Wastewater New York State Practice Exam

The optimal rotating speed in a rotating biological contactor (RBC) is best described by a speed that shears off growth, allowing for constant hungry growth to develop. This is critical in maintaining an effective biological treatment process.

In an RBC, microbial biofilm grows on the surface of rotating discs that are partially submerged in wastewater. The process relies on the growth of these microorganisms to effectively break down organic matter. By utilizing a speed that sufficiently shears off excess biomass, the RBC encourages the development of a thinner biofilm layer that is more active and less prone to becoming overloaded. This 'hungry growth' condition is ideal because it promotes a higher metabolic rate among the microorganisms, leading to more effective treatment of the wastewater.

The other described speeds could lead to inefficiencies. A steady speed that allows for full growth on all surfaces could result in a biofilm that is too thick, which may hinder the mass transfer of oxygen and nutrients and decrease overall treatment efficiency. A slow speed may not provide enough shear force to effectively manage the biomass, while a varying speed that adapts to flow rates could complicate operational consistency and stability in microbial activity. Thus, the best practice in RBC operation is to maintain a speed that encourages consistent and efficient microbial activity through