Biofilmele din staţia de tratare a apei. Grupe fiziologice de bacterii implicate în coroziune

Biofouling in water treatment plants and drinking water networks represents the inner surfaces colonization by microorganisms, with undesirable effects as pipes corrosion and water quality deterioration, well studied issues in present as impact of drinking water associated biofilms. Such biofilms are structured multispecific communities of bacteria, fungi, algae, protozoa and even invertebrates, embedded into a polymeric matrix adherent to the substrate. Biofilms are ubiquitous in water treatment plants and in water distribution networks, despite treatment and disinfection processes, which only acts as a selection factor in bacterial populations. This paper, as section of a complex study of bacterial communities specific to biofilms of water treatment plant and drinking water network in Cluj, describes the physiological groups of bacteria involved in corrosion: ammonifying, denitrifying, aerobic sulfur reducing, anaerobic sulfur reducing, sulfate reducing, sulfur oxidizing, iron reducing and manganese oxidizing. These physiological groups of bacteria were cultured and quantified in biofilm samples collected from two sampling points (clarifier and rapid sand filter), from January to September 2010. Meanwhile, a series of physical and chemical parameters of the raw water were registered (temperature, pH, turbidity, dissolved oxygen and organic substances). Descriptive analyses, including the mean values, variability, correlations and graphic displays were performed. The results revealed multiple correlations between the analyzed parameters, the microbial communities in biofilm from the clarifier evolved similarly to the biofilm from the sand filter. Bacterial load and frequency increased proportionally with biofilm’s age, the highest values per gram of biofilm being recorded in clarifier. The conclusion is that the biofilm from drinking water treatment plant contains a wide bacterial diversity, with freshwater and sediments origin, incoming from raw water sources.