What type of ponds are typically used following a trickling filter, activated sludge, or RBC plant?

The use of polishing ponds following processes like trickling filters, activated sludge, or rotating biological contactors (RBC) is primarily for secondary treatment and to further improve the quality of effluent before it is discharged or reused. Polishing ponds provide an additional stage of biological treatment, where remaining contaminants are further broken down by natural processes, including sun exposure and microbial activity.

These ponds typically allow for longer retention times, which enhances sedimentation and allows for the natural die-off of bacteria and other pathogens, ultimately leading to higher-quality effluents. The sunlight in the polishing pond can also lead to additional oxidation of organic substances and reduction of nutrients, primarily nitrogen and phosphorus, which may remain after earlier treatment stages.

While facultative ponds, aeration ponds, and anaerobic ponds have their specific uses in wastewater treatment systems, polishing ponds specifically serve the function of improving effluent quality through additional biological processes and sedimentation, making them well-suited for the final stage after primary treatments like trickling filters or activated sludge systems.