Influence of Plants and Organic Matter on the Nitrogen Removal in Laboratory‐Scale Model Subsurface Flow Constructed Wetlands Inoculated with Anaerobic Ammonium Oxidizing Bacteria

Anaerobic oxidation of ammonium has become an alternative for the treatment of wastewater with high ammonium loads, and it was also suggested to be involved in the nitrogen removal process in constructed wetlands. Nonetheless, its role has not been well evaluated as yet. In this paper, results of a lab‐scale study are presented focusing on the evaluation of the role of Anammox bacteria, plants, applied ammonia, nitrite nitrogen loads, and the presence of organic matter in nitrogen transformation processes in subsurface‐flow constructed wetlands. The inoculation of the experimental model wetlands with active Anammox biomass increased the total nitrogen and ammonium removal rates to values up to 5.7 g N/m² d, which is almost 10 times higher than those values reported for subsurface flow constructed wetlands. Although the presence of plants caused a higher removal rate, the role of the plants became less important with high nitrite influent concentration. Because the unplanted experimental system without the addition of any organic carbon source showed also high nitrogen removal rates, it can be concluded that beside the potential for “conventional” denitrification in the planted systems the main mechanism for explaining the high nitrogen removal rates obtained during the experiments was the anaerobic ammonia oxidation. The assay of the formation of hydrazine from hydroxylamine and the findings of the molecular biology tests fitted with the positive results for potential Anammox activity obtained in the bottle test. The addition of organic carbon, specifically acetate, apparently had no great influence on Anammox activity, which is in agreement with the findings reported by other authors. Nevertheless, the addition influenced the redox potential. Some questions are still left open, which are mainly associated with the scaling up of these results and the inoculation of Anammox biomass in full‐scale systems.