[Removal of Nitrate Nitrogen by Microbial Photoelectrochemical Cell: PANI/TiO₂-NTs as a Photoanode]

The use of microbial photoelectrochemical cells (MPECs) for the removal of contaminants is a cost-effective and environment-friendly method. Based on the preparation of polyaniline/titanium dioxide nanotube array (PANI/TiO₂-NTs) composite photoelectrodes, an MPEC system comprising PANI/TiO₂-NTs photoanode and biocathode was constructed and the removal performance of nitrate nitrogen (NO₃^--N) was studied. The experimental results showed that the PANI/TiO₂-NT electrode exhibited the best photoelectric performance when the PANI loading time was 80 s. Compared with the TiO₂-NTs electrode, the photocurrent density doubled. The light-driven MPEC system could realize autotrophic denitrification without an external voltage. The biodegradation of NO₃^--N conformed to the pseudo first-order kinetics. The higher the photoresponse current density, the better the denitrification performance of the system. When the initial concentration of NO₃^--N was 25 mg·L^-1 and the photoresponse current density increased from 0.17 mA·cm^-2 to 0.67 mA·cm^-2, the average denitrification rate increased from 0.83 mg·(L·h)^-1 to 2.83 mg·(L·h)^-1. High-throughput sequencing of the biocathode microbial membranes revealed that Pseudomonas (27.37%) was the dominant bacteria. It was considered that the photogenerated electrons generated by the PANI/TiO₂-NTs photoanode were transmitted to the cathode through an external circuit. Pseudomonas and other microorganisms with autotrophic denitrification and electrochemical activity directly used the electrons on the electrode as the sole electron donors for autotrophic denitrification reaction.