Nitrification Process

.5.2 Denitrification

The conversion of ionic nitrogen oxides, nitrate and nitrite, into atmospheric nitrogen by a heterogeneous assembly of mainly heterotrophic called denitrification , under anoxic conditions, denitrifying bacteria, through a series of intermediate gaseous nitrogen oxide products, as shown in equation (3), [Metcalf&Eddy, 2003], [Henze et al, 1997].

6NO3- + 5CH3OH → 3N2 + 5CO2 + 7H2O + 6OH (3) Substrate concentration, dissolved oxygen concentration, carbon source, temperature, pH and presence of inhibiting substances are the main factors that influence the denitrification process.

• Oxygen

Denitrification process is anaerobic as nitrate is the oxidizing agent. In other words, nitrate is used as an electron acceptor

Nitrified mixed liquor from the aerobic zone is introduced to the anoxic zone, providing chemically bound oxygen as nitrate or nitrite. Due to denitrification, the return activated sludge contains less nitrate, and as a consequence the anaerobic tank receives less nitrate. [ Richard l. Sedlak, 1991].

• Modified Bardenpho (5-stage process)

The 5-stage modified Bardenpho process contains anaerobic, anoxic, and aerobic tanks for the purpose of removal of nitrogen, phosphorus, and carbon (Figure 2.8). Complementary denitrification occurs in the second anoxic tank. The minimization of phosphorus release is realized in the secondary settling, and stripping of residual nitrogen gas occurs in the second aerobic tank. [ Richard l. Sedlak, 1991].

• (University of Cape Town)

The aim of the UCT process is to decrease the amount of nitrate introduced to the anaerobic zone especially in weaker wastewaters (Figure 2.9). The reduction of nitrate in the anaerobic tank is realized by the discharge of the return activated sludge to the anoxic tank. The internal recycles, where mixed liquor is recycled from the anoxic tank to