The recovery of ammonia–nitrogen during wastewater treatment and water purification is increasingly critical in energy and economic development. The concentration of ammonia–nitrogen in wastewater is different depending on the type of wastewater, making it challenging to select ammonia–nitrogen recovery technology. Meanwhile, the conventional nitrogen removal method wastes ammonia–nitrogen resources. Based on the circular economy, this review comprehensively introduces the characteristics of several main ammonia–nitrogen source wastewater plants and their respective challenges in treatment, including municipal wastewater, industrial wastewater, livestock and poultry wastewater and landfill leachate. Furthermore, we introduce the main methods currently adopted in the ammonia–nitrogen removal process of wastewater from physical (air stripping, ion exchange and adsorption, membrane and capacitive deionization), chemical (chlorination, struvite precipitation, electrochemical oxidation and photocatalysis) and biological (classical and typical activated sludge, novel methods based on activated sludge, microalgae and photosynthetic bacteria) classification based on the ammonia recovery concept. We discuss the applicable methods of recovering ammonia nitrogen in several main wastewater plants. Finally, we prospect the research direction of ammonia removal and recovery in wastewater based on sustainable development.