Initial Phosphate Concentration Research Articles

Optimization of photo fermentation in corn stalk through phosphate additive

Phosphorus is an essential nutrient for microbial growth which effectively influences the bio‑hydrogen production process. In the present study, the effect of phosphate concentration on simultaneous saccharification fermentation (SSF) hydrogen production by phototrophic microbial consortium has been investigated at various initial pH conditions (6, 7 and 8). The experimental results show that the hydrogen yield has been improved through the addition of phosphate, depending on initial pH and phosphate concentration. The maximum hydrogen yield of 63.09 ± 0.38 mL/g TS and highest energy conversion efficiency of 4.14 ± 0.02% from raw corn stalk were achieved at the phosphate concentration of 4 mmol/L with initial pH value of 6. We have shown that hydrogen yield for raw corn stalk can be enhanced by selecting appropriate amount of the additive. These results may help in optimization of the hydrogen production yield at industrial scale.

Removal of phosphate by Donnan dialysis coupled with adsorption onto calcium alginate beads.

In this study the removal of phosphates from solution by Donnan dialysis and by adsorption onto calcium alginate beads were studied separately and then together. This hybrid process was conducted in order to benefit from each process, and it is an original and new combination. First, the Donnan dialysis process was performed with different parameters: the type of counter-ion, the concentration of the counter-ion, the initial phosphate concentration, the pH of the solution and the choice of anion-exchange membranes. Donnan dialysis achieved 68% and 12.5% phosphorus removal with AMX and AFN membranes respectively. Then a preliminary study into the adsorption of phosphate onto calcium alginate beads was carried out. A full factor design was applied in order to determine the effect of the main parameters and their mutual interactions for the adsorption process. The removal of phosphate onto calcium alginate beads reached 82.5%. Finally, coupling Donnan dialysis with adsorption onto calcium alginate beads for the removal of phosphate reached 89.5% with the AMX membrane. This hybrid process can be considered to be a solution for improving the contact time and for enhancing the removal of phosphate by 10% compared to adsorption onto calcium alginate.

Efficient phosphate removal from contaminated water using functional raw dolomite powder

Phosphate, when present in water, forms one of the basic nutrients that lead to eutrophication and its associated negative impacts. The use of raw dolomite powder as an adsorbent was found to be very effective in the removal of phosphates from various waters and wastewater matrices. Ayoub and Kalinian (Water Environ Fed 78:353–361, 2006) reported phosphate removals, amounting to 100%, over more than 300 bed volumes at inflow concentrations between 0.30 and 0.40 mg/L. This marked achievement led to the present study with the objective of defining the effects of the various parameters involved in the process and determining the optimal operating condition to achieve effective and sustainable removal efficiencies. Experimental work was conducted by passing three types of influent water and two types of wastewater jacked with a phosphate salt (KH2PO4) through a fluidized column bed of dolomite powder, where the effect of various parameters, including system operation mode, adsorbent particle size, rate of flow through the bed (contact time), initial phosphate concentration, influent pH, and the presence of competing anionic solutes on the adsorption of phosphate was evaluated. The results asserted that the most effective mode of operation for the system was the fluidized bed configuration. Results further showed that the smaller-sized dolomite powder (< 0.074 mm) sustains better adsorption. Also, higher contact time and lower feed phosphate concentration result in increased adsorption. Adsorption capacity was found to decrease with increased influent pH values. Competitive adsorption with existing anions was noted to occur, leading to reduced efficiency in phosphate removal. The Thomas and Yoon–Nelson models were deemed to agree best with the experimental data, while the Thomas model was determined to be the most descriptive of the column runs and to produce the most accurate predictive results. The use of dolomite as an adsorbent in the removal of phosphates, considering its wide availability, ease of application and regeneration capability, if operated under optimal conditions as determined by the present study, will present a highly sustainable process with added advantages over the more complex and costly adsorbents.

Application of red-mud based ceramic media for phosphate uptake from water and evaluation of their effects on growth of Iris latifolia seedling

In the present study, we have produced red-mud based ceramic media (RMCM) as an adsorbent for removal of phosphate from aqueous solutions, and their application in a constructed wetland. Phosphate adsorption to RMCM was investigated by varying initial phosphate concentration, contact time, and temperature. Adsorption of phosphate to the surface of RMCM was confirmed by scanning electron microscope and energy dispersive X-ray spectroscopy. The surface area and pore volume of RMCM decreased significantly after phosphate adsorption. Experimental equilibrium data followed Langmuir and Sips model better than the Freundlich model. Kinetic data followed both pseudo first order and pseudo second order reactions. Thermodynamics suggested the phosphate adsorption process onto RMCM to be endothermic and spontaneous, and physisorption dominated. Fourier transform infrared spectrumof phosphate adsorbed RMCM did not show any PO specific bands thus ruling out role of chemical forces in phosphate adsorption. Overall, phosphate adsorption on RMCM was driven by physisorption. The RMCM promoted biomass growth and increased the surface area of roots in Iris latifolia. Together with RMCM, I. latifolia augmented removal of phosphate from aqueous solution. Based on their phosphate removal performance and plant-growth promoting effects, we believe that RMCM can be effectively used in constructed wetlands.

Fractionating various nutrient ions for resource recovery from swine wastewater using simultaneous anionic and cationic selective-electrodialysis

Different from current nutrient recovery technologies of recovering one or two nutrient components (PO43− or NH4+) from wastewater, this study aimed to fractionate various nutrient anions and cations simultaneously, including PO43−, SO42−, NH4+, K+, Mg2+ and Ca2+, into several streams. The recovered streams could be further paired together to produce high-value products. A novel electrodialysis process was developed by integrating monovalent selective anion and cation exchange membranes into an electrodialysis stack. Results revealed that nutrient recovery was achieved effectively by fractionating PO43− and SO42− into the anionic product stream, whereas bivalent cations (Mg2+ and Ca2+) were extracted in the cationic product stream and the monovalent cations (K+ and NH4+) were concentrated in the brine stream. For the permeation capabilities of anions, SO42− and Cl− possessed the higher preference, whereas PO43− permeated the membrane more difficult. As to the cations, the permeation sequence was: NH4+≈K+ >Ca2+>Mg2+≈Na+. Enhancing voltage values not only promoted ion migration rates, but also led to the increase of energy consumption. Although elevating initial phosphate concentration in the anionic product streams from 60 mg/L to 470 mg/L did not influence phosphate fractionation significantly, the current efficiency decreased from 3.55% to 0.65% and a remarkable increased of energy consumption from 29.42 kWh/kg NaH2PO4 to 160.13 kWh/kg NaH2PO4 was observed. Further experiments were conducted for phosphorus recovery by pairing two recovered product streams, which revealed that phosphate precipitation could be achieved by using inherent Ca2+ and Mg2+ in the wastewater without dosing external cation sources.

The removal of phosphates using electrocoagulation with Al−Mg anodes

The removal of phosphates, to levels below the detection limit, was achieved over a 30 to 60min period, depending on the initial phosphate concentration, with Al−Mg anodes in an electrocoagulation cell at 11.0mAcm−2 with a surface area to volume ratio of 11.7m−1. The Al−Mg alloy performed well in low chloride concentrations of 4.2mM NaCl and the complete removal of phosphates from two real water samples was achieved after a 15−min period. The removal efficiency, although depending on the initial pH, appears to depend on the evolution of pH during electrocoagulation with more efficient removal at a final pH of 7.5. Using the Freundlich adsorption model, the adsorption capacity, kF, was computed as 146mgg−1, corresponding to the adsorption of 146mg of phosphate per gram of the aluminium−hydroxy coagulant. The efficient removal of the phosphates was attributed to the low corrosion potentials and the lack of a passive region observed using polarisation and cyclic polarisation experiments, which in turn facilitate dissolution of the anode.

Recovery and utilization of phosphorus in wastewater by magnetic Fe3O4/Zn-Al-Fe-La layered double hydroxides(LDHs)

Layered double hydroxides (LDHs) are the promising minerals which can adsorb phosphates, moreover, phosphorus-containing LDHs can be used for fertilizers. In this study, we tested the ability of magnetic Fe3O4/Zn-Al-Fe-La -LDH to remove and recover phosphate from simulated sewage. Results demonstrated that a magnetic Fe3O4/Zn-Al-Fe-La-LDH dose of 1.2 g/l could achieve a maximum adsorption capacity of 169.5 mg/g under an initial phosphate concentration of 200 mg/L, an equilibrium contact time of 24 h and a pH of 4. The adsorption kinetics of phosphate onto the magnetic Fe3O4/Zn-Al-Fe-La-LDH were well governed by the pseudo-second-order kinetic model, and the adsorption data fit well to the Langmuir isotherms. After four adsorption-desorption cycles, the LDH still had an adsorption capacity of 31 mg/g, demonstrating its reusability. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis indicated that ion exchange occurred between phosphate and the interlayer anions, and that phosphate was inserted into the double structure of the adsorbent. ICP-OES analysis showed that the LDH was stable and did not release the metal ions into water. The phosphorus-adsorbed LDH (P-LDH) has the potential to be used as a slow-release fertilizer to increase the growth of the soybeans Glycine max. The absorption of the metal into the soybeans was also reduced, which proved that the application of this type of LDH is non-toxic to plants.

Phosphate Removal from Secondary Effluents Using Coal Gangue Loaded with Zirconium Oxide

Phosphorus from secondary effluents and coal gangue from coal mining have caused serious environmental problems. The feasibility of phosphate removal from secondary effluents using calcinated coal gangue loaded with zirconium oxide (CCG-Zr) was explored. Major influencing factors like the calcinated temperature, CCG-Zr ratio, adsorbent dose, time and solution pH, etc. were investigated. Newly developed CCG-Zr accomplished a significantly higher phosphate removal for phosphate (93%) compared with CCG (35%) at a calcinated temperature of 600 °C and CCG-Zr mass ratio of 1:1. For CCG-Zr the maximum phosphate removal rate (93%) was noted at an initial phosphate concentration of 2 mg/L within 20 min. The CCG-Zr displayed a higher phosphate removal rate (85–98%) over a wide range of solution pH (2.5~8.5). The adsorption isotherms fitted better to the Freundlich (R2 = 0.975) than the Langmuir model (R2 = 0.967). The maximum phosphate adsorption capacity of the CCG-Zr was 8.55 mg/g. These results suggested that the CCG-Zr could potentially be applied for the phosphate removal from secondary effluents.

Effective phosphorus removal using chitosan/Ca-organically modified montmorillonite beads in batch and fixed-bed column studies.

In this study, phosphorus removal from aqueous solution was investigated using chitosan/Ca-organically modified montmorillonite (chitosan/Ca-OMMT) beads in batch and fixed-bed column systems. The XPS spectra confirmed that the calcium ions on the surface of the beads play a dominant role in capturing phosphate ions through surface complexation. The batch adsorption experimental data were fitted with pseudo-second-order kinetics and the Langmuir isotherm. The maximum adsorption capacity of the chitosan/Ca-OMMT beads was found to be 76.15 mg/g at an initial phosphate concentration of 100 mg/L at 25 °C. High phosphate uptake is achieved over the wide pH range 3-11, as well as in the presence of competing anions such as Cl-, NO3-, SO42-, and HCO3-. Furthermore, the chitosan/Ca-OMMT beads can be easily regenerated using 0.1 mol/L NaOH as a desorption agent with more than 83.97% adsorption capacity remaining after five adsorption/desorption cycles. The Thomas, Yoon-Nelson, and Adams-Bohart models were applied to the experimental data to predict the breakthrough curves using non-linear regression; the Yoon-Nelson model showing the best agreement with the breakthrough curves. These findings demonstrate that chitosan/Ca-OMMT beads can be used as a cost-effective and environment-friendly adsorbent for the removal of phosphate from wastewater.

Synthesis of industrial solid wastes/biochar composites and their use for adsorption of phosphate: From surface properties to sorption mechanism

This paper demonstrates the synthesis of industrial solid wastes /biochars. The produced materials were characterized by means of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR). The composites were investigated for the phosphate removal from the aqueous solution. The effect of pH on removal rate was studied in the range from 3 to 12. The kinetic experimental data for phosphate adsorption was confirmed to follow pseudo-second-order kinetics with R2 > 0.99. Batch adsorption experiments revealed the suitability of the Freundlich model to describe the phosphate adsorption by FA B-F, CG B-F, while Langmuir model was suitable for B-F (where FA: fly ash, CG: coal gangue, B: biochar, and F: ferrite). The maximum adsorption capacities of the three different samples at an initial phosphate concentration of 30 mg/L were 2.39 mg/g with B-F, 3.08 mg/g with FA B-F, and 3.20 mg/g with CG B-F. The experimental results demonstrate that the industrial solid wastes/biochar is a promising alternative material for the restoration of eutrophic water.

Adsorption of phosphate on iron oxide doped halloysite nanotubes

Excess phosphate in water is known to cause eutrophication, and its removal is imperative. Nanoclay minerals are widely used in environmental remediation due to their low-cost, adequate availability, environmental compatibility, and adsorption efficiency. However, the removal of anions with nanoclays is not very effective because of electrostatic repulsion from clay surfaces with a net negative charge. Among clay minerals, halloysite nanotubes (HNTs) possess a negatively charged exterior and a positively charged inner lumen. This provides an increased affinity for anion removal. In this study, HNTs are modified with nano-scale iron oxide (Fe2O3) to enhance the adsorption capacity of the nanosorbent. This modification allowed for effective distribution of these oxide surfaces, which are known to sorb phosphate via ligand exchange and by forming inner-sphere complexes. A detailed characterization of the raw and (Fe2O3) modified HNTs (Fe-HNT) is conducted. Influences of Fe2O3 loading, adsorbent dosage, contact time, pH, initial phosphate concentration, and coexisting ions on the phosphate adsorption capacity are studied. Results demonstrate that adsorption on Fe-HNT is pH-dependent with fast initial adsorption kinetics. The underlying mechanism is identified as a combination of electrostatic attraction, ligand exchange, and Lewis acid-base interactions. The nanomaterial provides promising results for its application in water/wastewater treatment.

Adsorptive removal of phosphate from aqueous solutions by thermally modified copper tailings.

In this study, thermally modified copper tailings (TMCT) were used to adsorb phosphate in aqueous solutions through experiments. The characterization of TMCT and unmodified copper tailings (UMCT) was done by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The effects of pH, adsorbent dosage, contact time, and initial phosphate concentrations on phosphate adsorption were investigated. We studied the adsorption ability of TMCT and UMCT at 298K, and the Langmuir isotherm model closely described the adsorption isotherm data, indicating that the maximum adsorption capacity (Qmax) of the TMCT and UMCT was 14.25mgg-1 and 2.08mgg-1, respectively. In addition, the adsorption isotherms of TMCT were analyzed at 288K, 298K, and 308K, and the calculated Qmax of phosphate were 9.83mgg-1 at 288K, 14.25mgg-1 at 298K, and 11.55mgg-1 at 308K. Finally, the concentration of copper in the effluent was checked, and the content was 130mgL-1. Then, the effluent was adsorbed by Eichhornia crassipes stem biochar; after adsorption, the concentration of the secondary effluent was 0.7mgL-1, which is lower than the grade II classification (1.0mgL-1) of the integrated wastewater discharge standard (GB8978-1996). The results suggest that the TMCT can be effectively and environmentally friendly used to adsorb phosphate from aqueous solutions.

Fabrication of Phosphate-Imprinted PNIPAM/SiO₂ Hybrid Particles and Their Phosphate Binding Property.

A SiO2 microsphere imprinted by phosphate ions was prepared with the use of phosphate ion as the template molecule and tetraethoxysilane as the precursor. Thereafter, the imprinted SiO2 microspheres were modified with 3-(trimethoxysilyl)propyl methacrylate (TMSPMA@SiO2), followed by introducing the double bond. In the presence of TMSPMA@SiO2, using N-isopropylacrylamide as monomer, and potassium persulfate as initiator, polymer/inorganic hybrid particles (PNIPAM/SiO2) were prepared. Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption-desorption test, and transmission electron microscope were employed for the characterization of molecular imprinted SiO2 microspheres and PNIPAM/SiO2 hybrid particles. The effects of phosphate concentration, pH value, and adsorption temperature on the phosphate binding properties of PNIPAM/SiO2 hybrid particles were studied by UV-vis spectrophotometer. The experimental results shed light on the fact that the PNIPAM structure is beneficial for the improvement of the adsorption ability of phosphate-imprinted SiO2 microspheres. With the increase in the initial phosphate concentration, the adsorption capacity of hybrid particles to phosphate ions increased to 274 mg/g at pH = 7 and 15 °C. The acid condition and the temperature below the low critical solution temperature (LCST) of PNIPAM are favorable to the adsorption of phosphate ions by PNIPAM/SiO2 hybrid particles, and the maximum adsorption capacity can reach 287 mg/g (at pH = 5 and 15 °C). The phosphate imprinted polymer/inorganic hybrid material is expected to be put to use in the fields of phosphate ions adsorption, separation, and recovery.

Phosphorus recovery as calcium phosphate by a pellet reactor pre-treating domestic wastewater before entering a constructed wetland

Horizontal subsurface flow constructed wetlands poorly remove phosphorus from wastewater, resulting in phosphorus levels above the required limits in constructed wetland effluents. Since a pellet reactor can recover phosphorus through calcium phosphate precipitation/crystallization, using it as a pre-treatment system prior to horizontal subsurface flow constructed wetland could be a sustainable solution for phosphate scarcity. The operational conditions required for phosphate recovery in a pellet reactor were evaluated and compared with the Visual MINTEQ version 3.0 with the aim of checking its suitability to simulate the pellet reactor removal efficiencies. Such conditions include the initial phosphate concentration, pH, [Ca]/[P] molar ratio and hydraulic loading rate. The results showed an increase in phosphate removal efficiency with increased initial phosphate concentration, pH, [Ca]/[P] molar ratio and decreased hydraulic loading rate. However, the model calculation gave higher removal efficiencies than experimental results due to its inability to take into account the system kinetics which is an important component in pellet reactor operation and its assumption that precipitation reactions take place at constant pH. The effects of carbonate on phosphate precipitation were also investigated, and the removal efficiency of 61.9% without carbonate was improved to 63.2, 64.3 and 66.4% with a carbonate concentration of 0.25 mM, 0.5 mM and 2 mM, respectively, at pH 9, initial phosphate concentration of 1 mM, [Ca]/[P] molar ratio of 1.5 and hydraulic loading rate of 57 m/h. Thus, the presence of carbonates in domestic wastewater is advantageous as it promotes calcium phosphate precipitation in a pellet reactor.

Enhanced Removal of Phosphates by the Adsorbent Consisting of Iron Oxide Loaded on Porous Chitosan/Cellulose Acetate Particle

The effective and economical removal of phosphates from aqueous solution, mostly applied in waste water treatment, is one of the significant issues globally. Removal of phosphates ions in aqueous solution was analysed by chitosan blended with cellulose acetate, and iron oxide loaded chitosan-cellulose acetate adsorbents. The adsorbents were made in the form of beads. Batch experiments were performed to investigate the performance of the beads under various conditions on phosphate adsorption. Contact time, effect of initial phosphate concentration, adsorbent dosage, pH and temperature were investigated. Zeta potential measurements were also undertaken. The results showed that the adsorption process was highly pH dependent. The adsorption kinetics data were modelled with the application of adsorption reaction models and adsorption diffusion models. The results revealed that the pseudo 2nd order model was the best fitting in all cases. The experimental data were tested with Langmuir and Freundlich isotherms. The equilibrium data were well fitted to the Langmuir isotherm model with a maximum adsorption capacity of 958 μg/g. The Freundlich isotherm model also had a close fit with a maximum adsorption of 233 μg/g, which was very close to the experimental maximum adsorption. The mechanism of adsorption followed two stages in which the first one was fast followed by a slower gradual stage. SEM images showed that the adsorbent was macroporous. Fourier Transform Infrared Red (FT-IR) Spectroscopy, X-ray Diffraction Spectroscopy (XRD) and X-ray photoelectron Spectroscopy (XPS) showed that the phosphate adsorption on the HFO-CS/CA beads was due to surface complexes, and mainly involved Nitrogen atoms. HFO loading also increased surface area.

Adsorption Behavior of Inorganic and Organic Phosphate by Iron Manganese Plaques on Reed Roots in Wetlands

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.

Removal of Phosphate by Ivory Coast Shale in a Homogeneous Reactor and Under Hydrodynamic Conditions: Influence of Soluble Species

AbstractDeveloping low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L−1 showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

Use of Powdered Cockle Shell as a Bio‐Sorbent Material for Phosphate Removal from Water

In this study, powdered cockle shell was used as a bio‐sorbent material for the removal of phosphates in water. The SEM–EDX, XRD, and FT‐IR analyses showed that calcium carbonate (CaCO3) exists in aragonite state in powdered cockle shell. The influences of pH, initial phosphate concentrations and contact time were conducted in a series of batch sorption experiments. Among the various factors studied, the pH was turned out to be a key variable for phosphate removal. Based on the experimental results for pH, it was found that the phosphate is chemically sorbed onto aragonite surface. At lower phosphate concentration, roughly 88% of sorption efficiency was accomplished by powdered cockle shell. The Pseudo‐second‐order kinetic and the Langmuir isotherm model were fitted well to the sorption experimental data of phosphate because of their higher correlation coefficients (R2).

Effect of physical and chemical parameters on the β-Tricalcium phosphate synthesized by the wet chemical method

In this paper, the synthesis of nanosized powders β -Tricalcium phosphate β -Ca3(PO4)2 was studied by the wet chemical method at different values of reaction temperature, initial concentration of diammonium hydrogen phosphate (NH4)2HPO4, calcium nitrate tetrahydrate Ca(NO3)2·4H2O addition rate, pH of reaction and aging time. All these parameters have a great impact on the properties of the resulting β-TCP nano powders. Analysis results of morphology, structure of TCP powder from infrared (IR) spectra, X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the synthesized TCP powder had spherical crystal shape with crystallite size, calculated by XRD method, less than 60 nm, mono and biphasic structure composed of βTCP with pyrophosphate calcium or hydroxyapatite. The variation of the synthesis conditions did not affect the morphology, but it affect the size of crystallites and particles.

Hydrated lanthanum oxide-modified diatomite as highly efficient adsorbent for low-concentration phosphate removal from secondary effluents

The requirement to the phosphorus (P) emission from wastewater treatment plants (WWTPs) is becoming increasingly strict, which makes an advanced treatment for the low-concentration phosphate removal from secondary effluents indispensable. In present work, hydrated lanthanum (La) oxide-modified diatomite composites (La-diatomite) were fabricated by a facile method and employed as the highly efficient adsorbent for the low-concentration phosphate removal from simulating secondary effluents. Comparative experiments indicated that the La-diatomite treated by 0.1 mol/L LaCl3 exhibited the highest La availability (P/La molar ratio of 2.30) and performed good selectivity to phosphate adsorption even with the coexistence of competing anions and humic acid. The maximum P adsorption capacity reached to 58.7 mg P/g and the 96% P was removed quickly within 30 min at initial phosphate concentration 2 mg P/L. Insignificant La leaching was observed during the process due to the La stabilization by macroporous diatomite. Eight cycles of adsorption-desorption experiments revealed that the excellent repeated use property of La-diatomite. At the column test, La-diatomite showed superior treatment capacities of 3455 kg water/kg La-diatomite for simulated secondary effluents. The La-diatomite maintained high and stable adsorption effectiveness in wide pH range, which should be attributed to the synergistic effect of electrostatic interactions, ligand exchange and Lewis acid-based interaction. This work might provide a candidate for low-concentration phosphate removal from secondary effluent to alleviate the eutrophication.