This review provides a comprehensive overview of modern technologies for nitrogen-rich wastewater treatment, focusing on biological, physical, and chemical methods. The study highlights the effectiveness of simultaneous nitrification–denitrification (SND) in saline water, where aerobic and anoxic conditions with diverse microbial populations enable efficient nitrogen removal. Coupling anammox with denitrification enhances removal rates and reduces energy demand. Suspended growth bioreactors effectively treat diverse COD/N ratios and demonstrate resilience to low C/N ratios. Moving biofilm bioreactors show reduced mortality rates, enhanced sludge–liquid separation, increased treatment efficiency, and stronger biological structures. SND studies achieved ≥90% total nitrogen removal efficiency, with Defluviicoccus, Nitrosomonas, and Nitrospira as main microbial communities, while anammox–denitrification achieved 77% removal. Systems using polyvinyl alcohol/sodium alginate as a growth medium showed ≥75% removal. Air-lift reflux configurations exhibited high removal efficiencies, reducing costs and minimizing sludge formation. Microwave pretreatment and high-frequency electric fields improved ammonium removal. Adsorption/ion exchange, membrane distillation, ultrafiltration, and nanofiltration show promise in industrial wastewater treatment. AOPs and sulfate-based oxidants effectively eliminate nitrogen compounds. Tailoring treatments for cost-effective nitrogen removal, optimizing microbial interactions, and analyzing techno-economics are crucial. Nitrogen-rich wastewater poses significant environmental challenges, with nitrogen playing a vital role in the nitrogen cycle. Excess nitrogen in water leads to algal blooms, oxygen depletion, and eutrophication. Wastewater treatment plants (WWTPs) typically use primary and secondary treatments, but secondary effluents often exceed nitrogen and phosphorus standards. Advanced treatments, such as tertiary processes, are needed for effective nitrogen and phosphorus removal. Emerging contaminants in secondary effluent, such as PPCPs, antibiotics, and microplastics, require advanced treatment technologies. These include enhanced denitrifying phosphorus removal filters, pyrite-based autotrophic denitrification, and microalgae biological treatment systems. The study examines the characteristics of various wastewater types, including domestic, agricultural, and industrial wastewaters, highlighting their nitrogen and phosphorus content. Biological nitrogen removal involves microbial processes such as nitrification and denitrification, with anammox offering an energy-efficient alternative. Microalgae contribute to nitrogen removal by assimilating ammonium for growth. SND technology shows high efficiency, with graphene derivatives enhancing nitrogen removal. Anammox processes, which convert ammonium and nitrite to nitrogen gas, are energy-efficient and effective for treating nitrogen-rich wastewater. Combining conventional nitrification–denitrification with anammox improves removal efficiencies and reduces energy consumption. Suspended growth bioreactors, such as activated sludge and SBRs, are effective for nitrogen removal, with SBRs offering higher removal efficiencies due to their abilityThis review provides a comprehensive overview of modern technologies for nitrogen-rich wastewater treatment, focusing on biological, physical, and chemical methods. The study highlights the effectiveness of simultaneous nitrification–denitrification (SND) in saline water, where aerobic and anoxic conditions with diverse microbial populations enable efficient nitrogen removal. Coupling anammox with denitrification enhances removal rates and reduces energy demand. Suspended growth bioreactors effectively treat diverse COD/N ratios and demonstrate resilience to low C/N ratios. Moving biofilm bioreactors show reduced mortality rates, enhanced sludge–liquid separation, increased treatment efficiency, and stronger biological structures. SND studies achieved ≥90% total nitrogen removal efficiency, with Defluviicoccus, Nitrosomonas, and Nitrospira as main microbial communities, while anammox–denitrification achieved 77% removal. Systems using polyvinyl alcohol/sodium alginate as a growth medium showed ≥75% removal. Air-lift reflux configurations exhibited high removal efficiencies, reducing costs and minimizing sludge formation. Microwave pretreatment and high-frequency electric fields improved ammonium removal. Adsorption/ion exchange, membrane distillation, ultrafiltration, and nanofiltration show promise in industrial wastewater treatment. AOPs and sulfate-based oxidants effectively eliminate nitrogen compounds. Tailoring treatments for cost-effective nitrogen removal, optimizing microbial interactions, and analyzing techno-economics are crucial. Nitrogen-rich wastewater poses significant environmental challenges, with nitrogen playing a vital role in the nitrogen cycle. Excess nitrogen in water leads to algal blooms, oxygen depletion, and eutrophication. Wastewater treatment plants (WWTPs) typically use primary and secondary treatments, but secondary effluents often exceed nitrogen and phosphorus standards. Advanced treatments, such as tertiary processes, are needed for effective nitrogen and phosphorus removal. Emerging contaminants in secondary effluent, such as PPCPs, antibiotics, and microplastics, require advanced treatment technologies. These include enhanced denitrifying phosphorus removal filters, pyrite-based autotrophic denitrification, and microalgae biological treatment systems. The study examines the characteristics of various wastewater types, including domestic, agricultural, and industrial wastewaters, highlighting their nitrogen and phosphorus content. Biological nitrogen removal involves microbial processes such as nitrification and denitrification, with anammox offering an energy-efficient alternative. Microalgae contribute to nitrogen removal by assimilating ammonium for growth. SND technology shows high efficiency, with graphene derivatives enhancing nitrogen removal. Anammox processes, which convert ammonium and nitrite to nitrogen gas, are energy-efficient and effective for treating nitrogen-rich wastewater. Combining conventional nitrification–denitrification with anammox improves removal efficiencies and reduces energy consumption. Suspended growth bioreactors, such as activated sludge and SBRs, are effective for nitrogen removal, with SBRs offering higher removal efficiencies due to their ability