This lecture covers denitrification, a process where nitrate is reduced to N2 under anoxic conditions, resulting in the loss of nitrate to the atmosphere. It explains the four-step reduction of nitrate to N2, different nitrate reduction pathways, and the organisms involved. The lecture also discusses nitrate reduction to nitrite, dissimilatory nitrate ammonification, and its application in wastewater treatment. Denitrification is highlighted as a crucial anaerobic process in the nitrogen cycle, emphasizing its role in removing nitrogen from the environment.