How can an operator permanently increase the F:M ratio in the activated sludge process?

Increasing the wasting rate of sludge effectively raises the food-to-microorganism (F:M) ratio in the activated sludge process. This ratio is crucial because it represents the available organic material (food) compared to the amount of microorganisms that are treating that material.

By increasing the amount of sludge wasted, the total biomass in the system decreases, while the incoming organic load remains constant. As a result, there is relatively more food available for the remaining microorganisms, leading to a higher F:M ratio. This adjustment can enhance the treatment process's efficiency by promoting better growth conditions for the microorganisms that break down the organic waste.

Other options do not accomplish a permanent increase in the F:M ratio effectively. Reducing aeration time may compromise the oxygen availability needed for microbial respiration and growth, which could lead to poor treatment performance. Increasing the inflow of wastewater would dilute the biomass and contribute to a lower F:M ratio instead of increasing it. Although adding more microbial cultures may temporarily boost treatment capacity, it does not fundamentally change the relationship between food and microorganisms in a manner consistent with how the F:M ratio is calculated over time.