Occurrence And Sorption Mechanisms Of Nutritional Elements(P,Fe) In Lake Environments

Eutrophication is one of the major pollution problems for many freshwater lakes and can significantly impair water use, especially in lakes from the Yangtze Delta and the Southwestern Plateau in China. It is essential to study the species of nutrient elements in lake ecosystems and the effect of dissolved organic matter (DOM) on the fate and transport of phosphorus between sediment-water interface is one of the key elements for further understanding the mechanism of eutrophication. Restoration of these eutrophic lakes should fundamentally be managed by reducing the phosphorus.In this research, the fundamental objective was to(1) investigate the species, distributions and transport of inorganic and organic phosphorus in ecosystems of Lake Dianchi by solid and solution31P nuclear magnetic resonance spectroscopy;(2) study the sorption behavior of phosphorus with and without FA on surface sediment of Lake Dianchi.(3) prepared a selective Fe(Ⅲ) imprint sorbent for dissolved Fe(Ⅲ) separation and preconcentration from natural water samples; and (4) prepared an effective and environmentally safe phosphorus adsorbent for phosphorus control in eutrophic lakes. The major research achievements are summarized as follows:(1) Several P species, including orthophosphate, orthophosphate monoesters, phospholipids, DNA, pyrophosphate were detected by solution31P NMR. Results show that P in the extracts was dominated by inorganic orthophosphate with small amounts of pyrophosphate which may be partially of biogenetic. The forms of organic P compounds in blue algae, suspended matter and surface sediments are generally similar. Results indicate that orthophosphate monoesters dominate the organic P pool in all samples, followed by orthophosphate diesters which highly degradable in Dianchi lake waters. Solid state31P NMR spectroscopy revealed that polyphosphate was an important inorganic P species should be reconsidered in Lake Dianchi P cycling. Suspended matter and surface sediment contained more Ca and Mg species of inorganic and organic P. These results also indicate that using solid or solution NMR technology only may misleading our understanding about inorganic and organic P forms cycling in lake waters.(2) Effects of DOM extracted form soil on phosphorus sorption behavior between sediment-water interfaces were studied through sorption experiment. The results indicate that DOM did not show much effect on phosphorus sorption kinetics. The concentration of natural adsorbed phosphorus (NAP) and EPC0reduced significantly upon addition of FA with low phosphorus concentration. Under high concentration conditions, phosphorus sorption capacity was increased about40%when FA was added. Pseudo-second order kinetic equation and Langmuir equation are more suitable than others to describe the sorption behavior of phosphorus on the surface sediment of Lake Dianchi. The equilibrium constant K°was increased and the ΔG°values were decreased in the sorption process by adding FA indicate that much more phosphate adsorption sites at the surface sediment of Lake Dianchi should be formed.(3) A double template imprinted sorbent with chelating diamines was prepared by sol-gel process for the selective separation and enrichment of trace Fe(Ⅲ) from natural water samples prior to its determination by FAAS. Compared with the CTAB imprinted sorbent (CTAB-imp) and the Fe(Ⅲ) imprinted sorbent (Fe-imp), the double template imprinted sorbent (Fe-CTAB-imp) had higher selectivity and adsorption capacity for Fe(Ⅲ). The sorption isotherms on the Fe-CTAB-imp conformed to the Langmuir equation, and the theoretical sorption capacity was36.90±3.16mg/g. Furthermore, the Fe-CTAB-imp possessed fast sorption kinetics for Fe(Ⅲ) from aqueous solution with a saturation time of less than5min, and could be used repeatedly. Combined with FAAS, the method detection limit for Fe(Ⅲ) could reach the level of0.26ng/mL. This sorbent has been successfully applied to the separation and determination of trace Fe(Ⅲ) in reference materials, artificial seawater, fresh water and nearshore seawater samples with satisfactory results.(4) A novel phosphorus (P) adsorbent, magnesium oxide-modified diatomite (MOD) was developed and characterized in this study. The MOD was made through surface modification treatments, including NaOH treatment and magnesium hydroxide deposition on raw diatomite and subsequently calcinated in air at450℃. The specific surface area of72.53m2/g for the MOD, which is an113-fold increase over the raw diatomite (0.64m2/g). The surface modification also increased the point of zero charge values to9.6for the MOD from4.5for the raw diatomite. Phosphorus adsorption behavior and adsorption mechanism of MOD were investigated in the research. Because of increased surface area and surface charge, the maximum adsorption capacity of MOD at pH5.0was increased from4.5mg P/g of raw diatomite to45.72mg P/g. Phosphorus showed the best affinity of adsorption onto MOD among common anions. XRD and31P NMR spectra demonstrate that P is adsorbed on the surface layer of MOD. Phosphorus removal from lake water by MOD was examined. Phosphorus removal from lake water proceeded primarily through P adsorption onto the surface of MOD. When a dose of MOD of300mg/L was applied to lake water, a total phosphorus (TP) removal efficiency of above90%was achieved and a residual TP concentration was15.0μg/L which falls within the oligotrophic TP range (3.0-17.7μg/L).