Two-step granular activated carbon filtration in drinking water treatment

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Doctoral thesis (article-based)
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Date
2002-11-29
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Degree programme
Language
en
Pages
81, [81]
Series
Helsinki University of Technology, Laboratory of Water and Wastewater Engineering, Teknillinen korkeakoulu, vesihuoltotekniikan laboratorio, 33
Abstract
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.
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Keywords
adsorption, natural organic matter, optimization, biological processes
Other note
Parts
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
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Permanent link to this item
https://urn.fi/urn:nbn:fi:tkk-002104