Abstract:Phosphorus is an essential element for plants, animals, and other living organisms. The lack of phosphorus in aquatic environments can restrict primary productivity, a concern that has increasingly attracted global attention. However, the high phosphorus concentration leads to the eutrophication of water bodies, impacting human activities, compromising water quality, and causing notable economic losses. Therefore, studies on phosphorus removal and the recovery of phosphorus resources are important. In 2023, 27.3% of China’s important fishery waters in inland rivers exceeded the total phosphorus standard. The area of marine natural important fishery waters that exceeded the standard for reactive phosphate was 27.0%, and the area of seawater key aquaculture areas that exceeded the standard for reactive phosphate was 28.2%,. Aquaculture development is particularly important in the context of the ‘Big Food Concept’. The China’s total aquatic product output in 2023 was 71.16 million tons, an increase of 4.39% year-on-year, of which aquaculture production accounted for 81.6%. From 2022 to 2024, China’s provinces and municipalities introduced the aquaculture tail water discharge standard. For example, Shandong Province has implemented DB37 4676-2023, which sets a total phosphorus primary discharge limit of 0.7 mg/L and a secondary discharge limit of 1.0 mg/L. Recently, the rapid development of aquaculture tailwater phosphorus removal technology and phosphorus recovery technology based on physical, chemical, biological and ecological methods has provided strong support for aquaculture tailwater phosphorus removal and recycling. The current aquaculture tailwater phosphorus removal technology has made some progress. However, the advanced removal of phosphorus from the tailwater and phosphorus recovery technology requires further investigation. Enhancing the advanced removal of aquaculture tailwater is essential to ensure the sustainable development of aquaculture. This study classified the phosphorus in the water, examined the principle and current status of aquaculture tailwater phosphorus removal technology, and reviewed the application of phosphorus removal in the tailwater of the current aquaculture model. The principles and current status of phosphorus removal technology in aquaculture tailwater were discussed in terms of physical, chemical, and biological methods of phosphorus removal. The study indicated that the physical method of phosphorus removal technology in aquaculture primarily relies on adsorption and membrane separation technology, in which the high adsorption saturation of adsorbent materials and renewable is the key to adsorption of phosphorus removal, and the physical principle of membrane separation technology is the selective permeability of the membrane. Pollutant retention is achieved through the concentration difference between the two sides of the membrane, hydraulic pressure difference, and potential difference. The current membrane separation technology research methods continue to innovate and generally combine the membrane separation technology and biological method applied to aquaculture tail water phosphorus removal technology. Chemical phosphorus removal technologies such as precipitation, electro-flocculation, crystallization and depth oxidation are important for aquaculture tailwater phosphorus removal technology. These technologies are notable in phosphorus resource recovery and should not be ignored. Biological phosphorus removal technology is a primary method for phosphorus removal in aquaculture tailwater and mainly includes biofilm reactor, Biofloc, microalgae biological purification, bacterial and algal synergistic reactor, artificial wetland and other technologies. Biofilm reactors and Biofloc mainly rely on the role of phosphate accumulating organisms (PAOs) and denitrifying phosphate accumulating organisms (DPAOs), both of which have different processing capacities and biological responses to phosphorus in aerobic, anaerobic and anoxic stages. PAOs absorb phosphorus in aerobic conditions and release phosphorus in anaerobic conditions; DPAOs release phosphorus in anaerobic conditions and absorb phosphorus in the anoxic stage. Microalgae biological purification technology mainly uses the photosynthesis of microalgae and microalgae growth to absorb and remove phosphorus from the water. The microalgae bioreactor is a bacterial-algae synergistic reactor formed by combining microalgae and biofilm reactors to remove phosphorus. Artificial wetlands are a comprehensive phosphorus management method that integrates physical, chemical, and biological methods. This approach is becoming prominent as a crucial technique for phosphorus management in aquaculture tailwater. Current aquaculture modes such as recirculating aquaculture system (RAS), pond aquaculture and other modes, in which RAS mostly use biofilm reactors, bacterial and algal synergistic bioreactors and multi-level integrated aquaculture systems and other treatment methods, and in recent years, artificial wetlands are also gradually applied in the treatment of phosphorus in RAS tailwater. Artificial wetlands are used with sediment and microbial fuel cells to remove phosphorus from aquaculture tailwater. In phosphorus treatment in recirculating aquaculture tailwater, the bioecological method is gradually being used as the main method to treat phosphorus in tailwater, supplemented by physicochemical methods. The pond aquaculture tailwater phosphorus management is also based on bioecological methods, such as ‘three ponds and two dams’, artificial wetlands, multi-level integrated aquaculture treatment system and other methods to remove phosphorus. This study analyzed the aquaculture tailwater phosphorus removal technology, which can provide new ideas for tailwater phosphorus treatment and phosphorus resource recovery and promote the green development of aquaculture.
