Advanced oxidation processes (AOPs) based wastewater treatment plant-nitration process and Denitration reactions

The nitration reaction in the presence of nitrate/nitrite is a common reaction during the degradation of pollutants in natural water as it contains nitrate and nitrite ions, Chemical compounds containing nitro group (nitro-products) are a one of toxic by-products, that can be formed during wastewater treatment processes. In case of presence of nitrite or nitrate ions, the formation of nitro-products during advanced oxidation processes (AOPs) is very common. It is caused by the reactive nitrogen species (RNs) such as nitrate radical (NO3•), nitrite radical (NO2•), nitrogen oxide radical (NO•) and peroxynirite (ONOO–). In fact, the oxidative degradation of N-containing pollutants releases nitrate, nitrite and ammonium ions.

Nitration reactions may exist during all the biological degradation process Anaerobic or aerobic digestion.

NH₄⁺   + 2O₂ = NO₃^– +H₂O +2H⁺ -F(F=351K)

The key factors effect the performance of Denitration reaction as below:

• Denitration reaction in anaerobic digestion, add the reflux pump, 2 times of MBR Premeate flow rate from MBR Tank to anaerobic digestion, the dissolved oxygen in anaerobic digestion better around 0—0.5mg/L with Water temperature above 20 degree.

NO₃^– +10e^–+12H⁺ = N² +6H₂O

• During the Denitration reaction, the C/N≥4, Denitration reaction NO₃^– will change to the N₂;  if C/N≤4, Denitration reaction NO₃^– will change to the N₂O
• The wastewater PH≥5, Denitration reaction NO₃^– will change to the N2, the PH better around 7.5—8.5

Of course, the first step of good performance Nitration reactios and Denitration reaction, the bacteria activated sludge should be breed very good.