Phosphorus recovery from high-COD and strongly acidic wastewater by vivianite crystallization: feasibility and optimization of operating conditions

Acidified oil wastewater contains high concentrations of phosphorus and organic pollutants, which not only pose environmental risks but also contain recoverable phosphorus resources. However, its complex matrix (high COD and acidic environment) poses great challenges to phosphorus recovery technologies. This study successfully developed a new phosphorus recovery strategy adapted to the wastewater characteristics and optimized key operating parameters using response surface methodology. Key parameters including pH, Fe:P molar ratio, reaction time and residence time were investigated, clarifying their regulatory roles in the complex wastewater system. Under the optimal process conditions (pH = 7.77, Fe:P molar ratio = 2.24, reaction time = 2.23 h, and hydraulic residence time = 4.16 h), the phosphorus recovery rate reached 93.54%, and the vivianite crystallization rate reached 91.39%. Furthermore, a process parameter prediction model (the verification results and the model prediction was less than 2.1%) was established to produce vivianite crystallization with large particle size (d₅₀ = 113.4 μm) and uniform morphology, realizing synchronous wastewater treatment and phosphorus recovery. This study confirmed the feasibility and controllability of phosphorus recovery through vivianite crystallization in complex acidified oil wastewater matrices, providing a sustainable technical path for addressing the dual issues of phosphorus resource shortage and environmental pollution.