Analysis of the influence of hydraulic application rate and saturation heights in a vertical flow constructed wetland on nitrogen removal

ABSTRACT

The objective of this paper was to evaluate the influence of bottom saturation for two conditions: 15 and 25 cm of saturation, in vertical flow constructed wetland systems (VFCW) with a 75 cm bed, using different hydraulic application rates (HAR): 40, 70 and 100 mm d^-1. The removal efficiencies of chemical oxygen demand (COD), solids series, ammonium nitrogen (N-NH₄), total nitrogen Kjeldahl (TKN) were evaluated. For COD, columns with 15 cm of saturation obtained 85% efficiency and columns with 25 cm, 86%, with no significant difference between the heights of saturation and TAH studied. For N-NH₄, columns with 15 cm showed an efficiency of 74% and those of 25 cm, 68%. For total nitrogen (TN), columns with 15 cm resulted in 71% and with 25 cm in 74% efficiency, with a significant difference between the TAH for the saturation height of 25 cm. Also, for SST, efficiencies of 91 and 63% were obtained for 15 and 25 cm, respectively, with a significant difference between the saturation levels for the TAH of 40 and 100 mm d^-1. The results showed that, on average, a saturation height of 25 cm was more efficient in the removal of TN. With regard to HAR, the most efficient proved to be the intermediate one that was tested, because, despite not always having presented the greatest removals given the area used, it was the best. The background saturation enabled a good performance of TN removal and carbonaceous organic matter related to COD, thus demonstrating that this modification in a constructed wetland can improve the treatment of domestic effluents.

Keywords:
denitrification; effluent; bottom saturation; nitrification; construct wetland; saturation zone