Enhanced organic matter humification by hydroxyl radical generation during electric field-assisted aerobic composting

Electric fields have been documented to promote the humification of organic matter, but the mechanism is still unclear. Herein, our proposed a new pathway for hydroxyl radical (OH) generation through electroactive bacteria enhanced electron transfer, resulting in accelerated humification of organic matter during electric field-assisted aerobic composting (EAC). The results indicated that electric field significantly enhanced the generation of reactive oxygen species (ROS) and humification of organic matter, and the anode and cathode of EAC are the main production regions of singlet oxygen (1O2, maximum yield 83.2–132.8 μmol·kg−1) and OH (maximum yield 2343.4–2905.2 μmol·kg−1), respectively. Further investigations suggested that electroactive bacteria accumulated on electrodes increased the generation of OH by promoting the transfer of electrons from electrode to oxygen, whereas quenching the generated OH significantly suppressed the process of organic matter humification. Our findings suggest that the OH production through microbe-induced electron transfer is a primary cause of organic matter humification, representing an electric field-assisted strategy overlooked biochemical process.