Abstract
Inorganic and organic phosphate adsorption by iron–manganese (Fe–Mn) plaques extracted from reed roots was investigated. Scanning electron microscopy indicated the roots had rough surfaces and fine particles attached. X-ray photoelectron spectra indicated that Fe and Mn in the Fe–Mn plaques were mainly in the +III and +IV oxidation states, respectively. The contact time, initial phosphate concentration, and temperature effects on inorganic and organic phosphate adsorption were investigated by performing batch tests. Pseudo-second-order model described inorganic and organic phosphate adsorption, indicating the chemisorption was the dominant adsorption process. Langmuir and Freundlich isotherm models were fitted to the equilibrium data, and the Langmuir model fitted best. The maximum inorganic and organic phosphate adsorption capacities at 298 K were 7.69 and 3.66 mg/g, respectively. The inorganic and organic phosphate adsorption processes were spontaneous and exothermic. The inorganic phosphate adsorption capacity was higher than the organic phosphate adsorption capacity, and the presence of organic phosphate did not negatively affect adsorption at inorganic to organic phosphate molar ratios between 1:1 and 3:1. Fourier-transform infrared spectra before and after adsorption showed abundant functional groups on Fe–Mn plaques and that phosphate was probably adsorbed via replacement of hydroxyl groups and inner-sphere surface complexation.
Highlights
Discharges of domestic sewage and agricultural wastewater containing phosphorus-rich chemicals, such as detergents and chemical fertilizers, into lakes and rivers can cause nutrient enrichment, excess algal growth, and eutrophication [1,2,3]
features called iron–manganese (Fe–Mn) plaques were extracted from reed roots from a long-established wetland, and the abilities of the plaques to adsorb inorganic and organic phosphates were assessed
The reed roots with and without Fe–Mn plaques attached were examined by scanning electron microscopy (SEM) using an S-3500N instrument (Hitachi High-Technologies)
Summary
Discharges of domestic sewage and agricultural wastewater containing phosphorus-rich chemicals, such as detergents and chemical fertilizers, into lakes and rivers can cause nutrient enrichment, excess algal growth, and eutrophication [1,2,3]. In China, phosphorus residues in wastewater treatment plants effluent are generally removed primarily using a wetland system before the effluent is discharged into a water body. In such wetland systems, phosphorus is removed by plant uptake, media adsorption, and microorganism assimilation [4,5,6]. Chong et al [15] found that amorphous iron oxide on root surfaces caused phosphorus to accumulate in the rhizosphere It has been shown the phosphorus adsorption behaviors and mechanisms by Fe–Mn plaques are not clearly stated, and the influence between inorganic and organic phosphate is ignored. The contributions of Fe–Mn plaques to the removal of inorganic and organic phosphates in wetland systems need to be assessed to improve our understanding of how wetland system habitats may be managed to promote Fe–Mn plaques formation to effectively and sustainably remove phosphorus from water
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