Nitrogen removal in pilot-scale partially saturated vertical wetlands with and without an internal source of carbon

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

“…Additionally, based on the measurements of BOD 5 during the last 23 weeks of the study in the influent, interface and effluents ( Figure 3), it was found that the concentration of BOD 5 was reduced mainly in the FDZ and only tended to lower values when the wastewater drained through the SZ. Interestingly, these results demonstrated that the placement of corncob in the FDZ prevented that high increase in BOD 5 concentrations in the effluent observed in a previous similar study with the same wastewater during the initial four months of operation, with corncob in the SZ of PS VF wetlands [26]. Consequently, BOD 5 removals were very high, without statistical difference between the PS VF wetlands (p > 0.05), with 91.9% and 92.2% for SI and SII, respectively.…”

“…Nevertheless, after some months, the COD concentrations registered more stabilized values ( Figure 2B), reaching a significant decrease in both systems (p < 0.05) along the study, without significant differences between them, with efficiencies of 66.6% and 75% in SI and SII, respectively. It is important to note that the aforementioned slight increase in the COD concentrations was much lower in comparison to the increments observed by [26] in the effluents of PS VF wetlands with corncob added in the SZ during the first months of experimentation, treating the same wastewater evaluated in this study. Furthermore, similar to the BOD 5 , according to the measurements in the influent, interface and effluents during the last 23 weeks of the study, no significant reduction of COD was found after the SZ (Figure 4).…”

“…Then, the addition of an external carbon source could provide the carbon requirements for heterotrophic denitrification [24] such external sources have generally been added along the FDZ and SZ in different studies [19,21]. The use of a solid carbon source (SCS) appears more advantageous when compared to the expensive-soluble carbon sources like ethanol, methanol, glucose, etc., [26]. SCSs come from renewable resources and are generated as wastes in huge quantities, mainly in developing countries such as Mexico.…”

“…In a previous study we evaluated the use of corncob (CC), an abundant agricultural lignocellulosic residue in Mexico which was placed in the SZ of PS VF wetlands for the removal of TN and obtained an average efficiency of 73.0% for seven months (after a stabilization period of three months) that decreased in 11% for the next seven months [26]. In addition, a high release of biochemical oxygen demand (BOD 5 ) and chemical oxygen demand (COD) was registered in the effluents during the first months of operation coinciding with a higher removal of TN.…”

Impact of Ornamental Vegetation Type and Different Substrate Layers on Pollutant Removal in Constructed Wetland Mesocosms Treating Rural Community Wastewater

“…This indicated that the presence of vegetation favored the release of radial oxygen [27], and this allowed nitrification in the rhizosphere zone. After denitrification processes in the anaerobic area, this last process could only have been present in the mesocosms with no plants, and in minor proportions, since the presence of vegetation under anaerobic conditions also favors carbon exudation from the root, which intensifies the denitrification [28]. Based on data from the US Environmental Protection Agency (USEPA) [29], the maximum allowed limit of N-NO 3 to allow aquatic life in freshwater systems acutely should not exceed 3.0 mg/L and 10 mg/L for recreational and aesthetic bodies of water, respectively.…”