This comprehensive review covers modern technologies for treating nitrogen-rich wastewater, focusing on biological, physical, and chemical methods. Biological processes, such as simultaneous nitrification–denitrification (SND) and anammox, are highlighted for their effectiveness in removing nitrogen from saline water and diverse COD/N ratios. Suspended growth bioreactors and moving biofilm bioreactors are noted for their efficiency in treating wastewater with low C/N ratios and their ability to reduce sludge formation. The review also discusses the use of polyvinyl alcohol/sodium alginate as a growth medium and air-lift reflux configurations to enhance treatment efficiency. Physico-chemical methods, including adsorption/ion exchange, membrane distillation, ultrafiltration, and nanofiltration, are explored for their potential in industrial wastewater treatment. Advanced oxidation processes (AOPs) and sulfate-based oxidants are effective in eliminating nitrogen compounds from industrial wastewater. The techno-economic analysis of emerging technologies is crucial for their practical application in wastewater treatment. The review emphasizes the importance of tailoring treatments to cost-effective nitrogen removal, optimizing microbial interactions, and analyzing the techno-economics of advanced technologies.This comprehensive review covers modern technologies for treating nitrogen-rich wastewater, focusing on biological, physical, and chemical methods. Biological processes, such as simultaneous nitrification–denitrification (SND) and anammox, are highlighted for their effectiveness in removing nitrogen from saline water and diverse COD/N ratios. Suspended growth bioreactors and moving biofilm bioreactors are noted for their efficiency in treating wastewater with low C/N ratios and their ability to reduce sludge formation. The review also discusses the use of polyvinyl alcohol/sodium alginate as a growth medium and air-lift reflux configurations to enhance treatment efficiency. Physico-chemical methods, including adsorption/ion exchange, membrane distillation, ultrafiltration, and nanofiltration, are explored for their potential in industrial wastewater treatment. Advanced oxidation processes (AOPs) and sulfate-based oxidants are effective in eliminating nitrogen compounds from industrial wastewater. The techno-economic analysis of emerging technologies is crucial for their practical application in wastewater treatment. The review emphasizes the importance of tailoring treatments to cost-effective nitrogen removal, optimizing microbial interactions, and analyzing the techno-economics of advanced technologies.