The precipitation of struvite (MgNH₄PO₄·6H₂O) is considered to be a promising method for the recovery of phosphate from wastewater. In this review, the kinetic models, which are commonly used to explain the process of struvite crystallization, are described. The mixed-suspension mixed-product removal (MSMPR) model is based on the population balance equation (the size-dependent growth model and the size-independent growth model). Thereafter, the first-order kinetic fitting model that aligned with concentration changes in the substrate is summarized. Finally, the several physical and chemical factors that affected the efficiency of struvite crystallization are determined. The supersaturation ratio, which is seen as the driving force of struvite crystallization, is the main factor that influences crystallization; however, it cannot be used in practical applications of engineering because it is indirectly associated with the following factors: pH, the molar ratio of Mg:N:P, and the interference of foreign impurities. In this study, we present conclusions that should be used to guide further research studies, and encourage the engineering practice of wastewater treatment with struvite precipitation.

The aim of this study is to evaluate the anaerobic digestion and biogas production of plant biomass under high salinity by adopting a theoretical and technical approach for saline plant-biomass treatment. Two completely mixed lab-scale mesophilic reactors were operated for 480 days. In one of them, NaCl was added and the sodium ion concentration was maintained at 35.8 g-Na⁺·L⁻¹, and the organic loading rate was 0.58-COD·L⁻¹·d⁻¹–1.5 g-COD·L⁻¹·d⁻¹; the other added Na₂SO₄–NaHCO₃ and kept the sodium ion concentration at 27.6 g-Na⁺·L⁻¹ and the organic loading rate at 0.2 g-COD·L⁻¹·d⁻¹–0.8 g-COD·L⁻¹·d⁻¹. The conversion efficiencies of the two systems (COD to methane) were 66% and 54%, respectively. Based on the sulfate-reduction reaction and the existing anaerobic digestion model, a kinetic model comprising 12 types of soluble substrates and 16 types of anaerobic microorganisms was developed. The model was used to simulate the process performance of a continuous anaerobic bioreactor with a mixed liquor suspended solids (MLSS) concentration of 10 g·L⁻¹–40 g·L⁻¹. The results showed that the NaCl system could receive the influent up to a loading rate of 0.16 kg-COD/kg-MLSS·d⁻¹ without significant degradation of the methane conversion at 66%, while the Na₂SO₄–NaHCO₃ system could receive more than 2 kg-COD·kg⁻¹-MLSS·d⁻¹, where 54% of the fed chemical oxygen demand (COD) was converted into methane and another 12% was observed to be sulfide.