The F:M ratio in the wastewater treatment system at a national park in Wyoming was optimal from July through October. There was consistent organic carbon loading during this period due to tourist activity.
However, when the park closed for the winter, the biomass declined because of reduced influent flows. This caused treatment issues at the beginning of the next tourist season in May and June because biomass had declined during the slower recreation months from November through April.
Thousands of visitors arrived in the spring, and the park did not have the necessary biomass to process the increased loads. The Utilities Supervisor contacted BioLynceus® for a solution to help support biomass in the system year-round.
Figure 1. A small mechanical plant with a primary and secondary
clarifier similar to the National Park mechanical system.
The operator started adding ProBiotic Scrubber® II (PBII) to the collection lines, 0.05 MGD mechanical treatment plant (Figure 1), lagoon systems, septic tanks, RV dump stations, and pit toilets. This increased the biomass in the wastewater systems, enabling more efficient wastewater processing.
In addition to PBII, the operators dosed the mechanical treatment plant with BioLynceus® Candy Carbon® (CC) from November through May. This treatment provided an organic carbon food source for the biomass when
wastewater inputs were minimal. CC kept the plant biology active through the off-season, so there was no lag time in the treatment process when visitors arrived the following spring.
The bioaugmentation and organic carbon treatment helped promote TSS, BOD, and nutrient removal throughout the system. Additionally, NPDES permit violations were avoided at the treatment plant while the park was using BioLynceus® products.
The combined PBII and CC treatment sustained biomass in the system year-round and improved the quality of the treated wastewater. The F ratio was stabilized, allowing for more efficient wastewater processing.
Wastewater treatment systems serving seasonal populations often encounter issues with biomass stability. A consistent supply of organic carbon is required to sustain the biological growth and metabolism essential for treating wastewater. Variable influent carbon availability can affect biomass formation and function.
The organotrophic bacteria that facilitate biological oxygen demand (BOD) and total suspended solids (TSS) removal can be impaired by insufficient organic substrate availability.¹ The food-to-microbe ratio (F) of a system describes the relationship between the quantity of organic carbon and biomass.
The optimal F ratio can vary among treatment plants depending on operational and plant design factors.² However, when the F ratio in a system decreases below the optimal range, this may indicate an insufficient organic substrate supply, diminished biomass, or both.
Applying bioaugmentation and supplementing wastewater treatment systems with an external organic carbon source can help maintain a balanced biomass.
1 Gerardi, M. (2006). Wastewater Bacteria. Hoboken, New Jersey: John Wiley & Sons, Inc. Pp.73, 181.
2 Mishoe, G.H. (1999). F/M ratio and the operation of an activated sludge
process. Florida Water Resources Journal 3, 20–21.
BioLynceus® ProBiotic Scrubber® II and Candy Carbon® balance F:M in wastewater systems.