What Is an Evapotranspiration System?
Evapotranspiration is an onsite wastewater treatment and disposal method that provides an alternative to conventional soil absorption systems for areas where surface and groundwater protection is critical.
An ET system is unique in that it can discharge wastewater into the atmosphere via evaporation from the soil surface and/or plant transpiration, rather than directly into surface or groundwater. In other circumstances, however, the ET idea provides flexibility by combining seepage with evaporation as a backup option.
In semi-arid climates and places where yearly evaporation surpasses annual precipitation and wastewater application, an ET system is a viable alternative. ET refers to the total amount of water lost as a result of evaporation from the soil surface and transpiration by plants. ET systems are divided into three groups.
A pretreatment unit (often a septic tank or an aerobic unit) to remove settleable and floatable particles, as well as an ET sand bed with wastewater distribution pipes, a bed liner, fill material, monitoring wells, overflow protection, and a surface cover, are the essential components.
To improve the transpiration process, vegetation must be grown on the bed’s surface. The septic tank effluent runs into a sealed ET bed with continuous impermeable liners and precisely chosen sands in the lowest part.
The wastewater rises to the surface due to capillary action in the sand, where it evaporates as water vapour and escapes. Furthermore, vegetation transfers wastewater from the root zone to the leaves, where it is evaporated as a relatively pure condensate.
This design provides for complete evaporation and transpiration of wastewater while avoiding discharge to surrounding soil.
An evapotranspiration/absorption system (ETA) is a form of ET system that is an unsealed bed where evaporation and transpiration are the predominant means of disposal, although percolation is also utilised.
Both the atmosphere and the subsurface are discharged by the design.
The usage of mechanical devices in the third type of evapotranspiration system is still being researched.
It is a rotating disc unit, in which the discs revolve slowly, allowing the wastewater to evaporate over a vast surface area.
A concentric cylinder unit is a mechanical ET system in which driven air enters the cylinder’s centre, flows outward through wetted cloth wrapping, and is expelled as vapour.
Evapotranspiration Septic System Cost
The cost of an ET system is determined by the type of system, the location, and the wastewater parameters. The surface area of an ET bed, which is a function of the wastewater flow, determines its construction cost. The availability of adequate sand, the type and thickness of the liner utilised, a retaining wall (if needed), and the type of vegetation are all factors that affect the cost (usually native to the area).
The average cost of a three-bedroom home with a septic tank and an ET system is around $10,000 (minimum), although costs may vary based on site conditions.
Evapotranspiration septic systems range in price from $10,000 to $15,000 and are ideal for arid conditions and shallow soil. They have specialised leach fields that allow wastewater to evaporate from an open-air tank’s top.
Advantages & Disadvantages of Evapotranspiration Septic System
Advantages of Evapotranspiration Septic System
Here, the pros of Evapotranspiration Septic System are as follows.
- ET systems have the potential to overcome site, soil, and geological constraints, as well as land-based physical constraints, that prevent the implementation of subterranean wastewater disposal technologies.
- ET systems with impermeable liners lessen the possibility of groundwater contamination.
- The costs are comparable to those of other onsite systems.
- For sites with slowly permeable, shallow soils and high water tables, ET systems can be employed to complement soil absorption.
- These systems could be utilised for seasonal applications, such as summer houses or recreational parks in places where evaporation and transpiration rates are high, such as the southwest United States.
- The aesthetics of an ET system are improved by landscaping.
Disadvantages of Evapotranspiration Septic System
Here, the cons of Evapotranspiration Septic System are as follows.
- Climate conditions like as precipitation, wind speed, humidity, sun radiation, and temperature influence ET systems.
- These techniques are not appropriate in regions where land is scarce or the terrain is uneven.
- Because of their limited storage capacity, they are unable to store much winter wastewater for summer evaporation.
- Infiltration of precipitation has the potential to overburden the system.
- To avoid groundwater contamination, the bed liner must be watertight.
- ET systems are usually restricted to locations where yearly evaporation exceeds annual rainfall by at least 24 inches (i.e., arid zones).
- When the plant is dormant, transpiration and evaporation can be minimised (i.e., winter months).
- Salt buildup and other factors may eventually render vegetation and, with it, transpiration obsolete.