Polishing Ponds

POLISHING PONDS

Polishing is the tertiary and final effluent treatment process before wastewater can finally be disposed into natural water bodies. It involves

• removal of remaining suspensed solids and BOD that may be left after secondary effluent treatment
• polishing process starts with filtration. This is done by passing tertiary wastewater over filters made of bed of sand or charcoal
• This process allows particulater matter in the effluent to attach to filter media
• Next step is called lagooning. Here, the water is kept in natural condition with full exposure to air. The compartments where water is exposed to air are called polishing ponds
• These ponds are 5 - 10 feet deep and water is stored for 1 to 3 days.
• Sedimentation of degraded and non-degraded suspended particles at the bottom of the pond is facilitated in a natural way.
• Aquatic plants, invertebrates and weed eating fish are introduced in the polishing pond to absorb and consume any remaining particulate matter.
• The water may be rich with high phosphorus and nitrogen content which can promote growth growth of algal blooms
• Bacteria consume nutrients to produce products which can be removed fro wastewater easily.
• Fish keeps algal growth in check by eating algae and unnecessary weeds
• Eventually chlorine is added to water as allowed by local regulations to kill microbes and disinfect water
• Testing water before release, helps in measuring and improving the efficiency of polishing treatment.
• Once the water meets the strict regulatory criteria of the government, it can be safely released into the natural environment.