Gas circulation and fed-batch fermentation were applied for enhancing acetate production by mixed culture in a novel syntrophic acetogenesis and homoacetogenesis coupling system. The results show that the acetate yield in the fed-batch test with gas circulation is about 47% higher than that in the batch test without gas circulation. The fed-batch method helps to increase acetate yield by balancing hydrogen production in the acetogenesis phase (the 1st phase) and hydrogen consumption in the homoacetogenesis phase (the 2nd phase) of the coupling system. Gas circulation enhances mass transfer between different phases of the coupling system, hence resulting in increased homoacetogenesis in the 2nd phase and relief of the products (H-2) inhibition to syntrophic acetogenesis in the 1st phase. The effects of gas circulation and fed-batch fermentation on direct glucose conversion to acetate were also investigated. (C) 2007 Published by Elsevier Ltd.