Treatment of primary-settled urban sewage in pilot-scale vertical flow wetland filters: Comparison of four emergent macrophyte species over a 12 month period

The treatment of primary treated urban sewage by four emergent macrophytes has been compared over a twelve month period in separate gravel-based vertical flow constructed wetlands (300 litre interstitial volume). Nutrient removal in planted systems was greater than in the unplanted wetland especially for nitrogen and phosphorus and less so for BOD and suspended solids removal. The performance of most planted wetlands (especially Typha orientalis and Schoenoplectus validus) declined into autumn, particularly for nitrogen and phosphorus removal while a decline in plant ET was also observed, Baumea articulata, and to a lesser extent Cyperus involucratus, maintained high ET and nutrient assimilation throughout the trial period. As a consequence of the higher ET, dissolved solids (especially fixed salts) doubled in concentration during flow through wetlands planted with these two species, producing an effluent with a high sodium adsorption ratio and a reduced potential for re-use in irrigation.