nZVI-rGO/geotextile bioretention systems for enhanced and stable nitrate removal under carbon-limited stormwater conditions: Performance and mechanistic insights

A novel nZVI-rGO/Geotextile was developed via in situ growth. • nZVI-rGO/Geotextile enabled stable NO 3 − -N removal in bioretention. • The system achieved up to 98% NO 3 − -N removal over 120 days. • Low C/N denitrification was maintained with effluent NO 3 − -N of 0.55 mg/L. • Enhanced denitrification was linked to Fe stability and key gene enrichment. Bioretention systems have been widely applied for urban stormwater management, yet achieving efficient and stable nitrate (NO 3 − -N) removal under stormwater conditions with limited carbon availability remains a critical challenge. Herein, we report a supported nZVI-rGO/Geotextile prepared via an in-situ synthesis method for enhanced biological denitrification in bioretention systems. The nZVI-rGO/Geotextile amended bioretention system exhibited the outstanding NO 3 − -N removal performance during 120 days of operation, with NO 3 − -N removal efficiency of up to 98%, owing to the improved dispersibility and oxidation resistance of nZVI enabled by rGO nanosheets, along with its stable immobilization on the geotextile to reduce material loss. Moreover, ionic Fe release was observed in the nZVI-rGO/Geotextile bioretention system, which was associated with the higher reactivity of nZVI on the nZVI-rGO during denitrification. Importantly, under low C/N conditions, the introduction of nZVI-rGO/Geotextile maintained stable denitrification performance, with a comparable NO 3 − -N removal efficiency (~95%). Meanwhile, the nZVI-rGO/Geotextile exhibited decent material stability after denitrification in the bioretention system. Finally, metagenomic analyses revealed enriched key denitrifying taxa and enhanced genetic potential for downstream denitrification processes, which resulted in complete denitrification. Overall, this study offers new insights into the development of functional denitrification materials for stormwater treatment. Download: Download high-res image (442KB) Download: Download full-size image