What is the correct matching term for pre-denitrification?

Pre-denitrification is a biological process that primarily occurs in an environment lacking oxygen, known as an anoxic condition. This process is a key step in nitrogen removal, where nitrate (NO3-) is reduced to nitrogen gas (N2) in the absence of oxygen. During pre-denitrification, organic carbon is used as an electron donor by denitrifying bacteria to convert nitrate to nitrite (NO2-) and eventually to nitrogen gas.

The anoxic environment is crucial because denitrifying bacteria utilize nitrate instead of oxygen for respiration, which directly contributes to the reduction of nitrogen compounds present in wastewater. This step is typically part of a larger biological nutrient removal process, where different stages can include oxic (aerobic) conditions for nitrification and anoxic conditions for denitrification.

In contrast, the other terms refer to different conditions of oxygen availability. Oxic and aerobic conditions mean the presence of oxygen, which is essential for nitrification but not for denitrification. Mesophilic refers to a temperature range ideal for the growth of certain bacteria but does not specifically address the oxygen conditions required for pre-denitrification. Therefore, the term that accurately matches the required conditions for the pre-denitrification process is anoxic.