Pathways regulating the enhanced nitrogen removal in a pyrite based vertical-flow constructed wetland

In this study, two vertical constructed wetland using natural pyrite (P-VFCW) and quartz sand (C-VFCW) as substrate were constructed, and the enhanced nitrate removal mechanism by pyrite was further investigated. Results showed that the nitrate removal efficiency (NRE) of P-VFCW was 4% higher than that of C-VFCW with a C/N of 0. Interestingly, the difference on NRE between CWs markedly enlarged with C/N and hydraulic retention time (HRT) simultaneously increasing. At a COD/N of 6 and HRT of 24 h, the effluent average NO3--N and NO2--N concentrations in P-VFCW and C-VFCW were 2.36 +/- 2.64 mg/L/1.34 +/- 1.28 mg/L, 9.20 +/- 6.91 mg/L/5.57 +/- 3.68 mg/L, respectively, revealing pyrite could promote heterotrophic denitrification and avoid nitrite accumulation. After the whole operation, a better growth of Canna indica occurred in P-VFCW. High-throughput sequencing implied that denitrifying bacteria (Comamonas), iron oxidation and reduction microorganism (Thiobacillus) and the rhizosphere microorganism differed in CWs.

Automated summary

The study showed that vertical flow constructed wetlands using natural pyrite as substrate can enhance nitrate removal efficiency and promote heterotrophic denitrification to avoid nitrite accumulation. Additionally, the growth of plants in wetlands, particularly Canna indica, was better in wetlands using pyrite as substrate. High-throughput sequencing revealed differences in denitrifying bacteria, iron oxidation and reduction microorganisms, and rhizosphere microorganisms in the wetlands.