Role of vegetation (Typha latifolia) on nutrient removal in a horizontal subsurface-flow constructed wetland treating UASB reactor–trickling filter effluent

Abstract

The main objective of the work is to characterize the role of plants in a constructed wetland in the removal of nitrogen (N) and phosphorus (P). The experiments were carried out in a full-scale system in the city of Belo Horizonte, Brazil, with two parallel horizontal subsurface-flow constructed wetland units (one planted with Typha latifolia and one unplanted) treating the effluent from a system composed of an upflow anaerobic sludge blanket reactor and a trickling filter (TF). Each wetland unit received a mean flow of approximately 8.5 m³ d−1 (population equivalent around 60 inhabitants each), with a surface hydraulic loading rate 0.12 m3m−2d−1. The experiments were conducted from September 2011 to July 2013. Mean effluent concentrations from the wetlands were: (a) planted unit total nitrogen (TN) 22 mg L−1, ammonia-N 19 mg L−1, nitrite-N 0.10 mg L−1, nitrate-N 0.25 mg L−1, P-total 1.31 mg L−1; and (b) unplanted unit TN 24 mg L−1, ammonia-N 20 mg L−1, nitrite-N 0.54 mg mL−1, nitrate-N 0.15 mg L−1, P-total 1.31 mg L−1. The aerial part of the plant contained mean values of 24.1 gN (kg dry matter)−1 and 4.4 gP (kg dry matter)−1, and the plant root zone was composed of 16.5 gN (kg dry matter)−1 and 4.1 gP (kg dry matter)−1. The mean extraction of N by the plant biomass was 726 kgN ha−1y−1, corresponding to 17% of the N load removed. For P, the extraction by the plant biomass was 105 kgP ha−1y−1, corresponding to 9% of the P load removed. These results reinforce the reports that N and P removal due to plant uptake is a minor mechanism in horizontal subsurface-flow constructed wetlands operating under similar loading rates, typical for polishing of sanitary effluent.