An apparatus and method are provided for introducing high-concentration, high-pressure oxygen gas with or without high-pressure ozone gas into pumped sewage mains, also known as force sewage mains, a portion of the pumped sewage is diverted from the force sewage main for addition of the high-concentration, high-pressure oxygen gas with or without high-pressure ozone gas thereto and for mixing of the gases with the sewage following by reintroduction of the gas-containing sewage into the force sewage main to accomplish the elimination of hydrogen sulfide gas odor from sewage and sewer lines.