RESUMEN
The effect of nitrate, nitrogen oxide, sulphate, oxidized iron and manganese on the methane fermentation of cellulose was studied with the enrichment bacterial culture. The action of these oxidants on the enrichment culture growing on cellulose was compared to that on a pure methanosarcina culture in order to find out which stage of methane formation from cellulose was inhibited. Nitrate at the concentration of 2 g NaNO3 and more per litre of the medium inhibited the whole process of fermentation; at the concentration less than 2 g/l the production of methane was inhibited, and cellulose decomposition was accompanied with denitrification. Sulphate at the concentration of 2 g MgSO4 per litre had no effect on the formation of methane but the process was inhibited by the product of its reduction, i. e. sulphiade. Cellulose decomposition could be accompanied with sulphate reduction if sulphide produced in the process of the reduction were removed from the medium. In this case as well as in the presence of ferric iron, the production of methane was inhibited due to competition for the reducing agent.