The present invention provides improved systems and processes for performing sequential batch anaerobic composting (SEBAC) on high solids content wastes. In particular, the present invention provides improved flooded SEBAC systems that function more efficiently (i.e., higher conversion kinetics) at lower temperatures than conventional SEBAC systems. Further, the improved flooded SEBAC systems and processes of the subject invention enable efficient anaerobic digestion operation at a smaller reactor volume ratio as compared to conventional SEBAC systems, without the displacement of leachate and clogging as a result of entrapped biogas or an increased pressure drop (hydraulic). Further, the improved flooded SEBAC systems of the invention overcome concerns associated with leachate displacement as well as excessive pressure drops.