Phosphorus recovery from wastewater using light calcined magnesite, effects of alkalinity and organic acids

Abstract

To solve the problem of phosphorus pollution and resource crisis, phosphorus recovery by struvite crystallization has become a focus of research in recent years. In municipal wastewater, insufficient magnesium content and relatively low pH can be a limitation for struvite formation. A commercial magnesium source, light calcined magnesite (LCM), was used in this study for phosphorus recovery from wastewater without an adjustment of pH. Bench-scale jar test experiments were conducted to study the kinetics of phosphate removal by LCM. The effects of LCM dosage, initial phosphate concentration, carbonate alkalinity and organic acid content on the removal of phosphate was evaluated. Hydrolyzation of LCM released hydroxyl ions (OH−) during the reaction, increasing the solution pH from 7.63 to 8.62. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the composition and morphology of formed precipitates. At an LCM dosage of 200 mg/L, 84.5% of phosphate was removed mainly through the formation of struvite. Increased alkalinity and organic acid concentration in the solution inhibited struvite formation, and higher alkalinity promoted the formation of coarse crystal surfaces. Abundant global reserves of the magnesite ore resource reveal LCM may be a viable and cost-effective source of magnesium and hydroxyl reagent for phosphorus recovery from wastewater.