Bioaugmented constructed wetlands for efficient saline wastewater treatment with multiple denitrification pathways

Area of Science:

• Environmental Engineering
• Microbiology
• Wastewater Treatment

Background:

• Saline wastewater poses challenges for conventional treatment methods.
• Constructed wetlands (CWs) offer a potential solution for nitrogen removal (NR).
• Optimizing CWs for saline conditions requires understanding microbial communities and nutrient ratios.

Purpose of the Study:

• To quantify nitrogen removal capacity in saline wastewater using CWs.
• To evaluate the impact of carbon-nitrogen ratios (C/N) and bioaugmentation on NR.
• To identify key microbial groups involved in nitrification and denitrification.

Main Methods:

• Six laboratory-scale constructed wetlands were operated under high (6:1) and low (2:1) C/N ratios.
• Bioaugmentation with aerobic-denitrifying bacteria was tested.
• Molecular biology techniques were used to analyze microbial communities.
• Nitrogen species (NO3--N, TN) were quantified.

Main Results:

• High-efficiency nitrification was sustained throughout the experiment.
• Bioaugmentation promoted NO3--N and TN removal but denitrification varied with C/N ratio.
• Ammonia-oxidizing archaea, Nitrosomonas, and Nitrospira drove nitrification.
• Aerobic-denitrifying bacteria and sulfur-driven denitrifiers were dominant in denitrification.

Conclusions:

• Bioaugmentation with aerobic-denitrifying bacteria improves nitrogen removal in saline CWs.
• Salt-tolerant bacteria with multiple NR pathways are essential for saline wastewater treatment.
• Understanding microbial ecology and optimizing C/N ratios are crucial for CW design.