Utilization of Elemental Sulfur in Constructed Wetlands Amended with Granular Activated Carbon for High-Rate Nitrogen Removal

To investigate the role of granular activated carbon (GAC) on nitrogen removal performance of elemental sulfur-based constructed wetlands (S0-based CWs), three systems were constructed according to the different configurations in the functional layer, namely S-CW (S0 added in the functional layer), CSC-CW (GAC, S0 and GAC placed in layers in the functional layer) and SC-CW (S0 and GAC mixed evenly in the functional layer). In CSC-CW and SC-CW, the volumetric ratio of S0:GAC was 9:1. Three CWs were operated under four different hydraulic retention times (HRTs) ranged from 48 h to 6 h. Over the experiment, total inorganic nitrogen (TIN) removal rates of the three CWs were 3.1 – 23.6 g m−2 d−1, 3.5 – 24.1 g m−2 d−1 and 3.4 – 11.5 g m−2 d−1, respectively; CSC-CW remained high TIN removal efficiency (from 74.7 ± 20.2 % to 93.4 ± 1.9 %) while SC-CW had significant lower values when HRT = 6 h (29.8 ± 30.1 %). Mass balance and high-throughput sequencing analysis revealed that mixotrophic denitrification at the sulfur layer and simultaneous nitrification-denitrification (SND) at the rhizosphere played the major role in N removal from CSC-CW (> 95 %). GAC addition facilitated the growth of Iris pseudacorus with the final fresh weight increased from 33.9 gFW ind−1 to 82.3 gFW ind−1 in CSC-CW and 82.7 gFW ind−1 in SC-CW. This study optimizes the practical application of S0-based CWs amended with GAC for N removal from carbon-limited wastewater.