Abstract
The aim of this study was the isolation of bacterial strains which have the ability to decolorize synthetic dyes belonging to different chemical groups. The samples for bacterial isolation were collected from aqueous environments-two activated sludges and polluted local river. At the first stage of screening (performed on the solid media supplemented with two dyes-azo Evans blue or triphenylmethane brilliant green), 67 bacterial strains were isolated capable to decolorize the used dyes. In the further study, six dyes with different chemical structures were used: fluorone dyes (Bengal rose, erythrosine), triphenylmethane dyes (brilliant green, crystal violet), azo dyes (Evans blue, Congo red). Initial concentration of each of these chemicals in samples was 0.1 g/l. Obtained results showed that only 31 isolates were able to decolorize all six used dyes (with different efficiencies). Among them, 11 strains were isolated from the river (55% of isolates from this site) and 20 from activated sludges collected from two different treatment plants (15 from the first water treatment plant and 5 from the second which were 42 and 43% of isolated cultures respectively). The decolorizing microorganisms are mostly isolated from different industrial sewages (e.g., textile industry), but results of the study showed that water from polluted river as well as municipal wastewaters may be a precious source for isolation of bacterial strains with the wide spectrum and high decolorization potential. In general, there were no statistically significant differences between decolorization abilities of strains isolated from different sites. The group of dyes that was removed with the highest yield was triphenylmethanes (75.6%), followed by fluorones (70.0%) and azo group (60.9%). The analysis of decolorization efficiency of the individual dyes revealed the best removal results in case of triphenylmethane brilliant green (average removal 85.7%), followed by fluorone erythrosine (average removal 78.9%), triphenylmethane crystal violet (average removal 65.5%), azo Evans blue (average removal 64.4%), fluorone Bengal rose (average removal 61.0%), and azo Congo red (average removal 57.4%). Obtained results revealed that the dye susceptibility to decolorization depends on the characteristic chemical structure of given dye groups but more important is chemical structure of strictly given dye within the group.