Reed Beds are constructed wetlands planted with fragmites australis and provide a natural and sustainable form of sewage treatment.
Historically, the Reed Bed was the only form of small-scale sewage treatment available and were widely adopted to provide sewage treatment for domestic and commercial applications. However, as Reed Beds are believed to be primarily most effective during the growth phase of the fragmites australis reed, the Environment Agency does not typically accept the adoption of Reed Beds for ‘secondary treatment’ of domestic sewage.
Reed beds are still frequently employed for tertiary treatment or for polishing sewage treatment plant effluent in order to reach stringent effluent quality requirements. Reed beds are also frequently employed to reduce flow rates to sensitive watercourses in the summer months from seasonal applications such as caravan parks. Of course, reed beds can also be adopted to provide a natural, aesthetically pleasing face to otherwise industrial-looking sewage treatment plants in applications where brand, desire or belief requires this.
There are two main types of reed bed.
Horizontal flow (HF) reed beds are shallow lined structures which are constantly flooded to just below the gravel line. The effluent enters at one end and travels horizontally through the reeds bacteria rich root zone, before being discharged on the far side of the bed. The Common Reed Phragmites Australis is able to transfer oxygen from its leaves, down through its stem and rhizomes into the gravels around the root system creating a high population of micro organisms.
Vertical flow (VF) reed beds are lined, deeper structures made up of layers of various sized gravels planted with reeds. It is a free draining structure where effluent is delivered to the top of the bed in batches (by gravity dosing unit or electrical pump), floods the surface of the bed and drains through. Each batch traps oxygen in the bed leading to an aerated system. VF systems are more effective than HF systems at ammonia removal due to increased oxygen levels within them. VF systems have a smaller footprint than HF systems and can cope with stronger effluents.
VF and HF beds can be installed together in a Hybrid system to achieve a higher standard of discharge or where influent strength is higher.