Electron transfer-mediated synchronization of N,N-dimethylformamide catabolism and nitrate reduction driven by zero-valent iron

Abstract

The co-occurrence of N,N-dimethylformamide (DMF) and residual nitrogen in industrial wastewater presents significant challenges for conventional biological treatment. To overcome these limitations, this study developed an innovative zero-valent iron (ZVI) enhanced nitrate-reducing bioreactor (ZVI-NR) that establishes an efficient electron transfer pathway for simultaneous DMF mineralization and nitrate removal. The ZVI-NR system achieved complete DMF removal (100%) and high nitrate reduction efficiency (96.17% ± 1.50%), representing 40.37% ± 2.30% and 34.23% ± 1.30% improvements over conventional NR system. The key innovation involves establishing an Fe²⁺/Fe³⁺ electron shuttle system, coupled with the selective enrichment of iron-cycling genera (such as Dojkabacteria and Denitratisoma). These genera maintain iron bioavailability and facilitate extracellular electron transfer. The increased enzymatic activity (136.96%–161.23% for nitrate/nitrite reductases), and dynamic extracellular polymeric substance (EPS) secretion (154.73 ± 4.65 mg/g VSS) featuring α-helix-dominated protein structures that improve microbial aggregation (Dojkabacteria, Chryseobacterium and Arenimonas, etc.). The superior performance of the system is further attributed to dual metabolic regulation through feoAB-mediated Fe²⁺ transport and a formate dehydrogenase mediated mechanism that is hypothesized to contribute to the proton motive force. This study demonstrates a technological breakthrough in industrial wastewater treatment, which achieves stable and complete DMF mineralization at high loading rates. The unique iron-mediated electron transfer that enhances efficient DMF degradation and optimized nitrogen removal, addressing the challenge of treating refractory wastewater containing high organic and nitrogen loads.

Graphical abstract

Keywords

N,N-dimethylformamide / Mineralization / Iron-cycling / Electron transfer / Functional genes / Metabolic mechanism

Highlight

	● ZVI-NR system completely removed DMF, while it was 59.63% ± 2.30% for the NR system.
	● Fe2+/Fe3+ shuttle boosted microbial activity and iron bioavailability.• Enhanced enzymatic activity and EPS improved microbial aggregation.
	● Fe2+ transport and formate dehydrogenase enhanced ZVI-NR via proton motive.
	● Iron-driven electron distribution and bacterial response were elucidated.

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