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Updated: Aug 17, 2026

Deployment and Retrieval of Mineral Samplers
Published on: January 20, 2026
Ferrous iron-induced secondary mineral formation regulates organic carbon bioavailability and methane recovery from
Feifei Chu1, Fangmei Cheng2, Xiaomeng Zhang2
1College of Management Science and Engineering (College of Quality and Standardization), China Jiliang University, Hangzhou 310018, PR China.
Abstract:
Iron salt-based chemically enhanced primary treatment effectively captures organic carbon from municipal wastewater, providing a concentrated substrate for methane recovery through anaerobic digestion. However, methane production from iron salt-based chemically enhanced primary sedimentation (Fe-CEPS) sludge remains substantially lower than expected, and the mechanisms responsible for this reduction remain poorly understood. Here, the relationship between iron-bound organic carbon (Fe-OC) formation and methane production was investigated by combining anaerobic digestion experiments with iron mineral-glucose model systems. Increasing Fe dosage reduced methane yield from 221.1 to 74.7 mL CH4 g-1 VS while promoting Fe-OC accumulation. A strong negative correlation was observed between Fe-OC content and methane production. Fresh Fe-CEPS sludge contained only limited Fe-OC (<10% of total organic carbon), whereas Fe-OC accounted for approximately 26% of total organic carbon after anaerobic digestion, indicating that Fe-OC formed predominantly during digestion rather than during coagulation. Iron speciation analyses revealed extensive Fe(III) reduction accompanied by secondary iron mineral formation. Model experiments further demonstrated that Fe(II)-induced mineral transformation increased mineral crystallinity, enhanced organic carbon stabilization, reduced carbon bioavailability, and consequently suppressed methane production. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy further revealed progressively stronger spatial associations between organic carbon and iron minerals as mineral crystallinity increased. These findings reveal a previously unrecognized mechanism whereby Fe(II)-induced secondary iron mineral formation promotes Fe-OC accumulation and reduces organic carbon bioavailability during anaerobic digestion. Regulating iron mineral transformation may therefore represent an effective strategy for improving methane recovery from iron-enhanced primary sludge.
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