Denitrifying dephosphatation over nitrite: effects of nitrite concentration, organic carbon, and pH.

The effects of nitrite concentration, organic carbon and pH on denitrifying dephosphatation over nitrite were studied with batch tests. The results showed that anoxic initial phosphate uptake rate increased as nitrite concentration increased. For an initial phosphate of 8.5mgPL(-1) and an initial COD of 350mgL(-1), a nitrite level of 15.2mgN(gMLSS)(-1) was found to be appropriate. The anaerobic phosphate release rate decreased as anaerobic nitrite addition increased. The results suggest that to ensure effective phosphate release and subsequent phosphate uptake, anaerobic nitrite should be lower than 2mgNL(-1). Very high and very low initial COD concentrations both resulted in an adverse effect on denitrifying dephosphatation. The anaerobic phosphate release with different carbon sources followed the order: acetate>butyric acid>glucose. The suitable pH for anaerobic phosphate release and anoxic phosphate uptake was approximately 7.0 and 8.0, respectively.