Advanced Strategies to Accumulate Nitrite in Low-feed Concentrated Biological Reactors

Nitrate \({(\text{NO}}_{3})\) is found in surface and groundwater; in developing countries, people primarily intake water without any treatment. However, drinking water is detrimental to human beings, especially infants. Ammonium Oxidizing Bacteria (AOB) oxidize ammonium to Nitrite (NO₂) and then Nitrite Oxidizing Bacteria (NOB) to NO_3. Conversion of NO₂ into NO₃ required 0.5 mg/L of oxygen, and this caused an increase in the 25% running cost of the total oxygen supply in the reactor. Therefore, it is essential to restrict the process of NO₂ accumulation in the reactor using different control strategies. NO₂ accumulation in highly concentrated reactors is common. Little or no attention has been drawn to the accumulation of NO₂ in low-feed concentrated reactors (approximately 50 mg TAN/L or less) without any chemical inhibitors. In this review, the accumulation of NO₂ in low-concentrated reactors has been focused on. It was found that controlled strategies are mandatory for accumulating the NO₂ in the reactors without using any chemical inhibitors. Furthermore, NO₂ accumulation can be achieved by regulating pH, dissolved oxygen (DO), sludge retention time (SRT), real-time aeration control, anoxic conditions, and chemical inhibitors. On the other hand, the addition of chemicals (such as NH₂OH, copper (II) and arsenic (III), zinc oxide nanoparticles (ZnO-NPs), chromium (III), and Cr (IV)) for NOB suppression necessitated a costly supplementary treatment method to remove hazardous chemicals from treated water.

Graphical Abstract