NOVELTY - Biodegrading volatile fatty acid (VFA) in biological material that includes methanogenic microbe that produces methane gas as by-product of metabolism, where the VFA serves as an electron donor that may be subject to oxidation, involves treating the biological material with source of Fe(III) that serves as the terminal electron acceptor in a process of reduction from Fe(III) to Fe(III); and inoculating the biological material with an Fe(III)-reducing bacteria (FeRB) that is able to couple the oxidation of electron donor to the reduction of the source of Fe(III) to Fe(III).    USE - For biodegrading volatile fatty acid (VFA) in biological material that includes methanogenic microbe that produces methane gas as by-product of metabolism, where the VFA serves as an electron donor that may be subject to oxidation (claimed). The biological material includes swine waste.    ADVANTAGE - The method controls odor of a biological material; enhances methane production from the fermentation of biological material.    DETAILED DESCRIPTION - Biodegrading a volatile fatty acid (VFA) in a biological material that includes methanogenic microbe that produces methane gas as a by-product of metabolism, where the VFA serves as an electron donor that may be subject to oxidation, involves treating the biological material with source of Fe(III) that serves as the terminal electron acceptor in a process of reduction from Fe(III) to Fe(III); and inoculating the biological material with an Fe(III)-reducing bacteria (FeRB) that is able to couple the oxidation of an electron donor to the reduction of the source of Fe(III) to Fe(III). The biological material is treated with a source of Fe(III) in a sufficient amount that is effective to remove all VFA during oxidation of the VFA from the biological material such that the FeRB does not become limited for an electron acceptor due to depletion of Fe(III) during oxidation of the VFA, to thereby promote continuous removal of VFA so as to remove substantially all the VFA content in the biological material whereby the treating of the biological material with the source of Fe(III) and the inoculating of the biological material with the FeRB results in an increase in methane levels in the biological material as compared to a methane level of the biological material prior to the treating and inoculating.