Enhancing biocathode denitrification performance with nano-Fe3O4 under polarity period reversal

The presence of excessive concentrations of nitrate poses a threat to both the environment and human health, and the bioelectrochemical systems (BESs) are attractive green technologies for nitrate removal. However, the denitrification efficiency in the BESs is still limited by slow biofilm formation and nitrate removal. In this work, we demonstrate the efficacy of novel combination of magnetite nanoparticles (nano-Fe 3 O 4 ) with the anode-cathode polarity period reversal (PPR-Fe 3 O 4 ) for improving the performance of BESs. After only two-week cultivation, the highest cathodic current density (7.71 ± 1.01 A m −2 ) and NO 3 − -N removal rate (8.19 ± 0.97 g m −2  d −1 ) reported to date were obtained in the PPR-Fe 3 O 4 process (i.e., polarity period reversal with nano-Fe 3 O 4 added) at applied working voltage of −0.2 and −0.5 V (vs Ag/AgCl) under bioanodic and biocathodic conditions, respectively. Compared with the polarity reversal once only process, the PPR process (i.e., polarity period reversal in the absence of nano-Fe 3 O 4 ) enhanced bioelectroactivity through increasing biofilm biomass and altering microbial community structure. Nano-Fe 3 O 4 could enhance extracellular electron transfer as a result of promoting the formation of extracellular polymers containing Fe 3 O 4 and reducing charge transfer resistance of bioelectrodes. This work develops a novel biocathode denitrification strategy to achieve efficient nitrate removal after rapid cultivation.