Modelling of struvite recovery from anaerobically digested waste-activated sludge using response surface methodology

Abstract Waste-activated sludge (WAS) from urban wastewater treatment facilities contains nutrients like nitrogen, phosphorus, and potassium, which can be crystallized into struvite. The current study utilized response surface methodology (RSM) and a central composite design (CCD) to optimize phosphorus recovery from the supernatant of anaerobically digested WAS using key parameters such as Mg:P ratio and pH. A second-order polynomial equation was determined to correlate the parameters. Analysis of variance (ANOVA) was applied and showed that p -values for all the investigated parameters were less than 0.05, showing that they had a statistically significant effect on the phosphorus recovery. Phosphorus recovery exceeded 80% at pH values above 8 and Mg:P ratios greater than 1. Energy-dispersive X-ray spectroscopy ( SEM–EDX) showed the formation of uneven structure crystals and the presence of Mg, P, and O, indicating the formation of struvite. Low concentrations of interfering ions were found (K and Ca), meaning that Ca-P and K-P compounds might have formed in insignificant quantities. XRD and FTIR spectroscopy confirmed struvite formation. The study has demonstrated the feasibility of recovering phosphorus as struvite using MgSO 4 as a magnesium source, offering a sustainable solution for nutrient recovery from wastewater. Graphical abstract