Gaseous carbon and nitrogen emissions from microbial fuel cell-constructed wetlands with different carbon sources: Microbiota-driven mechanisms

As co-substrate, a carbon source is a crucial factor impacting the performance and process of microbial fuel cell-constructed wetlands (MFC-CWs). However, there is limited information regarding how different carbon sources regulate the emission of carbon and nitrogen gases from MFC-CWs. This study explored how the type of carbon source regulates the emission of carbon and nitrogen gases in MFC-CWs. Four types of carbon sources (i.e., glucose, sodium acetate, sucrose, and starch) were examined and evaluated for their pollutant removal efficiency and carbon and nitrogen gas emission characteristics in MFC-CWs. The results showed that the specific carbon source significantly influenced the performance of MFC-CWs, where electron transfer regulated denitrification, methane (CH4) production, and respiration. Glucose emerged as the most effective carbon source, enhancing COD (86.77%) and TN (93.85%) removal efficiency, while sucrose was effective for NH4+-N (93.79%) removal, and starch was beneficial for TP (91.99%) removal. In terms of gaseous emissions, MFC-CWs with glucose as a carbon source significantly (p < 0.05) promoted CH4 emission by regulating the abundance of mcrA and pmoA genes, and significantly (p < 0.05) suppressed CO2, N2O, and NH3 emissions by affecting nir and nosZ genes and electron competition. Overall, glucose was more effective than other carbon sources in promoting denitrification and reducing global warming potential (GWP). Our findings confirm the vital role of carbon sources in controlling nitrogen removal, carbon consumption, and gas emission reduction in microbial processes.