Interactions between methanogenic and nitrate reducing bacteria during theanaerobic digestion of an industrial sulfate rich wastewater

The effect of nitrate addition on the anaerobic digestion of an industrial sulfate rich wastewater was investigated using batch cultures. A high chemi cal oxygen demand/NO3-N ratio did not favor the dissimilatory nitrate reduc tion to ammonia. Denitrification was the main nitrate reduction pathway at all chemical oxygen demand/NO3-N ratios tested. A lag phase, presumably cau sed by a high initial sulfide content, preceded nitrate reduction to molecu lar nitrogen. During this lag phase, the methane production was not affecte d by nitrate concentrations as high as 500 mg NO3-N I-1, except for culture s inoculated with a cold-stored consortium. Sulfate reduction in the cultur es seemed to be directly prevented by nitrogen oxides. Methane production s lopped as soon as denitrification started. Concurrently, an increase of the redox potential and a transient nitrite production were observed. These ph ysical and chemical modifications would be responsible for methanogenesis i nhibition. Furthermore. sulfide was consumed during denitrification. It was suggested that denitrification using this electron donor occurred in the s ystem. Finally, it was shown that iron pre-treatment promoted both nitrate reduction to ammonia and the methanogenesis. It appeared that in a sulfide free environment, dissimilatory nitrate reduction to ammonia was the main n itrate reduction pathway. (C) 1999 Federation of European Microbiological S ocieties. Published by Elsevier Science B.V. All rights reserved.