Impacts of filamentous bacteria on chemical efficiency in wastewater treatment

The wastewater treatment chain of several municipal and industrial systems begins with biological treatment (MBBR, SBR, or activated sludge), followed by the chemical treatment of wastewater by coagulation or flocculation in a DAF or decanter.

When a biological treatment is unbalanced and combined with a set of conditions, as discussed later, an explosion of ‘filamentous’ bacteria can occur. The excessive presence of filamentous bacteria in biomass causes problems with sludge bulking and foaming in biological processes.

It is important to identify the causes of disturbances in biological processes that lead to an overpopulation of filamentous bacteria. When filamentous bacteria are responsible for foaming, it is necessary to address the primary cause of the problem rather than simply removing the foam with a defoamer.

Some possible reasons to explain the imbalance of biological treatment and the excessive presence of filamentous bacteria are:

• Low dissolved oxygen concentration (mg O2/l)
• Nutrient deficiency (mg/l)
  • NO2-N, NO3-N, NH4-N, and PO4-P
  • Ratio BOD: N : P
• Low sludge load (kg BOD/kg MES, day)
• Sludge age is too high (days).
• The presence of long-chain fatty acids or short carbon chains

To properly identify the filamentous organisms, present in the effluent, it is recommended to observe the effluent using a microscope.

Eikelboom and van Buijsen published their filamentous bacteria identification system in 1981 (Eikelboom and van Buijsen, 1981). This approach to identifying filamentous bacteria was updated and modified by Jenkins et al. (1993, 2003) and is used worldwide.

When the effluent contains a significant number of filamentous bacteria, the coagulation and flocculation of wastewater are often impacted. Chemical treatment can overcome the phenomenon of repulsion of flocs generated by filamentous devices by overdosing, but chemistry has its limitations.

Coagulation and flocculation of water containing a significant amount of filamentous bacteria.	Observation of filamentous bacteria affecting wastewater coagulation with Aluminum coagulant

Bulking Sludge – Slow settling and non-compaction of the sludge in the beaker even after a long settling time – a sign of filamentous bacteria in the effluent.

Useful link : The 10 Most prevalent filamentous bacteria

https://www.maine.gov/dep/water/wwtreatment/ten.pdf