Privileged in-situ deposited MnOx mediates efficient inorganic nitrogen removal during the treatment of actual mine-tailing wastewater in single-chamber microbial electrolysis cells

: Sustainable, cost-effective and stable single-chamber microbial electrolysis cells (MECs) for the treatment of typical actual mine-tailing wastewater (MTW) containing ternary components of dissolved manganese, inorganic nitrogen (NH4+-N and NO3--N) meeting the China national discharge standards of pollutants from the rare earths industry are demonstrated over 100 days fed-batch operation. The MECs inoculated with anammox granular sludge initially induced Mn removal and privileged the in-situ deposition of oxygen vacancies (Ov) rich nanoscale manganese oxides (MnOx) over the graphite felt electrodes. The deposited MnOx mediated, more preferentially, the biotic (rather than the electrochemical) conversion of inorganic nitrogen (NH4+-N: 91.3%; NO3--N: 92.3%; total N: 93.6%) with a 100% selectivity to N2, achieving appreciable increments (NH4+-N: 54.5-fold and 1.3-time; NO3--N: 3.4-time and 5.1-fold; total N: 8.7-fold and 1.9-time) over the abiotic controls and the open circuital conditions, respectively. The nitrogen removal processes were driven more influentially by bioanodic oxidation due to the greater variety of nanoscale MnOx deposited over the bioanodes presenting greater Ov. Moreover, the harboring of higher cytochrome b and riboflavin within the bioanodic extracellular polymeric substances with more exoproteins contributed to these processes, besides the properties of specific bioanodic and biocathodic microbial communities. The calcination of the MnOx deposited bioelectrodes and their reuse, confirmed a solid framework for further system development. Overall, this study explores new cost-effective and stable processes for treating actual MTW (containing dissolved manganese, NH4+-N and NO3--N) with simultaneous recovery/reuse of manganese, contributing to the sustainability of mineral mining and processing industries.