Anaerobic digestion (AD) is widely applied for sludge stabilization and energy recovery, but its operation is often affected by phosphate scaling, particularly struvite (MgNH 4 PO 4 ·6H 2 O) crystallization. To quantitatively examine the role of floc-like solid interfaces, diatomite, characterized by a porous silica framework, high specific surface area, and abundant surface hydroxyl groups, was employed as an interfacial model material in a constant-pH, constant-composition crystallization system. The results show that diatomite induced systematic non-linear variations in struvite crystallization kinetics. The induction time generally increased with increasing diatomite concentration, consistent with limited ion-surface interactions and interfacial charge regulation. The nucleation rate exhibited a rise-decline-plateau trend, reflecting the accumulation and subsequent saturation of heterogeneous nucleation sites. In contrast, the crystal growth rate showed a non-linear inhibition-promotion response, shifting from slight suppression at low diatomite concentrations to enhanced growth at higher concentrations, indicating a change in the interfacial environment for crystal growth. SEM, XRD, FTIR, and XPS analyses showed that diatomite modified crystal morphology and interfacial chemical environment without altering the crystal phase or lattice structure of struvite. These findings provide quantitative insight into interface-mediated heterogeneous crystallization, with implications for scale control and phosphorus recovery in anaerobic digestion side-streams. • Diatomite nonlinearly regulates struvite crystallization kinetics. • Induction time increases, while nucleation follows a rise–decline–plateau trend. • Growth shifts from slight inhibition to enhancement as diatomite dosage increases. • Interfacial effects, rather than phase change, dominate struvite kinetic regulation.
Li et al. (Fri,) studied this question.