What distinguishes trickling filters from RBCs (rotating biological contactors)?

The key distinguishing feature of rotating biological contactors (RBCs) is their design, which includes rotating disks partially submerged in wastewater. This rotation provides the necessary aeration and brings the biofilm in contact with both the wastewater and the air. The movement of the disks through the wastewater allows for optimal exposure and growth of microorganisms that break down organic matter.

Trickling filters, on the other hand, consist of fixed media where wastewater is distributed over the surface of the media, allowing gravity and aeration to facilitate biological treatment as the wastewater trickles down. This process does not involve any moving parts like the rotating disks in RBCs.

The other choices do not accurately describe the fundamental aspects of trickling filters in comparison to RBCs. For instance, stating that trickling filters are batch processes or require chemical additives misrepresents their continuous flow design and reliance on natural biological processes. Similarly, claiming that RBCs rely solely on gravity overlooks the crucial role of their mechanical rotation in the treatment process. Thus, the choice accurately highlights the unique operational principle of rotating biological contactors compared to trickling filters.