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 (S-based CWs), three systems were constructed according to the different configurations in the functional layer, namely S-CW (S added in the functional layer), CSC-CW (GAC, S and GAC placed in layers in the functional layer) and SC-CW (S and GAC mixed evenly in the functional layer). In CSC-CW and SC-CW, the volumetric ratio of S: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 d, 3.5 - 24.1 g m d and 3.4 - 11.5 g m d, 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 g ind to 82.3 g ind in CSC-CW and 82.7 g ind in SC-CW. This study optimizes the practical application of S-based CWs amended with GAC for N removal from carbon-limited wastewater.