Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI

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Drinking water quality is affected by the structure and physiology of the attached microbial communities in drinking water treatment, storage and distribution. In order to characterise microbial biofilms which occur during the drinking water treatment process, the present study aims to evaluate the spatial and temporal variability in enzymatic activity. Biofilm samples from clarification and from rapid sand filtration steps were analyzed in February, April, August and November 2011. Dehydrogenase, phosphatase and catalase enzymes were targeted. Heterotrophic bacteria were also quantified in biofilms, while raw water physical, chemical and microbiological parameters were monitored. High rates of phosphatase, catalase and dehydrogenase activities were recorded in biofilms developed in the clarification step. Increased numbers of sessile heterotrophic bacteria were found during spring and summer. The enhanced enzymatic activity registered during the cold season may be attributed to extracellular enzymes accumulation into the biofilm matrix. Also, the physiologically stressed state of bacteria, caused by drinking water treatment procedures may induce an intensive enzymatic activity. No significant difference was noticed in the intensity of enzymatic activities within biofilms developed on concrete and steel surfaces. However, higher catalase activity was registered on steel surfaces, where the accumulation of corrosion products and tuberculation were observed. A reduction in enzymatic rates throughout water purification process was recorded.

Keywords: catalase, dehydrogenase, drinking water biofilm, phosphatase, microbial activity.