Abstract: A vertical composting apparatus having an upper inlet for solid biodegradable material, at least two, stacked, discrete processing zones for processing the material separated by at least one agitating device separating the upper processing zone and the at least one lower processing zone; a waste inlet above the upper processing zone; a waste outlet below the lowest of the at least one lower processing zones; and a leachate retention system disposed between the upper and lower processings zones for capturing and diverting compost leachate from the upper processing zone back to the upper processing zone for further processing, or to a bio-remediation device, or to a suitable drain or receptable for disposal.