Development of nanoscale zirconium molybdate embedded anion exchange resin for selective removal of phosphate

Sustainable media feedstocks for cellular agriculture

The global food system is shifting towards cellular agriculture, a second domestication marked by cultivating microorganisms and tissues for sustainable food production. This involves tissue engineering, precision fermentation, and microbial biomass fermentation to establish food value chains independent of traditional agriculture. However, these techniques rely on growth media sourced from agricultural, chemical (fossil fuels), and mining supply chains, raising concerns about land use competition, emissions, and resource depletion. Fermentable sugars, nitrogen, and phosphates are key ingredients derived from starch crops, energy-intensive fossil fuel based processes, and finite phosphorus resources, respectively. This review explores sustainable alternatives to reduce land use and emissions associated with cellular agriculture media ingredients. Sustainable alternatives to first generation sugars (lignocellulosic substrates, sidestreams, and gaseous feedstocks), sustainable nitrogen sources (sidestreams, green ammonia, biological nitrogen fixation), and efficient use of phosphates are reviewed. Especially cellulosic sugars, gaseous chemoautotrophic feedstocks, green ammonia, and phosphate recycling are the most promising technologies but economic constraints hinder large-scale adoption, necessitating more efficient processes and cost reduction. Collaborative efforts are vital for a biotechnological future grounded in sustainable feedstocks, mitigating competition with agricultural land and emissions.

Material Design Strategies for Recovery of Critical Resources from Water

Population growth, urbanization, and decarbonization efforts are collectively straining the supply of limited resources that are necessary to produce batteries, electronics, chemicals, fertilizers, and other important products. Securing the supply chains of these critical resources via the development of separation technologies for their recovery represents a major global challenge to ensure stability and security. Surface water, groundwater, and wastewater are emerging as potential new sources to bolster these supply chains. Recently, a variety of material-based technologies have been developed and employed for separations and resource recovery in water. Judicious selection and design of these materials to tune their properties for targeting specific solutes is central to realizing the potential of water as a source for critical resources. Here, the materials that are developed for membranes, sorbents, catalysts, electrodes, and interfacial solar steam generators that demonstrate promise for applications in critical resource recovery are reviewed. In addition, a critical perspective is offered on the grand challenges and key research directions that need to be addressed to improve their practical viability.

Removal of Phosphate by Adsorption with 2-Phenylimidazole-Modified Porous ZIF-8: Powder and Chitosan Spheres

Due to rapid socioeconomic development, increased phosphorus concentrations can cause eutrophication of water bodies, with devastating effects on environmental sustainability and aquatic ecosystems. In this study, ZIF-8-PhIm was prepared for phosphorus removal using 2-phenylimidazole via the solvent-assisted ligand exchange (SALE) method. The structure and composition of ZIF-8-PhIm were characterized by various methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis. Compared to the ZIF-8 material, it exhibited a multistage pore structure with larger pore capacity and pore size, increased hydrophilicity, exposure of more adsorption sites, and also stronger electrostatic interaction. Under optimized conditions (T = 298 K, C0 = 150 mg/L, dose = 0.2 g/L), the adsorption capacity of ZIF-8-PhIm reached 162.93 mg/g, which was greater than that of the ZIF-8 material (92.07 mg/g). The Langmuir isotherm and pseudo-second-order kinetic models were suitable for describing the phosphate adsorption of ZIF-8-PhIm. The main effects of ZIF-8-PhIm on phosphate adsorption were Zn-O-P bonding and electrostatic interactions. It also had good regeneration properties. The ZIF-8-PhIm/CS spheres were prepared using chitosan (CS) as the cross-linking agent. The results of dynamic adsorption experiments on the spheres showed a saturation capacity of 85.69 mg/g and a half-penetration time of 514.15 min at 318 K according to the fitted results.

Sustainable Multi-Network Cationic Cryogels for High-Efficiency Removal of Hazardous Oxyanions from Aqueous Solutions

It is still a challenge to develop advanced materials able to simultaneously remove more than one pollutant. Exclusive cationic composite double- and triple-network cryogels, with adequate sustainability in the removal of Cr₂O₇^2- and H₂PO₄^- oxyanions, were developed in this work starting from single-network (SN) sponges. Chitosan (CS), as the only polycation originating from renewable resources, and poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA) and polyethyleneimine (PEI), as synthetic polycations, were employed to construct multi-network cationic composite cryogels. The properties of the composites were tailored by the cross-linking degree of the first network (SN5 and SN20, which means CS with 5 or 20 mole % of glutaraldehyde, respectively) and by the order of the successive networks. FTIR, SEM-EDX, equilibrium water content and compressive tests were used in the exhaustive characterization of these polymeric composites. The sorption performances towards Cr₂O₇^2- and H₂PO₄^- anions were evaluated in batch mode. The pseudo-first-order, pseudo-second-order (PSO) and Elovich kinetics models, and the Langmuir, Freundlich and Sips isotherm models were used to interpret the experimental results. The adsorption data were the best fitted by the PSO kinetic model and by the Sips isotherm model, indicating that the sorption mechanism was mainly controlled by chemisorption, irrespective of the structure and number of networks. The maximum sorption capacity for both oxyanions increased with the increase in the number of networks, the highest values being found for the multi-network sponges having SN5 cryogel as the first network. In binary systems, all sorbents preferred Cr₂O₇^2- ions, the selectivity coefficient being the highest for TN sponges. The high sorption capacity and remarkable reusability, with only a 4-6% drop in the sorption capacity after five sorption-desorption cycles, recommend these composite cryogels in the removal of two of the most dangerous pollutants represented by Cr₂O₇^2- and H₂PO₄^-.

Resin-based iron-manganese binary oxide for phosphate selective removal

Adsorption technology can effectively remove phosphorus from water and realize phosphorus recovery. Hence, it is used to curb the eutrophication of water and alleviate the crisis caused by the shortage of phosphorus resources. Resin has been attracting increasing interest as an ideal adsorption material; however, its practical application is greatly affected by environmental factors. To solve the competitive adsorption and pore blockage caused by humic acid and coexisting ions during the removal of phosphorus by ion-exchange resin, this study has developed an iron-manganese oxide-modified resin composite adsorbent (Fe/Mn-402) based on the nanoconfinement theory. The structural characterization results of XRD, FT-IR, SEM, and XPS showed that the iron-manganese binary oxide was successfully loaded on the skeleton of the strongly alkaline anion resin and showed good stability under both neutral and alkaline conditions. The batch adsorption experiments showed that the maximum adsorption capacity of Fe/Mn-402 for phosphorus can reach up to 50.97 mg g^-1 under the optimal raw material ratio (Fe:Mn = 1:1). In addition, Fe/Mn-402 shows good selectivity for phosphorus removal. Fe/Mn-402 can maintain good adsorption performance for phosphate even under high concentrations of SO₄^2-, HCO₃^-, and humic acid. The regenerated Fe/Mn-402 can be recycled without any obvious change in its treatment capacity. Hence, it is suitable for stable, long-term usage. In general, this work puts forward a new idea for the development of phosphorus-removal adsorbents for the treatment of wastewater containing coexisting ions and HA.

Phosphate removal from aqueous solution using calcium-rich biochar prepared by the pyrolysis of crab shells

Phosphorus is one of the main pollutants that cause water pollution, and phosphorus is a one-way cycle in the environment, and phosphorus resources will face exhaustion in the next 100 years. Therefore, the recovery and reuse of phosphorus resources have become very important. This article presents a study concerning the removal of phosphate from an aqueous solution by using a calcium-rich biochar prepared by pyrolysis of crab shells. The experimental results show that the optimal pyrolysis temperature of crab shells is 500 ℃, named CSB500, which is more conducive to the adsorption of phosphate. The process of phosphate adsorption conforms to the quasi-second-order kinetics and Freundlich model. On the other hand, the Langmuir isotherm model shows that when the reaction conditions are 25 ℃, 30 ℃, and 35 ℃, the maximum adsorption capacity of CSB500 for phosphate is 164.32 mg/g, 170.47 mg/g, and 209.35 mg/g, respectively. The characterization results show that the overall structure of CSB500 is good, the specific surface area is large, and the main component is calcium carbonate. The potential mechanisms of action in the process of phosphate adsorption may be electrostatic attraction, surface chemical precipitation, ligand exchange, and complexation.

Recovery of phosphorus from wastewater: A review based on current phosphorous removal technologies

Phosphorus (P) as an essential nutrient for life sustains the productivity of food systems; yet misdirected P often accumulates in wastewater and triggers water eutrophication if not properly treated. Although technologies have been developed to remove P, little attention has been paid to the recovery of P from wastewater. This work provides a comprehensive review of the state-of-the-art P removal technologies in the science of wastewater treatment. Our analyses focus on the mechanisms, removal efficiencies, and recovery potential of four typical water and wastewater treatment processes including precipitation, biological treatment, membrane separation, and adsorption. The design principles, feasibility, operation parameters, and pros & cons of these technologies are analyzed and compared. Perspectives and future research of P removal and recovery are also proposed in the context of paradigm shift to sustainable water treatment technology.

Zirconium Molybdate Nanocomposites’ Sensing Platform for the Sensitive and Selective Electrochemical Detection of Adefovir

Adefovir (ADV) is an anti-retroviral drug, which can be used to treat acquired immune deficiency syndrome (AIDS) and chronic hepatitis B (CHB), so its quantitative analysis is of great significance. In this work, zirconium molybdate (ZrMo₂O₈) was synthesized by a wet chemical method, and a composite with multi-walled carbon nanotubes (MWCNTs) was made. ZrMo₂O₈-MWCNTs composite was dropped onto the surface of a glassy carbon electrode (GCE) to prepare ZrMo₂O₈-MWCNTs/GCE, and ZrMo₂O₈-MWCNTs/GCE was used in the electrochemical detection of ADV for the first time. The preparation method is fast and simple. The materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and cyclic voltammetry (CV). It was electrochemically analysed by differential pulse voltammetry (DPV). Compared with single-material modified electrodes, ZrMo₂O₈-MWCNTs/GCE showed a vastly improved electrochemical response to ADV. Moreover, the sensor complements the study of the electrochemical detection of ADV. Under optimal conditions, the proposed electrochemical method showed a wide linear range (from 1 to 100 μM) and a low detection limit (0.253 μM). It was successfully tested in serum and urine. In addition, the sensor has the advantages of a simple preparation, fast response, good reproducibility and repeatability. It may be helpful in the potential applications of other substances with similar structures.

Upcycling Glass Waste into Porous Microspheres for Wastewater Treatment Applications: Efficacy of Dye Removal

Each year about 7.6 million tons of waste glasses are landfilled without recycling, reclaiming or upcycling. Herein we have developed a solvent free upcycling method for recycled glass waste (RG) by remanufacturing it into porous recycled glass microspheres (PRGMs) with a view to explore removal of organic pollutants such as organic dyes. PRGMs were prepared via flame spheroidisation process and characterised using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and Mercury Intrusion Porosimetry (MIP) analysis. PRGMs exhibited 69% porosity with overall pore volume and pore area of 0.84 cm³/g and 8.6 cm²/g, respectively (from MIP) and a surface area of 8 m²/g. Acid red 88 (AR88) and Methylene blue (MB) were explored as a model source of pollutants. Results showed that removal of AR88 and MB by PRGMs was influenced by pH of the dye solution, PRGMs doses, and dye concentrations. From the batch process experiments, adsorption and coagulation processes were observed for AR88 dye whilst MB dye removal was attributed only to adsorption process. The maximum monolayer adsorption capacity (q_e) recorded for AR88, and MB were 78 mg/g and 20 mg/g, respectively. XPS and FTIR studies further confirmed that the adsorption process was due to electrostatic interaction and hydrogen bond formation. Furthermore, dye removal capacity of the PRGMs was also investigated for column adsorption process experiments. Based on the Thomas model, the calculated adsorption capacities at flow rates of 2.2 mL/min and 0.5 mL/min were 250 mg/g and 231 mg/g, respectively which were much higher than the batch scale Langmuir monolayer adsorption capacity (q_e) values. It is suggested that a synergistic effect of adsorption/coagulation followed by filtration processes was responsible for the higher adsorption capacities observed from the column adsorption studies. This study also demonstrated that PRGMs produced from recycled glass waste could directly be applied to the next cyclic experiment with similar dye removal capability. Thus, highlighting the circular economy scope of using waste inorganic materials for alternate applications such as pre-screening materials in wastewater treatment applications.

Diatomite Composited with a Zeolitic Imidazolate Framework for Removing Phosphate from Water

Adsorption technology based on various adsorbents has been widely applied in wastewater treatment containing phosphate. A novel diatomite adsorbent composited with ZIF-8 (CZD) was developed for removing phosphate from water in this work. The chitosan was used to pre-modify the diatomite so that ZIF-8 could be anchored on the surface of the diatomite solidly and uniformly. The diatomite composited with ZIF-8 was then used to remove phosphate in water by an adsorption process, the process variables such as adsorption time, temperature, pH, and competitive ions were investigated. The electrostatic attraction was the primary mechanism of phosphate removal. The adsorption reached equilibrium within 90 min, and its sorption capacity increased when adsorption time and temperature increased. Especially, CZD had a rapid adsorption rate and 85% of the phosphate in the solution can be adsorbed within the first 10 min. The maximum phosphate adsorption capacities of the modified diatomite reached 13.46, 13.55, and 13.95 mg/g at 25, 35, and 45 °C, respectively. The removal efficiencies of CZD for phosphate were more than 98% and even came up to 100% at 45 °C. The adsorption isotherms fit well with the Langmuir isotherm model. The Freundlich isotherm and Temkin isotherm showed that the adsorption process is physical in nature. The kinetic data of the adsorption process were fitted by the pseudo-second-order kinetics. Thermodynamic parameters indicated that the adsorption process was endothermic. This adsorbent provided an alternative for phosphate removal on account of the high adsorption efficiency in a short time. Therefore, CZD could be a promising and eco-friendly phosphate adsorbent for wastewater treatment.

Fixed-bed column study of phosphate adsorption using immobilized phosphate-binding protein

Bio-adsorption using high-affinity phosphate-binding proteins (PBP) has demonstrated effective phosphorus removal and recovery in batch-scale tests. Subsequent optimization of design and performance of fixed-bed column systems is essential for scaling up and implementation. Here, continuous-flow fixed-bed column tests were used to investigate the adsorption of inorganic phosphate (orthophosphate, P_i) using phosphate-binding proteins immobilized on resin (PBP-NHS) targeting P_i removal to ultra-low levels followed by recovery. Time to breakthrough decreased with higher influent P_i concentration, smaller bed volume, and higher influent flow rates. The Thomas and Yoon-Nelson breakthrough models adequately described PBP-NHS resin performance with a correlation coefficient of R² > 0.95. The sharp S-shape of the breakthrough curves for both P_i-only solution and multi-ion solution indicated highly favorable and selective separation of P_i using PBP-NHS resin, beyond that achieved using LayneRT™, a commercial ion exchange resin. The P_i adsorption capacity of the PBP-NHS column was unaffected by competing anions, whereas capacity of the LayneRT™ column dropped by 20%. Tertiary wastewater effluent was also successfully treated in PBP-NHS column tests with a typical S-shaped breakthrough curve. Operating the fixed-bed column in multi-cycle mode evidenced the reusability of PBP-NHS resin with no significant decline in column performance. The results of this study contribute to efforts to scale up designs of PBP-NHS adsorption systems.

Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery. Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk, a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of FeOOH/anion exchanger nanocomposites (Fe/900s) with enhanced metal site utilization and reduced metal leakage risk. Compared to composites prepared using alkaline precipitation methods, Fe/900s performed comparably, with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L, a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO₄^2-/L, and high long-term resilience (with a capacity loss of ~14% after five cycles), along with substantially lower Fe loading amount (4.11 wt.%) and Fe leakage percentage. Mechanistic investigation demonstrated that contribution of the specific FeOOH sites to phosphate adsorption increased substantially (up to 50.97% under the optimal conditions), in which Fe(III)-OH was the dominant efficient species. The side effects of an excessively long reaction time, which included quaternary ammonium decomposition, FeOOH aggregation, and Fe(III) reduction, were discussed as guidance for optimizing the synthesis strategy. The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.

Chitosan based adsorbents for the removal of phosphate and nitrate: A critical review

The tremendous development in the industrial sector leads to discharging of the several types of effluents containing detrimental contaminants into water sources. Lately, the proliferation of toxic anions particularly phosphates and nitrates onto aquatic systems certainly depreciates the ecological system and causes a deadly serious problem. Chitosan (Cs) is one of the most auspicious biopolymer adsorbents that are being daily developed for removing of various contaminants from polluted water. This is due to its unparalleled benefits involving biocompatibility, non-toxicity, facile modifications and low-cost production. Nevertheless, chitosan displays considerable drawbacks including low adsorption capacity, low surface area and lack of reusability. Therefore, few findings have been established regarding the aptitude of modified chitosan-based adsorbents towards phosphate and nitrate anions. This review elaborates an overview for the current advances of modified chitosan based-adsorbent for phosphate and nitrate removal, in specific multivalent metals-modified chitosan, clays and zeolite-modified chitosan, magnetic chitosan and carbon materials-modified chitosan. The efforts that have been executed for enriching their adsorption characteristics as well as their possible adsorption mechanisms and reusability were well addressed. Besides, the research conclusions for the optimum adsorption conditions were also discussed, along with emphasizing the foremost research gaps and future potential trends that could motivate further research and innovation to find best solutions for water treatment problems facing the world.

Kinetic characteristics of mobile Mo associated with Mn, Fe and S redox geochemistry in estuarine sediments

Estuarine sediments are crucial repositories and incubators of molybdenum (Mo) during its transport from rivers to the ocean. Here, Mo mobility and related processes in estuarine sediments were explored using high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques. Better correlations were observed between dissolved Mn and Mo than between dissolved Fe and Mo, implying that Mn geochemistry plays a key role in dissolved Mo mobility via molybdate adsorption onto abundant Mn oxides and its substantial release upon intense Mn reduction. As a result, oxic intertidal sediments functioned as Mo sinks, and anoxic subtidal sediments functioned as Mo sources. The opposite vertical distributions between DGT-Labile S and DGT-Labile Mo indicated that the availability of labile Mo can be blocked by aqueous sulfide. However, the corresponding high concentrations of DGT-Labile S and dissolved Mo at subtidal sites demonstrated that the abundant dissolved Mo remobilized via Mn reduction was not effectively solidified by sulfide. Simulation with the DIFS model further verified that redox conditions and induced physicochemical processes are crucial factors controlling Mo mobility, with relatively low dissolved Mo concentrations but an adequate and steady resupply capacity of the bioavailable molybdate in intertidal sediments.

Smart ion imprinted polymer for selective adsorption of Ru(Ⅲ) and simultaneously waste sample being transformed as a catalyst

In this work, a temperature-sensitive block polymer PDEA-b-P(DEA-co-AM) was synthesized and then introduced into the preparation of a smart Ru(Ⅲ) imprinted polymer (Ru-IIP) to selectively adsorption Ru(Ⅲ) first. Then the waste Ru-IIP was converted into a catalyst in-situ for recycle. The structure and morphology of the prepared polymer were characterized by Fourier transform infrared spectrometer, Scanning electron microscope, BET surface area and Thermogravimetric analysis. The adsorption properties of the synthesized smart material were investigated in terms of adsorption pH, adsorption kinetics and adsorption isotherm. Results documented that the optimal adsorption temperature and pH were 35 °C and 1.5 respectively, the maximum adsorption capacity was 0.153 mmol/g, and the adsorption processes of Ru-IIP were more suitable to be expressed by pseudo-first-order kinetic and Langmuir model. The selectivity studied in different binary mixed solutions showed that Ru-IIP has good selectivity, and reusability results showed that Ru-IIP still maintains a good adsorption effect after 8 cycles. In addition, the waste Ru-IIP, a Ru(Ⅲ) remained waste sample was employed as the catalyst for the synthesis of imines, and result showed the mass of adsorbent would reduce after the completion of catalysis, which could not only catalyze the reaction but also reduce pollution.

High phosphate removal using La(OH)3 loaded chitosan based composites and mechanistic study

Our present study was to prepare a biomass-supported adsorbents with high adsorptive capacity and high selectivity to prevent the accelerated eutrophication in water body. To this end, different metal hydroxide (La, Zr and Fe) first was successfully loaded on chitosan microspheres. Then the quaternary ammonium group with different content was introduced into the adsorbent by polymerization. By comparison of adsorption properties, chitosan-La(OH)₃-quaternary ammonium-20% (CS-La-N-20%) has strong adsorption to phosphate (160 mg/g) by immobilizing nano-sized La(OH)₃ within a quaternary-aminated chitosan and it maintain high adsorption in the presence of salt ions. The pH results indicated that the CS-La-N-20% would effectively sequestrate phosphate over a wide pH range between 3 and 7 without significant La³⁺ leaching. What's more, adsorption capacity on the introduce of positively charged quanternary-aminated groups was significantly higher than that of the unmodified adsorbents at alkaline conditions. The column adsorption capacity reached 1300 bed volumes (BV) when phosphate concentration decreased until 0.5 mg/L at 6 BV/hr. The column adsorption/desorption reveals that no significant capacity loss is observed, indicating excellent stability and repeated use property. Characterizations revealed that phosphate adsorption on CS-La-N-20% through ligand exchange (impregnated nano-La(OH)₃) and electrostatic attraction (positively charged quanternary-aminated groups). All the results suggested that CS-La-N-20% can serve as a promising adsorbent for preferable phosphate removal in realistic application.

Phosphate removal using thermally regenerated Al adsorbent from drinking water treatment sludge

Alum sludge (AS) is an abundant and ubiquitous residue generated from drinking water treatment plants. AS was thermally treated to use as an adsorbent for phosphate removal from wastewater. Organic matter in the AS was a potential competitor and can deter phosphate adsorption. Pyrolysis and drying of AS were adopted to enhance phosphate removal by eliminating organic matter and enriching Al content. Adsorption kinetics showed that phosphate removal was highest with the AS pyrolyzed at 700 °C followed by 500 °C, air-dried and oven-dried (105 °C). Adsorption kinetic modelling showed that chemisorption is the operative mechanism of phosphate removal in all the AS. Adsorption isotherms also showed that the pyrolyzed AS and air-dried AS had similar adsorption capacity of 30.83-34.53 mg P/g AS. Al dissolution was less than 2 mg/g Al in all the AS samples. COD release was significant in the dried AS, up to 8.0 mg COD/g AS, whereas the pyrolyzed AS released less than 1 mg COD/g AS. FTIR and SEM-EDS analyses of the AS after phosphate adsorption showed the formation of aluminum-phosphate complex. Overall, the pyrolysis of AS at 700 °C was most effective in removing phosphate without leaving secondary pollution.

Preparation of composite sludge carbon-based materials by LDHs conditioning and carbonization and its application in the simultaneous removal of dissolved organic matter and phosphate in sewage

In this work, a novel carbon-based hydrotalcite-like compounds materials (LDO-SBCs) were prepared by coupling layered double hydroxides (LDHs) conditioning and pyrolytic carbonization, and characterized by X-ray diffraction (XRD), Thermogravimetric Analyzer (TGA), X-ray photoelectron spectroscopy (XPS) and Brunner-Emmet-Teller (BET) measurements. The synthesized LDO-SBCs composites were used in wastewater treatment for simultaneous removal of phosphate and dissolved organic matter (DOM). The adsorption of DOM and phosphate were well conformed to pseudo-second-order mode. Adsorption equilibrium was better fitted by Langmuir model for phosphate, while Freundlich model for DOM. Compared with the raw sludge carbon, the removal efficiency of DOM and phosphate by LDO-SBCs were increased by 8% and 13%, respectively. Based on the fluorescence spectrum and parallel factor analysis (PARAFAC), LDO-SBCs performed well in promoting the removal of protein substances (TPN and APN). Pore filling, hydrogen bonding, electrostatic adsorption and surface complexation might be dominant in the adsorption of DOM, while, surface complexation and ion exchange between the LDO layers were mainly responsible for the adsorption of phosphate. The difference of adsorption capacity of LDO-SBCs was related to the superior channel structure of composite materials and the composition of interlayer anions of LDO.

Evaluation of phosphate adsorption by porous strong base anion exchangers having hydroxyethyl substituents: kinetics, equilibrium, and thermodynamics

Phosphate anions are recognized as the main responsible for the eutrophication of surface waters. In this work, two strong base anion exchangers having either N,N-dimethyl 2-hydroxyethylammonium (SBAEx.2M) or N,N-diethyl 2-hydroxyethylammonium (SBAEx.2E) functional groups, as highly efficient sorbents in the removal of phosphate anions, are presented. The influence of the main parameters (pH, contact time, initial concentration of phosphate, temperature) on the adsorption performances was investigated in batch mode. Modeling the kinetics data by Lagergren, Ho and McKay, and Elovich kinetic models indicated chemisorption as the main mechanism of sorption. The sorption at equilibrium was modeled with Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherm models. The experimental isotherms were the best fitted by Langmuir and Sips isotherms, the maximum sorption capacity for phosphate anions being 233.88 mg g^-1 SBAEx.2M and 223.5 mg g^-1 SBAEx.2E, at pH 3, and 23 °C. Adsorption of phosphate anions in competitive conditions showed that the interference with co-existing anions was low in the case of Cl^- ions and much higher with SO₄^2- ions, the ion exchange having an important contribution in the adsorption process. The adsorption was spontaneous and endothermic, the degree of spontaneity increasing with the increase of temperature. The high level of reusability, the adsorption capacity decreasing with only ~ 7% in the case of SBAEx.2E and with ~ 9% in the case of SBAEx.2M, after five sorption/desorption cycles, recommends these SBAEx as promising adsorbents for phosphate removal.

Facile Fabrication of Calcium-Doped Carbon for Efficient Phosphorus Adsorption

High phosphorus concentrations mainly result in environmental problems such as agricultural pollution and eutrophication, which have great negative influence on many natural water bodies. In this work, calcium lignosulfonate was employed to produce calcium-doped char at 400 and 800 °C. To compare the phosphorus adsorption behaviors of the two carbon materials, batch adsorption experiments were conducted in a phosphorus microenvironment. The factors including the initial solution pH, phosphorus concentration, and adsorbent amount were considered, and the main characteristics of calcium-doped chars before and after adsorption were assessed. The results revealed that the phosphorus removal processes fitted both the Freundlich and pseudo-second-order-kinetic models. According to the Langmuir model, the maximum adsorption capacities of the two adsorbents obtained at 400 and 800 °C toward phosphorus (50 °C) were 53.22 and 17.77 mg/g adsorbent, respectively. The former was rich in calcium carbonate (CaCO₃) and hydroxyl and carboxyl groups, and it mainly served as a precipitant and a chelating agent, while the latter with a high surface area was dominant in P adsorption.

Selective removal of arsenic in water: A critical review

Selective removal of arsenic (As) is the key challenge for any of As removal mechanisms as this not only increases the efficiency of removal of the main As species (neutral As(III) and As(V) hydroxyl-anions) but also allows for a significant reduction of waste as it does not co-remove other solutes. Selective removal has a number of benefits: it increases the capacity and lifetime of units while lowering the cost of the process. Therefore, a sustainable selective mitigation method should be considered concerning the economic resources available, the ability of infrastructure to sustain water treatment, and the options for reuse and/or safe disposal of treatment residuals. Several methods of selective As removal have been developed, such as precipitation, adsorption and modified iron and ligand exchange. The biggest challenge in selective removal of As is the presence of phosphate in water which is chemically comparable with As(V). There are two types of mechanisms involved with As removal: Coulombic or ion exchange; and Lewis acid-base interaction. Solution pH is one of the major controlling factors limiting removal efficiency since most of the above-mentioned methods depend on complexation through electrostatic effects. The different features of two different As species make the selective removal process more difficult, especially under natural conditions. Most of the selective As removal methods involve hydrated Fe(III) oxides through Lewis acid-base interaction. Microbiological methods have been studied recently for selective removal of As, and although there have been only a small number of studies, the method shows remarkable results and indicates positive prospects for the future.

Facile and Safe Synthesis of Novel Self-Pored Amine-Functionalized Polystyrene with Nanoscale Bicontinuous Morphology

The chloromethyl-functionalized polystyrene is the most commonly used ammonium cation precursor for making anion exchange resins (AER) and membranes (AEM). However, the chloromethylation of polystyrene or styrene involves highly toxic and carcinogenic raw materials (e.g., chloromethyl ether) and the resultant ammonium cation structural motif is not stable enough in alkaline media. Herein, we present a novel self-pored amine-functionalized polystyrene, which may provide a safe, convenient, and green process to make polystyrene-based AER and AEM. It is realized by hydrolysis of the copolymer obtained via random copolymerization of N-vinylformamide (NVF) with styrene (St). The composition and structure of the NVF-St copolymer could be controlled by monomeric ratio, and the copolymers with high NVF content could form bicontinuous morphology at sub-100 nm levels. Such bicontinuous morphology allows the copolymers to be swollen in water and self-pored by freeze-drying, yielding a large specific surface area. Thus, the copolymer exhibits high adsorption capacity (226 mg/g for bisphenol A). Further, the amine-functionalized polystyrene has all-carbon backbone and hydrophilic/hydrophobic microphase separation morphology. It can be quaternized to produce ammonium cations and would be an excellent precursor for making AEM and AER with good alkaline stability and smooth ion transport channels. Therefore, the present strategy may open a new pathway to develop porous alkaline stable AER and AEM without using metal catalysts, organic pore-forming agents, and carcinogenic raw materials.

Performance analysis of hydrated Zr(IV) oxide nanoparticle-impregnated anion exchange resin for selective phosphate removal

The superior removal selectivity of hydrated zirconium oxide nanoparticle-impregnated porous anion exchange resin (ZAE) highlights its use as phosphate removal adsorbent. However, most research examines selective phosphate removal performance using randomly determined single content of hydrated zirconium oxide, and thus the use of the ZAE in real applications remains limited. Therefore, this study aimed to investigate the selective phosphate removal performance of ZAE with different content of hydrated zirconium oxide nanoparticle (HZO NP, represented by zirconium content) by considering various conditions. A molybdate intermediate method was devised to fabricate ZAE with high loaded HZO by weakening the Donnan exclusion to HZO precursors produced from the fixed positively charged host. Consequently, the resultant ZAE was characterized by 17.8 wt% of zirconium. ZAE exhibited an increased selectivity to phosphate against competing ions in the synthetic and simulated real water matrices for both batch and fixed-bed modes as the zirconium content of ZAE increased. High performance was retained, and regeneration led to possible reusability. The linear correlation between selective phosphate removal performances and zirconium content indicates that the zirconium content is a fundamental factor determining the ZAE phosphate adsorption removal. The HZO NPs within ZAE slow adsorption kinetics by blocking AE pores and provide specific adsorption sites for phosphate removal by inner-sphere complexation.

Recyclable adsorbents based on Fe3O4 nanoparticles on lanthanum-modified montmorillonite for the efficient phosphate removal

Montmorillonite (MMT) clay modified with lanthanum (La) ions and Fe₃O₄ nanoparticles was proposed for the effective removal of phosphate ions from aqueous solution. Characterisation of the adsorbent using FTIR, SEM, XRD, XPS, XRF, BET and VSM techniques were carried out. The effects of initial phosphate concentration, contact time, dosage and pH on the phosphorus adsorption were investigated. La-MMT/Fe₃O₄ exhibited an excellent adsorption capacity of up to 14.35 mg/g, with 97.8% removal within 60 min. Langmuir isotherm model fits well with the equilibrium isotherm data, with a maximum adsorption capacity of 15.53 mg/g at room temperature. The kinetic study was well fitted with pseudo-second-order kinetics, and the adsorption rate was mainly controlled by liquid-film diffusion. The manufactured adsorbent was effectively regenerated using 0.1 M NaOH solutions, with 90.18% adsorption efficiency remaining after six adsorption/desorption cycles. These results demonstrate that La-MMT/Fe₃O₄ provides an example of regenerable high-performance adsorbents for removal of PO₄^3- from wastewater.

Removal of Phosphate Ions from Aqueous Solutions by Adsorption onto Leftover Coal

High loadings of wastewater with phosphors (P) require purification measures, which can be challenging to realize in regions where the technical and financial frame does not allow sophisticated applications. Simple percolation devices employing various kinds of adsorbents might be an alternative. Here, we investigated the application of leftover coal, which was collected from Ethiopian coal mining areas, as an adsorbent for the removal of phosphate from aqueous solutions in a classical slurry batch set-up. The combined effects of operational parameters such as contact time, initial concentration, and solution pH on P retention efficiency was studied employing the Response Surface Methodology (RSM). The maximum phosphate adsorption (79% removal and 198 mg kg−1 leftover coal) was obtained at a contact time of 200 min, an initial phosphate concentration of 5 mg/L, and a solution pH of 2.3. The Freundlich isotherm was fitted to the experimental data. The pseudo second-order equation describes the experimental data well, with a correlation value of R2 = 0.99. The effect of temperature on the adsorption reveals that the process is exothermic. The results demonstrate that leftover coal material could potentially be applied for the removal of phosphate from aqueous media, but additional testing in a flow-through set-up using real wastewater is required to draw definite conclusions.

Low-cost chitosan-calcite adsorbent development for potential phosphate removal and recovery from wastewater effluent

Phosphorous (P) recovery from wastewater will become increasingly vital in the future as terrestrial rock phosphate deposits are expended. Effective management of P as a critical resource will require new techniques to recover P from wastewater, ideally in a form that can be used in agriculture as fertiliser. In this study, batch and fixed-bed column conditions were tested using a novel KOH deacetylated calcite-chitosan based adsorbent (CCM) for P removal from aqueous solutions and wastewater effluents. The unique characteristics of this adsorbent as a phosphate adsorbent were the result of rich surface functionality (amine and sulphur functional groups of the chitosan and proteins) and the CaCO₃ content (providing donor ligands; and additionally beneficial if the material were used as fertiliser, buffering soil acidification caused by nitrogen application). The maximum P adsorption capacity was determined to be 21.36 mgP/g (at 22 °C) and the endodermic process reached equilibrium after 120 min. The experimental data was best described using a Langmuir isotherm and a pseudo-second order kinetic model. The diffusion kinetic analysis highlighted the importance of both film and intraparticle mass-transport. Material characterisation suggested that the adsorption process involved interactions between P and functional groups (mostly -NH₃⁺) due to electrostatic interaction on the chitosan chain or involved ligand exchange with CO₃^2-. Analysis of materials using X-Ray Powder Diffraction (XRPD) and Thermogravimetric Analysis (TGA) indicated a microprecipitation-type mechanism may occur through the formation of hydroxylapatite (Ca₅(PO₄)₃(OH)). Desorption studies demonstrated that the P-laden CCM (derived from crab carapace) had the potential to be reused in soil amendment as a slow-release P fertiliser. The effects of different operating parameters were explored in a fixed-bed column, and the experimental data fitted well to the Clark model (R² = 0.99). The CCM also showed excellent P adsorption potential from secondary and final wastewater effluent in dynamic conditions, even at low P concentrations. Finally, a scale-up approach with cost analysis was used to evaluate the price and parameters needed for a potential large-scale P recovery system using this adsorbent.

Achieving low-cost, highly selective nitrate removal with standard anion exchange resin by tuning recycled brine composition

This study demonstrated the presence of a critical equivalent ratio of the competing anion (i.e., sulfate and bicarbonate) to chloride ion in recycled brine to achieve highly-selective nitrate removal from nitrate-rich groundwater in the standard-anion exchange resin (AER) (i.e., with trimethylamine functional groups) column process. With increasing bicarbonate (or sulfate):chloride equivalent ratio in brine used to circularly activate/regenerate the standard-AER column, considerable bicarbonate (sulfate) removal and dumping were observed. The critical bicarbonate (sulfate):chloride equivalent ratio of 2:5 (8:1) in brine effectively achieved zero net bicarbonate (sulfate) removal (<5%) from feedwater during long-term exhaustion-regeneration cyclic operation. The feed rate (6-18 BV/h) played a key role in determining the critical sulfate:chloride equivalent ratio in brine, while the feed sulfate concentration (145-345 mg/L) slightly changed the critical sulfate:chloride equivalent ratio. The use of optimized ternary brine (with a sulfate:chloride:bicarbonate equivalent ratio of 42:5:2) stably achieved long-term highly-selective nitrate removal from groundwater in the standard-AER column process with brine electrochemical treatment. The possible mechanism for nitrate selectivity included the modification of the sulfate: and bicarbonate:chloride equivalent ratios in the standard-AER column by the optimized brine in circular activation/regeneration mode; this changed the column elution and breakthrough curves, inhibited the competition of sulfate and bicarbonate for ion exchange sites during exhaustion according to the separation factor, and finally achieved selective nitrate removal from feedwater.

Phosphate recovery with granular acid-activated neutralized red mud: Fixed-bed column performance and breakthrough curve modelling

Granular acid-activated neutralized red mud (AaN-RM) has been successfully prepared with good chemical stability and physical strength. However, its potential for industrial application remains unknown. Therefore, the performance of granular AaN-RM for phosphate recovery in a fixed-bed column was investigated. The results demonstrated that the phosphate adsorption performance of granular AaN-RM in a fixed-bed column was affected by various operational parameters, such as the bed depth, flow rate, initial solution pH and initial phosphate concentration. With the optimal empty-bed contact time (EBCT) of 24.27 min, the number of processed bed volumes and the phosphate adsorption capacity reached 496.95 and 84.80 mg/g, respectively. Then, the saturated fixed-bed column could be effectively regenerated with a 0.5 mol/L HCl solution. The desorption efficiency remained as high as 83.45% with a low weight loss of 3.57% in the fifth regeneration cycle. In addition, breakthrough curve modelling showed that a 5-9-1 feed-forward artificial neural network (ANN) could be effectively applied for the optimization of the fixed-bed adsorption system; the coefficient of determination (R²) and the root mean square error (RMSE) evaluated on the validation-testing data were 0.9987 and 0.0183, respectively. Therefore, granular AaN-RM fixed-bed adsorption exhibits promising potential for phosphate removal and recovery from polluted water.

Synthesis optimisation and characterisation of chitosan-calcite adsorbent from fishery-food waste for phosphorus removal

Here, Box-Behnken design (BBD) approaches were utilised to optimise synthesis methodology for the chitosan-calcite rich adsorbent (CCM) made from fishery-food waste material (crab carapace), using low-temperature activation and potassium hydroxide (KOH). The effect of activation temperature, activation time and impregnation ratio was studied. The final adsorbent material was evaluated for its phosphorus (P) removal efficiency from liquid phase. Results showed that impregnation ratio was the most significant individual factor as this acted to increase surface deacetylation of the chitin (to chitosan) and increased the number of amine groups (-NH₂) in the chitosan chain. P removal efficiency approached 75.89% (at initial P concentration of 20 mg/L) under optimised experimental conditions, i.e. where the impregnation ratio for KOH:carapace (g/g) was 1:1, the activation temperature was 105 °C and the activation time was 150 min. Predicted responses were in good agreement with the experimental data. Additionally, the pristine and CCM material were further analysed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), Brunauer-Emmett-Teller technique (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Characterisation showed enhancements in surface chemistry (introducing positively charged amine groups), textural properties and thermal stability of the CCM.

Enhanced phosphate removal using zirconium hydroxide encapsulated in quaternized cellulose

Zirconium-based materials are efficient adsorbent for aqueous phosphate removal. However, current zirconium-based materials still show unsatisfied performance on adsorption capacity and selectivity. Here, we demonstrate a zirconium hydroxide encapsulated in quaternized cellulose (QC-Zr) for the selective phosphate removal. Zirconium hydroxide nanoparticles were simultaneously generated in situ with the QC framework and firmly anchored in the three-dimensional (3D) cross-linked cellulose chains. The maximum P adsorption capacity of QC-Zr was 83.6 mg P/g. Furthermore, the QC-Zr shows high P adsorption performance in a wide pH range, generally due to the electrostatic effects of quaternized cellulose. The enhanced adsorption of P was also achieved in the presence of competing anions (including Cl^-, NO₃^-, SO₄^2-, SO₄^4-) and humic acid (HA) even at a molar ratio up to 20 levels. The column adsorption capacity of QC-Zr reached 4000 bed volumes (BV) at EBCT = 0.5 min as the P concentration decreased from 2.5 to 0.5 mg/L. Mechanism study revealed that both -N⁺(CH₃)₃ groups and zirconium hydroxide were involved in phosphate adsorption via electrostatic interactions between -N⁺(CH₃)₃ and phosphate, and the formation of zirconium hydrogen phosphate (Zr(HPO₄)x). The ³¹P nuclear magnetic resonance (NMR) study implied that P surface-precipitated and inner-sphere complexed with zirconium hydroxide at a ratio of 3:1.

Selective Phosphate Removal from Water and Wastewater using Sorption: Process Fundamentals and Removal Mechanisms

Eutrophication of water bodies is a serious and widespread environmental problem. Achieving low levels of phosphate concentration to prevent eutrophication is one of the important goals of the wastewater engineering and surface water management. Meeting the increasingly stringent standards is feasible in using a phosphate-selective sorption system. This critical review discusses the most fundamental aspects of selective phosphate removal processes and highlights gains from the latest developments of phosphate-selective sorbents. Selective sorption of phosphate over other competing anions can be achieved based on their differences in acid-base properties, geometric shapes, and metal complexing abilities. Correspondingly, interaction mechanisms between the phosphate and sorbent are categorized as hydrogen bonding, shape complementarity, and inner-sphere complexation, and their representative sorbents are organic-functionalized materials, molecularly imprinted polymers, and metal-based materials, respectively. Dominating factors affecting the phosphate sorption performance of these sorbents are critically examined, along with a discussion of some overlooked facts regarding the development of high-performance sorbents for selective phosphate removal from water and wastewater.

Enhanced selective removal of arsenic(V) using a hybrid nanoscale zirconium molybdate embedded anion exchange resin

Selective removal of trace arsenic is crucial for obtaining safe drinking water. Here, the selective adsorptive performance of arsenate (As(V)) on a hybrid ZMAE (nanoscale zirconium molybdate embedded a macroporous anion exchange resin) was examined. It was found that the As(V) adsorption efficiency of ZMAE was almost retained in the presence of competing ions (NO₃^- or SO₄^2-) up an [SO₄^2-]/[As] or [NO₃^-]/[As] ratio of 150/1, whereas that of bare AE (anion exchange resin) was negligible for [SO₄]/[As] over 15/1. In addition, the As(V) maximum adsorption capacity of ZMAE was found to be 41.2 mg/g, which is in contrast with the negligible adsorption of bare AE under sulfate-rich condition. The enhanced arsenate selectivity of ZMAE can be attributed to the excellent selectivity of ZM NPs (zirconium molybdate nanoparticles), which contributed up to 45% of the adsorption capacity of ZMAE. The behavior of ZMAE towards arsenate was compared with that towards phosphate showing similar adsorption performances between them, which indicates the similar affinity of ZMAE towards arsenate and phosphate. Finally, ZMAE examined for fixed-bed column adsorption for As(V) removal from synthetic As(V) water was effective for up to 5100 BVs, treating As(V) from 0.1 mg/L to below 0.01 mg/L (meeting the WHO guidelines).

Selective adsorption of molybdate from water by polystyrene anion exchanger-supporting nanocomposite of hydrous ferric oxides

Molybdenum is an essential trace element for humans but can be harmful with excess assimilations or chronic exposures. In this study a polymer-functionalized nanocomposite (HFO-PsAX) was fabricated for selective adsorption of molybdate from aqueous solution. HFO-PsAX was prepared by grafting hydrous ferric oxide nanoparticles (HFOs) into the porous structure of a polystyrene anion exchanger (PsAX) by in situ synthesis method. The resultant HFO-PsAX exhibited greatly enhanced selectivity toward molybdate as compared with the matrix, PsAX, which is also a fair adsorbent for scavenging molybdate. The competitive abilities of the ubiquitous anions, i.e., chloride, carbonate, sulfate, and phosphate, on the adsorption of molybdate by HFO-PsAX followed the order: chloride < phosphate < carbonate < sulfate. The unexpectedly weak competitive ability of trivalent phosphate may be due to incompletely dissociated state and formation of molybdate-phosphate complexes. The optimal pH for the adsorption of molybdate was determined as pH≈4, which is associated with the dissociation constants of molybdic acid; certain adsorption capacities were also observed even under extremely alkaline condition (pH=14) for single-component molybdate solution. Temperature (10, 25, and 40°C) has negligible effect on the adsorption capacities by HFO-PsAX, and Freundlich model and Dubinin-Radushkevich (D-R), Temkin model can describe the adsorption isotherms well. The adsorption potential of Temkin model is calculated as ≈100J/mol, which is between those of physisorption and chemisorption process. Fixed-bed column adsorption experiments validated the potential of HFO-PsAX in treating Mo(VI) contaminated water for practical application, and the exhausted HFO-PsAX can be regenerated by a binary NaOH-NaCl solution (both 5% in mass) without loss in adsorption capacities.

Magnetic polymer-supported adsorbent with two functional adsorption sites for phosphate removal

In this paper, a new magnetic polymer-supported phosphate adsorbent MPVC-EDA-Ce was prepared by loading cerium (hydr)oxides onto ethylenediamine-functionalized polyvinyl chloride for the first time. MPVC-EDA-Ce showed excellent adsorption performances towards phosphate and easy recovery. The adsorption isotherm and kinetics of MPVC-EDA-Ce followed Langmuir monolayer model and the pseudo-second-order model, respectively. The pH results demonstrated that the MPVC-EDA-Ce could effectively remove phosphate in a wide range of pH with insignificant cerium leaching. Furthermore, analyses on adsorption mechanism and effect of competing anions demonstrated the formation of strong inner-sphere complexation between cerium (hydr)oxides and phosphate, which was a selective adsorption process, while positively charged quaternary ammonium groups adsorbed phosphate via relatively weak electrostatic attraction which was a non-selective adsorption process. The study provided a good reference to design novel phosphate adsorbents with two even more functional adsorption sites and a deep insight to investigate the adsorption mechanism towards phosphate.

Fabrication of a Novel Bifunctional Nanocomposite with Improved Selectivity for Simultaneous Nitrate and Phosphate Removal from Water

Phosphorus and nitrogen compounds are both the main sources of eutrophication and coexist in some municipal effluents or eutrophic waters; elimination of phosphorus and nitrogen from wastewater is becoming an imperative but also a hard task. Herein, an innovative bifunctional nanocomposite HFO@TPR was developed for synchronous nitrate/phosphate elimination from water. A macroporous polystyrene microspheres modified with triethylamine functional groups was synthesized as the host of HFO@TPR for selective nitrate removal, and Fe(III) hydroxide (HFO) nanoparticles were implanted inside as the active species for specific phosphate removal. Compared to other commercial adsorbents, HFO@TPR exhibited outstanding selectivity and preference toward nitrates and phosphates, and the coexisting anions exert an insignificant effect on adsorption performance. Such exceptional bifuntionality of HFO@TPR was achieved through two pathways, that is, nitrate was preferentially adsorbed by the fixed triethylamine groups through the electrostatic attraction, and phosphate was preferentially captured by the encapsulated HFO nanoparticles through the inner-sphere complexation. The exhausted HFO@TPR could be effectively regenerated by using a NaOH-NaCl mixed reagent for cyclic use with a relative constant efficiency. In addition, column adsorption experiments demonstrated that HFO@TPR could eliminate nitrate from 18 to <10 mg N/L with the treatment capacity of ∼600 bed volume (BV), and meanwhile remove phosphate from 2.5 to <0.2 mg P/L with the treatment capacity of ∼750 BV. We believe what we found in this study could advance the method on how to develop bifunctional adsorbents for synchronous removal of coexisting contaminants from water.

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^-, SO₄^2-, 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.

Zr4+ ions embedded chitosan-soya bean husk activated bio-char composite beads for the recovery of nitrate and phosphate ions from aqueous solution

Removal of nitrate and phosphate ions using Zr4+ ions embedded chitosan-soya bean husk activated bio-char composite beads (Zr-CS-SAC) was carried out by batch mode to overcome the environmental problems due to eutrophication. The adsorbent was well characterized by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) analysis with energy dispersive X-ray analyzer (EDX), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller surface analyzer (BET), thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) etc. The adsorption equilibrium models of Langmuir, Freundlich and D-R isotherms were evaluated and the results described that the Freundlich model was the best for both the adsorbates of nitrate and phosphates ions with respective capacities of 90.09 and 131.29 mg g-1 at 30 °C. Studies on thermodynamic parameters revealed the endothermic and spontaneous nature of the adsorption. Different kinetic models were studied and found that pseudo-second-order kinetic data were well fitted for adsorption process. These results suggested that Zr-CS-SAC composite beads as a promising adsorbent for the removal of nitrate and phosphate ions from water with good removal efficiency, adsorbability, recyclability and non- toxicity.

Synthesis of Positively Charged Polystyrene Microspheres for the Removal of Congo Red, Phosphate, and Chromium(VI)

Uniform positively charged polystyrene microspheres were synthesized and further examined as a new sorbent for water remediation. The structures of the resulting sorbent were characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. The adsorption performance of the sorbent was evaluated using three typical pollutants, namely, Congo red, phosphate, and Cr(VI). The adsorption isotherms were fitted by the Langmuir and Freundlich models, while the adsorption kinetics was analyzed by the pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations. The thermodynamic parameters of the adsorption process including changes of enthalpy, entropy and Gibbs free energy, and binding constant were obtained by isothermal titration calorimetry measurements. The effects of solution pH and competitive ions on the adsorption process were investigated. The adsorption isotherms could be better fitted by the Langmuir model, yielding maximum adsorption capacities of 18, 6.2, and 1.1 mg g^-1 for the adsorption of Congo red, Cr(VI), and phosphate, respectively. The adsorption kinetics could be best described by the pseudo-second-order equation. The spent sorbent was regenerated by washing with 1 M KOH and showed outstanding long-term cyclic performance. The findings suggested that the positive charges at the surface of polystyrene microspheres could serve as effective sites for the immobilization of anionic pollutants in solutions owing to the electrostatic attraction.