Identification of Filamentous Microorganisms Causing Filamentous Bulking and Factors Affecting Their Growth in a Petrochemical Wastewater Treatment Plant

Bulking (sludge bulking) is caused by the excessive growth of filamentous or non-filamentous bacteria in the process of wastewater treatment, which subsequently results in a reduction in the quality of the output of wastewater treatment plant. By identifying the main cause of bulking bacteria, we can recognize its formation and find solutions to specific bulking control. The proliferation of Nocardiaforms and Beggiatoa are due to the presence of excess oil compounds and sulfur compounds in the input wastewater, respectively. In this study, the identification of bulking bacteria was carried out in a petrochemical wastewater treatment plant using microscopic methods. Identification of filamentous bacteria was realized by microscopic studying of slides, based on morphological characteristics and their reaction to different staining; therefore, Beggiatoa and Thiothrix identified as predominant filamentous bacteria. According to results characteristics of these bacteria and effective growth factors, the abundance of sulfur compounds, the sulfur content and subsequently the growth of these bacteria are increasing. Thus they are prevented for the specific bulking control in a Petrochemical wastewater treatment plant by removing sulfuric acid in the pH adjustment of the balancing pond and replacement of hydrochloric acid.