How many milligrams per liter of alkalinity are required to convert 1 mg/L of nitrite to nitrate?

To determine how many milligrams per liter of alkalinity are needed to convert 1 mg/L of nitrite to nitrate, one must consider the chemical reactions involved in nitrogen transformation in wastewater treatment. The conversion process from nitrite (NO2-) to nitrate (NO3-) is known as nitrification and is carried out by nitrifying bacteria.

During this process, specifically the oxidation of nitrite to nitrate, a certain amount of alkalinity is consumed. This is typically expressed in terms of calcium carbonate equivalent (CaCO3). The stoichiometry of the nitrification process indicates that for every mole of nitrite that is oxidized to nitrate, a corresponding amount of alkalinity is required to maintain the system's pH.

Research and industry standards show that around 7.1 mg/L of alkalinity (as CaCO3) is generally needed to convert 1 mg/L of nitrite to nitrate. This value accounts for the necessary buffering capacity that supports bacterial activity while facilitating the oxidation of nitrite.

Thus, the requirement of 7.1 mg/L reflects the chemical and biological dynamics necessary for effectively converting nitrite to nitrate in wastewater treatment processes, making it the correct choice in this scenario.