An apparatus for removing contaminants from a gas stream includes a reaction chamber for receiving the gas stream; a gas-liquid contact assembly disposed in the reaction chamber; a sump disposed in the reaction chamber beneath the gas-liquid contact assembly, the sump containing a liquid scrubbing agent; a first inlet in communication with the sump for providing a reactive species to the liquid scrubbing agent in the sump for producing an oxidizing solution; a second inlet in communication with the reaction chamber for providing the gas stream to the reaction chamber; and a feed line having a first end in communication with the sump and a second end in communication with the reaction chamber above the gas-liquid contact assembly for dispensing the oxidizing solution to contact the gas-liquid contact assembly.