The function of the reedbed system is to carry out the tertiary treatment of the sewage that has previously passed through a biological primary and secondary treatment stage. The resulting effluent can either be re-used for irrigation, be put back into streams or into a leachfield.
The function of the vertical reedbed is to act as a tertiary treatment plant. The effluent that comes out of the packaging plant is dispersed over the reedbed surface through the distribuition pipe. This effluent (water) then percolates throught the reedbed. The water descends the bed, becoming trapped in the sand layer, like a sponge taking up water. This means that a dose of water can stay in the bed for a long time, until the next dose of water displaces it. This is one reason why the dose rate of approx 9.2 litres per sq metre (ie. 1 cm depth per sq metre) should not be much surpassed. If one goes above 10 litres, the dose will not be trapped within the bed but pass throught shortly after the dose. The object is the residence time should be as long as possible.
Within the top lay of sand the SS and BOD are removed and towards the bottom the amonia is removed.
The function of the dosing device is to dose the reedbed at intermittent times. This happens whenever the sewage entering the dosing cubicle reaches the 300 mm mark with the tank (approx 100 litres). When this mark is reached the doser is triggered off dosing the reedbed. ie the fuction of the dosing device is to feed the reedbed which is to carry out the tertiary treatment of the sewage.