Initial Phosphate Concentration Research Articles

Innovative iron‑manganese modified microalgae biochar for efficient phosphate iron removal from water: Preparation and adsorption mechanisms

This study developed a novel FeMn composite biochar (FMBC) with the pyrolysis raw resource of Chlorella, applying for phosphates removal from the aqueous. Under optimal conditions, the FMBC prepared from microalgae achieved a phosphate removal rate of approximately 91.6 % (adsorption capacity: 23.23 mg/g) within 120 min, demonstrating superior adsorption performance compared to the pristine biochar. Response Surface Methodology (RSM) was applied for FMBC preparation optimization. To improve the metal loading capacity of biochar, Ethylene Diamine Tetraacetic Acid (EDTA) was used as a chelating agent during the preparation process. The optimum preparation conditions for FMBC were Fe/biomass(w/w) ratio of 1.25, Mn/biomass(w/w) ratio of 1.10, pyrolysis time of 120 min, and pyrolysis temperature of 650 °C, which presented a large specific surface area (14.681 m2/g), pore volume (0.036 cm3/g) with the rich oxygen-containing functional groups. Phosphorus removal kinetic and isotherm process were better described by pseudo-second-order model and the Dubinin-Radushkevinch (D-R) isotherm. In addition, the optimal adsorption conditions for FMBC were as follows: biochar dosage of 0.1 g, initial pH of 7.0, adsorption temperature of 25 °C, and initial phosphate concentration of 50 mg/L. Physical adsorption, surface complexation, precipitation, electrostatic attractions, and ion exchange were responsible for phosphate adsorption process by FMBC. The main innovation of this study is the use of explosive growth algae to prepare metal-modified biochar for phosphorus removal from water bodies, to realize the goals of resource utilization of waste biomass and eutrophication control in water, which are significant for sustainable development.

Position-Specific Oxygen Isotope Analysis in Inositol Phosphates by Using Electrospray Ionization-Quadrupole-Orbitrap Mass Spectrometry.

Conventional isotope-ratio mass spectrometry measurements obscure position-specific isotope distributions in molecular compounds because these measurements require an initial step that converts compounds into simple gases by combustion or pyrolysis. Here, we used electrospray ionization (ESI)-based Orbitrap mass spectrometry to measure oxygen isotope ratios in the phosphate and hydroxyl moieties of inositol phosphates. A thermal hydrolysis experiment was conducted using 18O-labeled water to examine the position-specific oxygen isotope exchange in inositol hexakisphosphate (IP6) as well as its hydrolysis products IP5, IP3, and PO3 fragments. Measurement precisions of the position-specific and molecular-average oxygen isotope values of inositol phosphates were better than ±1.1‰ and ±0.5‰, respectively. Under optimized ionization and Orbitrap parameters, this level of precision was obtained within 30 min of run time at 60 μM initial concentration of inositol phosphate. The ability to measure phosphate-specific oxygen isotopes in inositol phosphate enabled the quantification of isotope exchange, which did not occur in phosphate on IP6, IP5, IP3, and PO3 fragments, meaning that the change in isotopes should have resulted from hydroxyls in the ring. Isotope mass balance calculations corroborated that hydroxyl oxygens are derived from 18O-labeled water. With the observed sensitivity and precision achieved in this study, Orbitrap IRMS proved to be a promising tool for investigating the position-specific oxygen isotopes in organophosphorus compounds. These outcomes open up numerous potential applications that can expand our understanding of phosphorus cycling in the environment.

Cell-Free Protein Expression by a Reconstituted Transcription-Translation System Energized by Sugar Catabolism.

Cooperation between catabolism and anabolism is crucial for maintaining homeostasis in living cells. The most fundamental systems for catabolism and anabolism are the glycolysis of sugars and the transcription-translation (TX-TL) of DNA, respectively. Despite their importance in living cells, the in vitro reconstitution of their cooperation through purified factors has not been achieved, which hinders the elucidation of the design principle in living cells. Here, we reconstituted glycolysis using sugars and integrated it with the PURE system, a commercial in vitro TX-TL kit composed of purified factors. By optimizing key parameters, such as glucokinase and initial phosphate concentrations, we determined suitable conditions for their cooperation. The optimized system showed protein synthesis at up to 33% of that of the original PURE system. We observed that ATP consumption in upstream glycolysis inhibits TX-TL and that this inhibition can be alleviated by the co-addition of glycolytic intermediates, such as glyceraldehyde 3-phosphate, with glucose. Moreover, the system developed here simultaneously synthesizes a subset of its own enzymes, that is, glycolytic enzymes, in a single test tube, which is a necessary step toward self-replication. As glycolysis and TX-TL provide building blocks for constructing cells, the integrated system can be a fundamental material for reconstituting living cells from purified factors.

Preparation of a novel LC@MWCNTs membrane and its application for enhanced phosphate removal and fouling control

To control the eutrophication originating from phosphate discharge, a novel adsorptive membrane was prepared by vacuum filtrating lanthanum carbonate modified multi-walled carbon nanotubes (LC@MWCNTs) on the UF membrane. The LC@MWCNTs were firstly made using an in-situ method by adding MWCNTs to LaCl3·7H2O solution and forming lanthanum carbonate under alkaline conditions. The adsorption experiments exhibited that the maximum adsorption capacity of LC@MWCNTs was 77.58 mg P/g at pH 5. And the phosphate adsorption by LC@MWCNTs was not predominantly reliant on electrostatic interaction, but rather achieved through chemical interactions. Then, the prepared LC@MWCNTs membrane was systematically evaluated for its phosphate removal efficiency and anti-fouling performance during filtration. With the initial phosphate concentration of 1 mg P/L and membrane flux of 378 L·m−2 h−1, the phosphate removal by LC@MWCNTs membrane approached almost 100 %. Moreover, the LC@MWCNTs membrane exhibited higher permeability (281.6 L·m−2h−1bar−1) and effectiveness for humic acid (HA) removal (75 %), and LC@MWCNTs membrane mitigated the fouling caused by HA. XPS, FTIR and XRD elucidated that phosphate removal by LC@MWCNTs membrane primarily through the formation of La-O-P inner-sphere complexes via ligand exchange, resulting in the formation of adsorption product LaPO4·0.5H2O. Under strong alkaline conditions, the LC@MWCNTs membrane rapidly restored its phosphate removal performance (30 min) with no significant detachment of the LC@MWCNTs layer, indicating its good recovery and reusability performance. Additionally, the LC@MWCNTs membrane could continuously remove phosphate from actual water, confirming its potential for future practical applications.

Modeling of phosphate speciation on goethite surface: Effects of humic acid

Iron (hydr)oxides and humic acid (HA) are important active components in soils and usually coexist in the environment. The effects of HA on the adsorption and subsequent immobilization of phosphate on iron (hydr)oxide surface are of great importance in studies of soil fertility and eutrophication. In this study, two types of goethite with different particle sizes were prepared to investigate the phosphate adsorption behaviors and complexation mechanisms in the absence or presence of HA by combining multiple characterization and modeling studies. The adsorption capacity of micro- (M-Goe) and nano-sized goethite (N-Goe) for phosphate was 2.02 and 2.04 μmol/m2, which decreased by ∼25% and ∼45% in the presence of 100 and 200 mg/L HA, respectively. Moreover, an increase in equilibrium phosphate concentration significantly decreased the adsorption amount of goethite for HA. Charge distribution-multisite surface complexation (CD-MUSIC) and natural organic matter-charge distribution (NOM-CD) modeling identified five phosphate complexes and their corresponding affinity constants (logKP). Among these phosphate complexes, FeOPO2OH, (FeO)2PO2, and (FeO)2POOH species were predominant complexes on the surface of both M-Goe and N-Goe across a wide range of pH and initial phosphate concentrations. The presence of HA had little effect on the coordination mode and logKP of phosphate on goethite surface. These results and the obtained model parameters shed new lights on the interfacial reactivity of phosphate at the goethite-water interface in the presence of HA, and may facilitate further prediction of the environmental fate of phosphate in soils and sediments.

Phosphate adsorption on dried alum sludge: Modeling and application to treatment of dairy effluents

This study evaluates Alum sludge from drinking water treatment plants for the efficient and cost-effective removal of phosphates from aqueous solutions. Extensive characterization and batch experiments have established that optimal phosphate removal was achieved with a sludge dosage of 20 g L−1 (at an initial phosphate concentration of 100 mg L−1), a pH of 5, a temperature of 23 °C, and a stirring speed of 200 rpm. These conditions significantly reduced phosphate levels, ensuring compliance with legal discharge limits. The Langmuir isotherm, pseudo-second-order kinetic and intraparticle diffusion models best described the adsorption process, highlighting the spontaneous and endothermic nature of the phenomenon. The sludge effectively reduced phosphate concentrations to acceptable levels when applied to dairy effluents. This study underscores the potential of Alum sludge as a viable solution for phosphate management in environmental cleanup efforts.

Phosphate removal by acid-activated and chitosan-composite clayey soils

Phosphate is a vital nutrient for aquatic organism growth, but excessive levels can lead to eutrophication, with detrimental effects on receiving water bodies. Adsorption using clay soils can address phosphate release and has gained attention owing to its cost-efficiency and environmental friendliness. To overcome the limited phosphate adsorption capacity of clay soils due to surface charges, the combined effects of acid activation and composite formation with chitosan were investigated. Kaolin and bentonite were selected for acid activation, while chitosan varieties with low, medium, and high molecular weights were chosen for composite formation. Batch tests were individually conducted on acid-activated clay soils and composites of acid-activated clay soils with chitosan over 24 h, varying the initial phosphate concentrations. For acid activation, clay soils were treated with 6N hydrochloric acid, whereas composite formation was achieved via combination with each chitosan variant. Acid-activated kaolin and bentonite individually exhibited phosphate removal efficiencies ranging 99.8–79.8% and 97.1–47.2%, respectively. Among their respective composites, acid-activated kaolin with medium-molecular-weight chitosan and acid-activated bentonite with low-molecular-weight chitosan had the highest phosphate removal efficiencies. Therefore, in contrast to kaolin, acid activation or composite formation of acid-activated bentonite with chitosan can improve its phosphate removal efficiency.

Simultaneous removal of ammonia nitrogen, phosphate, zinc, and phenol by degradation of cellulose in composite mycelial pellet bioreactor: Enhanced performance and community co-assembly mechanism

In this experiment, the prepared tea biochar-cellulose@LDH material (TB-CL@LDH) was combined with mycelium pellets to form the composite mycelial pellets (CMP), then assembled and immobilized with strains Pseudomonas sp. Y1 and Cupriavidus sp. ZY7 to construct a bioreactor. At the best operating parameters, the initial concentrations of phosphate (PO43--P), ammonia nitrogen (NH4+-N), chemical oxygen demand (COD), zinc (Zn2+), and phenol were 22.3, 25.0, 763.8, 1.0, and 1.0 mg L−1, the corresponding removal efficiencies were 80.4, 87.0, 83.4, 91.8, and 96.6%, respectively. Various characterization analyses demonstrated that the strain Y1 used the additional carbon source produced by the strain ZY7 degradation of cellulose to enhance the removal of composite pollutants and clarified the principle of Zn2+ and PO43--P removal by adsorption, co-precipitation and biomineralization. Pseudomonas and Cupriavidus were the dominant genera according to the high-throughput sequencing. As shown by KEGG results, nitrification and denitrification genes were affected by phenol. The study offers prospects for the simultaneous removal of complex pollutants consisting of NH4+-N, PO43--P, Zn2+, and phenol.

Oxalate modification enabled advanced phosphate removal of nZVI: In Situ formed surface ternary complex and altered multi-stage adsorption process

Nano zero-valent iron (nZVI) is a promising phosphate adsorbent for advanced phosphate removal. However, the rapid passivation of nZVI and the low activity of adsorption sites seriously limit its phosphate removal performance, accounting for its inapplicability to meet the emission criteria of 0.1 mg P/L phosphate. In this study, we report that the oxalate modification can inhibit the passivation of nZVI and alter the multi-stage phosphate adsorption mechanism by changing the adsorption sites. As expected, the stronger anti-passivation ability of oxalate modified nZVI (OX-nZVI) strongly favored its phosphate adsorption. Interestingly, the oxalate modification endowed the surface Fe(III) sites with the lowest chemisorption energy and the fastest phosphate adsorption ability than the other adsorption sites, by in situ forming a Fe(III)-phosphate-oxalate ternary complex, therefore enabling an advanced phosphate removal process. At an initial phosphate concentration of 1.00 mg P/L, pH of 6.0 and a dosage of 0.3 g/L of adsorbents, OX-nZVI exhibited faster phosphate removal rate (0.11 g/mg/min) and lower residual phosphate level (0.02 mg P/L) than nZVI (0.055 g/mg/min and 0.19 mg P/L). This study sheds light on the importance of site manipulation in the development of high-performance adsorbents, and offers a facile surface modification strategy to prepare superior iron-based materials for advanced phosphate removal.

Preparation of an activated adsorbent from water treatment plant sludge for phosphate removal from wastewater: optimization, characterization, isotherm, and kinetics studies

Abstract Purifying water for diverse uses is vital, but concerns lie with the sustainability and accessibility of purification materials. As such, this study converted readily available water treatment plant sludge (WTPS) into activated adsorbent for phosphate removal in wastewater. WTPS was activated via thermal activation at 300 °C temperature and chemical activation processes of 3 M acid concentration, 4 h activation time, and 75 °C activation temperature, and then characterized using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared, elemental analyzer, and differential scanning calorimetry. SEM and BET analyses revealed a highly porous adsorbent (279.2 m2/g) for efficient adsorption. On top of the activation process, preliminary experiments and numerical optimization using response surface methodology (RSM) were designed and conducted. Through optimizing conditions, it was found that 70 min of contact time, pH 3, 3 g/L adsorbent dose, and 30 mg/L initial phosphate concentration as optimal, yielding 83% removal efficiency. Furthermore, adsorption kinetics and isotherm models were examined and the second-order kinetics and Langmuir isotherm models indicated best fit. Notably, the activated sludge could be regenerated for three cycles before efficiency dropped below 70%. Thus, activated WTPS presents a promising, sustainable, and readily available adsorbent for phosphate removal in wastewater treatment.

Advanced thermodynamic approach to adsorption of charged adsorbates from aqueous electrolyte solutions

This study present estimation of the thermodynamic parameters and the influence of ionic activity coefficient on the thermodynamic equilibrium constant of adsorption of phosphates on fly ash. The adsorption was conducted over a wide range of initial phosphate concentrations at different pH values pH = (3; 7; 10). The adsorption results were treated using the Langmuir, Freundlich and Sips adsorption isotherms, which provide information about the maximum adsorption capacity. The Langmuir and Sips isotherms were a satisfactory fit to the adsorption data, especially at pH = 3, with an acceptable regression coefficient over the entire concentration range, Langmuir (r2 = 0.9737) and Sips (r2 = 0.9969). The estimated maximum phosphate sorption capacity of fly ash was 6.21 ± 0.68 (mmol·g−1) according to Langmuir and 4.19 ± 0.16 (mmol·g−1) according to the Sips model, at pH = 3.0. However, there is no data in the published literature for estimating the thermodynamic parameters of the phosphate adsorption process using thermodynamic models for activity coefficients. Novel approach of this paper was determination of the thermodynamic equilibrium constant and Gibbs free energy, using the Pitzer ion-interaction model to predict the nature of adsorption. The Pitzer-ion interaction model was used for the mixed ionic systems, taking into consideration the effect of other present ions besides phosphates in the equilibrium solution resulting from fly ash desorption. The procedure for comprehensive estimation of the ion activity coefficient at maximum adsorption capacity and the dimensionless thermodynamic equilibrium constant using Langmuir's and Sips’s constants was presented. The calculated value of the phosphate activity coefficient in the equilibrium solution was γH2PO4,e = 0.7003 ± 0.0027 and the converted molar activity coefficient was γH2PO4,e = 0.6903 ± 0.0027. The estimated values of Gibbs free energy were: ΔGL = −6.788 ± 0.521 kJ·mol−1 based on Langmuir equilibrium constant and ΔGa = −7.707 ± 0.527 kJ·mol−1 based on activity and thermodynamic equilibrium constant. According to Sips model, the adsorption process is even more spontaneous, with the Gibbs free energy calculated using the phosphate activity coefficient and the thermodynamic equilibrium constant, ΔGa = −9.707 ± 0.617 kJ·mol−1. Consideration of the ionic activity coefficient is particularly important for large, charged adsorbates at higher concentrations, as the absolute difference in free energy for adsorption is app. 12 %. The scientific contribution is reflected in obtaining the necessary and more accurate information for the improvement of adsorption processes and possibly for the upgrading of fly ash in overall wastewater treatment technology.

Magnesium or bentonite modified almond kernel biochar for phosphate adsorption from contaminated water solutions

The potential of almond kernel, physically activated by nitrogen/steam, or chemically activated by Mg2+ or bentonite and then by nitrogen/steam, to adsorb phosphate from wastewaters was evaluated. The performance of biochar was studied as a function of initial phosphate concentration, adsorbent dose, contact time and solution pH. The mechanism of adsorption was investigated by carrying out structural, chemical and mineralogical analyses of the material before and after phosphate adsorption, as well as by applying two isotherm models, simulating the experimental data. The results showed that the specific surface area increased about 260 times after activation. Adsorption of phosphate was fast within 30 min, while reached equilibrium after 12 h. For Mg2+ modified material a higher ionic strength facilitated the uptake of phosphate by the biochar up to 59%, in contrast to the bentonite modified material, where adsorption of phosphate was complete (100%) at an initial concentration of 50 mg/L, declining thereafter. Mg2+ modified material was best fitted by the Freundlich model, while bentonite modified material was best fitted by the Langmuir model. For an adsorbent dose of 2 g/L maximum phosphate adsorption capacity after Mg2+ or bentonite modification was 82 mg/g and 54 mg/g, respectively. In the case of Mg2+ modification the potential mechanisms of adsorption were surface precipitation, electrostatic attraction, chemical complexation or electron coordination between the phosphate ion and the adsorbent. For bentonite modification, chemical complexation and π-π electron coordination were the potential adsorption mechanisms.

Calcium ferrites for phosphate adsorption and recovery from wastewater.

In this study, calcium ferrites with different Ca : Fe atomic ratios (1 : 1, 1 : 2, 1 : 3 and 2 : 1) were prepared from Ca and Fe nitrates treated at 300, 700 and 900 °C and evaluated for phosphate adsorption and recovery from wastewater. TG, XRD, Mössbauer spectroscopy, SEM, VSM magnetic measurements, and BET analyses showed the formation of two different calcium ferrite phases, i.e., CaFe2O4 and Ca2Fe2O5 at 700 and 900 °C. The adsorption results indicated that the formation of calcium ferrite structure is critical for phosphate adsorption/recovery. Evaluation of the pH, initial phosphate concentration, contact time, coexisting ions and desorption conditions showed remarkable adsorption capacities of 62-75 mg g-1 for CaFe1:2-700 and 28-43 mg g-1 for CaFe1:2-900. The phosphate adsorption on the Ca ferrite surfaces is so strong that the recovery/desorption showed limited efficiencies, e.g., 15-39%.

Simplification of the pretreatment method for phosphate oxygen isotope measurement in phosphogypsum leachate

The stacking of phosphogypsum has caused considerable phosphorus pollution in water bodies near phosphogypsum yards through surface runoff and underground infiltration. The phosphate oxygen isotope (δ18Op) tracing method has served as a valuable tool for tracing phosphorus pollution in water. However, the existing δ18Op enrichment and purification methods are complex, costly, and inefficient for phosphate recovery, particularly for phosphogypsum leachate with complex compositions. Herein, a simplified and optimized pretreatment method for δ18Op measurement in phosphogypsum leachate was developed. Zirconium/polyvinyl alcohol (Zr/PVA) gel beads showed good selectivity for phosphate enrichment from water at different initial phosphate concentrations with appropriate Zr/PVA dosage. The optimal enrichment pH value was <7, and the concentrated phosphate on the Zr/PVA gel beads could be effectively eluted in an alkaline environment. Compared with the traditional Fe or Mg coprecipitation enrichment methods, impurities in the solution showed no obvious adverse effects on the phosphate enrichment process. Further, the phosphate solution eluted from the Zr/PVA gel beads was purified by a simple adjustment of the pH instead of cation exchange in the traditional purification process. Magnesium ions in the solution could be completely removed when the pH ranged from 3.17 to 6.15, and the phosphate recovery rate could reach 98.66% when the eluent pH was 5.02. Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy revealed that similar to traditional pretreatment method, the proposed method can obtain high-purity Ag3PO4 solids for δ18OP measurement and no isotope fractionation of δ18OP was observed. Therefore, this study provides a promising and reliable pretreatment method for δ18OP measurement, especially in complex phosphogypsum leachate.

Efficient recovery of phosphate by La-MOFs: An excellent adsorption performance and mechanism

Lanthanum-type metal-organic frameworks (La-MOFs) can be used to mitigate phosphate pollution in wastewater. Herein, La-MOFs was gained via the solvothermal method and its phosphate removal property was examined under various conditions, like variable initial phosphate concentration, solution pH, and co-existing ions. The material morphology, element composition, and crystal morphology of the La-MOFs was characterized using XRD, SEM, FTIR, and XPS. The phosphate removal mechanism was investigated by combining thermodynamic and kinetic analyses. The La-MOFs exhibited superior adsorption capability for surplus phosphate in water, and also had a high selectivity for phosphate in the complexed environment with some co-existing ions. Maximum adsorption was obtained at pH 4. The sorption procedure of La-MOFs aligned more with the Langmuir and pseudo-second order kinetic models, demonstrating monomolecular-layer-controlled chemisorption. And the maximum sorption capacity was 73.69 ​mg ​g−1. Electrostatic interactions and ligand exchange, which enabled the development of an La–O–P inner-sphere complexation, were identified as the primary mechanisms of phosphate removal. This research provides insights into the optimal conditions and mechanism of phosphate adsorption by La-MOFs.

Pushing the boundaries of phosphorylase cascade reaction for cellobiose production II: Model-based multiobjective optimization.

The inherent complexity of coupled biocatalytic reactions presents a major challenge for process development with one-pot multienzyme cascade transformations. Kinetic models are powerful engineering tools to guide the optimization of cascade reactions towards a performance suitable for scale up to an actual production. Here, we report kinetic model-based window of operation analysis for cellobiose production (≥100 g/L) from sucrose and glucose by indirect transglycosylation via glucose 1-phosphate as intermediate. The two-step cascade transformation is catalyzed by sucrose and cellobiose phosphorylase in the presence of substoichiometric amounts of phosphate (≤27 mol% of substrate). Kinetic modeling was instrumental to uncover the hidden effect of bulk microviscosity due to high sugar concentrations on decreasing the rate of cellobiose phosphorylase specifically. The mechanistic-empirical hybrid model thus developed gives a comprehensive description of the cascade reaction at industrially relevant substrate conditions. Model simulations serve to unravel opposed relationships between efficient utilization of the enzymes and maximized concentration (or yield) of the product within a given process time, in dependence of the initial concentrations of substrate and phosphate used. Optimum balance of these competing key metrics of process performance is suggested from the model-calculated window of operation and is verified experimentally. The evidence shown highlights the important use of kinetic modeling for the characterization and optimization of cascade reactions in ways that appear to be inaccessible to purely data-driven approaches.

Aluminium dross waste utilization for phosphate removal and recovery from aqueous environment: Operational feasibility development

The need to minimize eutrophication in water bodies and the shortage of phosphate rock reserves has stimulated the search for sequestration and recovery of phosphate from alternative sources, including wastewater. In this study, aluminium dross (AD), a smelting industry waste/by-product, was converted to high-value material by encapsulation in calcium alginate (Ca-Alg) beads, viz. Ca-Alg-AD and utilized for adsorptive/uptake removal and phosphate recovery from an aqueous environment. Encapsulation of AD in alginate beads solves serious operational difficulties of using raw AD material directly due to density difference constraining efficient contact of AD with pollutants present in water and post-treatment recovery of AD material. The phosphate removal was evaluated in both batch and continuous flow operation modes. The batch adsorption study revealed 96.86% phosphate removal from 10 mg L−1 of initial phosphate concentration in 70 min of optimal contact time. Further, the phosphate removal potential of Ca-Alg-AD beads turned out to be independent of solution pH, with an average of 95.93 ± 1.40 % phosphate removal in the 2–9 pH range. The result reflects phosphate adsorption on Ca-Alg-AD beads following a second-order pseudo-kinetic model. Ca-Alg-AD beads-based adsorption followed Freundlich and Langmuir isotherm models. Further, a continuous packed bed column study revealed a total phosphate adsorption capacity of 1.089 mg g−1. The chemical composition, physical stability, and surface properties of Ca-Alg-AD beads were analyzed by means of state-of-the-art analytical techniques, such as Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetry/Differential Thermal Analysis (TG/DTA). These characterization techniques comprehend the mechanism and influence of surface properties and morphology on the phosphate adsorption behaviour, which induce the involvement of multiple mechanisms such as ligand complexation, ion exchange, and electrostatic attraction for phosphate adsorption on Ca-Alg-AD beads.

Efficient separation of phosphate ions in water using tris(hydroxymethyl)aminomethane modified polyaniline-p-phenylenediamine composite membrane

In this study, polyaniline-p-phenylenediamine (PAPD) was employed as an amino monomer to fabricate a polyaniline-p-phenylenediamine composite membrane (PAPD/PES) with a nanoparticle-like surface morphology. Additionally, we used interfacial polymerization of Tris(hydroxymethyl)aminomethane (THAM) to hydroxylate the PAPD/PES composite membrane, resulting in the formation of a TPAPD/PES composite membrane. THAM is an economical and environmentally friendly monomer, rarely used for surface modification of composite membranes through interfacial polymerization. Following the introduction of THAM, a significant abundance of hydroxyl groups appeared on the membrane’s surface, enhancing its hydrophilicity and electronegativity. This, in turn, improved both flux and rejection capabilities. Simultaneously, the introduction of THAM led to the formation of a hydration layer growing on the membrane’s surface, further enhancing its antifouling performance. The optimal polymerization concentration (0.5 mol/L) of THAM was used to synthesize the TPAPD/PES composite membrane, resulting in a flux of 84.18 L m−2 h−1 bar−1, which was 1.46 times higher than that of the PAPD/PES composite membrane before polymerization. Additionally, the phosphate rejection rate was determined to be 92.14 % (with an initial phosphate concentration of 10 mg P/L). Long-time running and operating pressure tests results confirmed the remarkable stability of the TPAPD/PES composite membrane. Furthermore, the phosphate separation property of the TPAPD/PES composite membrane was evaluated using real wastewater samples (with an initial phosphate concentration of 1.03 mg P/L) as the research object. After separation, the permeate displayed a phosphate concentration of 0.28 mg P/L, meeting the first-class A standard for urban sewage treatment in China (0.5 mg P/L). This indicates that the prepared TPAPD/PES composite membrane has significant potential for practical application.

Recovery of phosphate using a zinc oxide/hydroxide and lanthanum hydroxide nanoflower adsorbent prepared via co-precipitation in water

Phosphorus is widely used in many industries, but the volume of mined phosphate rock is increasing by 2 % annually, leading to concerns about potential depletion within the next 100 years. Therefore, concern about the recovery and reuse of resources at the risk of exhaustion has increased dramatically. In this study, zinc oxide/hydroxide (ZnO/Zn(OH)2) and lanthanum hydroxide (La(OH)3) nanoflower (ZLNF) with excellent stability and high adsorption efficiency for phosphate were synthesized using low-cost co-precipitation method. The phosphate adsorption efficiency of the ZLNF was 73.2 %, higher than that of pure ZnO/Zn(OH)2 nanoflower (41.0 %) from 0.025 g of adsorbent in 20 mL of initial phosphate concentration of 50 mg/L. The ZLNF was also characterized according to the Zn/La molar ratio, preparation temperature, and pH. The Zn/La molar ratio affected the specific surface area and adsorption performance of the ZLNF, while phosphate adsorption was highly reliant on the pH of the solution, with the maximum adsorption efficiency observed at pH 3. The phosphate adsorption characteristics of the ZLNF were evaluated using isothermal adsorption, kinetic, and thermodynamic models, with the Langmuir and pseudo-second-order models deemed to be the most appropriate. Phosphate adsorption on ZLNF was thus concluded to be a monolayered homogeneous process, with chemical adsorption dominant. In addition, the Langmuir theoretical maximum adsorption capacity was 178.6 mg P/g, much greater than that of other materials reported in previous studies. The results of this study are thus expected to be very useful in the field of resource recovery.

Cerium(IV) chitosan-based hydrogel composite for efficient adsorptive removal of phosphates(V) from aqueous solutions

The excess presence of phosphate(V) ions in the biosphere is one of the most serious problems that negatively affect aqueous biocenosis. Thus, phosphates(V) separation is considered to be important for sustainable development. In the presented study, an original cerium(IV)-modified chitosan-based hydrogel (Ce-CTS) was developed using the chemical co-precipitation method and then used as an adsorbent for efficient removal of phosphate(V) ions from their aqueous solutions. From the scientific point of view, it represents a completely new physicochemical system. It was found that the adsorptive removal of phosphate(V) anions by the Ce-CTS adsorbent exceeded 98% efficiency which is ca. 4-times higher compared with the chitosan-based hydrogel without any modification (non-cross-linked CTS). The best result of the adsorption capacity of phosphates(V) on the Ce-CTS adsorbent, equal to 71.6 mg/g, was a result of adsorption from a solution with an initial phosphate(V) concentration 9.76 mg/dm3 and pH 7, an adsorbent dose of 1 g/dm3, temperature 20 °C. The equilibrium interphase distribution data for the Ce-CTS adsorbent and aqueous solution of phosphates(V) agreed with the theoretical Redlich-Peterson and Hill adsorption isotherm models. From the kinetic point of view, the pseudo-second-order model explained the phosphates(V) adsorption rate for Ce-CTS adsorbent the best. The specific effect of porous structure of adsorbent influencing the diffusional mass transfer resistances was identified using Weber-Morris kinetic model. The thermodynamic study showed that the process was exothermic and the adsorption ran spontaneously. Modification of CTS with cerium(IV) resulted in the significant enhancement of the chitosan properties towards both physical adsorption (an increase of the point of zero charge of adsorbent), and chemical adsorption (through the presence of Ce(IV) that demonstrates a chemical affinity for phosphate(V) anions). The elaborated and experimentally verified highly effective adsorbent can be successfully applied to uptake phosphates(V) from aqueous systems. The Ce-CTS adsorbent is stable in the conditions of the adsorption process, no changes in the adsorbent structure or leaching of the inorganic filling were observed.