Effect of discharge geometry on methylene blue degradation performance in electrohydrodynamic water treatment

Plasma-based water purification has emerged as a promising technique for degrading persistent organic pollutants without chemical additives, but the influence of reactor geometry on its efficiency remains insufficiently understood. This study investigates how geometric parameters affect degradation performance in needle-to-water discharge current corona discharge system using methylene blue as a pollutant. The discharge gap and water height were varied to evaluate their effects on both electrohydrodynamic behavior and pollutant degradation performance. The voltage sustaining constant current was measured, and the degradation performance was evaluated. The required voltage increased linearly with discharge gap, while the water height had a minimal influence. Degradation efficiency improved with shorter discharge gap, owing to a more concentrated discharge region and shorter transport of reactive species to the interface, and with lower water height due to reduced initial pollutant loading. In contrast, the degraded mass increased with water height because of larger solution volume and higher initial loading. These trends can be explained by a correlation incorporating current and geometric variables. Energy yield was highest under lower current, shorter discharge gap, and higher water-height conditions. The results demonstrate that reactor geometry directly influences the generation of reactive species, which affects energy consumption and degradation performance. The quantified relationships provide a practical basis for optimizing a system.