TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Apparatus: In the composting apparatus, the barrier includes at least one baffle angled inwardly from the side of the housing in the upper processing zone so as to define a passage between the upper processing zone and the lower processing zone. The barrier further includes at least one agitator disposed in the passage defined by the at least one baffle. The liquid barrier device is a leachate retention gate disposed immediately below the passage defined by the at least one baffle. The leachate retention gate includes a drain. The leachate retention gate is pivotally connected through an axle to mechanical device for swinging the gate downwardly into a open position, so as to permit compost material in the upper processing zone to pass from the upper processing zone into the lower processing zone, and then to raise the door back into a closed position for capturing and draining compost leachate. The leachate retention gate has an outboard gutter and an inboard gutter. The drain is disposed in the inboard gutter. The leachate retention gate has contiguous exterior sides generally conforming to the interior dimensions of the wall of the vessel housing, and clearances sufficiently tight to capture substantially all of the leachate dripping down through the passage while large enough to allow the leachate rentention gate to swing both downwardly and upwardly during operation. The mechanical device is at least one linear actuator. The leachate gate is angled when in the closed position. The leachate retention gate is sized to cover the passageway defined by the at least one baffles. The leachate retention gate is a telescoping slide gate mounted on the housing frame; or a clam shell gate having two halves which close together immediately below the passage. The composting apparatus further including a linear actuator operatively connected to the leachate retention gate. Preferred Method: In the method, step (d) involves diverting the captured leachate back to the upper processing zone for further processing. The step (e) involves diverting the captured leachate to a receptable for shipment to a disposal site or to other apparatus for bioremediation of the leachate; or diverting the captured leachate to a drain for disposal.