Treatment pond

Function

Waste treatment ponds are very efficient even though their design has not changed in years. The plants work well in nearly all environments and can treat most forms of wastewater produced. Treatment ponds are used for smaller purposes in the United States but are used for major cities and factories in the rest of the world, as it is a simple and effective method to treat water. Many improvements have been made to improve their effectiveness and efficiency at turning harmful chemicals and sewage into less harmful forms of the previous. With ponds there is a variety of key elements to take care of in order to be properly maintained for the wastewater to be properly treated. Factors such as oxygen levels and flow through the ponds are just a few of the critical factors to properly maintaining the ponds. These factors are constantly monitored to maintain the pond and gain information on what factors are working the best in order to speed up the breakdown of harmful chemicals at the most efficient rate. Treatment ponds that are aerobic, anaerobic or facultative flow through basins are used in order to begin the water treatment process. Anaerobic ponds are used to treat water with industrial waste whereas aerobic ponds are used to treat water contaminated from other plant processes. Facultative ponds are good to treat raw wastewater and water that was not treated properly in the other ponds because it is both aerobic and anaerobic. Aerobic ponds are saturated with dissolved oxygen throughout the entire pond and are shallow enough for light to penetrate the entire depth of the pond. Anaerobic ponds allow the solid waste to settle down at the bottom as a waste sludge while dissolving organic material.

Wastewater characteristics

Typically fresh wastewater has a musty odor and is cloudy with a grayish coloration as it is fresh and untreated. When deprived of oxygen the water becomes black from further with a foul odor. The odor is that of rotten eggs and the water becomes corrosive inviting problems to form in the pipes, so usually treatment workers try to keep it from getting too oxygen deprived while in pipes. Temperature can be anywhere between 45–75 °F (7–24 °C), but the temperature of water entering the system usually does not affect the pond, because it is designed to handle a variety of temperatures. The pH of the system is a huge factor in pond water characteristics with the water either being acidic 0.0–7.0 or basic 7.0–14.0. The pH levels are monitored to make sure that the water does not get too acidic and start to corrode the pipes. It is most desirable for the water to be more basic so as to prevent corrosion from the acid. Another set of characteristics is the contents of the water, like solids, suspended solids and dissolved solids. Dissolved solids are able to pass through most filters whereas suspended solids are just particles suspended in the water column easily caught in strainers or filters. Solids is just a general term for what would remain if all of the water was evaporated from a sample of the wastewater. To get into more technical terms colloidal solids are particles that are so small that they will not settle by gravity on their own. Settleable solids are pretty much self-explanatory as they are the solids that will settle on their own in a given period of time.

Sizing

When being designed there are several factors that go into planning the build such as climate of the region, cost and the best way to process the waste in the water. Once the pond has been designed the next thing that must be considered is the location of the pond. The size depends on the type of wastewater entering the pond, the type of pond and location in order to begin to size it. Depths usually range from between four and twenty feet deep with the type of bacteria and total amount of waste the plant must treat being the determining factor in the design of depth. With a key factor in determination of size being how much wastewater is going to be treated by the pond the question of how much surface area is needed varies from a few thousand feet to many acres. Anaerobic ponds must be designed to be far deeper than either aerobic or facultative ponds, this is in order to decrease the oxygen levels in the deeper parts of the ponds so the bacteria can do their jobs, eating the waste. Aerobic ponds must be shallower with a great surface area so that more oxygen can dissolve into the water giving the bacteria enough oxygen to properly function. Facultative ponds meet somewhere in the middle in their design with a large surface area and a fairly deep design to allow for both bacteria to function properly.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.

Ecology

Aerobic bacteria grow in the aerobic ponds and are able to decompose organic waste into oxidized products. Cyanobacteria are typically grown in aerobic ponds in order to provide the bacteria in the pond with plenty of oxygen. Anaerobic ponds contain anaerobic bacteria, which are able to breakdown complex organic waste into basic compounds that are less harmful to the environment. There are several kinds of algae that grow in treatment ponds such as green, red and brown algae. In most ponds both bacteria and algae are needed in order to maximize the decomposition of chemicals. Bacteria and algae work in tandem with bacteria breaking down the complex compounds and chemicals. Then the algae decompose the newly formed compounds and are able to produce oxygen for the bacteria that need it. Several types of invertebrates are present in the ponds here they maintain algae levels and help allow the sediment to settle on the bottom. With mosquitos being a problem for those who maintain the ponds the addition of mosquito fish and several other types of predatory fish is good in order to keep the bugs in check. They are primarily used for mosquito control as treatment ponds are fantastic breeding grounds for mosquitos. By adding the fish the ponds bug issues are controlled in a natural and environmentally friendly way without having to use harmful chemicals.

Other types

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.

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:

1. A water depth from 0–20 cm. Iris pseudacorus, Sparganium erectum may be placed here (temperate climates).
2. A water depth from 40–60 cm. Stratiotes aloides, Hydrocharis morsus-ranae may be placed here (temperate climates).
3. A water depth from 60–120 cm. Nymphea alba may be placed here (temperate climates).
4. A submerged water depth. Myriophyllum spicatum may be placed here (temperate climates).