A reed bed, or constructed wetland is an engineered structure – like a pond – normally rectangular in shape. It harnesses the natural ecological processes that break down organic matter in wastewater. They contain gravels that are usually planted with common river reeds (Phragmites Australis).
Contaminated liquid effluent is applied either at one end or across the entire surface (depending on the reed bed type), and collected from the other end by a series of drainage pipes or a weir outlet structure at the bottom.
As the effluent passes through the gravels in the reed bed, it comes into contact with the bacteria growing in the oxygen rich atmosphere of the root system and on the surfaces of the gravels. This is the primary agent that breaks down and digests the sewage in the effluent.
This is an environmentally friendly, low cost and entirely natural process.