A high-pressure system and method utilizing an input fluid. The system includes a reactor treating a material to produce an effluent having an energy content, a plurality of stages compressing the input fluid in a stepwise manner providing a high-pressure reactor input stream to the reactor, and a cascading effluent energy recovery system mechanically communicating with the plurality of stages. The cascading effluent energy recovery system imparts a portion of the energy content of the effluent into each of the plurality of stages powering that stage. The method includes receiving an input fluid, compressing the input fluid over a plurality of stages producing the high-pressure stream, providing the high-pressure stream to the reactor, recovering a portion of the energy content of the effluent at each of the plurality of stages, and using each the portion of the energy in compressing the input fluid at a corresponding respective stage.