Table Of ContentAlgal Blooms
and Membrane
Based Desalination
Technology
Loreen Ople Villacorte
ALGAL BLOOMS AND MEMBRANE BASED
DESALINATION TECHNOLOGY
LOREEN OPLE VILLACORTE
Cover image:
Aerial photo of a non-toxic “red tide” algal bloom caused by Noctiluca scintillans in New Zealand.
© Miriam Godfrey
ALGAL BLOOMS AND MEMBRANE BASED
DESALINATION TECHNOLOGY
DISSERTATION
Submitted in fulfillment of the requirements of
the Board for Doctorates of Delft University of Technology
and
of the Academic Board of the UNESCO-IHE
Institute for Water Education
for
the Degree of DOCTOR
to be defended in public on
Wednesday, 8 January 2014, 12:30 pm
in Delft, the Netherlands
by
Loreen Ople VILLACORTE
Master of Science in Water Supply Engineering
UNESCO-IHE Institute for Water Education
born in Cebu, the Philippines
This dissertation has been approved by the supervisor:
Prof. dr. M. D. Kennedy
Composition of Doctoral Committee:
Chairman Rector Magnificus TU Delft
Vice-Chairman Rector UNESCO-IHE
Prof. dr. M.D. Kennedy UNESCO-IHE/Delft University of Technology, supervisor
Prof. dr. ir. J.C. Schippers UNESCO-IHE/Wageningen University
Prof. dr. ir. J.S. Vrouwenvelder Delft University of Technology / KAUST
Prof. dr. ir. W.G.J. van der Meer Delft University of Technology
Prof. dr. ir. E. Roesink University of Twente
Dr. F. Hammes EAWAG Switzerland
Prof. dr. ir. D. Brdanovic Delft University of Technology, reserve member
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2014, Loreen Ople Villacorte
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Acknowledgement
This thesis project was carried out at UNESCO-IHE Institute for Water Education in
collaboration with the Wetsus Center of Excellence for Sustainable Water
Technology. I would like to express my sincere gratitude to my supervisors, Maria
Kennedy and Jan Schippers, for their guidance, encouragement, inspiration,
patience and trust in shaping and completing this thesis research to its current
form. Thanks are due to the Wetsus Center of Excellence for Sustainable Water
Technology for their financial support and for the unique opportunity of having
productive interactions with both the academia and the water industry. I am also
grateful for the valuable support and advice of Gary Amy, Harvey Winters and Hans
Vrouwenvelder of the Water Desalination and Reuse Center (WDRC-KAUST) during
the course of this project.
I would like to express my appreciation to Rinnert Schurer and Evides Waterbedrijf
for their assistance in the sampling, monitoring and analyses in Jacobahaven and de
Biesbosch. I am grateful for the support and valuable feedbacks from the R & D
group in Pentair X-flow (Bastiaan Blankert, Remon Dekker, Frederik Spenkelink,
Ferry Horvath, Stefan van Hof, etc.,). It has been a learning experience interacting
with both Evides and Pentair as it has given me a good sense of reality of how
scientific research can be applied in practice.
Nine master students and interns contributed to this research, namely: Ramesh
Duraisamy, Barun Karna, Muna Gharaibeh, Vaidotas Kisielius, Zanele Nyambi, Dino
Berenstein, Katarzyna Micor, Shalane Mari and Heather Ross Oropeza. An
acknowledgement is not enough to describe the important contribution of Yuli
Ekowati and Helga Calix. Their skills and coolness in performing some of the most
challenging experiments in this project are really admirable.
The completion of this thesis may not be possible without the technical/non-
technical support of my colleagues/peers (in alphabetical order): Abdulai Salifu,
Andrea Radu, Andrew Maeng, Anique Karsten, Arie Zwijnenburg, Assiyeh Tabatabai,
Bernadeth Lohmann, Caroline Plugges, Changwon Ha, Chantal Groenendijk, Chol
Abel, Claudia Dreszer, Don van Galen, Elodie Loubineaud, Emmanuelle Prest, Erik
Roesink, Evan Spruijt, Ferdi Battes, Florian Beyer, Frank Wiegman, Fred Kruis,
Giuliana Ferrero, Helga Calix, Herman Smit, Hilde Prummel, Jan Bahlman, Jelmer
Dijkstra, Joe Woolley, Jolanda Boots, Juma Hamad, Koos Baas, Laurens Welles,
Lute Broens, Lyzette Robbemont, Maikel Maloncy, Mark van Loosdrecht, Mieke
Kliejn, Nirajan Dhakal, Paula van den Brink, Paul Buijs, Peter Heerings, Peter Stroo,
Saaed Baghoth, Sergio Salinas-Rodriguez, Sheng Li, Stefan Huber, Tanny van der
Klis, Tarek Waly, Thomas Neu and Victor Yangali. I would also like to thank all the
participants of the Wetsus research theme “Biofouling” for the fruitful discussions
over the last 4 years.
Perhaps more people have directly or indirectly supported me over the last 4 years. I
sincerely apologize to those who are not mentioned in this acknowledgement.
Special thanks to my friends and extended family in the Netherlands, who have been
very accommodating all through these years, namely: Els and Joost, Trudy and
Geert Jan, Lucille and Arjen, Henk and Ruben, the International Student Church of
Delft and many more. I am very grateful to my family in the Philippines for their
never-ending support even from afar. I am indebted to my parents for pushing all the
odds to send me to university, a precious opportunity they did not have themselves.
This important milestone is dedicated to them.
And finally, to my loving wife Helga and my sweet little daughter Elsi, this would
have been a very difficult journey without your daily inspiration, patience and
understanding. Thanks for letting me see the most beautiful side of life. I always feel
very blessed to be surrounded by you.
Loreen Ople Villacorte
5 December 2013
Delft, the Netherlands
Summary
Seawater desalination technology has been rapidly growing in terms of installed
capacity (~80 million m3/day as of 2013), plant size and global application. However,
seawater reverse osmosis (SWRO) systems are prone to operational problems such as
membrane fouling. To minimize fouling, pre-treatment of seawater is necessary
upstream of the SWRO system. The pretreatment in most SWRO plants, specifically in
the Middle East, comprise coagulation followed by granular media filtration (GMF)
pre-treatment. In recent years, however, low pressure membranes such as
ultrafiltration (UF) are increasingly being used as a preferred alternative to GMF. As
more extra large SWRO plants (>500,000 m3/day) are expected to be installed over the
coming years, frequent chemical cleaning (>1/year) of the SWRO will be unfeasible
and installing a reliable pre-treatment system will be even more important.
An emerging threat to SWRO is the seasonal proliferation of microscopic algae in
seawater called algal blooms. These natural phenomena can potentially occur in most
coastal areas of the world where SWRO plants are installed. Recent severe algal bloom
outbreaks in the Middle East region in 2008 and 2013 have caused clogging of GMF
pre-treatment systems which also resulted in inacceptable quality (silt density index,
SDI>5) of GMF effluent. The latter eventually led to temporary shutdown of several
SWRO plant mainly due to concerns of irreversible fouling of the downstream SWRO
membranes. The poor performance of GMF during algal blooms has shifted the focus
of the desalination industry to UF as a main pre-treatment for SWRO. Thus, an
extensive investigation on the impact of algal blooms on both UF and RO membranes
is required.
The goal of this study is to understand the adverse impact of seawater algal bloom on
the operation of UF and RO membrane systems. Furthermore, this study aims to
develop/improve methods to investigate the characteristics and the membrane fouling
potential of algae and algal organic matter (AOM). The ultimate goal is to provide
engineers/operators with a better understanding as well as reliable assessment tools
to develop robust processes and effective operation strategies to maintain stable
operation in membrane-based desalination plants during an algal bloom.
The potential problems which may occur in membrane-based desalination plants (UF
pre-treatment followed by SWRO) during treatment of algal bloom impaired waters
are: (1) particulate fouling in UF due to accumulation of algal cells and their detritus,
(2) organic fouling in UF or RO due to accumulation of AOM, and (3) biological fouling
6 ALGAL BLOOMS AND MEMBRANE BASED DESALINATION TECHNOLOGY
in RO initiated and/or enhanced by AOM. These potential issues were addressed in
this study by performing both theoretical and experimental analyses.
The first step to a better understanding of the effects of algal bloom on membrane
filtration was to perform characterization studies with batch cultures of common
bloom-forming marine (Chaetoceros affinis, Alexandrium tamarense) and freshwater
(Microcystis sp.) algae. The bloom forming algae showed different growth patterns and
AOM production at different phases of their life cycles. The AOM which the algae
produced wa extracted and characterized using various microscopic,
choromatographic and spectrophotometric techniques. The main finding is that AOM
comprise mainly biopolymers (e.g., polysaccharides, proteins) while the remaining
fractions comprise refractory organic matter (e.g., humic-like substances) and/or low
molecular weight biogenic substances. Polysaccharides with associated sulphate and
fucose functional groups were ubiquitous among biopolymers produced by the 3 algal
species. Furthermore, these biopolymers were capable of adhering to clean UF and RO
membranes but the adhesion was much stronger on membranes already fouled by
algal biopolymers. Some indications show that this adhesive fraction of AOM is mainly
made up of transparent exopolymer particles (TEP).
Further investigations were performed to monitor the presence of TEP in membrane-
based desalination systems. For this purpose, the two existing methods to measure
TEPs were first modified or further improved in terms of their applicability in studying
different pre-treatment processes and membrane fouling. Various improvements were
introduced mainly to minimize the interference of dissolved salts in the sample, to
decrease the lower limit of detection, to measure both particulate and colloidal TEPs
(down to 10 kDa) and to develop a reproducible calibration method with a standard
polysaccharide (Xanthan gum). Successful application of the two methods (with
modifications and improvements) was demonstrated in monitoring TEP accumulation
in algal cultures and TEP removal in the pre-treatment processes of 4 RO plants.
Long term (~4 years) TEP monitoring in the raw water of an SWRO plant in the
Netherlands showed spikes in the TEP concentration typically coinciding with the
spring algal bloom (March-May), which were mainly dominated by diatoms and/or
Phaeocystis. Further monitoring of the fate of TEP through the treatment processes of
4 RO plants showed substantial reductions in TEPs and biopolymer concentrations
and membrane fouling potential (in terms of the modified fouling index-ultrafiltration,
MFI-UF) after UF (with and without coagulation), coagulation–sedimentation-filtration
and coagulation-dissolved air flotation-filtration treatments. On the other hand, lab-
scale membrane rejection experiments demonstrated that complete removal of algal-
derived biopolymers may be possible by using UF membranes with lower molecular
weight cut-off (≤10 kDa). Overall, results from both lab-scale and full-scale plant
experiments showed significant correlations between TEP concentration and MFI-UF,
an indication that TEPs likely have a major role in the fouling of UF pre-treatment
systems and possibly in SWRO systems, if not effectively removed by the pre-
treatment process.
The role of algae in the fouling of capillary UF membranes was investigated based on
theoretical and experimental analyses. Results show that membrane fouling of UF
SUMMARY 7
during filtration of algal bloom impacted water is mainly due to accumulation of TEPs
on membrane pores and surfaces, rather than the accumulation of algal cells. This
was corroborated by the correlation (R2>0.8) between MFI-UF and TEP concentration
and not with algal cell concentration (R2<0.5).
Additional investigations were performed to verify if algal cells can cause severe
plugging in capillary membranes. Theoretically, algal cell transport through an inside-
out driven capillary UF is mainly influenced by inertial lift, which may cause plugging
problems as it enhances deposition of algal cells at the dead-end section of the
capillary. Hydraulic calculations suggest that severe plugging due to significant
accumulation of large algal cells (>25 µm) may cause substantial increase in
membrane and cake resistance due to localised increase in flux during constant flux
filtration. Such potential problems can be addressed by shortening the period between
filtration cycles, lowering the membrane flux and/or introducing a small cross-flow
(bleed) at the dead-end of the capillary.
Fouling in capillary UF membranes by biopolymers from bloom-forming marine algae
were further investigated in relation to the solution chemistry of the feed water.
Lowering the pH of the feed water resulted to an increase in UF membrane fouling
potential of biopolymers. Varying the ionic strength in the feed water led to
substantial variations in fouling potential. The role of mono- and di- valent cations on
the fouling potential of biopolymers was also investigated by varying the cation
composition of the feed water matrix. Among the major cations abundant in seawater,
Ca2+ ions demonstrated a significant influence on the fouling propensity of AOM in
terms of MFI-UF and non-backwashable fouling rate. Furthermore, the effect of
solution chemistry on the fouling behaviour of algal biopolymers, in terms of hydraulic
resistance and backwashability, is substantially different to what was observed in
model polysaccharides (e.g., sodium alginate and gum xanthan) traditionally used in
UF fouling experiments. This indicates that model polysaccharides such as sodium
alginate and gum xanthan are not reliable in simulating the fouling propensity of algal
biopolymers in seawater.
The last phase of the study demonstrated the important role of AOM on biofilm
development in SWRO system by performing accelerated biological fouling
experiments (8-20 days) in cross-flow capillary UF membranes (10 kDa MWCO) and
spiral wound RO membranes (using MFS). It was illustrated in these experiments that
when biodegradable nutrients (CNP) are readily available in the feed water, the
substantial presence of AOM - either in the feedwater or on the membrane/spacers -
can accelerate the occurrence of biofouling in SWRO. However, when nutrients are not
readily available in the feed water, direct organic fouling by AOM may occur but with
a much lower fouling rate than when nutrients (N,C,P) are readily available. These
findings were supported by the results of growth potential tests (using flow cytometry)
whereby the net growth of bacteria in natural seawater increased with increasing
AOM concentration. Consequently, effective removal of AOM from RO feed water is
necessary to minimise biofouling in SWRO plants affected by algal blooms.
Overall, this study demonstrates that better analytical parameters and tools are
essential in elucidating the adverse impacts of algal bloom in seawater on the
