The effect of aboveground biomass harvesting on nutrients removal in a constructed wetland treating municipal sewage

Abstract

The study was performed at the constructed wetland treating municipal sewage from 200 population equivalent. The aim of the study was to evaluate the role of Phalaris arundinacea and Phragmites australis harvesting on nutrient removal. The highest phosphorus concentrations in leaves were found in the re-grown P. arundinacea in October (3.12 m g−1), followed by those in June (2.68 mg g−1) and July (2.67 mg g−1). Phosphorus concentrations in P. australis leaves were higher in July (2.14 mg g−1) than in September (1.79 m g−1). Phosphorus concentrations in stems were lower and varied between 1.07 mg g−1 in P. australis in September and 2.21 mg g−1 in P. arundinacea regrowth in October. Nitrogen leaf concentrations varied between 21.0 mg g−1 in P. arundinacea in June and 33.7 mg g−1 in P. arundinacea regrowth in October. In stems, the highest concentration was observed in P. australis in July (18.6 mg g−1) while the lowest N concentration was measured in July in P. arundinacea (3.8 mg g−1). The results showed that there was no difference between nutrients standing stock in a single harvested of P. arundinacea as compared to double harvested biomass. There was a significant higher biomass and consequently higher standing stock in P. arundinacea in the inflow zone as compared to outflow zone. Biomass and nutrients standing stocks in P. australis were significantly higher than that in P. arundinacea. The phosphorus sequestered in the aboveground biomass represented 6.3% of the inflow P load and phosphorus in the harvested biomass represented 44% of removed P load. For nitrogen, the respective values represented 14% and 41.6%. The data indicate that to remove 20% of the inflow annual load via biomass cutting, the inflow load should not exceed 20 g P m−2 yr−1 and 300 g N m−2 yr−1.