[Population Dynamics and Key Influencing Factors of <i>Microthrix parvicella</i> Caused Sludge Bulking].

Given the frequent occurrence of the sludge bulking phenomena caused by <i>Microthrix parvicella</i> （<i>M. parvicella</i>） overgrowth during the low-temperature period in the full-scale municipal wastewater treatment plant, the filamentous bacteria dynamics of the <i>M. parvicella</i> population were systematically investigated during the completed bulking period using the multi-dimensional integrated filamentous monitoring method combined with the molecular quantitative method. A lab-scale reactor was constructed and successfully simulated bulking phenomena under the low-temperature condition. The trend of dominant filamentous bacterial shift and the main influencing parameters were estimated during the bulking period, to verify the key factors for filament growth and extinction of the sludge bulking phenomenon in the full-scale plant. The results showed that the bulking-caused <i>M. parvicella</i> was characterized by significant changes in the diversity of filamentous bacteria, and the dominant filamentous bacterial succession was reflected in the competition between the skeleton filamentous bacteria Type 0092 and Type 0041 and <i>M. parvicella</i>. At lower temperatures, sludge loading was an important controlling factor for the competitive growth advantage of <i>M. parvicella</i>： when the temperature was lower （approximately 15°C）, low sludge loading [0.05 kg·（kg·d）^-1] could lead to the stabilized elevation of <i>M. parvicella</i>, and with the loading increased to 0.1 kg·（kg·d）^-1 or more, <i>M. parvicella</i> populations showed a targeted decline despite the presence of the low temperature factor.