Microscopic detection of dominant bulking producing filamentous bacteria in Isfahan oil refinery water recycling unit plant by the buried slide technique

Bulking is the floation of sludge flocculent due to excessive growth of filamentous or non filamentous microorganisms in the process of wastewater treatment that can lead to further deterioration of treatment process and effluent quality. Nocardiaforms and Beggiatoa build-up are due to presence of excess oil component and sulfur in the system, respectively. Hence by identifying the main cause of bulking bacteria, we can recognize its formation and finding solutions to specific bulking control. This study was carried out to identify the main microorganisms responsible for the bulking at Isfahan oil refinery water recycling unite by using microscopical methods and buried (or contact) slide technique. Buried slide is a useful technique to analyze environmental samples in which a microscope slide is embedded in an expected sample. The contact slide method might have a bias toward selective colonization by using specific thin agar cover on the slide. By microscopic studying of different slides, identification of filamentous bacteria was carried out based on morphological characteristics and their reaction to different staining. Dominant filamentous bacteria were identified as nocardioforms actinomycete and Nostocoida limicola. Nostocoida limicola belongs to the genetic category of the budding Planctomycete. For the first time, the budding formations of these bacteria were clearly seen in contact slides in this study. Furthermore some relationships were found between the dominance of these bacteria and the conditions of the wastewater treatment plant, which based on them, the methods to specific bulking control could be obtained.