TERTIARY-TREATMENT IN A VERTICAL FLOW REED BED SYSTEM - A FULL-SCALE PILOT-PLANT FOR 200-600 PE

In Strengberg, Lower Austria, a vertical flow reed bed system (gravel/ sand) was chosen as a new type of tertiary treatment which was designe d as a full scale pilot plant with various possibilities of operationa l use. The surface of the vertical flow pilot plant amounts to about 6 00 m(2) 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 interva ls. 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 gradua lly raising the influent load. The efficiency and operational reliabil ity within the whole year period (summer/winter)are considered to be a n important factor for establishing general dimensioning approaches. T he pilot plant has been in operation for more than one year now. Diffe rent operational stages up to a hydraulic load of 1.3 m(2).p.e.(-1) (i .e. 0.75 m(2).p.e.(-1)) were carried out. The average chemical oxygen demand (COD) of the reed bed effluents varied from 1 to 20 mg.l(-1). N ot surprisingly the ammonium (NH4-N) results showed more variation. Re sults, thus far, indicate NH4-N removal efficiencies between 40% and 9 0%. (C) 1997 IAWQ. Published by Elsevier Science Ltd.