What is the recirculation ratio for a trickling filter?

The recirculation ratio for a trickling filter is defined as the ratio of the flow rate of the recirculated effluent (Qr) to the flow rate of the incoming influent (Q). This relationship is crucial in understanding how trickling filters operate, as recirculation helps to optimize the treatment process by increasing the biological loading on the filter media, thereby enhancing the breakdown of organic matter.

When the recirculation ratio (Qr/Q) is maximized, it means that a significant portion of the treated effluent is being sent back to the filter, allowing for improved contact time and interaction between the microorganisms and the organic pollutants. This can lead to a more efficient operation of the trickling filter system, promoting better treatment outcomes.

In contrasting this with the other options, the other formulas either do not appropriately reflect the intended relationship between recirculation and influent flow or are combinations of the flow rates that do not yield a ratio. Hence, the correct representation of the recirculation ratio is precisely Qr divided by Q, which captures the essence of recirculation in the treatment process.