Polydopamine modification accelerates the enrichment of electroactive microorganisms and enhances nitrate removal in microbial electrochemical denitrification systems (MEDS)

Under low carbon-to-nitrogen (C/N) ratio conditions, microbial electrochemical autotrophic denitrification offers promising application potential as it operates independently of external organic carbon. However, its implementation is often constrained by long startup periods and low nitrate removal efficiency, mainly due to the delayed enrichment of electroautotrophic microorganisms and limited electron transfer within biofilms. To overcome these limitations, this study proposes a simple and scalable electrode-interface modification strategy using bioaffinity polydopamine (PDA) coatings on carbon felt electrodes. Compared with unmodified electrodes, PDA-modified electrodes enabled rapid colonization of functional microorganisms during the startup phase, leading to significantly enhanced nitrate removal efficiency and shortened acclimation time. Mechanistic analysis indicated that PDA modification improved electrode hydrophilicity and biocompatibility, thereby promoting the selective enrichment of electroactive microorganisms on the cathode surface. Electrochemical characterization confirmed that electron acquisition during denitrification was predominantly mediated by direct electron transfer. Moreover, functional gene prediction revealed increased abundances of genes associated with both denitrification metabolism and electron transfer pathways. Overall, this work provides a practical and scalable strategy to accelerate startup and enhance the performance of microbial electrochemical denitrification systems, offering important implications for low-C/N wastewater treatment technologies.