Addition of Corn Cob in the Free Drainage Zone of Partially Saturated Vertical Wetlands Planted with I. sibirica for Total Nitrogen Removal-A Pilot-Scale Study

The aim of this 15-month study was to evaluate and compare two partially saturated (PS) vertical flow (VF) wetlands for total nitrogen (TN) removal. The PS VF wetlands, evaluated in duplicate, were added with corncob (CC) in two different heights of the free-drainage zone (FDZ). The FDZ had a height of 40 cm and the saturated zone (SZ) had a height of 30 cm. The configuration of the system I (SI) was a 20 cm-corncob bed above the SZ followed by a 20 cm-tezontle bed; in system II (SII) the order of the beds were inverted. The SZ was added with tezontle with a size of 1-2 cm. Weekly measurements of water quality parameters including oxygen demand (BOD5), chemical oxygen demand (COD), color, total suspended solids (TSS), organic nitrogen (Org-N), ammonium (NH4+), nitrate (NO3-) and nitrite (NO2-), were taken in the influent and effluents, and interfaces (nitrate and nitrite). Measurements of pH, dissolved oxygen (DO) and oxidation-reduction potential (ORP) were taken in the SZ. The addition of CC in the FDZ did not interfere with the capacity of the PS VF wetlands for BOD5, COD, TSS and true color removal, reaching mass removal efficiencies of 91.9% and 92.2%, 66.6% and 75%, 89.8% and 92%, 63.3% and 66.0%, for SI and SII, respectively; without significant difference between the systems (p > 0.05). The CC in the FDZ neither interfered with the PS VF wetlands nitrification capacity. The removal of TN was similar in SI and SII (p > 0.05), attaining average mass removal efficiencies of 68.2% and 66.0%, respectively. These efficiencies were not sufficiently high due to the limited denitrification process in the SZ as a result of the absence of biodegradable carbon, generated and consumed in the FDZ.