A scalable photovoltaic-type photoelectrotrophic denitrification reactor for selective conversion nitrate to nitrogen via isolating reactive oxygen species

• A proof-of-principle of a scalable photovoltaic type PEDeN reactor was demonstrated. • The ROS were completely isolated from denitrifiers during irradiation. • The NO 3 − was 100% reduced to N 2 with minimal N 2 O emission by the novel reactor. • The NO 3 − reduction was light-dependent process and could continue without chemicals. Photoelectrotrophic denitrification (PEDeN) is an innovative denitrification process with great potential for nitrate (NO 3 − ) removal from carbon-deficient wastewater. However, the inevitable presence of reactive oxygen species (ROS) significantly undermines the sustainability of PEDeN, including inducing substantial nitrous oxide (N 2 O) accumulation and declining system’s performance. This work demonstrates a proof-of-principle of a photovoltaic (PV)-type PEDeN reactor, where the dominant ROS, including hydrogen peroxide and hydroxyl radicals, are completely isolated from denitrifiers. This way enabled NO 3 − to be selectively reduced (100%) to nitrogen with minimal N 2 O emission. The maximum accumulated N 2 O-N relative to input NO 3 − -N was 11.3%, significantly lower than that in hybrid systems, such as Thiobacillus denitrificans -CdS (72.1%) and Thiobacillus denitrificans -AQS (95.5%). After eliminating ROS, the NO 3 − removal efficiency in each cyclic experiment reached 100% and the nitrogenous intermediators, such as nitrite and N 2 O, could be minimized via enhancing the photocurrent. Importantly, NO 3 − reduction continued even when no chemicals was added, indicating that water can serve as the end electron donor. This study introduces a PV-type PEDeN reactor concept for sustainable nitrate removal via mitigating the toxic effects of ROS and it will offer a cost-effective, environmentally friendly, and scalable technology for removing NO 3 − pollutants from carbon-deficient wastewater.