Nitrous oxide mitigation in biochar-pyrite-based bioretention systems via zonal microenvironment regulation

Area of Science:

• Environmental Engineering
• Water Quality Management
• Microbial Ecology

Background:

• Bioretention systems (BRS) are crucial for urban stormwater management, but struggle with simultaneous nitrogen removal and mitigation of nitrous oxide (N2O) emissions.
• Addressing N2O production during nitrogen removal is essential for optimizing BRS performance and reducing greenhouse gas impacts.

Purpose of the Study:

• To evaluate the efficacy of biochar-pyrite-based BRS (BPB-BRS) in enhancing nitrogen removal and reducing N2O emissions compared to other configurations.
• To elucidate the microbial and functional mechanisms behind the improved performance of BPB-BRS under various environmental conditions.

Main Methods:

• Construction and comparison of biochar-pyrite-based BRS (BPB-BRS), biochar-pyrite BRS (BP-BRS), pyrite-amended BRS (P-BRS), and a control (CK-BRS).
• Testing under varying antecedent drying durations, rainfall intensities, and influent nitrate loadings.
• Analysis of microbial communities (sulfur-oxidizing bacteria, electroactive bacteria), electron transport system activity, and key denitrification genes (nosZ, nirS, nirK).

Main Results:

• BPB-BRS achieved high total nitrogen removal efficiencies (59.2%-85.7%) and significantly reduced N2O emissions (39.3%-84.6%).
• Enhanced microbial populations, including sulfur-oxidizing and electroactive bacteria, and increased electron transport system activity were observed in BPB-BRS.
• Biochar demonstrated zone-specific functions, improving NH4+-N retention and nitrification in the vadose zone and facilitating electron transfer for denitrification in the submerged zone.

Conclusions:

• The integrated biochar-pyrite coupling in BPB-BRS promotes efficient nitrogen removal and N2O mitigation by enhancing microbial processes and electron transfer.
• Biochar's dual role in managing wet-dry cycles and facilitating denitrification contributes to the system's overall effectiveness.
• BPB-BRS offers a promising low-carbon solution for sustainable urban stormwater management, achieving simultaneous water quality improvement and greenhouse gas reduction.