Key Takeaways & Executive Findings
- •• • ZFM column achieved 88% nitrate and 78% OFL removal, outperforming ZF (nitrate ~?%, OFL ~?%) and M controls, demonstrating synergistic enhancement. • • Active iron concentration in ZFM effluent was 0.68 mg·L−1 vs 0.48 mg·L−1 in ZF, indicating improved iron cycling and availability. • • Microbial involvement in ZFM maintained stable pH and lower ORP, preventing passivation and extending ZVI/FeS2 longevity. • • Key functional bacteria (norank_f_Fermentibacteraceae, norank_f_Anaerolineaceae, Longilinea, Anaerolinea) increased by 2.93%, 0.55%, 1.53%, 0.62%, respectively, correlating with enhanced contaminant removal.
Abstract
Groundwater contamination by nitrate and antibiotics has become a global concern. This study evaluated the continuous performance of permeable reactive barrier (PRB) columns packed with zero-valent iron (ZVI) and pyrite (FeS2) combined with denitrifying microorganisms (ZFM) for simultaneous removal of nitrate and ofloxacin (OFL). Control columns included soil (S), microorganisms (M), and ZVI/FeS2 (ZF). Over 30 days of continuous operation, the ZFM column achieved average removal efficiencies of 88% for nitrate and 78% for OFL, significantly higher than controls. The ZFM system maintained higher active iron concentration (0.68 mg·L−1) compared to ZF (0.48 mg·L−1), mitigated pH increase, and sustained lower oxidation-reduction potential (ORP), favoring stable performance. XRD and XPS analyses revealed that microbial involvement promoted FeS formation (2θ=30.1°) and reduced ZVI passivation, extending material lifespan. High-throughput sequencing showed that while overall microbial diversity remained stable, key functional populations including norank_f_Fermentibacteraceae, norank_f_Anaerolineaceae, Longilinea, and Anaerolinea increased in abundance by 2.93%, 0.55%, 1.53%, and 0.62%, respectively, enhancing nitrate and OFL removal. These findings demonstrate that integrating microorganisms with ZVI/FeS2 in PRB systems offers a promising approach for remediating combined nitrate and antibiotic contamination in groundwater.
1. Introduction
Groundwater contamination by nitrate and antibiotics poses severe risks to human health and ecosystems. Nitrate levels in landfill-adjacent aquifers in China often exceed the national standard (≤10 mg·L−1), with reported averages up to 140.42 mg·L−1. Fluoroquinolone antibiotics, particularly ofloxacin, are frequently detected at concentrations up to 1300.25 ng·L−1. Conventional PRB systems using zero-valent iron (ZVI) suffer from surface passivation and limited reactivity. Combining ZVI with pyrite (FeS2) improves reactivity and cost-effectiveness, but the system still faces slow mineral dissolution and incomplete denitrification.
This study introduces a novel approach by integrating denitrifying microorganisms into a ZVI/FeS2 PRB system. The microbial community accelerates iron cycling, reduces passivation, and enhances contaminant removal. Continuous column experiments over 30 days demonstrate that the coupled system (ZFM) achieves superior nitrate and ofloxacin removal compared to abiotic controls, while maintaining stable hydraulic and chemical conditions. This work addresses the critical bottleneck of long-term performance and material longevity in PRB technology, offering a viable solution for remediating complex groundwater pollution.
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LI Zhou, XIN Xinju, LIU Xin, CHEN Fangfang, LUO Jing, RAN Jing, SHI Qianqian, WEN Yu (2026). Continuous Performance of Permeable Reactive Columns Combining ZVI/FeS2 with Microorganisms for Removal of Nitrate and Ofloxacin from Water. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202509086
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Frequently Asked Questions
What are the long-term stability and potential failure mechanisms of the ZFM PRB column under continuous operation beyond 30 days?
The study observed stable performance over 30 days, with ZFM maintaining higher active iron (0.68 mg·L−1) and lower ORP, which mitigates passivation. However, long-term stability may be compromised by gradual accumulation of precipitates, microbial community shifts, or depletion of reactive iron. Further research is needed to assess performance over extended periods and under varying influent conditions.
How does the cost of ZVI/FeS2 combined with microorganisms compare to conventional PRB systems for full-scale groundwater remediation?
While ZVI and FeS2 are relatively low-cost materials, the addition of microbial cultivation and maintenance may increase operational costs. However, the enhanced removal efficiency and extended material lifespan could offset initial investments. A detailed techno-economic analysis is required to quantify cost-effectiveness against legacy PRB systems.
What are the key microbial mechanisms responsible for enhanced nitrate and OFL removal in the ZFM system?
The increase in functional bacteria such as norank_f_Fermentibacteraceae (2.93%) and Anaerolineaceae (0.55%) suggests enhanced fermentative and syntrophic activities. These microorganisms likely facilitate iron reduction, providing Fe(II) for abiotic nitrate reduction and OFL degradation, while also contributing to denitrification. Metagenomic analysis would further elucidate specific metabolic pathways.
How does the presence of OFL affect the microbial community and denitrification efficiency in the ZFM column?
OFL at 20 µg·L−1 may exert selective pressure on the microbial community. The study observed shifts in functional populations, indicating adaptation. However, the impact of OFL on denitrification kinetics and microbial viability requires further investigation, especially at higher antibiotic concentrations.
What are the scalability challenges for implementing ZFM PRB systems in real-world aquifers with complex geochemistry?
Scaling up requires consideration of heterogeneous aquifer conditions, groundwater flow rates, and competing electron acceptors. The laboratory column used a controlled flow rate of 0.8 m·d−1 and synthetic groundwater. Field conditions may introduce variability in pH, dissolved oxygen, and microbial competition, necessitating pilot-scale trials to validate performance and design parameters.
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