With the aforementioned apparatus for the biological removal of phosphorus, the phosphorus dissolved out from the sludge by solubilization can be transferred via the aforementioned fermentation tank to the separated liquid in the aforementioned second solid/liquid separating means, in the same way as in the previously described apparatus for the biological removal of phosphorus, and so the phosphorus removal efficiency is increased.
In any of the three immediately aforementioned apparatus for the biological removal of phosphorus, there may be provided a means whereby some of the raw water is supplied to the aforementioned fermentation tank.
A substrate such as organic material brings about the release of phosphorus in the anaerobic tank, and organic acids are especially effective as substrates. With the aforementioned apparatus for the biological removal of phosphorus, some of the raw water is supplied to the aforementioned fermentation tank, the fermentation treatment is carried out and organic acids are produced, and these are introduced into the anaerobic tank, and so the phosphorous release rate in the anaerobic tank is increased and it is possible to carry out phosphorus removal more efficiently.
The apparatus of this invention can be used to treat various types of phosphorus-containing water, such as town sewage, industrial effluent and river water for example.