Electron storage and resupply modes during sulfur cycle enhanced nitrogen removal stability in electrochemically assisted constructed wetlands under low temperature

In this work, an electrochemically assisted vertical flow constructed wetland (E-VFCW) achieved efficient PO43--P (92.9-96.6%), NO3--N (50.8-91.8%) and TN (38.8-73.1%) removal from synthetic sewage effluent within 1-12 h at 12 degrees C. Abiotic reduction, Fe(II)-, S- and H-2-dependent denitrification, as well as coupling of fermentation, acetogenesis and heterotrophic denitrification might facilitate NO3--N removal in the E-VFCW. Particularly, electron resupply for NO3--N reduction by the in-situ deposited FeS, FeS2 and S-0 in the E-VFCW would occur during electron supply-demand disequilibrium situations (e.g., lower HRT or temperature). Stoichiometric results suggested that 21.7-278.7 mmol e(d)(- )(-1) from the in-situ deposited S contributed to NO3--N reduction under HRT of 1-6 h at 12 degrees C, which improved the resilience capabilities of the E-VFCW to temperature and nitrogen loads fluctuations. Overall, this work provides new insights into the modes of S cycle mediating NO3--N conversions in the E-VFCW under low temperature.