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

Abstract

The effect of nitrate addition on the anaerobic digestion of an industrial sulfate rich wastewater was investigated using batch cultures. A high chemical oxygen demand/NO 3-N ratio did not favor the dissimilatory nitrate reduction to ammonia. Denitrification was the main nitrate reduction pathway at all chemical oxygen demand/NO 3-N ratios tested. A lag phase, presumably caused by a high initial sulfide content, preceded nitrate reduction to molecular nitrogen. During this lag phase, the methane production was not affected by nitrate concentrations as high as 500 mg NO 3-N l −1, except for cultures inoculated with a cold-stored consortium. Sulfate reduction in the cultures seemed to be directly prevented by nitrogen oxides. Methane production stopped as soon as denitrification started. Concurrently, an increase of the redox potential and a transient nitrite production were observed. These physical and chemical modifications would be responsible for methanogenesis inhibition. Furthermore, sulfide was consumed during denitrification. It was suggested that denitrification using this electron donor occurred in the system. 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 nitrate reduction pathway.