ultra-low pressure ultrafiltration for decentralized drinking water treatment

163 Pages·2011·7.21 MB·English

DISS. ETH NO. 19134

ULTRA-LOW PRESSURE ULTRAFILTRATION FOR
DECENTRALIZED DRINKING WATER TREATMENT

A dissertation submitted to

ETH Zurich

for the degree of

Doctor of Sciences

presented by

MARYNA PETER

M.S. Chem. Technol. and Eng.
National Technical University of Ukraine “KPI”

born 15.12.1981

citizen of Ukraine

accepted on the recommendation of
Prof. Dr. Willi Gujer
Dr. Wouter Pronk
Prof. Dr. TorOve Leiknes

2010

Abstract

Inadequate access to microbiologically safe drinking water continuously threatens the health
and well-being of about a billion people, primarily in developing countries. Effective, low-
cost and robust technologies are needed to redress this situation and meet the Millennium
Development Goals for drinking water. Although ultrafiltration technology has become
affordable for decentralized water treatment in developing countries, its widespread
application is limited by membrane fouling and biofouling. Conventionally, regular
backflushing, disinfection and chemical cleaning are applied in order to limit fouling,
resulting in complex, expensive and maintenance intensive systems not suitable for
application in developing countries. The goal of this thesis was to investigate a new approach
to ultrafiltration and fouling control in order to develop a low-cost membrane-based
decentralized system and reduce energy and chemical demand in membrane systems in
general.

The stabilization of flux during dead-end ultrafiltration without backflushing, cross-flow or
chemical cleaning under ultra-low pressure has not been observed before. This phenomenon
allows gravity-driven ultrafiltration of surface water without any maintenance and pre-
treatment at stable flux values of 4-10 L·h-1·m-2 for at least 6 months of operation at a
hydrostatic pressure of 40-150 mbar, which corresponds to a height difference of about 0.4 -
1.5 m.

In this thesis, the phenomenon of flux stabilization is documented and evidence is provided
that flux stabilization is related to biological processes leading to structural changes in the
fouling layer. The development of cavities, channel networks and heterogeneous structures
causes the decrease in resistance of the fouling layer. These processes counteract the increase
of resistance of the fouling layer due to deposition, physico-chemical interactions and pore
constriction due to irremovable fouling. The concentrations of biopolymers and low
molecular weight compounds, the dissolved oxygen concentration and the concentration of
colloidal humic acids are the major factors affecting flux stabilization. It is concluded that
biofouling, always considered to be the major limitation of membrane processes and
associated with reduced performance, actually causes stabilization of flux.

The phenomenon of flux stabilization can be implemented in simple low cost gravity-driven
ultrafiltration systems for decentralized drinking water treatment. The stable flux value of 4-
10 L·h-1·m-2 is sufficient to cover daily needs of water for drinking and cooking for a family of
five people using less than 0.5 m2 of membrane. While no pretreatment, pumps, chemicals or
process control is required, the system costs could be kept low, especially when such systems
can be produced or assembled locally. Furthermore, possibilities exist to further increase the
capacity of the system. It is shown that the flux can be enhanced by intermittent operation as
well as manual forward flushing of the membrane.

There is a great potential for application, but also a need for further investigation and system
development of the ultra-low pressure ultrafiltration technology. Further investigation of the
mechanisms of flux stabilization should enable prediction of the impact of feed water quality
and operational parameters on the stable flux, and could lead to new strategies to improve the
performance. Decentralized systems based on this concept should be further evaluated in field
studies in order to assess maintenance requirements, financing schemes, system lifetime and
socio-economic aspects. Furthermore, the phenomenon of flux stabilization can be explored in
membrane bioreactors for wastewater treatment and re-use as well as in nanofiltration.

Zusammenfassung

Momentan haben weltweit ungefähr eine Milliarde Menschen kein Zugang zu keimfreien
Trinkwasser. Ihre Gesundheit und ihr Wohlergehen sind dadurch gefährdet, wobei besonders
Menschen in Entwicklungsländer davon betroffen sind. Einfache, effektive und
kostengünstige Technologien werden benötigt um dem entgegenzuwirken und schließlich
somit auch die Millenium Development Goals für Trinkwasser zu erreichen.
Ultrafiltrationstechnologien in der dezentralen Wasseraufbereitung sind bereits in den
Industrieländern zu erschwinglichen Preisen auf dem Markt. Probleme durch das auftretende
Fouling und Biofouling der Membranen verhindern jedoch eine breite Anwendung. So
müssen gängige Methoden wie Rückspülung, Desinfektion und chemische Reinigung
eingesetzt werden, um dieses Fouling zu verringern oder weitestgehend zu vermeiden. Dies
führt allerdings zu komplexen, teuren und auch wartungsintensiven Systemen, die so nicht in
Entwicklungsländern eingesetzt werden können.

Ziel der vorliegenden Dissertation war es, einen neuen Ansatz zu erforschen, wie man mittels
Ultrafiltration und einer möglichen Kontrolle des Foulings ein günstiges und einfaches
dezentrales Membransystem, welches einen geringeren Energie- und Chemikalenverbrauch
hat, entwickeln kann.

Die Stabilisierung des Durchflusses während einer Ultrafiltration im Dead-End Betrieb, ohne
jegliche Rückspülung oder chemische Reinigung wurde bisher noch nicht entdeckt. Gerade
aber dieses Phänomen ermöglicht eine schwerkraftgetriebene Ultrafiltration von
Oberflächenwasser ohne große Wartung und Vorbehandlung. So sind Durchflussraten von 4-
10 L.h-1m-2 während mindestens sechse Monaten Betrieb und einem hydrostatischem Druck
von 40-150 mbar möglich. Dies würde einer Höhendifferenz von ca. 0.4- 1.5 m entsprechen.
Das Phänomen der Stabilisierung des Durchflusses wird in dieser Dissertation beschrieben
und es wird gezeigt, dass die Stabilisierung mit biologischen Prozessen zusammenhängt,
welche Veränderungen in der Struktur der Foulingschicht bewirken. So bewirkt die
Entstehung von Hohlräumen, kanälchenartigen Netzwerken und verschiedenartiger Strukturen
eine Abnahme der Widerstandsfähigkeit der Faulschicht. Dem wiederum stehen Prozesse
gegenüber, welche eine Zunahme der Widerstandsfähigkeit, durch Sedimentation,
physikalisch-chemische Einwirkungen und irreversible Porenverblockung, verursachen.
Haupsächlich beeinflussen folgende Faktoren die Durchflussstabilierung: die Konzentration
von Bipolymeren und leichten, niedermolekularen Stoffen, sowie die Konzentration von
gelöstem Sauerstoff und kolloidaler Huminsäuren. So scheint das Biofouling, welches
allgemein als grösste Einrschränkung bei Membranprozessen gilt, hier für die Stabilisierung
des Durchflusses verantwortlich zu sein.

Dieses Phänomen der Durchflussstabilisierung kann für einfache, kostengünstige,
schwerkraftgetrieben Ultrafiltrationssysteme für die dezentrale Trinkwasseraufbereitung
verwendet werden. Die dauerhafte Durchflussrate von 4-10 L.h-1m-2 genügt bei der
Verwendung von 0.5 m2 Membranfläche, um den Wasserbedarf für Trinken und Kochen einer
fünfköpfigen Familie zu decken. Da keine Vorbehandlung, Pumpen, Chemikalien oder
Steuerungseinheiten benötigt werden, können die Systemkosten gering gehalten werden und
ermöglichen besonders eine Produktion vor Ort. Zudem kann die Kapazität des Systems noch
weiter gesteigert werden: bei periodischem Betrieb und bei manueller Spülung der Membrane
kann der Durchfluss vergrössert werden.

Neben dem hohen Potential für die Anwendung, besteht aber auch noch Bedarf an weiteren
Untersuchungen und der Entwicklung eines Systems für die Ultrafiltrationstechnologie unter
ultra tiefen Druckverhältnissen. Weitere Untersuchungen zum Mechanismus der
Durchflussstabilisierung sind nötig, um z.B. den Einfluss der Rohwasserqualität zu
quantifizieren und Möglichkeiten für Optimierung zu finden. Dezentrale Systeme welche auf
dem hier geschilderten Ansatz basieren, sollten in Feldstudien weiter bewertet werden um
Wartungsaufwand, Finanzierungsmodelle, Lebensdauer des Systems und sozio-ökonomische
Aspekte abzuschätzen und zu betrachten. Zudem kann das Phänomen der
Durchflussstabilisierung in Membran Bioreaktoren von Abwasserreinigungsanlagen und
Brauchwasser-recycling und in der Nanofiltration weiter erforscht werden.
Acknowledgements
I would like to thank my supervisor Wouter Pronk that he believed in me 6 years ago and
gave me a chance to start this work. I appreciated greatly his advice, encouragement and
freedom to explore new ideas or look for answers, as well as his support in any situation. I
also enjoyed long discussions during our trips abroad or extended coffee breaks, which built
a good base for a life-long collaboration and friendship.
I would like to thank Frederik Hammes for the supervision of the microbiological part of this
work. I enjoyed a lot his knowledge, help and creativity, always positive feedback and ability
to find solutions to every problem and in any situation.
I would like to thank Willi Gujer and Markus Boller for their helpful ideas and suggestions,
critical remarks and an outside insight into my work.
Many thanks to TorOve Leiknes for reviewing this thesis, supporting me and introducing me
to the top membrane scientists on every membrane conference, and for explaining the art of
writing an EU proposal.
I would like to thank all my students, interns and ZVs: Jonas Margot, Max Grau, Rostislav
Mudryk, Weija Li and Karin Borkmann for their precise and creative work, new ideas and fun
during long days in the lab or office. I appreciated a lot your help.
The EU project Techneau not only supported this work financially, but also helped me to
build a network and get acquainted with scientists and private sector in Europe and South
Africa. Many thanks to WP 2.5 partners: Boris Lesjean and Eric Hoa (KompetenzZentrum
Wasser Berlin), Laurent Pred’Homme (Opalium) and Chris Swartz (Chris Swartz
Engineering) for frequent meetings and discussions during joint development and operation
of the pilot plant. Many thanks also to Chris Buckley (Durban University of Technology) and
Jean Vergain (ICRC) for the exiting discussions and shearing of their experience.
Many thanks to Jacqueline Traber, Marius Vital, Adriano Joss, Hans-Ueli Weilenmann, Urs
von Gunten and Chris Zurbrügg for their support in the lab, experimental hall or meeting
room on different stages of my work.
I am thankful to Eawag Particle Team: Ralf Kägi and Brian Sinnet, to Urs Ziegler, Caroline
Aemissegger and Andres Kaech from the Center for Microscopy and Image Analysis of the
Zurich University and Stephan Handschin from Electron Microscopy Center of the ETH
Zurich for their support in Microscopy.
I would like to thank also my former supervisors and colleagues: Igor Astrelin, Natalja
Tolstopalova, Tatjana Obushenko and Vladimir Ledovskich from the National Technical
University of Ukraine and Walter Peter and Eugen Müller from Clariant for shearing their
knowledge and experience as well as giving me confidence and finally a chance to come to
Switzerland and Eawag.
I appreciated a lot a great working atmosphere at Eng and SWW departments, Wave21 group
and profited a lot from collaborations with Umik, W&T and Sandec. Many thanks to everyone
who was there to help or to laugh. And, of course, many thanks to all my colleagues who
became my friends during last 4 years: Markus Gresch, Silvana Velten, Thomas Hug, Jakob
Helbing, Damian Dominguez, Marc Neumann, Maaike Ramseier, David Kaelin, Bastain Etter,
Nico Derlon, Jörg Rickermann, Doris Jermann, Bettina Sterkele, Christian Abegglen and
David Dürenmatt.
I would like to thank my family in Kyiv: Larisa, Anatolij and Pavel Varbanets, and in Itingen:
Elsbeth and Walter Peter for their confidence and support.

My husband Fabian Peter was the most important reason of this work. It would have not
happened without him and it is devoted to him.
Table of contents

Introduction ................................................................................................................... 1

Chapter 1: Review: Decentralized Systems for Potable Water and the Potential of
Membrane Technology ................................................................................................. 9

Chapter 2: Stabilization of flux during ultra-low pressure ultrafiltration...................... 45

Chapter 3: Mechanisms of membrane fouling during ultra-low pressure
ultrafiltration ................................................................................................................. 67

Chapter 4: Intermittent operation of ultra-low pressure ultrafiltration for
decentralized drinking water treatment ......................................................................... 91

General conclusions and outlook .................................................................................. 107

Appendix A: Operation and maintenance of decentralized drinking water treatment
systems based on ultra-low pressure ultrafiltration ....................................................... 121

Appendix B: Low-pressure ultrafiltration and membrane fouling by polysaccharides 139

Curriculum Vitae ........................................................................................................... 153