In Strengberg, Lower Austria, a vertical flow reed bed system (gravel/sand) was chosen as a new type of tertiary treatment which was designed as a full scale pilot plant with various possibilities of operational use.
The surface of the vertical flow pilot plant amounts to about 600 m2 and is divided into four beds whereby two different depths of substrate are used. The application of the conventional plant effluent is carried out in intermittent flushes and at changeable time intervals. Final nitrification and partial denitrification and elimination of phosphorus are the main goals to be achieved. In the framework of the present research project the load limits will be determined by gradually raising the influent load. The efficiency and operational reliability within the whole year period (summer/winter) are considered to be an important factor for establishing general dimensioning approaches. The pilot plant has been in operation for more than one year now. Different operational stages up to a hydraulic load of 1.3 m2.p.e.−1 (i.e. 0.75 m2.p.e.−1) were carried out. The average chemical oxygen demand (COD) of the reed bed effluents varied from 1 to 20 mg.1−1. Not surprisingly the ammonium (NH4-N) results showed more variation. Results, thus far, indicate NH4-N removal efficiencies between 40% and 90%.