Apparatus and methods to eliminate contaminants of concern, including poly- and perfluoroalkyl substances (PFAS), from a dewatered refuse feedstock. A dryer receives the dewatered feedstock and a working fluid in a closed loop, and outputs a dried feedstock at least partially dried with heat recovered from the working fluid. The dried feedstock is gasified to produce a producer gas that is combusted in a thermal oxidizer to produce a heated flue gas. The heated flue gas is cooled in a heat exchanger that transfers heat from the heated flue gas to the working fluid. Recovered heat may be further used to generate electricity. Vapor generated by drying the feedstock may be condensed and separated into recovered solids streams and a water stream suitable for industrial reuse. Cooled flue gas is conditioned and filtered with hydrated lime to capture decomposed contaminants of concern.