Nitrogen and phosphorus uptake and biomass production in four riparian plants grown in subsurface flow constructed wetlands for urban wastewater treatment

Abstract

Riparian woodlands play a multiple ecological and environmental role, including control of non-point source pollution and increasing of nutrients retention. Four riparian species (Arundo donax L., Salix purpurea L., Populus euphratica Olivier and Tamarix gallica L.) were tested comparatively in tertiary treatment and/or secondary one under a Mediterranean climate. Mesocosm inlets and outlets have been sampled every two weeks, during 21 successive months, and analyzed to determine nitrogen (N) and phosphorus (P) contents. Growth, biomass production and/or NP contents of macrophytes were monitored during three successive vegetation periods. Results show that A. donax presents a higher growth rate (2.39 cm d^-1) during the vegetation period, and a large harvestable biomass (118-134 t dry weight.ha^-1.y^-1) and aboveground N/P accumulation (1.55-2.13 t N.ha^-1.y^-1/0.16-0.17 t P.ha^-1.y^-1). S. purpurea and T. gallica show medium performances in this respect. In addition, A. donax-Mesocosm retains more particulate and dissolved forms of total nitrogen and total phosphorus, and orthophosphates in both treatment levels. In tertiary treatment, the annual collecting of aboveground biomass contributes to the export of 31.4% N-14.1% P and 14.5% N-7.71% P removed, by A. donax and T. gallica mesocosms in the same order. Collecting biomass of riparian plant grown in subsurface flow constructed wetland promotes more N retention when compared to the P one.

Keywords: Biomass collecting; Constructed wetland; Macro-elements; Macrophytes; Phytoremediation.