Vertical flow and combination reed beds

Vertical flow reed bed systems are much more effective than horizontal flow reed-beds not only in reducing BOD and SS levels but also in reducing ammonia levels and eliminating smells. This makes them more suited to industrial usage. They can be considerably smaller and will also cope with much stronger effluents. This more stringent method of waste water treatment can, in the long run if properly designed and installed save thousands in chemical treatments.

In combining the two types of reedbed the treatment is even more effective, the waste water fist passes through the vertical flow bed. This is effectively a gravel filled tank with a hole at the bottom, similar to a plug hole. Water enters the top of the bed amongst Phragmites australis (Common Reed) and trickles through the gravel where it passes aerobic bacterial communities.

Once it reaches the bed base most of the suspended solids have been removed, the biological oxygen demand (BOD) content significantly reduced and nitrification occurred (the breaking down of ammonia to nitrates). The water is then collected by drainage pipes which lead to the horizontal bed

This is an anaerobic bed, comparable to the vertical flow tank except that the water is traveling horizontally. Water enters one end of the bed and moves through in a horizontal manner, effectively filling the bed and displacing all air, until it is allowed to escape at the far end.

The microbial fauna of this bed convert much of the nitrates to nitrites and nitrogen gas (denitrification) and consume any pathogens in the water. From there on the water may be used for a variety of purposes having achieved the desired levels of purity. Depending on the site this may be for irrigation, plumbed back through the system or discharged to a water course.

It is worth noting that discharge consents will still be required by the Environment Agency for any waste water entering water courses. Reedbed waste water treatment can only be carried out if accompanied by a stringent monitoring procedure to ensure that the process is functioning correctly.