A mobile waste processing system and method is disclosed for processing materials in a tank, typically an underground storage tank. A mobile fluid processing module is disposed adjacent to or over the tank, and sealingly connected to the tank through a tank riser. Support equipment, which may include an electric power module, a chiller module, a heating module, and a control and monitor module, are disposed a distance from the processing module, and connected thereto. A pump and optionally a dispersal nozzle are deployed from the processing module into the tank, and effluent is extracted for processing. The processing trailer includes effluent processing equipment such as an evaporator and demister, condenser, vacuum pump, and interim storage tank. The effluent is processed, and at least a portion is removed. Some of the processed effluent may be returned to the tank.