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Water Treatment 2: Reed Bed

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A

Nowadays subsurface flow wetlands are a common alternative in Europe for

the treatment of wastewater in rural areas. Mainly in the last 10 to 12 years there

has been a significant growth in the number and size of the systems in use.

Compared to common treatment facilities, wetlands are lower in cost investment,

lesser to maintain, and are ideal for densely populated rural or suburban areas

rather than urban areas.

B

The Common Reed has the ability to transfer oxygen from its leaves, down

through its stem and rhizomes, and out via its root system. As a result of this action,

a very high population of micro-organisms occurs in the root system, with zones of

aerobic, anoxic, and anaerobic conditions. Therefore with the waste water moving

very slowly and carefully through the mass of Reed roots, this liquid can be

successfully treated.

C

A straightforward definition of a reed bed is if you have dirty water in your

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pool or water, which is heavily polluted, Reed Beds will be planted to make the

water clean again. This is good for ecology and living organisms and fish in the

water. Reed Beds have a wide range of qualities and are acceptable for cleaning

everything from secondary to tertiary treatment of mild domestic effluent, to rural

waste and even heavy industrial contaminants. The reason why they’re so

effective is often because within the bed’s root sector, natural biological, physical

and chemical processes interact with one another to degrade or remove a good

range of pollutants. Reed beds can be built in a number of variants, but mainly

they are of the horizontal flow or vertical (down) flow configuration where

water flows through the beds horizontally or vertically.

HORIZONTAL FLOW REED BED SYSTEMS

D

Horizontal-flow wetlands may be of two types: free-water surface-flow (FWF)

or sub-surface water-flow (SSF). In the former the effluent flows freely above

the sand/gravel bed in which the reeds etc. are planted; in the latter effluent

passes through the sand/gravel bed. In FWF-type wetlands, effluent is treated by

plant stems, leaves and rhizomes. Such FWF wetlands are densely planted and

typically have water-depths of less than 0.4m. However, dense planting can limit

oxygen diffusion into the water. These systems work particularly well for low

strength effluents or effluents that have undergone some form of pretreatment

and play an invaluable role in tertiary treatment and the polishing of effluents.

The horizontal reed flow system uses a long reed bed, where the liquid slowly