Effect of acetic acid on struvite precipitation: An exploration of product purity, morphology and reaction kinetics using central composite design.

Phosphorus recovery has attracted increasing interest due to the potential depletion of phosphorus resources. One promising solution is to recover phosphorus via struvite precipitation from wastewater or other waste that is in rich of phosphate. However, product quality control during such process is always challenging due to the variation and complexity of wastewater compositions. For example, subcritical wet oxidation (SCWO) effluent is rich in phosphorus and nitrogen but contains a large amount of acetic acid, while its effect on struvite recovery is hardly known. Therefore, central composite design (CCD), considering pH, acetic acid level, Mg level and Ca level, was used to evaluate the effect of acetic acid on struvite purity, phosphorus removal, morphology and reaction kinetics. The experimental data were statistically analysed by analysis of variance (ANOVA) and principal components analysis (PCA). The results indicate that pH and Mg level have a significant impact on phosphorus removal (pH: p-value < 0.0001, Mg: p-value < 0.0001) and struvite purity (pH: p-value = 0.0410, Mg: p-value < 0.0001), Ca level only affects the struvite purity (p-value = 0.0333). The presence of acetic acid, within the studied range (8.77-34.53 mM), has a negligible effect on struvite morphology, phosphorus removal and reaction kinetics, but a slightly positive effect on struvite purity. Findings of this research would be beneficial to determine the feasibility of acetic acid-rich wastewater as a phosphorus source for struvite recovery.