This project is a research on the application of nitrogen and phosphorus removal technologies in wastewater treatment plants within the field of environmental protection, including the development of low-carbon simultaneous nitrogen and phosphorus removal processes, energy saving and carbon reduction control for nitrogen and phosphorus removal processes, and scientific prediction and control of greenhouse gas emissions. I. Project Background The concept of sustainable development has put forward new requirements for the functions of urban wastewater treatment plants, such as pollution reduction, low-carbon treatment, and energy recovery. Under the new circumstances, the nitrogen and phosphorus removal process, which is a key link in urban wastewater treatment, also faces new transformation requirements, that is, it urgently needs to achieve low-carbon nitrogen and phosphorus removal treatment while improving the water quality requirements of effluent. II. Technical Content and Innovation The project includes three aspects of technical content: ① Development of low-carbon simultaneous nitrogen and phosphorus removal processes: In response to the problem of insufficient carbon sources in urban wastewater treatment plants in China, The first development of a fully mixed anoxic denitrification and phosphorus removal dual sludge intermittent flow process and a plug flow anoxic denitrification and phosphorus removal continuous flow process, screening nitrate-reducing polyphosphate bacteria as electron acceptors, coupling nitrogen removal and phosphorus removal in a 'one carbon for two uses' manner, successfully achieving the goal of low-carbon source and low energy consumption for simultaneous nitrogen and phosphorus removal. ② Energy saving and carbon reduction control of nitrogen and phosphorus removal processes: In response to the problem of unstable nitrogen and phosphorus removal and low compliance rates caused by fluctuations in water quality and quantity of urban sewage in China, developed low-carbon operation technology based on biochemical kinetics and carbon-nitrogen-oxygen balance, humus soil activated sludge enhanced phosphorus removal technology, activated sludge-biofilm composite enhanced nitrification technology, and internal carbon source enhanced nitrogen and phosphorus removal technology. For the first time, it achieved comprehensive optimization of multiple objectives such as stable effluent compliance, energy saving, and carbon source intensive utilization. ③ Prediction and control of greenhouse gas emissions: In response to the challenges of inaccurately quantifying CO2 and N2O emissions from wastewater treatment plants in China and the lack of greenhouse gas control technologies, a calculation model for CO2 and N2O emissions from denitrification and phosphorus removal processes in wastewater treatment plants was first constructed. An N2O reduction control strategy was proposed, laying a theoretical and technical foundation for achieving greenhouse gas emission reduction targets in wastewater treatment. The main innovations are: the first proposal of the 'dual-carbon' theory domestically, and the development of a new carbon-saving denitrification and phosphorus removal process with optimized separation; based on the concept of intensive carbon source utilization, in-depth development of energy-saving and carbon reduction control technologies for denitrification and phosphorus removal; introduction of the 'carbon footprint' concept, and the first study on the characteristics and control methods of greenhouse gas emissions in the wastewater treatment process in China. III. Technical Indicators 1) The low-carbon new process saves 45% of carbon sources. The developed denitrification and phosphorus removal dual-sludge intermittent flow process and the plug-flow continuous flow process allow for an influent C/N ratio as low as 4~7. The total nitrogen removal rate has increased by 20%, saving on carbon sources in situ by 45%, reducing sludge volume in situ by 45%, and saving on aeration by 25%. 2) Regulation and control have achieved a saving of more than 10% in total energy consumption. Developed low-carbon operation technology based on biochemical kinetics and carbon-nitrogen-oxygen balance, saving operating costs by more than 10%; developed enhanced phosphorus removal technology using humus soil activated sludge, increasing the total phosphorus removal rate by 25%; developed composite enhancement nitrification technology with activated sludge-biofilm, improving the low-temperature nitrification effect by 30%; developed internal carbon source enhancement denitrification and phosphorus removal technology, increasing the fermentation acid production rate by 30%. 3) Precisely quantified CO2 and N2O emission factors. Obtained the actual carbon emissions of wastewater treatment plants in China: 0.08t/m3 during construction, and 0.11t/(m3 wastewater/d) during operation; The typical denitrification and phosphorus removal processes in our country's sewage treatment plants have an N2O emission factor of 0.095% to 3.44%. IV. Authorized Patents and Papers The research results of this project have had a significant impact both domestically and internationally. A total of 81 papers have been published in international water treatment authoritative journals such as 'Water Research' (including 31 SCI-indexed papers), and 21 patents have been applied for. V. Application and Benefits Many of the project's achievements have been successfully applied in sewage treatment plants in Shanghai, Jiangsu, Zhejiang, Anhui, and other places, with a total application scale reaching 2.125 million tons per day. The annual nitrogen emission has been reduced by 460 tons, the annual sludge production has been reduced by 4300 tons (calculated at an 80% moisture content), the annual carbon source saving has been 1209 tons, the annual electricity saving has been 308,000 kilowatt-hours, and the economic and social benefits are very significant.