Evaluation of extremely shallow vertical subsurface flow constructed wetland for nutrient removal

摘要

Mesocosm-scale vertical subsurface flow constructed wetlands (SSF, 0.5m length, 0.3m width)nwith different reed-bed thickness, including standard SSF (SD, 0.6m deep), shallow SSF (S, 0.3mndeep) and extremely shallow SSF (ES, 0.075m deep) were set up at sewage treatment plant andntheir nutrient removal efficiencies from the sewage plant effluent were compared under threenhydraulic loading rate (HLR) conditions of 0.15, 0.45 and 0.75m3nm22nd21n. A very interestingncharacteristics was found for the extremely shallow SSF, in which a high nitrogen removalnefficiency was obtained despite the effective hydraulic retention time was only 1/8 times as longnas the standard SSF. The results of kinetic analysis confirmed that the high volumetric nitrogennremoval efficiency observed in the extremely shallow SSF did not depend on high responsenagainst the water temperature but on much higher basic nitrogen removal activity compared withnother SSF. The phosphorus removal depending on the adsorption to sand in the reed-bed filternwas, however, the lowest in the extremely shallow SSF although the volumetric removalnefficiency was much higher compared with other SSF. Results of morphological analysis ofnrhizosphere collected from respective reed-bed suggested that the extremely shallow SSF lead tona very high-density rhizosphere, resulting in a high basic nitrogen removal activity and volumetricnphosphorus removal efficiency.