A door assembly for a microwave reactor including a microwave waveguide to direct microwaves from an external microwave source to inside the microwave reactor, and having a waveguide interface for preventing backflow of a process gas into the waveguide; an inlet for entry of matter to be treated in the microwave reactor; a first seal at the periphery of the door assembly to sealably interface with a static front of the microwave reactor; a second seal inserted into a groove on an inside face of the door assembly to sealably interface with an opening of a microwave reactor drum, the groove having a width of about 12.9 inches (32.766 cm) divided by an integer, and the second seal configured to prevent solids and liquids from flowing outside of the reactor drum; and a ring choke to contact a choke arranged on the periphery of the opening of the reactor drum.