Abstract: A substrate processing apparatus comprises a process chamber and an effluent treatment apparatus comprising a hydrogenation reactor, scrubber, combustor, and a controller to operate the process chamber and effluent treatment apparatus. In the hydrogenation reactor, hydrogen-containing gas is used to treat chamber effluent to form a hydrogenated effluent comprising hydrogen chloride gas. A scrubber sprays water through the hydrogenated effluent to dissolve the hydrogen chloride gas. An oxygen-containing gas is added to the treated effluent during a combustion step to further abate the effluent.