Application of MgO-modified palygorskite for nutrient recovery from swine wastewater: effect of pH, ions, and organic acids

In this study, MgO-modified palygorskite (MgO-PAL) was used for simultaneous recovery of ammonia nitrogen (AN) and phosphate, and the effects of pH, ions, and organic acids on nutrient recovery were investigated. The highest removal amount of AN and phosphate separately reached 42.6 mg/g and 69.8 mg/g at pH of 9.0, 0.6 g/L dosage of modified palygorskite, and 180 min of the reaction time. MgO-PAL provided a wide range of pH (3–9) for nutrient removal. Mg released concentration was tested to investigate the removal mechanisms. The individual presence of four cations (K+, Ca2+, Na+, and Mg2+) showed negative effect on AN removal at different mass concentrations. However, those cations, except Na+, exhibited positive influence on phosphate removal. Compared with SO42−, CO32−showed more negative effect on nutrient removal due to the reaction between Mg2+ and CO32−. The results showed that the nutrient removal amount and the morphology and composition of collected products were not affected in the presence of acetic acid. Citric acid, humic acid, and fulvic acid displayed the inhibition effects on the morphology of the crystallized products.