A new concept to hybridize solid state fermentation (SSF) and submerged fermentation (SmF) reactors by introducing a system that recycles the substrate is described. Two separate experiments were conducted to examine the effects of including a wash cycle in the SSF reactor, and introducing a recycling process for the excess sludge from the SmF reactor. After 25 days, both experiments reached a steady state of similar to 170 g(volatile material, VM) day(-1) decomposition rate which was compatible to a loading rate of 186 gVM day(-1) under the conditions used. The SSF reactor alone decomposed 92% of the total organic load with the introduction of the recycling system. A reduction of 10 times in the size/volume of the proposed system was achieved compared to the conventional activated sludge method. These experiments confirmed the feasibility of the new system proposed. (C) 2002 Elsevier Science Ltd. All rights reserved.