The potential and the impact factors for phosphorus recovery from wastewater via struvite precipitation

Phosphorous (P) is an essential nutrient for living organisms, and there is a concern regarding the challenges of both supply uncertainty and the linked aquatic eutrophication. Phosphorus recovery through struvite precipitation technology has attracted much attention in research as it prevents eutrophication and forms a slow-release fertilizer that serves as an alternative source of P in both synthetic wastewater (SW) and real waste (RW). However, only inorganic soluble P is involved in the reaction. Therefore, the ratio of organic P, which is up to 30%–40% of total P in real wastewater systems, leads to a variation of P recovery rates in practice. There is a lack of knowledge on the underlying differences and the factors causing the disparity in the P recovery, and few studies have attempted to quantify the gap in the P recovery rates of SW and RW. Data mining was conducted using 103 studies with 1186 observations to quantify the P recovery rate in SW and RW, establish the underlying factors affecting the P recovery, and derive solutions. Results showed that P recovery rate in SW (83.6%) was higher than that in RW (76.9%). A large variation in the P recovery rate (20.4% to 99.9%) in RW was detected since it was more sensitive to pH and foreign ions, such as calcium. Magnesium and calcium were found to impact struvite crystallization; magnesium had a positive impact at a specific Mg∶P ratio between 1 and 2, with SW being more sensitive, while calcium inhibited struvite formation. P precipitation is an abiotic process, and organic P concentration plays a crucial role in the total P recovery rate. Aeration played an important role in the mineralization of organic P. Therefore, supplying aeration at a flow rate of 6 L∙min⁻¹ was beneficial for both total and inorganic P recovery. Increasing the Mg∶P ratio was not a crucial factor for P recovery in practice, but it significantly impacts the components of the precipitate.