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

In this study, nitrogen oxides (NO
_X
) and sulfur oxides (SO
_X
) are removed using a wet-type plasma reactor without chemical agents. An NO and SO
₂
mixed gas is prepared and sent to the reactor. In the reactor, NO is oxidized to NO
₂
by air plasma first, and then NO
₂
and SO
₂
are absorbed into a water film on the inner wall of the reactor. The wastewater from the reactor contains nitrate ions (NO
₃
^-
), nitrite ions (NO
₂
^-
), sulfite ions (SO
₃
^2-
), and sulfate ions (SO
₄
^2-
). The nitrogen compounds such as NO
₃
and 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 NO
₃
^-
and NO
₂
^-
after the NO
_X
and SO
_X
removal. The results show that more than 98% of the NO
_X
and SO
₂
are removed, and the NO
₃
^-
and NO
₂
^-
ions in the wastewater are reduced by the Ar plasma; 25.6 mg of NO
₃
^-
and 2.06 mg of NO
₂
^-
are removed for 50 min. However, the pH does not increase with the reduction of these ions. In other words, NO
₃
^-
and NO
₂
^-
could not be reduced to N
₂
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 NO
_X
and SO
_X
. Further investigations are required for the treatment of wastewater containing NO
₃
^-
and NO
₂
^-
.