**2. Selection of carbon sources in process design**

Heterotrophic denitrification occurs in the presence of both nitrate and biodegradable organic substances under anoxic conditions. If a denitrification system is placed after a secondary wastewater treatment process, intrinsic biodegradable organic substances are essentially


**Table 1.** Kinetic information of selected carbon sources [1].

depleted before the denitrification unit. Under these situations, external supplementation of organic substances (electron donors) is usually needed to generate dedicated microbial communities. Generally, an external carbon source, such as methanol, ethanol, acetic acid, glycerol, sugar, or molasses, is used as a supplement. Another commercial product worth mentioning is MicroCTM. It is manufactured by Environmental Operating Solutions Inc. (Bourne, MA) and is an environmentally benign, proprietary wastewater treatment chemical containing a mixture of organic compounds, mainly glycerol. It contains 670,000 mg/L chemical oxygen demand (COD) with a specific gravity of 1.22 g/mL at 25°C.

The stoichiometric reaction C/N ratio, yield, specific growth rate, and Arrhenius temperature factor are different for different carbon sources, some of which are summarized in **Table 1**. It should be advised that these parameters were obtained with municipal wastewater under different acclimation and feeding conditions and microbial compositions, and the use of these parameters should be with care.
