What Is a Polishing Pond?

Wastewater treatment facilities are designed to process industrial and domestic inflows biologically. Polishing ponds are the final stage in water treatment to make it suitable for discharge into natural waters.

Purpose

• Polishing ponds are designed to increase hygienic quality of wastewater before it is recharged into public waters. They act as the final stage in satisfying the legal and environmental regulatory standards set by local and federal governments.

Discharge Criteria

• The concentration of specific parasites and fecal coliforms determines whether the water is ready to be discharged. Because fecal coliforms take longer to remove from wastewater, they are the best indicator as to how well a polishing pond is working.

Water Detention

• Polishing ponds will hold water for one to three days--a shorter period than stabilization ponds, which are designed to remove larger waste particles that settle to the bottom.

Pond Depth

• Ponds range in depth from 5 to 10 feet deep, compared with stabilization ponds at 3 to 5 feet deep. The greater depths decrease algae's ability to grow. If allowed to enter a natural lake or stream, algae can form large mats that prevent sunlight from reaching native, more beneficial aquatic vegetation.

Fish

• Grass carp

  Grass carp are stocked sometimes to reduce the amount of organic material being discharged. They consume submersed weeds and, though rarely, algae.