Water Research 39 (2005) 2394–2406 Elimination of microcystins by water treatment processes— examples from Sulejow Reservoir, Poland Tomasz Jurczak a,Ã , Malgorzata Tarczynska a,{ , Katarzyna Izydorczyk b , Joanna Mankiewicz b , Maciej Zalewski a,b , Jussi Meriluoto c a Department of Applied Ecology, University of Lodz, Banacha 12/16, 90-237 Lodz, Poland b International Centre for Ecology, Polish Academy of Sciences, Tylna 3, 90-950 Lodz, Poland c Department of Biochemistry and Pharmacy, A ˚ bo Akademi University, Tykisto¨katu 6A, 20520 Turku, Finland Received 20 November 2004; received in revised form 11 March 2005; accepted 6 April 2005 Available online 31 May 2005 Abstract Eutrophication is a serious problem in Polish freshwaters. Mass occurrences of toxic cyanobacteria in reservoirs cause problems in the production of safe drinking water and the diversity of produced toxins complicates monitoring of freshwaters. The aim of this study was to estimate the efficiency of water treatment processes in the removal of microcystins (MCs), cyanobacterial hepatotoxins. Elimination of microcystins was studied at two waterworks, which supply drinking water to the city of Lodz from Sulejow Reservoir. The consecutive steps of pre-oxidation, coagulation, sand filtration, ozonation and chlorination used in the water treatment showed effective elimination of microcystins in water from Sulejow Reservoir in 2002 and 2003. The highest total concentration of microcystin (variants MC-RR, MC-YR, MC-LR) amounted to 6.7 mgl À1 in raw water and was detected on the 13th of August 2002. In 2003 the water utility decided to increase the contribution of ground water in the production of drinking water. This resulted in a decrease of microcystin in water during and after the treatment process. The current management strategy of the waterworks company includes mixing of surface water and ground water, which reduces the hazards caused by toxic cyanobacterial blooms in the reservoir. r 2005 Elsevier Ltd. All rights reserved. Keywords: Microcystins; Cyanobacteria; Drinking water; Water treatment process; Removal 1. Introduction As in many countries, eutrophication is a problem also in Polish freshwaters, particularly for many water utilities and for recreational water use (Tarczynska et al., 2001). The presence of MC-LR, MC-RR and MC- YR has been detected in earlier samples from Polish freshwaters (Jurczak et al., 2004). Mass occurrences of toxic cyanobacteria in reservoirs complicate production of safe drinking water and the diversity of produced toxins calls for advanced monitoring techniques. The provisional guideline value of microcystin-LR in drinking water recommended by the World Health Organization (WHO) is 1 mgl À1 . The Polish Ministry of Health has incorporated the same concentration in Polish legislation (Dz. U. number 203, position 1718) in 2002 (WHO, 1996; Ministry of Health Regulation, 2002). In 2002 Poland was the first country in Europe and one of the five countries in the world (including Australia, New Zealand, Canada and Brazil), which ARTICLE IN PRESS www.elsevier.com/locate/watres 0043-1354/$-see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2005.04.031 Ã Corresponding author. Tel./fax: +48426354530. E-mail address: tjurczak@biol.uni.lodz.pl (T. Jurczak). { Deceased.