A reactor apparatus, includes: a reactor chamber having an inlet through which treatment liquid containing by-products is introduced and having an interior space; a burner at a lower end portion of the reactor chamber to burn waste gas; a guide member above the burner and configured to allow the treatment liquid to flow outwardly of the burner; a water reservoir between the burner and the guide member, the water reservoir having a double pipe structure having an inner wall portion and an outer wall portion, and through which water supplied through a water inlet is configured to flow between the inner wall portion and the outer wall portion; and a cover member coupled to an upper end portion of the water reservoir and configured to cover a space between the inner wall portion and the outer wall portion, wherein an upper end of the outer wall portion is above an upper end of the inner wall portion, wherein a plurality of bumps are on a bottom surface of the cover member spaced apart from each other in a circumferential direction, the plurality of bumps configured to form a gap of several hundred pm between the bottom surface of the cover member and an upper surface of the inner wall portion of the water reservoir.