Numerical analysis of coupling ozonation in nitrite oxidation through denitrification process for nitrogen removal from wastewater in a bioreactor

Excessive nitrogen in wastewater is released into natural water as a result of urbanization, industrial and agricultural activities, posing a serious threat to the water ecosystem. Elevated nitrogen concentrations in ponds, lakes, and rivers exacerbate eutrophication and algal blooms, compromising ecosystem sustainability and water quality. Within the nitrogen cycle, nitrite is an intermediate component in both nitrification and denitrification processes. Nitrite oxidation and denitrification are related processes that each have distinct functions at various phases and are complimentary by nature. Nitrate is created when nitrite is oxidized, and nitrate is an essential substrate for denitrification. This study evaluates the effects of ozone concentration on nitrite oxidation in bioreactors with four models of different baffle heights. Furthermore, different operating conditions, including fluid velocity and ozone content, were investigated. The normalized averaged source terms and NO₃⁻ withdrawal rates were considerably low at shorter baffles compared to taller ones, up to 47.4 % and 58 % less, respectively. A threshold of the baffle height was observed. The performance could increase rapidly before the threshold but a slight change after that. The normalized NO₃⁻ concentrations increased by about 59.3 % at the highest inlet velocity compared to the base model. Higher velocity also could increase NO₃⁻ withdrawal rates up to 124.4 %. The normalized average source term, the normalized concentration of the product, and the normalized reduction rate in the reactor showed an almost linearly rising relationship with the ozone concentration ratio.