What is the effect of a Low F/M ratio on sludge production?

• A. It increases sludge production
• B. It reduces sludge production
• C. It has no effect on sludge production
• D. It causes sludge to become more fragile

Answer: (B)

Low F/M ratio means there is not enough food relative to the amount of microorganisms. With limited substrate, the microbes can’t grow much, so the yield of new biomass is reduced. Since excess sludge is largely the biomass that’s produced, sludge production decreases. Endogenous metabolism may consume some existing cells for maintenance, but that doesn’t create more sludge. So the overall effect is a reduction in sludge production.