Effect of biological treatment and ultraviolet (UV)-C radiation disinfection process on wastewater bacterial community as assessed by denaturing gradient gel electrophoresis (DGGE) fingerprints

The rotating biological contactor (RBC) process was frequently used for the biological wastewater treatment in order to remove pollutants and to improve the water qualitybefore discharge to the environment. The presence of bacteria species in the secondary treated wastewater indicates the necessity of a tertiary treatment process [ultraviolet (UV)-C radiation disinfection] to reduce the number of living organisms in the water. Denaturing gradient gel electrophoresis (DGGE) method using 16S rDNA was commonly used for a direct comparison of structural diversity among different microbial communities. In the present study, community in treated and untreated wastewater from RBC treatment plantwas investigated using DGGE coupled with sequence analysis of 16S rRNA gene fragments from bands of interest. The analysis of the DGGE profiles and the sequence of the dominant DGGE bands showed a variability of the bacterial community with season. DGGE patterns of samples collected in summer were more complex than those collected in winter. In addition, the investigation of the effect of increasing UV253.7 germicidal doses on the bacterial community, in secondary treated wastewater effluent, revealed variabilityin bacterial tolerance to UV253.7 radiation. This variability is inter-specific and is dependent on the UV-C dose used and the bacterial specie irradiated. Consequently, this study demonstrated that DGGE method coupled with sequencing provides precise information on RBC and UV-C wastewater treatment process.   Key words: Wastewater, biological treatment, bacterial communities, polymerase chain reaction - denaturing gradient gel electrophoresis (PCR-DGGE), 16S rDNA, ultraviolet (UV)-C radiation disinfection.