The system includes a source of solid, liquid or sludge waste and a source of waste gas. A waste conversion device receives the solid, liquid or sludge waste and converts it into a hydrogen-rich gas. An internal combustion engine receives as fuel the hydrogen-rich gas and the waste gas and burns them to produce mechanical work. A generator is operatively connected to the internal combustion engine to generate electricity. Some of the generated electricity may be used to power the waste conversion device. The system allows for high-efficiency, lean-burn operation while reducing the amount of waste converted to hydrogen-rich gas.