The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Nanofiltration as a Refining Phase in Surface Water Treatment

Riina Liikanen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Civil and Environmental Engineering for public examination and debate in Auditorium R1 at Helsinki University of Technology (Espoo, Finland) on the 10th of November, 2006, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-8414-6)   [2789 KB]
Dissertation is also available in print (ISBN 951-22-8413-8)

Abstract

The residual organic matter in conventionally treated drinking waters may be sufficient for the formation of harmful disinfection by-products, and for supporting bacterial growth in distribution networks. Thus, nanofiltration has been proposed as an option for enhancing the organic matter removal from high organic load containing source waters. Given that little is known of the success of nanofiltration in removing residual organic matter from chemically pre-treated and rather pure surface waters, further research was required. In addition, more information was needed regarding fouling, operation, cost and environmental impact of nanofiltration process as a refining phase in surface water treatment. Long-term pilot-scale studies at an operating water treatment plant as well as laboratory-scale test runs using real and model feed waters were employed to evaluate the applicability of the nanofiltration process.

Nanofiltration resulted in high and stable removal of organic matter after conventional surface water treatment in all circumstances that were studied. However, the nanofiltered water showed surprisingly high potential for microbial growth, and contained enough microbially available carbon and phosphorus for bacterial growth. Thus, disinfection using small dosage of chlorine is recommended as a safety barrier and for suppressing microbial growth in distribution systems after nanofiltration. In the cases studied, the use of nanofiltration membranes with high organic matter, and lowered inorganic matter retention, optimally met the requirements for treated water quality, as well as for the productivity and fouling of the membranes. However, the studied pre-treated feed waters caused intense flux decline of nanofiltration membranes and required short membrane cleaning intervals at the studied operational parameters. The results of the study also indicate that most feed water constituents, organic material, inorganic precipitates and micro-organisms, affect membrane fouling. Accordingly, it seems impossible to remove the membrane fouling tendency from surface waters.

The study supports the consideration of nanofiltration as an efficient and reliable option for improving the quality of conventionally treated surface water in varying circumstances. However, in applications not requiring substantial improvement of organic matter or ion removals other process options may be more suitable and cost effective compared to nanofiltration.

This thesis consists of an overview and of the following 6 publications:

  1. Liikanen R., Yli-Kuivila J. and Laukkanen R. (2002), Efficiency of various chemical cleanings for nanofiltration membrane fouled by conventionally-treated surface water, Journal of Membrane Science, 195, 265-276. © 2002 Elsevier Science. By permission.
  2. Liikanen R., Yli-Kuivila J., Tenhunen J. and Laukkanen R. (2006), Cost and environmental impact of nanofiltration in treating chemically pre-treated surface water, Desalination, 201, 58-70. © 2006 Elsevier Science. By permission.
  3. Liikanen R., Miettinen I. and Laukkanen R. (2003), Selection of NF membrane to improve quality of chemically treated surface water, Water Research, 37, 864-872. © 2003 Elsevier Science. By permission.
  4. Liikanen R., Kiuru H., Tuhkanen T. and Nyström M. (2003), Nanofiltration membrane fouling by conventionally treated surface water, Water Science and Technology: Water Supply, 3, 183-190.
  5. Matilainen A., Liikanen R., Nyström M., Lindqvist N. and Tuhkanen T. (2004), Enhancement of the natural organic matter removal from drinking water by nanofiltration, Environmental Technology, 25, 283-291.
  6. Liikanen R., Kiuru H., Peuravuori J. and Nyström M. (2005), Nanofiltration flux, fouling and retention in filtering dilute model waters, Desalination, 175, 97-109. © 2005 Elsevier Science. By permission.

Keywords: nanofiltration, surface water treatment, water quality, membrane fouling, membrane cleaning, cost

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© 2006 Helsinki University of Technology

Last update 2011-05-26