###### Abstract  
Phosphogypsum is a kind of solid waste that occupies land resources and harms the environment. It can be used as a solidified material, but the utilization of phosphogypsum is limited by its impurities and weak strength performance. This study aimed to use microbial-induced carbonate precipitation (MICP) to improve the water stability, permeability, and hydraulic erosion resistance of phosphogypsum and evaluate its impact on the environment. In this paper, the phosphogypsum samples and artificial slopes were prepared and solidified by spraying various concentrations of bacteria solution and cementation solution to achieve microbial modification. The water stability and permeability test were used to calculate the mass of spalling under water shaking and the permeability coefficient. A rainfall scouring test was carried out to estimate the erosion resistance. The erosion degree was quantitatively calculated using 3D laser scanning technology. The results show that the microorganism treatment can improve water stability and reduce the permeability coefficient, while the differences between the content of CaCO\({}_{3}\) in the outermost layer and in the inner layer gradually increase with the increase in bacterial concentration, and the permeability coefficient was reduced uniformly. The sediment loss of the slope after MICP treatment was much less than that of the untreated slope, and the connection force between the particles was strengthened. By observing the morphology of the scoured samples, we found that the treated particles were aggregated and flocculated with more macropores, which led to the formation of erosion pits under scouring. The pH of the outflow of the modified slope was neutral, and the heavy metal elements were fixed by microbial action and carbonate, which is not harmful to the environment. phosphogypsum; microbial-induced carbonate precipitation (MICP); water stability; hydraulic erosion resistance; rainfall scouring test 20221212783122331231  
and other impurities, which will affect the crystallization time of phosphogypsum crystals and reduce its mechanical properties. It is necessary to reduce the harmful influence by washing, flotation, calcination or adding other chemical stabilizers. A single treatment method cannot meet the conditions of use, and multiple methods are often required in combination, though this increases the treatment time and cost at the same time. Some scholars have argued that phosphogypsum can be used in building materials, such as gypsum board, by adding an appropriate amount of modifier, and it is also commonly used as a cement retarder [5; 6]. It is found that the use of pretreated phosphogypsum can replace natural gypsum as a cement retarder, which has no negative impact on cement strength [7]. Some studies recommend mixing phosphogypsum with other chemical additives for use as roadbed material, or as fillings to improve the mechanical strength and water stability of the composites [8; 9; 10; 11]. By adding an artificial cementitious agent, including cement, lime and fly ash, to solidify phosphogypsum, the solubility of the pollutants is reduced, and it can be used as a backfill stabilizer and structure layer of pavement [12; 13]. The increase in temperature can also remove the impurities and heavy metal ions on the surface so that it can be reused [14]. The main composition of phosphogypsum is CaSO\({}_{4}\) 2H\({}_{2}\)O, which can react with cement or lime to formulate pozzolanic products under an alkaline environment. The product of the chemical reaction between phosphogypsum and cement hydrate is ettrinigite, which provides the main skeleton with strength support, but the excessive production of by-products will expand the material and result in potential heaving failure [15; 16]. At present, the treatment and application of solid waste is a research hotspot, and the modification and reuse of phosphogypsum are of great significance to the sustainable development of phosphogypsum resources.