Performance investigation of struvite high-efficiency precipitation from wastewater using silicon-doped magnesium...

In this study, a new adsorbent of silicon-doped magnesium oxide (SMG) was developed for the recovery of nutrients from wastewater. The adsorption conditions including adsorbent dosage, initial solution pH, contact time, coexisting substances, N/P molar ratios, and reaction temperature were investigated. Analysis of field emission scanning electron microscopy-energy dispersive spectrometer (FESEM-DES) and specific surface areas (BET) showed that SMG was a mesoporous adsorbent with S_BET of 108.31 m²/g. The recycled sediment (RS) was identified as almost pure struvite via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The recovery efficiencies of SMG reached 43.25% of ammonia nitrogen and 97.31% of phosphate at dosage of 0.3 g/L, initial solution pH of 7.0, contact time of 20 min, and temperature of 298 K. Under the optimal reaction conditions, the maximum adsorption capacities of SMG were 170.93 mg/g of ammonia nitrogen and 420.89 mg/g of phosphate at N/P molar ratio of 1.5:1. Coexisting humic acid (HA), calcium (Ca²⁺), acetic acid (AA), and ferric ions (Fe³⁺) in nutrient solution hindered the struvite ordered precipitation. The adsorption process followed pseudo-second-order and Elovich kinetic models and was well described by both the Langmuir and Freundlich isotherms at room temperature. All results indicated that the most likely mechanism of nutrients recovery from wastewater was chemical precipitation and proved that SMG was a high-efficiency adsorption material in a wide pH range of 3.0-9.0 for simultaneous recovery of nutrients from wastewater.