Initial Phosphate Concentration Research Articles

Phosphate removal by Ce(III)‐impregnated crosslinked chitosan complex from aqueous solutions

A novel adsorbent, Ce(III)‐impregnated crosslinked chitosan complex (Ce‐CCS) was prepared by the methods of membrane‐forming and crosslinking for the removal of phosphate from aqueous solutions. Ce‐CCS was characterized by FTIR, X‐ray diffraction, and scanning electron microscopy combined with EDAX techniques. The adsorption of phosphate onto the Ce‐CCS was determined in batch systems as a function of initial phosphate concentration, pH, contact time, and co‐anions. The maximum adsorption occurred at pH 3 or so. The presence of co‐anions decreased the adsorption of phosphate onto the Ce‐CCS. Ce‐CCS showed a higher adsorption capacity than crosslinked chitosan (CCS) due to the introduction of Ce(III). The equilibrious data by the Ce‐CCS were fitted well with Freundlich isotherm model. The kinetic data followed the pseudo‐second‐order model. Phosphate adsorption mainly included the surface complexation and electrostatic attraction between Ce‐CCS and phosphate. Besides, the Ce‐CCS was prone to regeneration with 0.1 mol/L HCl solution. POLYM. ENG. SCI., 57:44–51, 2017. © 2016 Society of Plastics Engineers

Phosphate removal using zinc ferrite synthesized through a facile solvothermal technique

To develop a phosphate adsorbent in powder form that is easily separated from water, we prepared magnetic spinel zinc ferrite using a facile solvothermal technique. Characterization of zinc ferrite was done by VSM, XRD, TEM, and FTIR measurements. We found that zinc ferrite crystallized as a cubic ZnFe2O4 phase (JCPDS card no. 89-1010). It had a saturation magnetization of 34.95emu/g, which allowed easy separation using a magnet. Phosphate adsorption under different initial phosphate concentrations, solution pH values, ionic strengths, temperatures, contact times, as well as in the presence of competitive ions, was investigated. Data from kinetic experiments fit well the pseudo-second-order model. The maximum adsorption capacity obtained by fitting adsorption isotherm data to the Langmuir model ranged within 5.23–6.28mg/g at different temperatures. Thermodynamic parameters indicate that phosphate adsorption by zinc ferrite is an endothermic and spontaneous process. The amount of phosphate adsorbed increased with decreasing pH and increasing ionic strength. Zinc ferrite showed good selectivity for phosphate. Results suggest that phosphate adsorbed onto the zinc ferrite surface via formation of an inner-sphere complex.

Removal of phosphate using iron oxide nanoparticles synthesized by eucalyptus leaf extract in the presence of CTAB surfactant

This study investigated the use of cetyltrimethylammonium bromide (CTAB) as a stabilizer in green synthesis to improve the reactivity of iron oxide nanoparticles (IONP). Results show that efficiency in removing phosphate increased from 71.0% to 97.3%. To understand how to improve the reactivity of IONP by CTAB: firstly, characterizations of IONP before and after phosphate removal by SEM, EDS, FTIR, XPS show the adsorption of P onto the IONP; secondly, batch experiments indicate that the adsorption capacity of phosphate increased when temperature or initial phosphate concentration increased and decreased with an increase in both adsorbent dose and pH. Adsorption followed the pseudo-second-order kinetics model and the equilibrium data fitted well to the Langmuir isotherm. Thermodynamic data confirmed the spontaneous and endothermic nature of the adsorption process. Finally, it was proposed that the adsorption of phosphate using CTAB-modified IONP was mainly associated with inner-sphere complexing mechanism and electrostatic attraction.

Kinetics, isotherms and multiple mechanisms of the removal for phosphate by Cl-hydrocalumite

A laboratory study was conducted to evaluate phosphate removal from aqueous solutions by a CaAl-Cl layered double hydroxide (Cl-hydrocalumite). Cl-hydrocalumite was prepared by co-precipitation and was characterized by scanning electron microscopy equipped with energy-dispersive spectrometer (SEM-EDS), powder X-ray diffraction (PXRD), and Fourier transform infrared (FTIR). SEM demonstrated that a crystalline structure was synthesized and PXRD or FTIR spectra revealed that the structure was Cl-hydrocalumite. Adsorption experiments were performed as a function of contact time and initial phosphate concentration. Phosphate adsorption reached equilibrium within 10h, followed by a pseudo-second-order kinetic model with R2=0.999. The experimental data followed the Langmuir and Fedlich-Peterson isotherm models, and showed a maximum adsorption capacity of ~182.5mgg−1. The Freundlich constant n=3.18>1, represented a favorable phosphate adsorption process. SEM-EDS, PXRD, and FTIR analyses of P-hydrocalumite (after adsorption) were used to elucidate adsorption mechanisms. EDS results indicated that chloride was topotactic, exchanged by phosphate to generate P-hydrocalumite, and partial Cl-hydrocalumite was dissolved. The PXRD and FTIR spectra indicate that P-hydrocalumite was a mixture with a new precipitate, brushite. Phosphate adsorption by Cl-hydrocalumite was topotactic anion exchange combined with dissolution–precipitation. Cl-hydrocalumite was a cost-effective and excellent phosphate adsorbent.

Ammonia nitrogen removal from acetylene purification wastewater from a PVC plant by struvite precipitation

Acetylene purification wastewater (APW) usually contains high concentrations of ammonia nitrogen (NH4-N), which is generated during the production of acetylene in a polyvinylchloride manufacturing plant. In this study, a struvite precipitation method was selected to remove NH4-N from the APW. Laboratory-scale batch experiments were performed to investigate the effects of the initial APW pH, phosphate (PO4(3-)) concentration, magnesium (Mg(2+)) concentration, and sources of PO4(3-) and Mg(2+) on NH4-N removal. The results indicated that the initial APW pH had a significant effect on the removal of NH4-N, while the other factors had relatively minor effect. The NH4-N could be effectively removed at an optimum initial APW pH of 9.5, when Na2HPO4·12H2O and MgSO4·7H2O were both applied to NH4-N at a ratio of 1.2. Under these conditions, the efficiency of removal of NH4-N, total nitrogen and chemical oxygen demand were 85%, 84% and 18%, respectively. The X-ray diffraction analysis indicated that the precipitates were dominated by struvite. The scanning electron microscopy analysis of the precipitates showed a typical morphology of stick-like and prismatic crystals with coarse surface. The energy dispersive spectroscopy analysis indicated that the precipitates contained P, O, Mg and Ca.

Investigation of phosphate adsorption by a polyethersulfone-type affinity membrane using experimental and DFT methods

A fabricated polyethersulfone (PES)-type affinity membrane was employed for the removal of phosphate from the aqueous solution. Influences of pH, contact time, temperature, and initial phosphate concentration, as well as the coexistent Cl−, SO42-, Ca(II), and Mg(II) on the phosphate adsorption were evaluated. The adsorption kinetics and the adsorption isotherms of this membrane toward phosphate were investigated. In addition, the insight into the phosphate uptake at an atomic-scale was revealed by the density functional theory calculations. The coexistent Cl– and SO42- showed a disturbance on the uptake of phosphate; conversely, the presence of Ca(II) and Mg(II) increased the uptake of phosphate. The negative influence of SO42- was more remarkable than that of Cl– due to the notably nucleophilic nature of this anion. The accelerating role of Ca(II) was stronger than that of Mg(II), because the Ca(II)-loaded membrane exhibited a more stronger affinity to phosphate than the Mg(II)-loaded form. Lagergren second-order and Langmuir models were suitable for describing the adsorption kinetics and adsorption isotherms, and the phosphate adsorption onto the membrane was a spontaneous and endothermic process.

Study on an effective industrial waste-based adsorbent for the adsorptive removal of phosphorus from wastewater: equilibrium and kinetics studies.

In this work, an effective adsorbent for removing phosphate from aqueous solution was developed from modifying industrial waste--lithium silica fume (LSF). The characterization of LSF before and after modification was investigated using an N2 adsorption-desorption technique (Brunauer-Emmett-Teller, BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Studies were conducted to investigate the effect of adsorbent dose, initial solution pH, contact time, phosphate concentration, and temperature on phosphate removal using this novel adsorbent. The specific surface area for modified LSF (LLSF) is 24.4024 m(2)/g, improved 69.8% compared with unmodified LSF. XRD result suggests that the lanthanum phosphate complex was formed on the surface of LLSF. The maximum phosphate adsorption capacity was 24.096 mg P/g for LLSF, and phosphate removal was favored in the pH range of 3-8. The kinetic data fitted pseudo-second-order kinetic equation, intra-particle diffusion was not the only rate controlling step. The adsorption isotherm results illustrated that the Langmuir model provided the best fit for the equilibrium data. The change in free energy (△G(0)), enthalpy (△H(0)) and entropy (△S(0)) revealed that the adsorption of phosphate on LLSF was spontaneous and endothermic. It was concluded that by modifying with lanthanum, LSF can be turned to be a highly efficient adsorbent in phosphate removal.

Operational parameter impact and back propagation artificial neural network modeling for phosphate adsorption onto acid-activated neutralized red mud

In this research the combination of neutralization activation and acid activation processes was employed to improve the physicochemical characters of red mud. In order to better understand the phosphate adsorption behaviors and further improve the phosphate adsorption performance of acid-activated neutralized red mud (AaN-RM), for the first time the impact of operational parameters on phosphate adsorption onto AaN-RM was systematically investigated, and back propagation artificial neural network (ANN) modeling was conducted. The results demonstrated that phosphate adsorption capacity of AaN-RM decreased with the enhancement of adsorbent dosage and the concentration of the competing ion (carbonate), while it increased with the increase of initial phosphate concentration and contact time. The optimal adsorption temperature and initial solution pH for phosphate adsorption onto AaN-RM were 50°C and 4.0, respectively. Moreover, a 6-10-1 feed forward ANN structure with trainlm algorithm was successfully constructed for predicting the phosphate removal by AaN-RM. The RMSE and R2 values for two subsets (training and validation subset, and testing subset) were 3.06 and 2.61, and 0.9932 and 0.9969, respectively. Furthermore, the importance analysis showed that contact time and initial phosphate concentration were the most influential parameters on phosphate removal by AaN-RM, the importance of which reached 24.64% and 22.16%, respectively.

Effect of phosphate on U(VI) sorption to montmorillonite: Ternary complexation and precipitation barriers

Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface.

Basic Oxygen Furnace steel slag aggregates for phosphorus treatment. Evaluation of its potential use as a substrate in constructed wetlands

Basic Oxygen Furnace (BOF) steel slag aggregates from NW Spain were tested in batch and column experiments to evaluate its potential use as a substrate in constructed wetlands (CWs). The objectives of this study were to identify the main P removal mechanisms of BOF steel slag and determine its P removal capacity. Also, the results were used to discuss the suitability of this material as a substrate to be used in CWs.Batch experiments with BOF slag aggregates and increasing initial phosphate concentrations showed phosphate removal efficiencies between 84 and 99% and phosphate removal capacities from 0.12 to 8.78 mg P/g slag. A continuous flow column experiment filled with BOF slag aggregates receiving an influent synthetic solution of 15 mg P/L during 213 days showed a removal efficiency greater than 99% and a phosphate removal capacity of 3.1 mg P/g slag. In both experiments the main P removal mechanism was found to be calcium phosphate precipitation which depends on Ca2+ and OH− release from the BOF steel slag after dissolution of Ca(OH)2 in water.P saturation of slag was reached within the upper sections of the column which showed phosphate removal capacities between 1.7 and 2.5 mg P/g slag. Once Ca(OH)2 was completely dissolved in these column sections, removal efficiencies declined gradually from 99% until reaching stable outlet concentrations with P removal efficiencies around 7% which depended on influent Ca2+ for limited continuous calcium phosphate precipitation.

Phosphate removal from solution by composite of MCM-41 silica with rice husk: Kinetic and equilibrium studies

Composite of MCM-41 silica with rice husk was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTAB) as an organic template, aqueous ammonia solution (NH4OH) and rice husk. Rice husk served as not only a silica source but also as a substrate for the deposition of MCM-41. The synthetic hybrid composites were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) and tested as sorbents for phosphate from aqueous solution. Kinetic data and equilibrium uptake isotherms were measured. The effects of different experimental parameters such as contact time, initial phosphate concentration, solution pH, adsorbent mass, and the presence of competitive ions on phosphate uptake were investigated. The phosphate uptake kinetics were found to be fast and equilibrium was achieved after 30 min. The phosphate uptake was found to be highly pH dependent. Studies on the effects of competing ions, without keeping the initial pH constant, indicated that phosphate uptake and Kd values decreased in the presence of CO32− and NO3−, but SO42− ions showed little or no effect. With keeping the initial pH constant at 6, the presence of these competing ions had no clear effect on the uptake of phosphate. The phosphate uptake by composite of rice husk with MCM-41 could be described well by the Langmuir isotherm equation. Adsorption kinetic data correlated well with pseudo-second-order model, which suggested that the uptake process might be chemical sorption.

The preparation of a cross-linked cerium (III)-loaded alginate bead adsorbent for the removal of phosphate from wastewater

The aim of this study was to prepare a cross-linked cerium(III)-loaded alginate bead (denoted as SA-Ca-Ce) and to apply it to remove phosphate from aqueous solution. The adsorption behaviors were investigated by the batch experiments at various experimental parameters including contact time, initial phosphate concentration, solution pH, temperature, and coexisting anions. The results showed that the Langmuir model is more suitable than the Freundlich model for well elucidation of the experimental data, and the maximum adsorption capacity is calculated to be 41.39 mg/g at 318 K. The adsorption of phosphate, which followed pseudo-second-order kinetics, is a chemisorption process. The phosphate adsorption had a slight decrease with the increasing of pH. The coexistence of other anions in solutions has an adverse effect on phosphate adsorption with the extent following the order: HCO3- > SO42- > Cl−. The phosphate adsorption mechanism was also investigated by scanning electron microscopy, Fourier transform infrareds spectroscopy. The electrostatic interactions and Lewis acid ligand were manifested to be two main mechanisms for phosphate adsorption onto SA-Ca-Ce. All the results indicated that the SA-Ca-Ce has a considerable potential for the phosphate removal from contaminated waters.

Phosphate adsorption from aqueous solutions by Zirconium (IV) loaded cross-linked chitosan particles

In this work, Zirconium (IV) loaded cross-linked chitosan (CCP-Zr) was prepared by membrane-forming and cross-linking, and characterized by FTIR, XRD, SEM and EDX. Batch of experiments were performed to investigate the effects of various factors on the adsorption of phosphate onto CCP-Zr, including adsorbent dosage, initial phosphate concentration, pH value and the presence of co-ions. The experimental data were analyzed by the different adsorption kinetic and isotherm models. The results showed that the kinetic data were well fitted to the pseudo second-order model, and only 20 min was enough to reach adsorption equilibrium. The isotherm data were best described by the Langmuir isotherm model with the maximum monolayer adsorption capacity of 71.68 mg/g at pH 3 and 303 K. The adsorption mechanism was possibly attributed to the electrostatic attraction and ion exchange reaction between CCP-Zr and phosphate ions.

Phosphate adsorption by a Cu(II)-loaded polyethersulfone-type metal affinity membrane with the presence of coexistent ions

A polyethersulfone (PES)-type metal affinity membrane loading Cu(II) was employed to remove phosphate from the solution. Techniques of scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and solid-state nuclear magnetic resonance spectroscopy (NMR) were used to characterize the membrane. Effects of pH, initial phosphate concentration, temperature, contact time, as well as the coexistent Cl−, SO42−, Mg(II), and Ca(II) on the phosphate adsorption by this membrane were evaluated. The adsorption kinetics and the adsorption isotherms of the membrane toward phosphate were investigated. In addition, the breakthrough curves of the membrane were measured. The coexistent Cl−, SO42−, Mg(II), and Ca(II) ions decreases the phosphate uptake of the membrane. Their negative effects on the uptake of phosphate follow the order: SO42−>Mg(II)>Cl−>Ca(II), considering the existent concentrations of them in seawater. Adsorption isotherms and adsorption kinetics of this metal affinity membrane toward phosphate are fitted to the Langmuir and the Lagergren second-order models. The phosphate uptake of the membrane is a spontaneous and endothermic process. In spite of the presence of these four ions, the PES-type metal affinity membrane shows an excellent uptake of phosphate. Therefore, the PES-type metal affinity membrane loading Cu(II) will be valuable for removing phosphate from seawater.

Optimization of phosphate removal from drinking water with activated carbon using response surface methodology (RSM)

The presence of phosphate in water has become a worldwide problem because of improving eutrophication and decreasing the quality of water. In this work, phosphate (PO43-) removal from water using activated carbon was studied and main process parameters such as initial phosphate concentration (C0), adsorbent dosage, and pH of solution have been optimized to obtain maximum removal. Central composite design in response surface methodology (RSM) package has been used to perform the experimental design according to RSM analysis, the phosphate removal model proved to be highly significant with very low probability value (<0.0001). Based on the developed predictive model, the optimum conditions were 0.53 (g/50 mL) adsorbent dosage, pH 4, and C0 = 11.62 (mg/L) for having 95.41% of phosphate removal. This optimum predicted result was investigated by performing the corresponding experiment, and it was observed that the experiment and model result were fitted well. Kinetic data were analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations. According to the results, adsorption of phosphate onto activated carbon is an effective approach and economical alternative process in comparison with common applications.

A novel peat-based biosorbent for the removal of phosphate from synthetic and real wastewater and possible utilization of spent sorbent in land application

Removal of potentially harmful phosphorus compounds from wastewater by adsorption onto biosorbents is a cost-effective alternative to the conventional treatment methods. Raw peat and peat modified with iron(III) hydroxy ions were used in this study to remove phosphate ions from synthetic solution and household wastewater. Interaction of iron(III) ions with carboxylic groups of peat occurred during peat modification, which was confirmed by the FTIR technique. The effect of the initial phosphate concentration, pH, contact time, temperature, and ionic strength was studied in batch experiments. It was found that the sorption capacity increased with the increasing temperature, i.e. the maximum sorption capacity of the modified peat was 9.64 mg P/g at 2°C and 11.53 mg P/g at 40°C, respectively, indicating the endothermic nature of the sorption. Besides, the Langmuir equation was used to describe the sorption isotherms quantitatively. Given that the spent biosorbent did not exhibit phytotoxicity and the concentration of heavy metals did not exceed the limit values, the phosphate-saturated modified peat may be utilized as an organic fertilizer in agricultural land application.

Phosphorus availability modifies carbon production in Coccolithus pelagicus (Haptophyta)

The coccolithophore Coccolithus pelagicus (Wallich) Schiller fixes CO2 into particulate organic carbon (POC) through photosynthesis and into particulate inorganic carbon (PIC) in the form of calcite. To examine the role of phosphorus (P) availability in the production of POC and PIC, C. pelagicus subsp. braarudii (Gaarder) Geisen et al. was grown in semi-continuous cultures at three initial phosphate concentrations (P-replete, 1, and 0.5μM [P]). Reduced P-availability (1 and 0.5μM [P]) decreased POC production, while PIC production only decreased when phosphate concentrations became growth limiting (0.5μM [P]). This decrease has not been observed previously in batch cultures, highlighting the inadequacy of the batch culture approach with regard to determining carbon production. The reduction in growth rate by 50% at 0.5μM [P] was accompanied by a doubling in cell volume (and POC). PIC production was halved, resulting in a lowered PIC to POC ratio. The average number of coccoliths per cell (and PIC content) remained the same among treatments, despite the significant change in cell size. Our data suggest that POC production in C. pelagicus is more sensitive towards a moderate reduction in phosphorus availability than PIC production. Once phosphorus availability limits cell division, however, phosphorus resources are invested into POC rather than PIC production. This reduces cell density and sinking rates, indicating that coccoliths do not act as ballast for reaching deeper nutrient-rich layers under nutrient limitation.

Behaviour of Waterworks Alum Sludge for Phosphate Removal

In the agricultural sector, fertilizer and animal waste are main pollutants to water course. Excessive phosphorus in water bodies may increase the growth of algae and aquatic plant in a pond which leads to eutrophication phenomena. Disposal of alum sludge in landfills can lead to contaminant issues thus, researchers are searching for ways to reduce excessive disposal of waste including alum sludge in landfills. This study provides available options in disposing alum sludge. In this study, continuous column tests were conducted with different initial pH and contact initial phosphate concentrations. The Scanning Electron Microscope indicates that rough alum sludge surface will accelerate the phosphate adsorption rate. This result shows that phosphate removal rate is higher in acidic condition but lower in alkaline condition. In wastewater treatment industries, changing wastewater to pH 4 needs a large amount of chemical additive and suggests that the pH 7 ±0.5 is more suitable in wastewater applications.

Application of nanofilter in removal of phosphate, fluoride and nitrite from groundwater

At present, nanofiltration (NF) technologies find the ever greater use in the water industry, particularly, drinking water supplies. The concentrations of most anions in the groundwater sources are much higher than surface water and in some cases are higher than drinking water standards. In this regard, the aim of this study was to investigate the possibility of application of nanofilters in removing phosphate, fluoride, and nitrite from aqueous solutions. In this research, the effect of different factors including initial concentrations of nitrate, phosphate, and fluoride along with the flow rate were investigated. The results showed that with an increase in the initial concentrations of phosphate, fluoride, and nitrite, along with an increase in flow rate, the removal efficiencies decreased. The maximum removal efficiencies for phosphate, fluoride, and nitrite were 98, 82, and 87%, respectively. According to the findings, NF membrane could be recommended for removing nitrates, fluoride, and phosphate from aqueous solutions.

English

The aim of the present study was the removal of phosphate and nitrate by sodium alginate seagrass (Cymodocea rotundata) beads from aqueous solutions. The adsorption characteristics of phosphate and nitrate on the seagrass beads were optimized under different operational parameters like adsorbent dosage, initial concentration of phosphate and nitrate, retention time and pH. The results showed that 71% of phosphate and 62% of nitrate removal was obtained using this seagrass beads. It is concluded that seagrass beads is a relatively efficient, low cost and easily available adsorbent for the treatment of nutrients rich wastewater. &nbsp; Key words: Biosorption, seagrass, Cymodocea rotundata, nutrients, beads.