Horizontal subsurface-flow constructed wetland removal efficiency using Cyperus articulatus L.

Abstract

Constructed Wetlands (CW) are a suite of natural wastewater treatment systems that are governed by biological, chemical and physical processes. These processes, in tandem, regulate the removal of organic and inorganic wastewater pollutants. Both aquatic microorganisms and aquatic macrophytes can transform and uptake contaminants from wastewater and achieve higher removal efficiencies. The aim of this study was to evaluate the effect of Cyperus articulatus, a Colombian native aquatic macrophyte, on removal of dissolved organic matter and nitrogenous compounds from domestic wastewater. Experiments were conducted in replicate pilot-scale Horizontal Subsurface Flow Constructed Wetlands (HSSF CWs). Four (4) wetland treatment units were installed in parallel. Two were planted with C. articulatus and the other two remained as unplanted controls. The experimental system was hydraulically connected to a 760L septic tank, which functioned as a primary treatment module and fed experimental wetland treatment units. Each wetland unit was filled with granite gravel (8mm average diameter and approximately 40% porosity) to a depth of 0.5m. During a period of four-months, each treatment unit was provided with 29Lday−1 of clarified domestic wastewater, ensuring a Hydraulic Retention Time of three (3) days. Wastewater samples from influent and effluents were collected twice each week in order to monitor temporal/spatial changes in concentration of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N). At the end of the experiment, plant biomass was collected and dried to constant weight to facilitate calculations and reporting of plant biomass on a dry matter basis. Although this was a preliminary study of short duration, results showed that high organic matter removal efficiency can be achieved (91% in systems planted with C. articulatus, compared with 80% in unplanted wetlands). NH4+-N removal was significantly improved in planted systems, averaging 85% vs. 40% for unplanted systems (p<0.05). Total biomass production by C. articulatus was 5.0 (±0.16) kg.m−2. In conclusion, results obtained in this short duration study indicate that C. articulatus could be a promising species for treating domestic wastewater in the Colombian Caribbean region.