Bacterial strains were isolated from two different wastewater treatment plants (Katowice, Swibie, south Poland). Daily flow of wastewater treatment in Swibie was 250 m3/day (sewage farm) and in Katowice 43,000 m3/day. Samples of sewage were taken from inlet to wastewater treatment plant in Katowice and from biological ponds in Swibie. Isolation was done on Nutrient Agar (BTL) with 0.1 g l−1 of brilliant green. Two strains (Sz6 originate from Swibie and SDz3 from Katowice) with highest effectiveness of decolourization in isolation phase were chosen to the experiment. They were classified by the API 20NE test (Biomerieux) as Pseudomonas fluorescens.