Electrical Discharges in a Bubble Column Reactor—A Novel High Throughput Reactor Design for Water Treatment

Plasma-based water treatment is a potential alternative for conventional wastewater purification techniques. However, an efficient implementation of the plasma technology on an industrial scale is challenging due to inherent multiphase nature of the process. In general, contaminant removal efficiency strongly depends on the plasma-liquid contact area and the highest treatment efficiencies are observed in reactors with high area-to-volume ratios, e.g., designs utilizing liquid atomization or thin water films. Overall performance of such designs, however, is limited by low liquid throughput.<br/>This work investigates contaminant removal performance of a tubular bubble column reactor with a concentric rod-cylinder electrode configuration. A surfactant, rhodamine B dye, and a non-surfactant, caffeine, were used as model contaminants. The effect of hydrodynamic regimes on degradation was investigated by varying the gas flow rate, the initial bubble size, the characteristic reactor dimension, and surface tension of the treated solution. The effect of discharge properties on degradation was assessed by varying the input energy and the operating gas composition. Ultimately, we show that continuous sparging of gas is a superior method for contact area enhancement for the applied electrode configuration that results in competitively high removal rates and yields high degradation energy efficiencies. Future directions for the reactor scale up are also discussed.