Anaerobic respiration
This term describes the metabolic processes in anaerobic life forms that generate ATP by a process that depends on a chemiosmotic mechanism where the ultimate electron acceptor is not oxygen.  The reduced product of the electron transport chain is therefore not water.  Methanogens in the reticulo-rumen use part of the carbon dioxide that they take up from the growth environment for this purpose; the product of its reduction is methane.  Other organisms can use fumarate reductase for ATP production by anaerobic respiration.  Fumarate is reduced by NADH to succinate in a redox cycle which achieves charge separation across a membrane and ATP synthesis is driven by dissipation of the energy inherent in the electrochemical ion gradient.