Enhanced nitrogen removal by simultaneous nitrification-denitrification and further denitrification (SND-DN) in a moving bed and constructed wetland (MBCW) integrated bioreactor

With the main objective of improving the removal of nitrogen from domestic wastewater and more sustainably, a moving bed and constructed wetland (MBCW) integrated bioreactor was fabricated and evaluated with continuous and intermittent aeration operations. The hybrid system achieves average removal efficiencies up to 90.4 ± 0.8% of chemical oxygen demand (COD), 91.8 ± 1.2% of ammonia nitrogen (NH₄⁺-N), and 77.0 ± 2.6% of total nitrogen (TN), respectively, through a simultaneous nitrification-denitrification and further denitrification (SND-DN) process. This occurs through an intermittent aeration operation followed by continuous aeration with a dissolved oxygen (DO) of 4.0 mg L^-1 due to the complementary and coordinated action of mixed biocarriers. It has resulted in the improvement of the efficiency of SND from 5.9 to 35.3% and in the removal via wetland for DN, between 2.42 and 2.45 g m^-2·d^-1, respectively. The analysis of extracellular polymeric substances (EPS) and high-throughput sequencing demonstrated the enhanced SND mechanism and the evolution of microbial species within the biofilm structure. The total relative abundance of nitrifying bacteria, more aggregated outside the biofilm, decreased by 7.66% compared to denitrifying bacteria, mostly accumulated inside, which increased by 5.49%, respectively.