Removal efficiency of subsurface vertical flow constructed wetlands for different organic loads

Using subsurface vertical flow constructed wetlands (SSVFCWs) with intermittent loading it is possible to fulfil the stringent Austrian effluent standards regarding nitrification. For small plants (less than 500 persons) standards for ammonia nitrogen concentration have to be met at water temperatures higher than 12 °C, effluent concentrations and treatment efficiencies for organic matter have to be met the whole year around. According to the Austrian design standards the required surface area for SSVFCWs treating wastewater was 5 m² per person. Within the first part of an Austrian research project the goal was to optimise, i.e. minimise the surface area requirement of vertical flow beds. Therefore, three SSVFCWs with a surface area of 20 m² each have been operated in parallel. The organic loads applied were 20, 27 and 40 g COD/m²/d, which corresponds to a specific surface area requirement of 4, 3 and 2 m² per PE, respectively. The paper compares the effluent concentrations and elimination efficiencies of the three parallel operated beds. It could be shown that a specific area demand of 4 m² per person is suitable to be included in the revision of the Austrian design standard. Additionally it could be shown that during the warmer seasons (May–October) when the temperature of the effluent is higher than 12 °C the specific surface area might be further reduced; even 2 m² per person has been proven to be adequate.