Effects of Nitrate Concentration in Main Anoxic Zone on Denitrifying Dephosphatation

The effects of nitrate conocentration in the main anoxic zone on denitrifying clephosphatation capability were conducted based on modified University of Cape Town (MUCT) process. Meanwhile the relation between optimal nitrate concentration (Nopt) and influent C/N ratio was evaluated, in which the influeat chemical oxygen demand (COD) concentration was stabilized at (290±10)mg/L, the influent total phosphorus (TP) concentration was stabilized at (7.0±0.5)mg/L. The results indicated that: (1) the nitrate concentration in the main anoxic zone had an effect on denitrifying dephosphatation capability, and the average percentages of anoxic phosphorus uptake in total phosphorus uptake (1/2) incased with nitrate concentration increasing,i.e., increasing from 62.1% at 2.0 mg/L to63.7%, 65.6%,68.1%, and 72.3% at 2.2, 2.4, 2.6 and 2.8 mg/L,respectively; (2) the Nopt as fumction of influent C/N ratio could be calculated by the equation: y = 0.67X2 -7.79X + 22.21; the maxinum of anaxi phosphorus uptake in total phosphorus uptake (η()) as function of the Noptcold be calculated by the equation, y =0.77-0.33e-(x/1.52). The Nopt was the important control parameter that must be optimized for operation of conventional biological mutrient removal activated sludge (BnRAS) system.