Behaviour of a Two-Stage Vertical Flow Constructed Wetland with Hydraulic Peak Loads

The behaviour of a two-stage vertical flow (VF) constructed wetland (CW) system with hydraulic peak loads has been investigated. The CW system was constructed for the Barenkogelhaus which is located on top of a mountain 1,168 m above sea level. The Barenkogelhaus has 70 seats and 16 rooms for overnight guests and is a popular site for day visits especially during weekends and public holidays. The system was designed for a hydraulic load of 2,500 L. day(-1) with a specific surface area requirement of 2.7 m(2) per person equivalent. It was built in fall 2009 and started operation in April 2010 when the restaurant was reopened. Samples have been taken between July 2010 and June 2013. In general, the measured effluent concentrations were low and the removal efficiencies high. Even in winter effluent BOD5, COD and NH4-N concentrations have been only slightly above the limit of detection for these parameters. Using the two-stage VF CW system, nitrogen elimination efficiency of more than 70 % could be achieved without recirculation. At hydraulic peak loads, i.e. at events at the Barenkogelhaus with more than 100 visitors with a hydraulic load > 100 % of the design load, a very robust treatment performance could be observed. The final effluent concentrations of COD and NH4-N did not rise during these peak loads and remained around the limit of detection.