Natural nitrogen cycle has been disturbed by the raise of anthropogenic nitrogen fixations. Anthropogenic disturbance on the environment causes eutrophication, decrease in biodiversity, acidification of soil and raise in nitrous oxide emission. To restore the balance, nitrogen is required to be removed via processes such as wastewater treatment. However, it is suggested that nitrous oxide emission occurs during wastewater treatment process. Investigation on the nitrous oxide emission during wastewater treatment process was necessary. Through literature reviews, the nitrous oxide emission...