Microthrix Parvicella - The filament that can cause foaming problems on aeration basins during winter months

Microthrix parvicella is a filamentous bacterium that causes bulking and foaming in activated sludge systems. It becomes a bigger problem in winter months for several reasons:
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• Temperature Sensitivity: Microthrix parvicella thrives at lower temperatures, which are common in winter. As temperatures drop, the metabolic activities of other bacteria slow down, giving it a competitive advantage.
• Reduced Settling Rates: The filamentous nature of Microthrix parvicella leads to poor settling in the secondary clarifiers. In winter, the slower metabolic rates of other bacteria exacerbate this issue, resulting in increased sludge volume and poor effluent quality.
• Foaming Issues: It is one of the bacteria capable of growth on Fats, Oils, Grease (FOG)  producing hydrophobic foam, which can lead to operational problems in aeration basins and secondary clarifiers. The cold weather can make it more difficult to control and remove this foam.
• Bulking Problems: When over abundant, filaments lead to bulking, where the sludge fails to compact in the clarifier bed. This is particularly problematic in winter when the overall biological activity is reduced, making it harder to manage the sludge.

Mitigating Microthrix parvicella foaming involves several strategies:

• Optimize FOG Removal: Reducing fats, oils, and grease (FOG) in the influent also reduces  Microthrix parvicella's food source. This can be achieved through improved pretreatment processes such as grease traps and skimmers.
  
• Maintain Proper Aeration: Ensuring adequate oxygen levels in the treatment process also favors development of healthy floc forming biomass. Regular monitoring and adjustment of aeration rates are essential.
  
• Chemical Dosing: The use of chemicals for disinfection (targeting filaments via oxidation) can help control the growth of filamentous bacteria. However, this approach should be used with caution to avoid negative impacts on the overall treatment process especially in winter months.
  
• Sludge Management: Proper sludge handling and disposal practices can prevent the accumulation of filamentous bacteria. Regular sludge wasting and maintaining appropriate sludge age are important factors.
  
• Foam Control Agents: The application of foam control agents, such as silicone-based antifoams, can help reduce foam formation and improve operational efficiency.
  
• Surface Wasting: Removing foam and sludge from the surface of the aeration basin can help control foaming organisms such as M. parvicella and Nocardia forms.