Abstract
Since phosphorus, a non-renewable and non-substitutable resource, has become the principal contributor and limiting factor to water eutrophication, achieving phosphorus removal and recovery from wastewater is pretty essential. Even though struvite crystallization process has been widely used for phosphate (P) recovery in wastewater treatment, its application is hampered by difficulties controlling small particle size and crystal growth. This study was conducted to control the settleability of struvite by calculating and predicting the struvite-settling percentage (Ps), which is always affected by the initial concentration of P (CP), solution pH (pH), reaction time (t), reaction temperature (T), agitation rate (Ar), and inlet flow velocity (vf) of the fluidized bed reactor. The results showed that the settleability of struvite could be enhanced by increasing T and decreasing pH, Ar, or vf, and would perform worse with overlong t or excessive CP. The dynamic variation process of the solution supersaturated index (SI) combined with the phase equilibrium theory and Ostwald ripening mechanism explained the above results sufficiently. The logistic model was chosen to predict the Ps under multi-factors, but the accuracy needs to be improved.
Highlights
IntroductionWhat’s more, many factors affect the process of struvite crystallization or supersaturation index (SI) all the time, like the initial concentration of P, the molar ratio of Mg and P, the solution pH value, coexisting ions (such as calcium ion, carbonate ion, suspended solids and heavy metal ions), the inlet flow velocity of fluid bed reactors (FBR) and so on
The struvite-settling percentage (Ps), a quantifiable index of settleability, is the key dependent variable of this study. Some quantifiable factors, such as the solution basic parameters - initial concentration of P (CP) and solution pH value, the thermal parameter - reaction temperature (T), and the dynamic parameters - reaction time (t), agitation rate (Ar) and inlet flow velocity, were chosen to be the components of the Ps predicted model after their impact laws and mechanisms were analyzed based on the dynamic variation processes of supersaturation index (SI)
The mechanisms of struvite settleability were explained based on the theory of phase balance
Summary
What’s more, many factors affect the process of struvite crystallization or SI all the time, like the initial concentration of P, the molar ratio of Mg and P, the solution pH value, coexisting ions (such as calcium ion, carbonate ion, suspended solids and heavy metal ions), the inlet flow velocity of FBR and so on. The struvite-settling percentage (Ps), a quantifiable index of settleability, is the key dependent variable of this study Some quantifiable factors, such as the solution basic parameters - initial concentration of P (CP) and solution pH value (pH), the thermal parameter - reaction temperature (T), and the dynamic parameters - reaction time (t), agitation rate (Ar) and inlet flow velocity (vf), were chosen to be the components of the Ps predicted model after their impact laws and mechanisms were analyzed based on the dynamic variation processes of SI
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