Constructed Wetland

Constructed wetlands are created artificially to improve the quality of water. These wetlands are designed on the lines of natural wetlands which are considered as the earth's kidney as they filter the pollutants from the flowing water. These wetlands utilize all the natural processes including wetland vegetation, soils, and associated microbes for improving water quality.

How are they built?
Constructed wetlands are normally constructed on uplands, floodways or outside floodplains. By doing so damage to the natural to natural wetlands and other aquatic resources is avoided. Wetlands are constructed through following methods:

• Excavation
• Backfilling
• Grading
• Diking and
• Water control structure (To establish desired hydraulic flow patterns)

How do treatment wetlands work?
Constructed wetlands are generally constructed for wastewater with low suspended solid content whereas the COD concentration should be below 500 mg/l. These are considered as an excellent and most effective technology to upgrade septic tank of high quality. There are three basic treatment systems of constructed wetlands:

• The overland treatment system
• Vertical flow filter
• Horizontal flow filter

The water is distributed on carefully contoured land by channels and sprinkles for overland treatment. Horizontal filter on the other hand is simply operated and can be maintained easily. In vertical filter water is distributed by distribution device to two or three filter beds.

Types of Constructed Wetlands

Surface Flow Wetlands
The important components of surface wetlands are shallow basin, soil or other medium to support the roots of vegetation, and a water control structure for maintaining the shallow depth of water. Wetlands that are constructed for treating mine drainage or agricultural runoff are surface flow wetlands. In these type of wetlands layer which is near surface is aerobic whereas substrate and deeper layer are anaerobic.

Subsurface Flow Wetlands
The main constituents of the subsurface flow wetland are sealed basin with a porous substrate of rock or gravel. The water level in this type of wetland remain below the top of the substrate. Subsurface wetlands are suitable for those wastewater that have low solid concentration and whose flow system is uniform.

Hybrid System
Hybrid system or multistage system different cells are fabricated for different types of reactions. They are suitable for mine drainage.

External Resources
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