Denitrifying Dephosphatation via Nitrite under Anoxic Conditions

Denitrifying dephosphatation is a cost-effective method for simultaneously removing nitrogen and phosphorus due to its lower chemical oxygen demand (COD) requirement, reduced aeration, and decreased sludge production. In batch experiments, denitrifying dephosphatation of 20 +/- 1 mg PO4-P/l using nitrite was studied at N/P ratios of 2, 3, and 4. The effects of both limiting and non-limiting COD, provided by sodium acetate as a carbon source, on the activity of denitrifying phosphorus-accumulating organisms (DPAOs) were investigated. In all batch tests, at ratios N/P of 2, 3, 4, increasing the C/N ratio led to higher NO2-N and P removal rates and efficiencies. In all batch tests, at ratios N/P of 2, 3, 4, the highest denitrification and anoxic phosphorus uptake rates were recorded under the following conditions: at C/N ratio of 4 and N/P ratio of 2, C/N ratio of 3 and N/P ratio of 3, and C/N ratio of 2 and N/P ratio of 4. In tests with limited carbon sources (N/P of 2 and C/N < 4, N/P of 3 and C/N < 3, and N/P of 4 and C/N < 2), both denitrification and P uptake rates and efficiencies increased with rising C/N ratios. However, the batch tests with COD overdose resulted in increased denitrification rate but deteriorated P removal rate and efficiency. In the tests with a C/N ratio of 7, the P removal efficiencies were 75 +/- 3 %, 68 +/- 2 %, and 62 +/- 4 % at N/P ratios of 2, 3, and 4, respectively.