Optimization of an atmospheric pressure direct-contact DBD for the treatment of aqueous pharmaceutical solutions

Abstract

Summary form only given. Ozone has been widely used in water treatment due to its extreme reactivity and its strong oxidizing properties. Technologies using electrical discharges generated directly over or in the fluid to be treated are being studied because they may prove to be cheap and effective. In this research project, a hybrid gas-liquid atmospheric pressure dielectric barrier discharge (DBD) reactor has been designed and used to treat pharmaceutical solutions. The liquid is sandwiched inside a parallel plate DBD and thus, directly exposed to the plasma-forming region. Oxygen or air flows above the liquid to be treated. The application of 10 kV on the high voltage electrode, at an average frequency of 17.5 kHz, induces plasma streamers in the gas phase. The power dissipated in the DBD (50 W on average) is monitored from the measure of the Lissajou figure. It is believed that the transport of ozone generated in the gaseous gap into the liquid solution is enhanced by the agitation of the free surface, itself induced by the streamers. The formation of additional oxidizers in the liquid solution such as hydroxyl radicals and hydrogen peroxide is also suspected. The effects of treatment time (1-15 minutes), discharge gap (3-4 mm), gas flow rate (20-400 cc/min), composition of the gas (pure oxygen or air) is being investigated to determine the optimum parameters for the treatment of aqueous pharmaceutical solutions. The optimization is being performed by monitoring the absorbance at 600 nm of solutions in which potassium indigo trisulfonate is diluted. This molecule dyes water in blue due to its C=C bond which can be broken by oxidation, resulting in the decrease in absorbance of the solution at 600 nm. The DBD reactor is more efficient with oxygen than with air; the difference in color removal is 30% when comparing the results obtained with an oxygen flow of 160 cc/min to an air flow of 160 cc/min after a treatment time of 7 minutes and with a discharge gap of 3.9 mm. It is also found that the extent of color removal increases with treatment time; color removal is 93% after 7 minutes compared to 47% after 3 minutes with an oxygen flow of 25 cc/min and a discharge gap of 3.9 mm. The optimum values for the operating parameters will be used to degrade sulfamethoxazole, an antibiotic, in water. The results will be compared to those of collaborators obtained using conventional degradation procedures