In 1977, Engelbert Broda predicted the existence of two chemolithoautotrophic microorganisms capable of oxidizing ammonium to dinitrogen gas on the basis of thermodynamic calculations. It was thought that anaerobic oxidation of ammonium would not be feasible, assuming that the predecessors had tried and failed to establish a biological basis for those reactions. By the 1990s, Arnold Mulder's observations were just consistent with Richard's suggestion. In their anoxic denitrifying pilot reactor, ammonium disappeared at the expense of nitrite with a clear nitrogen production. The reactor used the effluent from a methanogenic pilot reactor, which contained ammonium, sulphide and other compounds, and nitrate from a nitrifying plant as the influent. The process was named "anammox," and was realized to have great significance in the removal of unwanted ammonium.