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

Area of Science:

• Environmental Engineering
• Water Treatment Technologies

Background:

• Nitrate contamination in water bodies is a significant environmental concern.
• Constructed wetlands (CWs) are effective in removing nitrogen pollutants.
• Investigating novel substrates for enhanced CW performance is crucial.

Purpose of the Study:

• To evaluate the enhanced nitrate removal mechanism by pyrite in vertical constructed wetlands (VFCWs).
• To compare the performance of VFCWs using pyrite (P-VFCW) versus quartz sand (C-VFCW).

Main Methods:

• Construction and operation of two parallel VFCWs with pyrite and quartz sand substrates.
• Systematic variation of carbon-to-nitrogen ratio (C/N) and hydraulic retention time (HRT).
• Analysis of effluent nitrate and nitrite concentrations, plant growth, and microbial community structure via high-throughput sequencing.

Main Results:

• P-VFCW exhibited a 4% higher nitrate removal efficiency (NRE) than C-VFCW at a C/N of 0.
• The performance difference increased with elevated C/N and HRT.
• At a COD/N of 6 and HRT of 24h, P-VFCW achieved significantly lower effluent NO3--N and NO2--N concentrations.
• Pyrite promoted heterotrophic denitrification and mitigated nitrite accumulation.
• Enhanced growth of Canna indica was observed in P-VFCW.
• Distinct microbial communities, including denitrifying and iron-related bacteria, were identified in P-VFCW.

Conclusions:

• Natural pyrite is a superior substrate for enhancing nitrate removal in VFCWs.
• Pyrite facilitates efficient denitrification and minimizes nitrite buildup.
• The microbial community shifts in pyrite-based CWs contribute to improved nitrogen removal and plant health.