Filaments at beneficial levels versus filamentous bulking (severe)
When it comes to wastewater treatment, filamentous bacteria often get a bad rap. However, these microorganisms play a crucial role in the treatment process, especially when present in moderate numbers. Let’s dive into how filamentous bacteria contribute to wastewater treatment and the challenges posed by their overgrowth.
The Good: Floc Macrostructure and Waste Degradation
Filamentous bacteria grow in long, thread-like strands, forming a mesh that provides a support structure for other bacteria to attach to as they form floc. With a filamentous backbone reinforcing the floc, floc size tends to increase, and the individual floc is less susceptible to sheer forces. Solids separation is best when you have larger, denser floc.
Another benefit of filamentous bacteria is their ability to thrive in conditions with low substrate concentration and oxygen levels, making them efficient in degrading wastes even in challenging environments. Additionally, some filamentous organisms also oxidize sulfides which are inhibitory to both AOB and NOB (Nitrifiers).
The Bad: Overgrowth and Its Consequences
While filamentous bacteria are beneficial in moderate numbers, their overgrowth can lead to significant problems in wastewater treatment plants. Excessive filament growth can cause sludge bulking and foaming, which interfere with the compaction of settled sludge and reduce the efficiency of the treatment process. When filaments dominate, they create interfloc bridging, which lowers floc density and makes it difficult for the sludge to settle properly.
This overgrowth can be triggered by various factors, including changes in pH, dissolved oxygen levels, and macronutrient availability. Identifying and controlling these factors is essential to prevent filamentous bacteria from becoming a nuisance.
Tracking Filament Populations
When you conduct a microscopic exam, remember that filamentous bacteria are not all bad. In moderate numbers, they provide essential support for floc formation and efficient waste degradation. To tracking filament abundance, we suggest using phase contrast microscopy and to help you see the filaments with greater clarity. Note how many filaments are extending from the floc or in free solution, these are the filaments most likely to cause bulking. For daily exam purposes, you do not need to fully ID every filament present, we are simply monitoring their abundance. It is also important to monitor for conditions that favor filamentous overgrowth, can help prevent major bulking and foaming events. Key is to find the triggers that lead to bulking issues in your system and correlate bulking events to other operational factors. If you know certain events favor filamentous bulking, you can take steps to control before the situation gets out of hand.