Comparing the fluence-based efficiencies, the k3 value at 265 nm was significantly higher than the others in both batch and flow-through reactors (p < 0.001), which is attributable to the highest UV absorbance of DNA at 265 nm among the others [22]. A significant difference was observed between the batch and flow-through reactors in the k3 values for emissions at 265 and 280 nm (p < 0.001), indicating the deterioration of fluence-based efficiency in the flow-through reactor, as compared to the batch reactor. The decrease in k3 values from the batch to flow-through reactor was about 29% for 265 nm and 32% for 280 nm. Lower inactivation efficiency in continuous flow systems than in batch tests was reported in earlier studies using mercury UV lamps ( [30] for review), and such reduction may partially arise from the heterogeneous hydraulic condition in the flow-through reactor.