*4.4.7.2. Biological removal of nitrogen*

The nitrification and denitrification processes are responsible for N2O production (Figure 37). Figure 38 shows a nitrification/denitrification system for biological removal of nitrogen.

**Figure 34.** Mechanism of attached growth media in an RBC system [2].

**Figure 33.** Schematic diagram of air-drive RBC [2].

28 Wastewater Treatment Engineering

*4.4.7. Biological removal of nutrients*

*4.4.7.1. Biological phosphorous removal*

*4.4.7.2. Biological removal of nitrogen*

flow.

The RBC consists of media, shaft, drive, bearings, and cover (Figure 34). The RBC hardware consists of a large diameter and closely spaced circular plastic media that is mounted on a horizontal shaft supported by bearings and is slowly rotated by an electric motor. The plastic media are made of corrugated polystyrene or polyethylene material with different designs, dimensions, and densities. The model designs are based on increasing surface area and firmness, allowing a winding wastewater flow path and stimulating air turbulence [1, 2].

It is widely agreed that microorganisms utilize acetate and fatty acids to accumulate poly‐ phosphates as poly-β-hydroxybutyrate, which is an acid polymer. The precise mechanism is based on the production and regeneration of adenosine diphosphate (ADP) within the bacteria, and it involves the adenosine triphosphate (ATP). Phosphate removal requires true anaerobic conditions, which occur only when there is no other oxygen donor [3]. Figure 36 shows a phosphate removal process. This process needs long narrow tanks for maintenance of plug

The nitrification and denitrification processes are responsible for N2O production (Figure 37). Figure 38 shows a nitrification/denitrification system for biological removal of nitrogen.
