Ultrafiltration as pretreatment to reduce algae bloom in reverse osmosis plants

ida world congress 2013
October 20-25
On desalination and water reuse
china
tianjin
desalination:
a promise for the future
ULTRAFILTRATION AS
PRETREATMENT TO
REDUCE ALGAL
BLOOM IN REVERSE
OSMOSIS PLANTS
Jorge J. Malfeito
R&D Director
Acciona Agua
Spain

International Desalination Association desalination: a promise for the future october 20-25, 2013
Nutrients Consequence
Algal
Bloom
Problems in
Desalination
Plants
SolutionEffective
Pretreatment
Total Removal
of Microalgae in
treated water
But Membrane
Performance
Decline
Cause Potential
Foulants
Pore Blocking
Cleanings
Secreted EPS
Attached EPS
Microalgae Cake
Human
Activities
Water
Eutrophication
??

Scenedesmus
Microalgae
Selected Membrane
UFP-100-E-35
(MWCO 100,000, 0.92 m2)

pore
blockage
pore
constriction
cake
formation
membrane
secreted
EPS
high flux
attached
EPS
microalgae
water algal bloom
low flux
Adapted from Drews 2007

To cultivate a type of algae for generating algal
blooms.
To characterize the EPS that remain attached to
the cell surface.
To characterize the EPS secreted into its growth
medium.
To assess the influence of three variable in UF
during an algal bloom. Study of the evolution of
TMP.

The algae selected is approximately 10
µm of size and is ellipsoidal in shape.
It belongs to Scenedesmus genus
(100% green algae).
Contaminants can reduce the growth of the desired
algae. There are two ways to reduce contamination:
Rotifer
Ciliated protozoan Flagellated protozoan
Algae contaminants
Collecting the algae
every day.
Using a closed reactor.

Petri Plate
(Arnon Medium)
5 days
50 mL flask
150 mL flask
8 L flask
Recirculation, CO2 addition
Natural Light
3 days
Light, AirLight
3 days
Air, Light
1 weekCentrifugation
Dry weight ~ 10%
(collected once a day)
Tubular closed reactor
Light
Light

AlgaeLabAnalyser is an equipment that:
 Measures the content of algae in terms of
chlorophyll-a.
 Uses 6 LEDs for fluorescence excitation for algae
differentiation with a fixed emission wavelength at
680nm.
 Algae fluorescence is due principally to
chlorophyll-a.
 The presence of other pigments allow the algae
differentation.

Algae Type Excitation wavelength (nm)
Green algae 470 nm Chlorophyll-a and -b
Blue-green algae
610 nm photosynthetic antenna pigment
phycocyanin
470 nm chlorophyll-a low intensity
Diatoms
525 nm
470 nm chlorophyll-a and –c.
Cryptophytae 570 nm phycoerythrin
Other fluorescence
matther
Excitation wavelength (nm)
Yellow substances 370 nm
AlgaeLabAnalyser
AlgaeLabAnalyser was used to calculate
the algae concentration of the UF
experiments (µg/l chlorophyll-a).

 Cell count was carried out by Neubauer chamber.
 Cell count was correlated with the chlorophyll-a concentration.
Cell count
Cell/L
Chlorophyll-a
(Chl-a)
 Observation on the microscope
of the number of cells in the
central squares using a chamber.
 Calculation of the number of cells
taking into account:
 Surface of central squares
 Dilution factor of the sample
 Depth of the chamberChl-a Cell count
100 µg/L 5.72·108 cell/L
550 µg/L 3.15·109 cell/L
1000 µg/L 5.72·109 cell/L
Linear relationship
Neubauer
Chamber
0 200 400 600 800 1000
0
1
2
3
4
5
6
7
CountCell(cell/L)x10
9
Chlorophyll-A (g/L)

Extracellular polymeric substances (EPS) are high-molecular weight
compounds secreted by microorganism, e.g. microalgae, into their
environment.
Composition
Polysaccharides
(40-95%)
Proteins
Other
macromolecules
Classification
Attached to cell
surface
Secreted into its
growth medium
Characterization
Attached to cell surface:
• EEM fluorescence
• FTIR-ATR
• EPS quantification
Secreted into its growth
medium:
• LC-OCD
• EPS quantification

 Secreted EPS by filtration (0,45 µm).
Extraction of the EPS attached to the cell surface:
Extraction with NaClO4
Desalination 250 (2010)648-652
Determination biopolymer
content of secreted and
attached EPS.
 Proteins.
 Carbohydrates.
Lowry method
Journal of Biological Chemistry
193(1951)265-275
Antrone method
Industrial Water Wastes 7(1962)17-22
0
10
20
30
40
800
900
1000
Carbohydrates
Concentration[mg/galgae]
secreted EPS
Attached EPS extracted by NaClO4
Proteins

Biopolimers
Humic
substances
Building
Blocks
LMW Acid
compounds
LMW neutral
compounds
time (min)Detectorsignal
Black OCD
Blue UVD
Green OND
 Size exclusion chromatography:
• Separates NOM into six fractions to get meaningful results.
 Three detectors:
• OCD detector. Infrared detector for the Organic carbon.
• UVD detector ( 254 nm). Organic parameters like SUVA.
• OND detector ( 220 nm). Organic and inorganic bound nitrogen.

0 50 100 150
0,0
0,5
1,0
1,5
Low molecular
weight neutrals
Low molecular
weight acids
TOC[Relativeunits]
Elution time [min]
OCD signal
Algal EPS
Biopolymers
 LC-OCD allows to:
• Separate algal EPS NOM.
• Determine the chemical
composition.
Fraction Composition
Biopolymers (proteins
and polysaccharides)
70.8 %
Humic substances -
Building Blocks -
Low molecular weight
acids (LMWA)
17.3 %
Low molecular weight
neutrals (LMWN)
11.9 %
 Excreted EPS from
Scenedesmus presents:
• High content of biopolymers
(polysaccarides and proteins).
• Absence of humic substances.

Ex (nm) / Em (nm) Identification
225-230 nm/330-340 nm Tryptophan-like
280 nm/330-340 nm
Tryptophan-
and protein-like
Region Description
Chemical
funcionality
I Aromatic protein Tyrosine-like
II Aromatic protein Tryptophan-like
III Fulvic acid-like -
IV
Soluble microbial
by-product-like
Tyrosine-,
tryptophan-l and
protein-like
V Humic acid-like -
Excitation
(200-290 nm)
Emission
(300-400 nm)
 Fluorescence cromophores of attached
EPS belong to protein and aminoacid
substances.

Band (cm-1) Identification
3282 cm-1 Hydrogen bonded
OH
2923 cm-1
and 2850
cm-1
Aliphatic CH2
1627 cm-1 Amide I band (C=O
amide bound)
1533 cm-1 Amide II band (N-H
amide bound)
1225 cm-1 Phosphate group in
nucleic acids
1063 cm-1 Polysaccharide-like
substances
 FTIR-ATR spectrum shows some infrared bands related to EPS
structure.
4000 3500 3000 2500 2000 1500 1000
80
85
90
95
100
Phosphate
Amide II (N-H)
Amide I (C=O)
Aliphatic CH2
Transmittance[%]
Wavenumber [cm
-1
]
Algal EPS
O-H
Polysaccharide-like
substances
 Protein (amide bands) and polysaccharides functional
groups are identified in attached EPS.

Operation conditions:
UF flux: 54 LMH
BW flux: 2.5xUF flux
UF (in-out) 100,000
MWCO
Dead-end configuration

 Optimized Responses:
 TMP after 1 hour filtration (minimization).
 TMP after 11 hour filtration (minimization).
 An experimental design was done to optimize the experimental part and to
determine which factors are the most important during the UF process.
 Three variables at three levels were selected. It was required an L9 inner/outer
array matrix.
 Fixed conditions: Flux Filtration, Temperature and Flux Backwash.
Trial Filtration time [min] Algal concentration [µg/L] BW duration [s]
1 30 100 30
2 30 550 60
3 30 1000 90
4 60 100 60
5 60 550 90
6 60 1000 30
7 90 100 90
8 90 550 30
9 90 1000 60

Trial
Filtration
Time [min]
Chl-a Conc.
[µg/L]
BW
Duration [s]
1 30 100 30
2
3
4 60 100 60
5
6
7 90 100 90
8
9
0 2 4 6 8 10 12 14 16 18 20
0
500
1000
1500
2000
2500
3000
3500
TMP(bar)
Time (h)
Trial 1
Trial 4
Trial 7
In the three experiments with 5,72·108 cell/L (100 µg/L of
Chl-a) (plotted in black symbols), TMP has no significant
increase independent of the filtration conditions (filtration
time and BW duration).
A stable operation can be reached with these algal
concentration.

Trial
Filtration
Time
[min]
Chl-a Conc.
[µg/L]
BW
Duration
[s]
1 30 100 30
2 30 550 60
3
4 60 100 60
5 60 550 90
6
7 90 100 90
8 90 550 30
9
0 2 4 6 8 10 12 14 16 18 20
0
500
1000
1500
2000
2500
3000
3500
TMP(bar)
Time (h)
Trial 1
Trial 4
Trial 7
Trial 5
Trial 2
Trial 8
 When the algal concentration was 3,15·109 cell/L (550 µg/L of Chl-a)
(plotted in red symbols) the filtration conditions began to present
significant effect in TMP values.
 Lower BW duration and higher filtration time produced higher TMP (3,2
bar in 13 hours), this effect is clearly appreciated in trial 8.
 With this algal concentration two trials showed TMP values lower of 500
mbar, thus in these trials no relevant effect was shown.

Trial
Filtration
Time [min]
Chl-a Conc.
[µg/L]
BW
Duration [s]
1 30 100 30
2 30 550 60
3 30 1000 90
4 60 100 60
5 60 550 90
6 60 1000 30
7 90 100 90
8 90 550 30
9 90 1000 600 2 4 6 8 10 12 14 16 18 20
0
500
1000
1500
2000
2500
3000
3500
TMP(bar)
Time (h)
Trial 1
Trial 4
Trial 7
Trial 5
Trial 2
Trial 8
Trial 3
Trial 9
Trial 6
 In all cases with the highest algal concentration 5,72·109 cell/L (1000 µg/L
of Chl-a) (plotted in blue symbols) a severe increase in TMP was
observed.
 Filtration conditions present an important effect in TMP values. Lower
filtration time and higher BW duration produce a soft slope in TMP
evolution (trial 3).
 It is not able to reach an stable operation with these algal concentration.

 The effects are sorted from most significant to least significant.
 The length of each bar is proportional to the standardized effect weight.
 The vertical line shows the significance level.
 Any bars that extend to the right of that line indicate effects that are statistically
significant at the 5% significance level.
 The colour of the bar indicates the influence of the effect on the response.
Pareto chart at 1h
 Algae concentration is relevant.
 A major algae concentration higher
TMP values are observed.
Pareto chart at 11h
 All variables are significant.
 Operation for a long time needs longer
BW and shorter filtration time.

 It is dominated by pore blockage on
the surface that forms a cake layer.
 Algae concentration is a crucial
variable.
Initial Stage (Response 1h)
Later Stage (Response 11h)
 A more compact and nonporous
cake cause internal pore blockage of
the membrane.
 Filtration time and BW duration
start showing influence in the TMP
Evolution.
Clean-in-place (CIP) is
needed to restore fouled
membranes
Journal of Membrane Science 57(1991)271-287
Water Research 46(2012)4783-4789

Filtration with desionized water (30 min)
CEB with 100ppm NaClO soaking 15 min
Filtration with 100ppm NaClO (1 hour)
CEB (Chemical Enhanced BW)
Soaking 15 min with 100ppm NaClO
Backwash (BW)Fouled UF membrane needs an
optimized clean-in-place (CIP) to
restore the flux by algae and its
EPS fouling.
CIP using 100ppm NaClO at pH 12
almost restore the initial flux.
NaClO oxidizes NOM and could
destroy algae cells.
The use of NaOH initiate the
hydrolisis of functional groups
of EPS.
It helps to inhibit and destroy
the EPS gel layer.
Cleaning steps (CIP)

Factor Value
Filtration time 30 min
Chlorophyll a
(Algae concentration)
100
µg/L
BW duration 88 s
Optimized DOE Response TMP (11h)
Chlorophyll a was not detected in the
permeate
No lysis is produced during the UF process
Chlorophyll a
MW = 893.49 g/mol
Cell Membrane
Exterior Cell
Interior Cell

UF is able to achieve a total removal of the selected algae. No chlorophyll –
a was detected in any permeate.
No lysis was produced during the UF treatment.
According to the different analytical techniques employed to
characterize and quantify the EPS: POLYSACCHARIDES and
PROTEINS are the principal components.
EPS extraction by NaClO4 was the most effective to extract the EPS
in higher concentration.
During UF experimentation the most critical parameter showing
influence in the TMP was the algal bloom concentration.
The variables, filtration time and BW duration, start to have influence in
TMP values when filtration run go ahead and/or when the algal bloom has
an extreme algae concentration.

European Union
Investing in Your Future
European Regional
Development Fund 2007-13
THIS RESEARCH HAS BEEN CO-FINANCED BY THE
EUROPEAN REGIONAL DEVELOPMENT FUND (ERDF)
AND CDTI.
Co-Authors: R. Sandín, B.Corzo, E. Ferrero, J.Bacardit

Ultrafiltration as pretreatment to reduce algae bloom in reverse osmosis plants

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