New process for simultaneous removal of nitrogen and sulphur under anaerobic conditions

A granular activated carbon (GAC) anaerobic fluidised-bed reactor treating vinasse from an ethanol distillery of sugar beet molasses was operated for 90 days, the first 40 days of start-up followed by 50 days of operation at constant organic loading rate of 1.7g COD/Ld. The reactor showed good perfo rmance in terms of organic matter removal but an anomalous behaviour in ter ms of unusual high concentrations of molecular nitrogen in the biogas. The analysis of the different nitrogenous and sulphur compounds and the mass ba lances of these compounds in the liquid and gas phases clearly indicated an uncommon evolution of nitrogen and sulphur in the reactor. About 50% of th e nitrogen entering the reactor as total Kjeldahl nitrogen (TKN) was remove d from the liquid phase appearing as N-2 in the gas phase. Simultaneously, only 20% of the S-SO42- initially present in the influent appears as S-S2- in the effluent or S-I-IS in the biogas, indicating that 80% of the sulphur is removed. This behaviour has not been reported previously in the literat ure. These observations may suggest a new anaerobic removal process of ammo nia and sulphate according to an uncommon mechanism involving simultaneous anaerobic ammonium oxidation and sulphate reduction. (C) 2001 Elsevier Scie nce Ltd. Ail rights reserved.