A method for treating waste water which comprises passing the water through a series of steps including sequentially passing the water through an aeration step, and then a plurality of treatment cells wherein each treatment cell comprises a trickle filter cell. The waste water is subsequently subjected to a denitrification step and to a dephosphorization step. It is then passed through a trickle filter cell and optionally may be treated by passing through a cell wherein the waste water is in contact with peat moss.
