EnAlgae goes beyond research
Algae-art @ Children’s University
Blue and green pigment extraction for paint
High school pupils: introduction to MaB-flocs
Wetenschap in de kijker: 23-24 Nov. 2014
Milieu-on-tour
Standard operation procedures and best practices
for MaB-floc SBR pilot reactor
Future research
Valorisation of MaB-floc biomass of Alpro
Increase the added-value
Increased inclusion in shrimp feed?
Biorefinery concept?
Process optimisation
Increased N and P removal via micronutrients
Phosphorous polishing of effluent
(Proof-of-principle in tropical aquaculture areas)
Availability: light, heat, wastewater,
experience in algae and ponds,
large aquaculture industry
Need for: wastewater treatment and
aquaculture feed ingredients
Size matters.
Micro-algae
MaB-floc
Size matters.
Size matters.
Thank you
for 5 years
of MaB-floc
research !
Looking forward
to a future
MaB-floc
cooperation !
Sofie.VanDenHende
@ugent.be
Veerle.Beelen
@ugent.be
Size matters.
Han.Vervaeren
@ugent.be