Filament Index & SVI 🦠. The importance of combining data with process expertise.
This example from a 6 MGD (~22,000 m3/d) plant shows how operational parameters and biological analysis together create an opportunity for proactive decision making and help prevent COSTLY upsets.
2 definitions:
Filament Index reflects the relative abundance of filamentous bacteria. In this plant, during stable operation, it typically ranges between 1 and 2.
SVI is a routine daily measurement that reflects how well the sludge settles and compacts.
In most periods, the Filament Index (purple) and SVI (red) move together (image from Maji platform):
Higher SVI often corresponds with higher filament levels.
Lower SVI usually corresponds with fewer filaments.
This expected correlation is seen throughout the year.
The circled region in July shows something different. Within a short period, the Filament Index increased from 1 to 3, while the SVI remained low and stable at around 70.
This disconnect is the key point:
A biological shift occurred during a period when the settling performance appeared normal. Traditional settling measurements alone did not reflect this change.
Further examination showed that a foaming filament (Nocardia) began to develop. In its early stages, this type of Nocardia usually does not influence SVI, which explains why settling remained unchanged even though the Filament Index increased.
Once this was recognized, the plant team addressed the underlying conditions that allowed this change to occur.
There are 3 important steps here:
1. Early warning - receive a RED flag.
2. Accurate understanding - what happened?
3. Take action - do the correct steps "kill it" when small.
The team built the correct strategy (In this case, deal with FOGs). Result:
A few weeks later, filament levels decreased, and the usual correlation between SVI and the Filament Index returned.
Almost 0 costs. 0 Regulatory fines.
This example highlights how combining routine operational & biological data with Maji supports earlier recognition of process changes and helps maintain stability before issues escalate.