How does increasing the F/M ratio influence sludge age?

How does increasing the F/M ratio influence sludge age?

• A. Higher F/M ratio leads to longer sludge age.
• B. The F/M ratio has no effect on sludge age.
• C. Increasing F/M ratio increases growth rate and reduces sludge age.
• D. Only affects temperature.

Answer: (C)

F/M ratio represents how much food is available per microorganism. When you increase F/M, the microbes have more substrate per cell, so their growth rate rises and they produce biomass faster. In a activated sludge system, that accelerated biomass production means solids are replaced more quickly, which lowers the average time those solids stay in the system—the sludge age. So a higher F/M leads to a higher growth rate and a shorter sludge age. If F/M is reduced, growth slows and the sludge age tends to increase. Temperature isn’t the factor here; the relationship is about biomass growth and turnover driven by substrate availability.

F/M ratio represents how much food is available per microorganism. When you increase F/M, the microbes have more substrate per cell, so their growth rate rises and they produce biomass faster. In a activated sludge system, that accelerated biomass production means solids are replaced more quickly, which lowers the average time those solids stay in the system—the sludge age. So a higher F/M leads to a higher growth rate and a shorter sludge age. If F/M is reduced, growth slows and the sludge age tends to increase. Temperature isn’t the factor here; the relationship is about biomass growth and turnover driven by substrate availability.