What is the correct sequence of steps in the nitrification-denitrification process?

In the nitrification-denitrification process, the sequence described in the correct answer reflects the biological transformation of nitrogen compounds in wastewater treatment.

The process begins with organic nitrogen, which is found in organic matter. Bacteria break down this organic nitrogen, producing ammonia through a process called ammonification. After this step, ammonia is then oxidized to nitrite by nitrifying bacteria, specifically through the action of ammonia-oxidizing bacteria. Following this, another group of bacteria converts nitrite into nitrate.

The final phase of the process is denitrification, where other types of bacteria use the nitrate as an electron acceptor in the absence of oxygen, reducing it to nitrogen gas (N2). This nitrogen gas is then released into the atmosphere, completing the nitrogen cycle.

This sequential conversion is fundamental in dealing with nitrogen compounds in wastewater, as each step plays a crucial role in reducing the environmental impact of nitrogen in discharges. Understanding this sequence is essential for effective wastewater treatment design and operation, as it helps to manage nutrient loading in receiving waters.