Nitrogen Removal in Wastewater Treatment: How It Works

The first step in nitrogen removal is the biological conversion of ammoniacal nitrogen into nitrate—a process known as nitrification.

In the presence of oxygen and specialized nitrifying bacteria, ammonium (NH₄⁺) is oxidized to nitrate (NO₃⁻), according to the following reaction:

NH₄⁺ + 2O₂ → NO₃⁻ + 2H⁺ + H₂O

At Bionest, this transformation takes place in an aerobic reactor containing our proprietary treatment media.

Once nitrates are formed, they must be removed to prevent environmental discharge. This is achieved through denitrification, an anoxic process (without dissolved oxygen) that reduces nitrates to harmless nitrogen gas (N₂), which is released into the atmosphere.

Simplified reaction:

C₁₀H₁₉O₃N + 10NO₃⁻ → 5N₂ + 10CO₂ + 3H₂O + NH₃ + 10OH⁻

Effective denitrification requires:

• A carbon source to sustain denitrifying bacteria
• An anoxic environment (no dissolved oxygen)
• Carbon supplementation, if influent wastewater lacks sufficient organic carbon

One practical approach is recirculating treated water from the aerobic reactor back into the primary treatment tank, where conditions are naturally low in oxygen and carbon is more readily available. In many systems, a significant portion of denitrification can occur in this primary zone.

In some cases, a dedicated denitrification reactor may be added downstream. If so, an external carbon source may be required. The process is typically finalized with a polishing aerobic step to remove excess carbon (measured as COD).