A treatment pond is a type of pond which is constructed to treat lightly polluted water or wastewater. A treatment pond may be used in combination with a rainwater reservoir to form an ecological, self-purifying irrigation reservoir or swimming pond (natural pools).
Rooftop water purifying ponds are being used on rooftops. These green roofs can be built from a simple substrate or with plant-based ponds. Plants used include calamus, Menyanthes trifoliata, Mentha aquatica.
Usually, common reed or Phragmites australis are used in treatment ponds (e.g., in greywater treatment systems to purify wastewater). In self-purifying water reservoirs (used to purify rainwater), other plants are used as well. These reservoirs need to be filled with 1/4 lavastones and water-purifying plants.
Treatment ponds use a wide variety of plants, depending on the local climate and other conditions. Plants are generally chosen which are indigenous, for environmental reasons and optimum performance. In addition to water purifying (de-nutrifying) plants, plants that supply oxygen, and shade are added in ecological water catchments, ponds. This allows a complete ecosystem. Local bacteria and non-predatory fish may be added to eliminate pests. The bacteria are usually grown by submerging straw in water and allowing bacteria from the surrounding air to form on it. Plants are divided in four water depth-zones:
- A water depth from 0–20 cm. Iris pseudacorus, Sparganium erectum may be placed here (temperate climates).
- A water depth from 40–60 cm. Stratiotes aloides, Hydrocharis morsus-ranae may be placed here (temperate climates).
- A water depth from 60–120 cm. Nymphea alba, may be placed here (temperate climates).
- A submerged water depth. Myriophyllum spicatum may be placed here (temperate climates).
Three non-predatory fish (surface, bottom and ground-swimmers) are chosen. This ensures the fish 'get along'. Examples for temperate climates are:
- Surface swimming fish: Leuciscus leuciscus, Leuciscus idus, and Scardinius erythrophthalmus
- Middle-swimmers: Rutilus rutilus
- Bottom-swimming fish: Tinca tinca
- "Ecologic water basins used for agriculture/irrigation". Oieau.fr. Retrieved 2010-10-05.
- SwimPond Incorporated. "reservoirs made self-purifying through addition of treatment pond". Swimpond.com. Retrieved 2010-10-05.
- "Overview of lavafilters". Stowa-selectedtechnologies.nl. Retrieved 2010-10-05.[dead link]