(423a) Plasma-Based Advanced Oxidation: Effects of Reactor Design on the Degradation of Organic Contaminants

To improve the feasibility of plasma-based water treatment technology and asses the possibility of the technology scale up, a study was conducted to identify and characterize the design parameters that influence treatment effectiveness and the physical phenomena that determine treatment efficiency. The effect of several reactor design parameters, broadly grouped into three categories, on the degradation of 5 mg/L Bisphenol A (BPA) and 5 mg/L Rhodamine B (RhB) was investigated. These parameters include: (1) reactor geometry (e.g., electrode material and shape, electrode spacing, reactor diameter, and ground electrode plate area), (2) electrode configuration, and (3) contact between plasma and the treated solution.

Results indicate that changing the reactor geometry, particularly minimizing the distance between the high voltage electrode and the grounded electrode, increasing the reactor radius, and increasing the area of the grounded electrode plate increase the peak current (i.e., input power) and thus the removal rates of BPA and RhB. Discharges in a gas contacting water were found to be about four times as effective as discharges directly in water. Prior to maximizing the contact between plasma and the treated solution, the described reactor optimization increased the extent of BPA removal from 10% to 90% in less than 1 h and RhB from 5% to 95% in less than 30 minutes.

The contact between the plasma and the treated solution was found to be strongly influential. The effect of contact was investigated by testing several new reactor configurations featuring a discharge between a high voltage and a grounded electrode placed above water surface and within the liquid feed stream as it fell from above the surface of the solution. These high-contact configurations were twice as effective as the optimized gas phase discharge. A final alteration involved generating bubbles on the liquid surface by introducing the gas feed through a ceramic diffuser beneath the liquid surface, to present a more favorable interface for the plasma to travel along and to increase mass transfer of plasma radicals into the treated solution. This strategy again doubled the efficiency, yielding a G₅₀ value about 2 orders of magnitude higher than that of the original reference configuration with both electrodes immersed in water.