What happens to microbial populations if there are changes in F/M ratio?
Microbial populations in wastewater are continually changing. The F/M or influent organic make-up and concentrations have a significant impact on the microorganisms that are present in wastewater treatment systems. Temperature, pH, D.O., inhibitory chemicals, and macro-nutrients are all factors that influence microbial populations.
What is Food to Mass Ratio?
The food entering the bioreactor and the microorganisms in the bioreactor must be in balance for the activated sludge process to work successfully.
-A high F:M ratio indicates that there is a greater amount of food (measured as BOD, COD, or TOC) than microorganisms available to consume it.
-A low F:M ratio indicates that there are a lot of microorganisms but not enough food. Bacteria creates a thicker slime layer, lose their motility, and clump together to form a dense floc that settles well in the clarifier only when food supply is limited.
The "M" part of the equation is also known as mass, which stands for biomass. Regardless of how "M" is defined, it is a critical quantity that may be measured, tracked, and adjusted to enable mechanical wastewater treatment systems to maintain effective treatment.
Disadvantage of High F/M ratio
The bacteria are active and multiply quickly when the F:M ratio is high, but they are also more scattered in suspended growth bioreactors. A high F:M ratio causes bacteria to disperse, making it difficult for them to build a good, large, dense floc. As a result, a high F:M ratio will frequently result in turbid effluent and poor settling sludge in the secondary clarifier.By incorporating additional treatment microorganisms (bio-augmentation) into wastewater processes, high F:M can be reduced.
The equation below shows the conventional formula for calculating the food-to-mass (microorganism) ratio;
If you work for a municipal wastewater treatment plant, all of your organic concentration data will most likely be measured as BOD-5, which you can plug directly into the calculation.
However, if you run an industrial wastewater treatment plant, your organic contents would most likely be measured as COD or perhaps total organic carbon (TOC). The COD or TOC concentrations cannot be used to replace the BOD concentration.
But, what about Microbial Populations in aerated lagoons?
There are substantial amounts of organics at the influent, but modest microbial populations. Microorganisms with fast growth rates benefit from this. Other growth constraints include inhibitory chemicals and harsh environmental conditions.
In lagoons, for example, soluble BOD-5 is reduced by 80% in the middle of the process, and species with new growth strategies take over. Ciliates and other advanced forms are preferred by indicator protozoa. In such a system, the connection between entering BOD and active microorganisms has a significant impact on wastewater treatment efficiency. Thus, balancing F:M in wastewater treatment plants is a dynamic process that often necessitates operational changes.
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