Wastewater bacteria growing in long chains of cells with high surface area are termed filamentous organisms. When you mention filamentous bacteria to most operators, the discussion usually focuses on the problem of filamentous bulking where the filaments interfere with secondary clarifier or MBR function. The truth is that filaments are not always a problem and MLSS benefits from having some filaments to function as a backbone providing macrostructure to floc.
Filamentous bacteria thrive and grow rapidly under conditions such as:
- Low Dissolved Oxygen
- Sulfides & organic acids (seen with low D.O.)
- Fats, oils & grease (FOG) – Nocardia forms (Gordonia sp.) and M. parvicella
- Very low F/M or low nutrients (N & P)
Positive Aspects of Filamentous Bacteria
- Floc Formation
Filamentous bacteria serve as the backbone of floc formation. They provide a structure for other bacteria to attach to, which helps in forming larger floc particles. These larger particles settle more efficiently in the clarifier, improving the overall quality of the effluent. - BOD Removal
They are effective in removing Biochemical Oxygen Demand (BOD) from the wastewater, which is essential for reducing the organic load. - Clarifier Efficiency
In moderate amounts, filamentous bacteria help in filtering out fine particulate matter, thus enhancing clarifier efficiency.
Negative Aspects of Filamentous Bacteria
- Sludge Bulking and Foaming
Excessive growth of filamentous bacteria can lead to sludge bulking and foaming. This occurs when the filaments extend dramatically from the floc particles, causing poor settling and potential washout of solid material from the system. - Interference with Separation
High concentrations of filamentous bacteria can interfere with the separation and compaction of activated sludge, leading to poor settling and increased Total Suspended Solids (TSS) carryover. - Impact on Sludge Volume Index (SVI)
They can affect the Sludge Volume Index (SVI), which is a measure of the settleability and compaction of the sludge. Poor settleability can result in operational challenges for the wastewater treatment plant.
While filamentous bacteria are essential for the structural integrity and efficiency of the activated sludge process, excessive proliferation can cause significant operational issues. Use of microscopic exam, SV30/SVI testing, and Microbial Community Analysis (MCA) testing can track filamentous populations and help with system management.
If you have any specific questions or need further details, feel free to ask!