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.

Two-Step Granular Activated Carbon Filtration in Drinking Water Treatment

Riku Vahala

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 29th of November, 2002, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-6173-1)   [885 KB]
Dissertation is also available in print (ISBN 951-22-6163-4)


In the treatment of Finnish surface waters, the main objective is to reduce natural organic matter (NOM) before the water is disinfected. In many treatment plants, granular activated carbon (GAC) filtration is applied for the enhanced removal of NOM after conventional treatment. The aim of this study was to assess the performance of two-step GAC filtration in NOM removal and to determine its effects on the water quality in the distribution system. Furthermore, the optimal operation conditions of the existing process scheme at Helsinki Water's treatment plant after installing two-step GAC filtration and UV disinfection was evaluated.

The study revealed that the major factors influencing the effective NOM removal in GAC filtration are the choice of GAC type and the frequency of regeneration. Other factors, such as empty bed contact time and biological degradation rate, were of minor importance. However, even the fully exhausted "old" GAC effectively decreased the assimilable organic carbon (AOC) and the regrowth of heterotrophic bacteria in the distribution system. The most interesting finding of the study was that introducing GAC filtration and UV disinfection increased the nitrification in the chloraminated distribution system.

Introducing GAC filtration is a challenge for the more efficient use of the existing treatment process. Although optimal ozonation probably provided the highest biological activity in the following exhausted GAC filters, alone it does not justify the use of ozone. After installing GAC filtration and UV disinfection, the role of ozone is rather to provide an additional barrier against unexpected changes in the source water quality.

This thesis consists of an overview and of the following 9 publications:

  1. Vahala R., Ala-Peijari T., Rintala J., Laukkanen R. (1998) Evaluating ozone dose for AOC removal in two-step GAC filters. Water Science and Technology 37(9), 113-120.
  2. Vahala R., Långvik V.-A., R. Laukkanen R. (1999) Controlling AOX and THM formation by ozonation and two-step GAC filtration. Water Science and Technology 40(9), 249-256.
  3. Vahala R., Niemi R.M., Kiuru H., Laukkanen R. (1999) The effect of GAC filtration on bacterial regrowth and nitrification in a simulated water main. Journal of Applied Microbiology Symposium Supplement, 85, 178-185.
  4. Vahala R., Moramarco V., Niemi R.M., Rintala J., Laukkanen R. (1998) The effects of nutrients on NOM removal in BAC filtration. Acta hydrochimica et hydrobiologica, 26(3), 196-199.
  5. Vuorio E., Vahala R., Rintala J., Laukkanen R. (1998) The evaluation of drinking-water treatment performed with HPSEC. Environment International 24(5/6), 617-623.
  6. Vahala R., Rintala J., Järvinen A. (1996) Removal of TOC by two-step GAC filtration in cold humic waters. Proceedings of NOM workshop, September 18-19, Poitiers, France.
  7. Vahala R., Miettinen I.T., Laukkanen R. (1998) The effect of contact time, pH and ozone dose on the formation of biodegradable NOM during ozonation. Proceedings of IOA Conference on Ozonation and AOPs in Water Treatment, September 23-25, Poitiers, France, 31-1-8.
  8. Vahala R., Miettinen I.T., Korhonen S., Laukkanen R. (1998) Evaluation of operational conditions for intermediate ozonation. Proceedings of AWWA Water Quality Technology Conference, November 1-4, San Diego, California.
  9. Mikola A., Vahala R., Laukkanen R. (1999) The response of two-step GAC filters to backwashing. Proceedings of AWWA Water Quality Technology Conference, October 31-November 4, Tampa, Florida, CD-ROM.

Keywords: adsorption, natural organic matter, optimization, biological processes

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© 2002 Helsinki University of Technology

Last update 2011-05-26