WATER POLLUTION (S SENGUPTA AND L NGHIEM, SECTION EDITORS) Nitrogen Cycle in Engineered and Natural Ecosystems—Past and Current Aiswarya Rani Pappu 1 & Ananda Shankar Bhattacharjee 1 & Sunayna Dasgupta 1 & Ramesh Goel 1 # Springer International Publishing AG 2017 Abstract Due to modern urbanization and rapid population growth, the nitrogen cycle has been significantly disturbed with- in differing ecosystems. Focusing specifically on imbalances present in an aquatic ecosystem, it is imperative that the waste- water engineering community addresses the need to conserve energy and resources better by developing more effective tools for application in wastewater treatment plants. The Academy of Engineers recently identified nitrogen cycle management as one of the 14 predominant challenges that engineers need to be ad- dressing in the immediate future. This validates a definite sense of urgency to find practical solutions for implementation in wastewater treatment plants. In order to determine the best means for effective nitrogen cycle management, an in-depth ex- amination of disturbances in the cycle provide an understanding of what is needed to resolve these issues. This article provides an in-depth discussion of past research, developments found in present studies, as well as providing potential strategies for im- proving the future of nitrogen cycle management. Keywords Nitrification . Denitrification . Anammox . DAMO Introduction Nitrogen (N) is an essential component required of all organ- isms on the planet. It is known to exist in multiple chemical forms and several oxidation states (redox range from -3 to +5); such as dinitrogen gas, nitric oxide, nitrous oxide, nitrite, nitrate, and ammonium [32, 204]. Until the late twentieth cen- tury, it was assumed that all microorganism-mediated reac- tions of the nitrogen cycle were known. However, recent find- ings suggested that the nitrogen cycle was significantly more complex than it was originally understood to be. Prior to these recent studies, the main components of the nitrogen cycle involved nitrogen fixation to ammonium by nitrogen-fixing microorganisms, followed by either assimilation or nitrifica- tion and the subsequent release of dinitrogen gas via denitrification. Management of the nitrogen cycle in the environment has been identified as one of the 14 grand challenges by the Academy of Engineering [122]. Engineers have used the nov- el biochemical reactions observed in natural ecosystems to implement applications for wastewater treatment processes. As a result, utilizing nitrogen-removing technologies in waste- water treatment has expanded tremendously. The overall ob- jective of this article is to promote a better understanding of nitrogen cycling by reviewing past research, examining its newly discovered modifications, and discussing the applica- tions of these findings in wastewater treatment processes. The Overall N Cycle An Overview of Different Components of N Cycle The ecological significance of the nitrogen cycle lies in its ability to regulate the availability of fixed nitrogen to biota. Dinitrogen gas, as the major component of the Earth’ s atmo- sphere, is readily available to nitrogen-fixing prokaryotes. These bacteria and archaea reduce the dinitrogen gas to am- monium and incorporate it into the biomass, making it This article is part of the Topical Collection on Water Pollution * Ramesh Goel rgoel@civil.utah.edu 1 Department of Civil and Environmental Engineering, University of Utah, Salt Lake City, UT 84112, USA Curr Pollution Rep DOI 10.1007/s40726-017-0051-y