What is a Horizontal Flow Reed-bed?

A horizontal flow reed-bed is one in which effluent is applied at one end and discharges from the other.  The bed remains full of water at all times. In the Sub-Surface Flow type the level of the water is carefully controlled so that it is always 25-50 mm below the surface of the gravel media.

Horizontal flow reed-beds are generally low in oxygen and will de-nitrify the effluent converting the nitrogenous compounds into free nitrogen gas which escapes to the atmosphere.