American Water College Practice Test

When the recirculation rate in a trickling filter is too low, it can lead to a reduced biological activity in the filter media. This is because the trickling filter relies on the constant movement of wastewater over the media to provide adequate exposure for microorganisms. If the recirculation rate is insufficient, the dissolved organic matter and nutrients may not be effectively contacted with the biofilm on the media, leading to decreased biochemical oxygen demand (BOD) removal. Additionally, stagnant areas may develop, which can cause ponding and prevent proper aeration, further exacerbating the issue. Together, these factors highlight the importance of maintaining an appropriate recirculation rate to ensure efficient treatment and avoid the consequences of low rates.