Granular activated carbon (GAC)-driven microbial electron shuttle boosts denitrification and mitigates N2O in cold and carbon-limited biofilm system
X. Yang (Ocean University of China, TU Delft - Sanitary Engineering, Chinese Academy of Sciences, Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering (MEGE))
Mingchen Yao (Chinese Academy of Sciences)
Peng Li (China Water Environmental Group Limited)
J. P. Van Der Hoek (Waternet, TU Delft - Sanitary Engineering)
Lujing Zhang (China Water Environmental Group Limited)
Gang Liu (Chinese Academy of Sciences, TU Delft - Sanitary Engineering)
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Abstract
Background: Denitrification in wastewater treatment is severely limited under low-temperature and low-carbon (“dual-low”) conditions, hindering sustainable nitrogen removal. Biofilm systems, though energy-efficient, suffer from reduced efficiency in such environments due to impaired interspecies electron transfer (IET). Granular activated carbon (GAC), a conductive mediator, offers potential to enhance IET between electroactive microorganisms (EAMs) and denitrifiers, yet its role in dual-low systems remains underexplored. This study investigates GAC’s capacity to optimize biofilm functionality and mitigate greenhouse gas (GHG) emissions under these constraints. Results: Under dual-low conditions (4–6°C, C/N = 4), GAC increased denitrification efficiency by 19.4–21.9% and reduced N2O emissions by 10.6–22.9%. Metatranscriptomes revealed upregulation of denitrifying genes (e.g., nosZ) and electron transport pathways (e.g., omcB in Geobacter). FISH/SEM confirmed GAC-driven coacervates of EAMs and denitrifiers, linked by nanowires, enhancing direct electron transfer. Microbial diversity decreased, but functional redundancy improved, with Pseudomonas fluorescens and Geobacter sulfurreducens dominating. TOC removal rose under low temperatures, indicating enhanced carbon utilization. Conclusions: GAC fosters synergistic EAM-denitrifier partnerships, enabling efficient denitrification and GHG mitigation in cold and carbon-limited (“dual-low”) biofilm systems, advancing sustainable wastewater management.
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