Performance of a Wet-Type Nonthermal Plasma Reactor for NOx, SOx, and Wastewater Treatment

In this study, nitrogen oxides (NOx) and sulfur oxides (SOx) are removed using a wet-type plasma reactor without chemical agents. An NO and SO2 mixed gas is prepared and sent to the reactor. In the reactor, NO is oxidized to NO2 by air plasma first, and then NO2 and SO2 are absorbed into a water film on the inner wall of the reactor. The wastewater from the reactor contains nitrate ions ( ${\rm{NO}}_{3}^{\rm{-}}$ ), nitrite ions ( ${\rm{NO}}_{2}^{\rm{-}}$ ), sulfite ions ( ${\rm{SO}}_{3}^{{\rm{2-}}}$ ), and sulfate ions ( ${\rm{SO}}_{4}^{{\rm{2-}}}$ ). The nitrogen compounds such as ${\rm{NO}}_{3}^{\rm{-}}$ and ${\rm{NO}}_{2}^-$ are harmful to human health and the environment; therefore, they must be treated before disposal. Accordingly, we treat the wastewater using argon (Ar) plasma to remove ${\rm{NO}}_{3}^{\rm{-}}$ and ${\rm{NO}}_{2}^{\rm{-}}$ after the NOx and SOx removal. The results show that more than 98% of the NOx and SO2 are removed, and the ${\rm{NO}}_{3}^-$ and ${\rm{NO}}_{2}^-$ ions in the wastewater are reduced by the Ar plasma; 25.6 mg of ${\rm{NO}}_{3}^{\rm{-}}$ and 2.06 mg of ${\rm{NO}}_{2}^-$ are removed for 50 min. However, the pH does not increase with the reduction of these ions. In other words, ${\rm{NO}}_{3}^{\rm{-}}$ and ${\rm{NO}}_{2}^{\rm{-}}$ could not be reduced to N2 but be converted to other ions. From these results, it is confirmed that the wet-type discharge plasma reactor is useful for the simultaneous removal of NOx and SOx. Further investigations are required for the treatment of wastewater containing ${\rm{NO}}_{3}^{\rm{-}}$ and ${\rm{NO}}_{2}^{\rm{-}}$ .