Phosphate removal from wastewaters by a naturally occurring, calcium-rich sepiolite

Desalination RO reject brine as a novel-based porous geopolymer for phosphorus removal from contaminated media

Desalination reverse osmosis reject brine-based porous geopolymer (RO/GP) was produced and investigated as an improved adsorbent for phosphorus (P) removal from tainted seawater, brackish water, river water, and municipal wastewater effluent. The RO reject brine/geopolymer was produced by reacting metakaolin and fly ash with a Na-alkali activator and anhydrous RO brine as a sacrificial template. The influence of RO reject brine content on water absorption, porosity, mechanical, and structural properties were examined. The developed RO-based geopolymers exhibited the greatest porosity (58.3-84.2 % vol%), a significant ratio of open porosity to total porosity (67.7-92.1 %), and outstanding compression strength (3.6-10.4 MPa). The produced RO/GP structure has an adsorption capacity of 92.4 mg-P/g. The sequestration reaction of phosphorus by RO/GP is of pseudo-second-order kinetic behavior via Chi-squared (χ2), RMSE, and determination coefficient (R2) values. Regarding their agreement with Langmuir behavior, the phosphorus adsorption uptakes occur in homogeneous and monolayer states. The reaction is exothermic, spontaneous, and favorable. The RO/GP exhibits significant affinity for phosphorus co-existing with Cl-, Na+, SO42-, K+, HCO3-, and Ca2+. The RO/GP shows high safety during the adsorption investigation, with a total cost of 0.32 $/kg-P.

Effect of Surface Treatment of Nanocrystalline CeO2 on Its Dephosphorylation Activity and Adsorption of Inorganic Phosphates

The surface of nanocrystalline cerium oxide (CeO2) was treated with various chemical agents by a simple postmodification method at 25 °C and atmospheric pressure. Hydrogen peroxide, ammonium persulfate, deionized water, ascorbic acid, and ortho-phosphoric acid were used in order to study and evaluate their effect on surface materials, such as surface area, crystallite size, number of surface hydroxyl groups, particle morphology, and Ce3+/Ce4+ ratio. Paraoxon-methyl (PO) decomposition and inorganic phosphate adsorption were used to evaluate the effect of surface treatment on catalytic and adsorption properties. CeO2 surface was studied by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and acid-base titration. While the treatment procedure affected the number of surface hydroxyl groups and the amount of bulk surface oxygen vacancies, only negligible changes were observed in the Ce3+/Ce4+ ratio. Interestingly, surface treatment affected the ability to decompose PO, but only a small effect on inorganic phosphate adsorption was observed, indicating the robustness of CeO2 for the latter. A mechanism for possible interaction of the used chemicals with the CeO2 surface was proposed.

Optimization of the adsorption performance of herbal residues as lanthanide ion-modified carriers for phosphate by fly ash and its application

In order to mitigate the harmful effects of eutrophication in water bodies, the applications of lanthanum-modified materials for phosphate removal from wastewater have attracted much attention. Unlike conventional adsorbents, plant wastes usually have poor adsorption abilities and are difficult to be reused for desorption of phosphate due to their small pore sizes and ununiform loading of modified ions. In this paper, a composite adsorbent (LC-MM) was synthesized by hydrothermal treatment of waste traditional Chinese medical materials (MMs) with load of lanthanum carbonate and co-heating treatment with coal fly ash (CFA), which was applied to remove phosphate from water. The results showed that maximum adsorption capacity of LC-MM was 52 mg g-1, and the LC-MM showed appreciable adsorption capacity of phosphate for agricultural wastewater in the presence of complex interfering ions and for urban surface waters with low phosphate concentrations. Five adsorption-desorption cycles showed good reusability. The mechanism study showed that the La3+ ions were more uniformly distributed on the surface of the absorbents with the introduction of Fe3+, Al3+, Mg2+ and Ca2+ ions in CFA. The ligand exchange between phosphate and carbonate, the internal spherical complexation formed by lanthanum ion and phosphate, and surface chemical precipitation attachment are the main reasons why the adsorption capacity of LC-MM approached or even surpassed that of conventional lanthanum-modified adsorbents. In conclusions, this work proposed an effective method for the modification of plant materials.

Removal of Phosphorus with the Use of Marl and Travertine and Their Thermally Modified Forms-Factors Affecting the Sorption Capacity of Materials and the Kinetics of the Sorption Process

The paper presents new reactive materials, namely marl and travertine, and their thermal modifications and the Polonite^® material, analyzing their phosphorus removal from water and wastewater by sorption. Based on the experimental data, an analysis of the factors influencing the sorption capacity of the materials, such as the material dose, pH of the initial solution, process temperature, surface structure, and morphology, was performed. Adsorption isotherms and maximum sorption capacities were determined with the use of the Langmuir, Freundlich, Langmuir-Freundlich, Tóth, Radke-Praunitz, and Marczewski-Jaroniec models. The kinetics of the phosphorus sorption process of the tested materials were described using reversible and irreversible pseudo-first order, pseudo-second order, and mixed models. The natural materials were the most sensitive to changes in the process conditions, such as temperature and pH. The thermal treatment process stabilizes the marl and travertine towards materials with a more homogeneous surface in terms of energy and structure. The fitted models of the adsorption isotherms and kinetic models allowed for an indication of a possible phosphorus-binding mechanism, as well as the maximum amount of this element that can be retained on the materials' surface under given conditions-raw marl (43.89 mg P/g), raw travertine (140.48 mg P/g), heated marl (80.44 mg P/g), heated travertine (282.34 mg P/g), and Polonite^® (54.33 mg P/g).

Removal of As(V) from aqueous solution using modified Fe3O4 nanoparticles

The removal of arsenic contamination from the aqueous environment is of great importance in the conservation of the Earth's water resources, and surfactants are a promising material used to modify magnetic nanoparticles to improve adsorption properties. Therefore, it is important to develop efficient and selective adsorbents for arsenic. Surface modification of Fe₃O₄ was carried out using anionic, cationic and zwitterionic surfactants to obtain composite Fe₃O₄@SDS, Fe₃O₄@CTAB, Fe₃O₄@SNC 16 and Fe₃O₄@NPC 16 (collectively referred to as Fe₃O₄@surfactants). The synthesized composite Fe₃O₄@surfactants magnetic nanoparticles were characterized by XRD, TEM and FTIR. The As(V) removal characteristics of the composite magnetic nanoparticles from the aqueous solution were evaluated by adsorption batch experiments which indicated the possibility of effective application of the surfactant-modified Fe₃O₄ magnetic nanoparticles for the removal of As(V) from aqueous solution. The adsorption equilibrium of the composites was reached in 30 min and the kinetic data followed the pseudo-second-order model. Langmuir equation could represent the adsorption isotherm data very well. Moreover, under the identical conditions, Fe₃O₄@CTAB showed maximum capacity of adsorption for As(V) (55.671 mg g^-1), with its removal efficiency being much higher than that of the other composites. In addition, the Fe₃O₄@surfactants composite magnetic nanoparticles retained 93.5% of its initial arsenic removal efficiency even after re-using it five times. The mechanism of arsenic adsorption by Fe₃O₄@surfactants composite magnetic nanoparticles was proved to be complexation via electrostatic attraction, which was mainly innersphere in nature.

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.

Simultaneous adsorption of phosphate and tetracycline by calcium modified corn stover biochar: Performance and mechanism

It is important to solve the problems of biomass treatment and combined contaminants removal in environmental remediation. In this study, a calcium (Ca) modified biochar (CaBC800) was fabricated using corn stover (CS) as a raw material to remove phosphate and tetracycline (TC). The experimental results indicate that CaBC800 can adsorb both inorganic phosphate and organic TC. The entire adsorption process corresponds to pseudo-second-order kinetics and Langmuir adsorption isotherm. The maximum adsorption capacities of phosphate and TC were 33.944 and 33.534 mg/g, respectively. The phosphate adsorption was demonstrated to mainly depend on the chemical precipitation by Ca²⁺ and ligand exchange by hydroxyl groups from CaBC800. Meanwhile, hydrogen bonding from oxygen functional groups and π-π interactions from aromatic rings are the main adsorption mechanisms of TC. This study provides a new adsorbent to efficiently remove phosphate and TC, and the simultaneous adsorption indicates the application potential of CaBC800 in wastewater remediation.

Removal effects of a biomass bottom ash composite on tailwater phosphate and its application in a rural sewage treatment plant

Tailwater phosphate from sewage treatment plants and biomass bottom ash (BA) from power plants has become a global concern for the sustainable environmental development and resource management. However, there are large gaps in the understanding of the removal mechanisms and application conditions of BA on tailwater phosphate. In this study, the removal effect and mechanism of BA and its composites were fully discussed using a series of experiments, including adsorption, desorption, characterization, and incubation experiments. It was found that the combination of BA and red soil at a rate of 4:1 (C_BA) could remove 92.44% of phosphate from tailwater in 3-10 h. Its adsorption process was well fitted by the pseudo-second-order kinetic and Freundlich isotherm adsorption models. The mechanism of phosphate adsorption primarily included ligand exchange, physical adsorption, chemical precipitation, electrostatic attraction, and ion exchange. The C_BA could be used as a better substrate for constructed wetlands because it was effective under wide application conditions, which varying pH values (4.0-8.0), initial concentrations of tailwater phosphate (0.5-5.0 mg L^-1), and even extreme temperatures (heat and cold). Moreover, Hippuris vulgaris L. was optimized and combined with the C_BA to deeply remove 57.45-76.06% of phosphate from a rural sewage treatment plant. The phosphate concentration after treatment could reach below the limit values of the Grade III or IV standard (GB 3838-2002), though the C_BA contained and released phosphate. This study can help provide a recycling route for both BA and tailwater phosphate resources, extend the industrial chain of biomass power plants, and improve the surrounding water environment.

Competitive adsorption of pollutants from anodizing wastewaters to promote water reuse

Anodizing wastewater contains principally phosphate (PO₄^3-) anions according to previous studies, but with the purpose to promote water reuse in this type of industry, a complete characterization of wastewater was made to remove other anions and cations also present in significant concentration. Particularly, the adsorption of sodium (Na⁺), potassium (K⁺), fluoride (F^-), sulfate (SO₄^2-) and phosphate (PO₄^3-) was studied using different sorbents such as: coconut shell activated carbon, bone char, bituminous coal activated carbon, natural zeolite, silica, anionic and cationic exchange resins, a coated manganese-calcium zeolite, coconut shell activated carbon containing iron and iron hydroxide. All sorbents were characterized using FT-IR spectroscopy, potentiometric titration, nitrogen adsorption isotherms at 77 K, X-ray diffraction and SEM/EDX analysis to study the adsorption mechanism. The adsorption studies were performed in batch systems under constant agitation using both standard solutions of each ion and real anodizing wastewater. Results showed that, in general, the adsorption of all anions and cations is higher when mono-component standard solutions were used, since in the anodizing wastewater all species are competing for the active sites of the adsorbent. Na⁺ present in anodizing wastewater was efficiently adsorbed on coated manganese-calcium zeolite (20.55 mg/g) and natural zeolite (18.55 mg/g); while K⁺ was poorly adsorbed on all sorbents (less than 0.20 mg/g). Anions such as F^-, SO₄^2- and PO₄^3-, were better adsorbed on the anionic resin (0.17, 45.38 and 2.92 mg/g, respectively), the iron hydroxide (0.14, 7.96 and 2.87 mg/g, respectively) and the bone char (0.34, 8.71 and 0.27 mg/g, respectively). All these results suggest that adsorption is a promising tertiary treatment method to achieve water reuse in the anodizing industry.

Treatment of environmental contamination using sepiolite: current approaches and future potential

To evaluate the potential of sepiolite-based materials to resolve environmental pollution problems, a study is needed which looks at the whole life cycle of material application, including the residual value of material classified as waste from the exploitation of sepiolite deposits in the region or from its processing and purification. This would also maximize value from the exploitation process and provide new potential for local waste management. We review the geographical distribution of sepiolite, its application in the treatment of potentially toxic elements in soil and across the wider landscape, an assessment of modification and compositional variation of sepiolite-based applications within site remediation and wastewater treatment. The potential of sepiolite-based technologies is widespread and a number of processes utilize sepiolite-derived materials. Along with its intrinsic characteristics, both the long-term durability and the cost-effectiveness of the application need to be considered, making it possible to design ready-to-use products with good market acceptance. From a critical analysis of the literature, the most frequently associated terms associated with sepiolite powder are the use of lime and bentonite, while fly ash ranked in the top ten of the most frequently used material with sepiolite. These add improved performance for the inclusion as a soil or wastewater treatment options, alone or applied in combination with other treatment methods. This approach needs an integrated assessment to establish economic viability and environmental performance. Applications are not commonly evaluated from a cost-benefit perspective, in particular in relation to case studies within geographical regions hosting primary sepiolite deposits and wastes that have the potential for beneficial reuse.

Applicability of ferric(III) hydroxide as a phosphate-selective adsorbent for sewage treatment

This research was undertaken to evaluate the usability of ferric(III) hydroxide for phosphate removal from sewage. Batch adsorption experiments, partly fixed bed column experiments, were conducted to study the influence of various factors, competing anions and contact time on the adsorption of phosphate on ferric(III) hydroxide. Processing ferric iron in the form of akaganeite (β-FeOOH) greatly increased the adsorption capacity for phosphate. The optimum phosphate removal was observed in the pH_eq ≤ 6.0. All results from this study demonstrate the potential usability of β-FeOOH as a good phosphate-selective adsorbent for the phosphate removal system for a sewage treatment plant.

Zirconium-modified natural clays for phosphate removal: Effect of clay minerals

Excessive amount of phosphate entering water bodies may cause eutrophication and have detrimental effects on ecosystems. Clay-based materials have been drawing attractive attention in mitigating phosphate release to aquatic environment. In this study, we prepared a series of zirconium (Zr)-modified clays to investigate the effect of clay structure and expansion property on phosphate adsorption. Kaolinite, montmorillonite, and vermiculite were selected as three representative natural clays for Zr modification, and the resulting Zr-modified clays were characterized using various techniques that included powder X-ray diffraction, scanning electron microscopy, and zeta potential measurement. Different Zr-modified clays exhibited substantially different phosphate adsorption behaviors, which may be related to the distinct structural and expansion properties of each clay substrate. Particularly, Zr-modified montmorillonite had fastest phosphate adsorption kinetics and highest phosphate adsorption capacity among all Zr-modified clays, which may be attributed to the good expansion property of montmorillonite that favored the uniform intercalation of Zr species, making the adsorption sites easily accessible by phosphate. Furthermore, all Zr-modified clays showed robust performance for phosphate adsorption under various water chemistry conditions. Combined aqueous sorption and solid characterization analyses suggested that formation of inner-sphere surface complexes may be the primary mechanism for phosphate adsorption by Zr-modified clays.

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.

Use of calcined sepiolite in removing phosphate from water and returning phosphate to soil as phosphorus fertilizer

We investigated the application of cheap but efficient sepiolite for the removal of phosphate and the use of phosphate-adsorbed sepiolite for rice cultivation. Sepiolite was calcined under different temperatures to improve its phosphate adsorption capacity; the sepiolite calcined at 950 °C (950-SPL) was found to have highest adsorption capacity. As the calcination temperature increased, the amount of Ca eluted from sepiolite also increased, resulting in the formation of Ca-P precipitates. Phosphate adsorption on 950-SPL reached equilibrium within 12 h. Both the Langmuir and Freudlich models were not well-fitted to the equilibrium adsorption model because phosphate at initial concentration was fully removed by 950-SPL. The maximum adsorption capacity of 950-SPL with respect to phosphate was 172.34 mg/g. The phosphate adsorption of 950-SPL was endothermic and spontaneous. Phosphate adsorption at pH 3 was two times higher than at pH 11. The presence of bicarbonate significantly influenced the decrease of phosphate by 950-SPL. A breakthrough of column packed with 950-SPL/sand was not observed during >200 h. The phosphate fraction in 950-SPL was mainly composed of apatite-P and residual fraction. A toxicity test using Daphnia magna showed that the toxic units of 950-SPL corresponded to no acute toxicity. Tiller number, shoot height, shoot dry weight and total dry weight were significantly higher in P-adsorbed 950-SPL application than control. It can be concluded that calcined sepiolite can be effective in the removal of phosphate and that the sepiolite after phosphate adsorption can be used as a P fertilizer in soil.

Reactive Materials in the Removal of Phosphorus Compounds from Wastewater-A Review

Modern technologies designed to treat wastewater containing phosphorus compounds are based on the processes of adsorption and precipitation. In addition, more environmentally friendly and cheaper materials are being sought to ensure greater conformity with overarching assumptions of green chemistry and sustainable development. Against that background, this paper offers a review and analysis of available information on the considered reactive materials that have the capacity to remove phosphorus from wastewater. These materials are categorised as natural (with a sub-division in line with the dominant sorption groups of Al/Fe or Ca/Mg), waste, or man-made. Notably, most studies on sorbents have been carried out in laboratory systems via experimentation under static conditions. Among the natural materials, opoka has the highest sorption capacity of 181.20 g P/kg, while red mud (in the waste material category) is most efficient at binding phosphorus with a level of 345.02 g P/kg. Finally, among the group of commercial materials, Rockfos^® has the highest sorption capacity of 256.40 g P/kg. In addition, this paper recognises the effect of composition, pH, and physical properties on a reactive material's capacity to absorb phosphorus, as well as the possibility for further potential use in the production of fertilisers.

Effects of sediment oxidation on phosphorus transformation in three large shallow eutrophic lakes in China

Oxidation of surface sediments is an important means for altering phosphorus (P) exchanges across sediment-water interface (SWI) in shallow lakes. In this study, the potential and composition of regenerated oxidation capacity (OC) of surface sediments were evaluated in three large shallow lakes (Tai Lake, Chao Lake, and Dianchi Lake) in China; the transformation of sedimentary P was quantified through P fractionation scheme. The composition of the regenerated OC differed among these three lakes, with Fe(III) and SO₄^2- dominant in Dianchi Lake, Mn(IV) and Fe(III) in Chao Lake and Tai Lake. Oxidation of sediments enhanced the transformation of sedimentary P and altered P exchanges across the SWI. In Chao Lake, the HCl-P was transformed to BD-P; in Tai Lake, the NaOH-P was involved too, and transformed to BD-P; whereas in Dianchi Lake, an increase in NH₄Cl-P was also observed except for the transformation from HCl-P to BD-P. The sediment-to-water flux of P was enhanced with 0.17 mg/g DW in Dianchi Lake and 0.08 mg/g DW in Chao Lake, while a contrary water-to-sediment flux of P was observed in Tai Lake, reaching 0.01 mg/g DW. This study advances our knowledge on the impacts of sediment oxidation on P cycles in lakes, which will be beneficial to eutrophication control.

Response of methanogens in calcified anaerobic granular sludge: Effect of different calcium levels

Inhibition of high calcium during anaerobic wastewater treatment has been studied in recent years, focusing on calcium precipitates in anaerobic granule but neglecting the effect of functional microbes. In this study, key factors of calcification and microbial behaviors especially methanogens of calcified anaerobic granule (AnGS) were investigated in batch assays with calcium level varying from 0 to 5 g L^-1. The results showed that the COD removal efficiency and specific methane activity of calcified AnGS were restrained with calcium addition, especially high calcium (>2 g L^-1), and little tolerance of calcified AnGS to Ca²⁺ was underlined compared with non-calcified AnGS. Analysis of calcium mass flow from solution to sludge validated the formation of calcium precipitates influenced by calcium concentration, pH and HCO₃^-. Besides, death of microbes in outer layer of anaerobic granules was triggered by calcium precipitation. Most importantly, aceticlastic Methanothrix genus was the dominant methanogen, and its relative abundance was correlative negatively with cumulative decrease of bulk Ca²⁺. Hydrogenotrophic Methanobacterium was enriched at higher calcium level, and it suggested that hydrogenotrophic methanogenesis could play a role in alleviating the inhibition of high calcium.

Investigation into lanthanum-coated biochar obtained from urban dewatered sewage sludge for enhanced phosphate adsorption

Phosphate adsorption using metal-modified biochar has awakened much attention and triggered extensive research. In this study, the effect of lanthanum (La)-modified sludge using impregnation-co-precipitation was used for phosphate adsorption. Consequently, La-coated biochar at a pyrolysis temperature of 600 °C had the highest phosphate adsorption and the lowest heavy metal leaching potential. The treatment of virgin biochar with alkali before La loading was found to be beneficial for the increase of phosphate adsorption capacity. The adsorption kinetics was well depicted by the pseudo-second-order model, and indicating that intraparticle diffusion played a crucial role in the adsorption process. The good fitness between adsorption data and the Langmuir isotherm model showed a maximal adsorption capacity of 93.91 mg/g, where phosphate absorption was highly correlated to its concentration in the solution. The La-coated biochar showed high adsorption capacity when the solution pH varied from 3.0 to 6.0, and was insensitive to the coexisting chloride, nitrate, sulfate, bicarbonate and citrate. Moreover, the adsorption mechanism was further explored by using Zeta potential analysis, FTIR and XPS, indicating that the phosphate is adsorbed through electrostatic attraction in the form of the inner-sphere complexation. All the results suggested that the sludge-based biochar, as a support material for La, could serve as a promising adsorbent for phosphate in real applications.

Experimental and model study for fluoride removal by thermally activated sepiolite

The present investigation demonstrates the preparation of thermally activated sepiolite for effective removal of fluoride via adsorption from an aqueous solution. The thermal treatments on sepiolite were conducted at different temperatures (300-950 °C) for 4 h in an N₂ atmosphere, and the thermally activated sepiolite was characterized using a field emission scanning electron microscope (FESEM), X-ray diffractometry (XRD), X-ray fluorescence (XRF), a differential scanning calorimetry-thermogravimetric analyzer (DSC-TGA), and a surface area analyzer. Sepiolite that was treated at 950 °C was shown to have a higher fluoride removal efficiency than other temperatures. The fluoride removal was evaluated under different experimental conditions such as solution pH, adsorbent dose, reaction time, initial concentration, temperature, presence of co-existing ions, and reuses. The kinetic and equilibrium adsorption results were well described by the pseudo-second-order kinetic model and Langmuir isotherm, respectively, and adsorption of fluoride onto thermally activated sepiolite was endothermic and spontaneous in nature. The Langmuir maximum adsorption capacity (169.95 mg/g) was superior to the literature value. The thermally activated sepiolite was also effective in a continuous flow system for treating fluoride. Thus, this thermally activated sepiolite is expected to be used as an effective adsorbent for the removal of fluoride in water.

Removal of phosphate from aqueous solution using MgO-modified magnetic biochar derived from anaerobic digestion residue

A novel MgO-modified magnetic biochar (MgO@MBC) was made by chemical co-precipitation of Mg²⁺/Fe³⁺ on anaerobic digestion residue (ADR) and subsequently pyrolyzing at different temperatures. MgO@MBC was used for phosphate recovery from aqueous solution. The physicochemical properties of MgO@MBC were comprehensively investigated using TEM-EDS, FT-IR, XRD, VSM, N₂ adsorption-desorption and TGA. Results showed that MgO/γ-Fe₂O₃ nanoparticles were successfully deposited onto the surface of BC. The effects of reaction temperature, initial solution pH, MgO@MBC dosage, coexisting anions and phosphate concentration on the removal of phosphate by MgO@MBC were researched. Additionally, the adsorption process of phosphate onto MgO@MBC was well described by the pseudo second-order and pseudo first-order models, which indicated a chemisorption and physisorption process. Besides, the maximum adsorption capacity of MgO@MBC for phosphate by the Langmuir model were 149.25 mg/g at 25 °C. Moreover, the thermodynamic study suggested that the adsorption of phosphate onto MgO@MBC was a spontaneous and endothermic process. The adsorption mechanisms including physical absorption, surface electrostatic attraction, surface complexation and precipitation were revealed. It could be concluded that MgO@MBC exhibited high removal efficiency of phosphate and excellent magnetic property for the recovery. MgO@MBC could be utilized as a magnetically recoverable adsorbent to realize phosphate recovery and MgO@MBC after the adsorpion of phosphate could be applied in agricultural production as a fertilizer.

Removal of phosphate from aqueous solution by dolomite-modified biochar derived from urban dewatered sewage sludge

Excessive phosphorus emission is mainly responsible for eutrophication. Recently, the application of modified biochars for phosphorus removal from aqueous solution has set off a boom. In the present study, a novel modified biochar was developed, from urban sewage sludge by decorating dolomite according to the dried mass ratio of sludge to dolomite being 1:1. The experimental results showed that the adsorption process preferred lower pH, with the biochar under investigation exhibiting high phosphate removal efficiency of 96.8% at the adsorbent dosage of 2.6 g/L and the initial solution pH of 4.5. Moreover, for the tested biochar, the phosphate removal kinetics data at different temperatures were all well fitted by the pseudo-second-order model, thereby establishing the endothermic nature of the adsorption process. Furthermore, the phosphate removal data upon being well fitted by the Langmuir model showed the maximal removal capacity of 29.18 mg/g. Further, for determining the mechanism involved in the removal process, SEM, XRD, and FTIR analysis were carried out, which in turn revealed that the phosphate combines with the biochar via electrostatic attraction, thereby forming a new outer-sphere surface complex and inner-sphere surface complex in the acidic condition. Additionally, the calcium and magnesium precipitation of phosphate may contribute to the removal of phosphate in the adsorption process. The presence of SO₄^2-, HCO₃^-, and C₅H₇O₅COO^- could negatively affect the removal of phosphate, while CH₃COO^- had a positive effect on the adsorption of phosphate on the biochar. Thus, an economic assessment showed that the proposed adsorption process had a commercial attraction.

Phosphate Mine Tailing Recycling in Membrane Filter Manufacturing: Microstructure and Filtration Suitability

Ceramic membrane filters based on industrial by-products can be considered to be a valorization alternative of phosphate mine tailings, even more so if these ceramic membranes are used in the industrial wastewater treatment due to their good mechanical, chemical, and thermal resistance. The depollution of textile industry rejections with this method has not been studied in detail previously. In this work, ceramic membrane filters have been manufactured from natural clay and phosphate mine tailings (phosphate sludge). Blends of the abovementioned materials with a pore-forming agent (sawdust, up to 20 wt. %) were investigated in the range 900–1100 °C using thermal analysis, X-ray diffraction, scanning electron microscopy, and mercury porosimetry. Ceramic properties were measured as a function of firing temperature and sawdust addition. Filtration tests were carried out on samples with advantageous properties. The results showed that gehlenite together with diopside neoformed from lime decomposed carbonates and breakdown products of clay minerals, while calcium phosphate derived from partial decomposition of fluorapatite. Both quartz and fluorapatite resisted heating. The results of the experimental design showed that the variations of physical properties versus processing factors were well described by the polynomial model. Filtration results are quite interesting, allowing these membranes to be used in industrial effluent treatment.

Adsorption recovery of phosphate from aqueous solution by CaO-biochar composites prepared from eggshell and rice straw

CaO-biochar composites were prepared by mixed ball milling and pyrolysis of agricultural wastes eggshell and rice straw. The resulting CaO-biochar composites (E-C) showed excellent performance for phosphate adsorption from aqueous solution in a wide range of solution pH (5-11), and a maximum adsorption capacity of 231 mg/g could be obtained by E-C sample that was prepared from the eggshell and rice straw with a mass ratio of 1:1 (E-C 1:1). The adsorption of phosphate onto the E-C samples could be well described by pseudo-second-order (R² > 0.975) and Langmuir models (R² > 0.979). Thermodynamic analysis revealed that the adsorption process was spontaneous (ΔG⁰ < 0) and endothermic (ΔH⁰ > 0). This work provides a promising method to prepare functionalized biochar adsorbents from agricultural wastes for the recovery of phosphate from aqueous solution, and the phosphate adsorbed CaO-biochar composites can be directly applied as a slow-release fertilizer to farmland soil, which have the functions of improving soil physical structure, increasing soil fertility, and regulating soil pH.

A facile fabrication of sepiolite mineral nanofibers with excellent adsorption performance for Cd2+ ions

In this work, sepiolite mineral nanofibers are facilely prepared by a microwave-hydrogen peroxide method, and the bulk densities of the samples are adopted to evaluate the defibering effect.

Immobilization of powdery calcium silicate hydrate via PVA covalent cross-linking process for phosphorus removal

Calcium silicate hydrate (CSH) is a popular material used for phosphorus removal in recent years. In this work, a novel immobilized material, polyvinyl alcohol-CSH (PVA-CSH), was prepared using a 1:10 weight ratio of CSH powder to 8% PVA solution and then used for phosphorus removal. Samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The adsorption mechanism and practical application properties of phosphorus wastewater were studied by sequential batch and continuous flow experiment. The results showed PVA-CSH possessed a porous network structure and an average pore diameter of 24.94 ± 0.11 nm. Furthermore, the CSH functional groups were unaffected by PVA immobilization. Compared with CSH, PVA-CSH did not easily lose CSH after being immobilized by PVA, and the duration of efficient phosphorus removal stage was approximately 20 h longer than that of CSH. In addition, the effluent turbidity of PVA-CSH was 0.11 ± 0.03 NTU during the continuous operation period, which was significantly lower than CSH. In summary, this research study demonstrated the significant potential of PVA-CSH for practical phosphorus removal.

Performance and mechanisms of thermally treated bentonite for enhanced phosphate removal from wastewater

Optimization of clays as adsorbent for low concentration phosphorus removal from wastewater has received increasing attention in recent years. This study explored the feasibility of using bentonite as an adsorbent for phosphate (P) removal from synthetic wastewater, by assessing the performance of thermally treated bentonite for P removal and elucidating the mechanisms of P adsorption. Natural bentonite (B25) was thermally treated at 100-1000 °C (B100-B1000) for 2 h. Physical and chemical properties were measured by the SEM, XRD, pore size distribution, EDX, and cation exchange capacity (CEC) methods. Thermal treatment increased P sorption capacity of bentonite and that B800 had a higher P sorption capacity (6.94 mg/g) than B25 (0.237 mg/g) and B400 (0.483 mg/g) using the Langmuir isotherm equation. Study of sorption kinetics indicated that B800 rapidly removed 94% of P from a 10 mg P/L solution and the pseudo-second-order equation fitted the data well. The Ca²⁺ release capacity of B800 (1.31 mg/g) was significantly higher than that of B25 (0.29 mg/g) and B400 (0.40 mg/g) (p < 0.05). The initial pH level had a smaller impact on P removal efficiency for B800 than that of B25 and B400. Ca-P was the main fraction of P adsorbed onto B800, and Ca₁₀-P was the main species (41.4%). The main factors affecting the phosphorous adsorption capacity of B800 were changed crystal structure, strong calcium release capacity, and improved stability in different pH solutions. The results demonstrated that thermally treated bentonite (B800) has the potential to be an efficient adsorbent for removal of low-concentration phosphorus from wastewater.

Nano-rod Ca-decorated sludge derived carbon for removal of phosphorus

Recovering phosphorus (P) from waste streams takes the unique advantage in simultaneously addressing the crisis of eutrophication and the shortage of P resource. A novel calcium decorated sludge carbon (Ca-SC) was developed from dyeing industry wastewater treatment sludge by decorating calcium (Ca) to effectively adsorb phosphorus from solution. The X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques were used to characterize the Ca-SCs, followed by isotherm and kinetic sorption experiments. A preferred design with CaCO₃ to sludge mass ratio of 1:2 was found to have a sorption capacity of 116.82 mg/g for phosphorus. This work reveals the crucial role of well-dispersed nano-rod calcium on the Ca-SC surface for the sorption of phosphorus. Moreover, the decoration of nano-rod calcium was found to further promote the uptake of phosphorus through the formation of hydroxylapatite (Ca₅(PO₄)₃(OH)). Thus, the development of decorated Ca-SC for sorption of phosphorus is very important in solving the P pollution and resource loss.

Enhanced phosphorus flux from overlying water to sediment in a bioelectrochemical system

This report proposed a novel technique for the regulation of phosphorus flux based on a bioelectrochemical system. In the simulated water system, a simple in situ sediment microbial fuel cell (SMFC) was constructed. SMFC voltage was increased with time until it was 0.23V. The redox potential of the sediment was increased from -220mV to -178mV during the process. Phosphorus concentration in the water system was decreased from 0.1mg/L to 0.01mg/L, compared with 0.09mg/L in the control. The installation of a SMFC produced an external current and internal circuit, which promoted the transfer of phosphate in overlying water to the sediment, enhanced the microbial oxidation of Fe(2+), and increased the formation of stable phosphorus in sediment. In conclusion, phosphorus flux from the overlying water to sediment was enhanced by SMFC, which has the potential to be used for eutrophication control of water bodies.

Ca(2+) and OH(-) release of ceramsites containing anorthite and gehlenite prepared from waste lime mud

Lime mud is a kind of solid waste in the papermaking industry, which has been a source of serious environmental pollution. Ceramsites containing anorthite and gehlenite were prepared from lime mud and fly ash through the solid state reaction method at 1050°C. The objective of this study was to explore the efficiency of Ca(2+) and OH(-) release and assess the phosphorus and copper ion removal performance of the ceramsites via batch experiments, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that Ca(2+) and OH(-) were released from the ceramsites due to the dissolution of anorthite, gehlenite and available lime. It is also concluded that gehlenite had stronger capacity for Ca(2+) and OH(-) release compared with anorthite. The Ca(2+) release could be fit well by the Avrami kinetic model. Increases of porosity, dosage and temperature were associated with increases in the concentrations of Ca(2+) and OH(-) released. Under different conditions, the ceramsites could maintain aqueous solutions in alkaline conditions (pH=9.3-10.9) and the release of Ca(2+) was not affected. The removal rates of phosphorus and copper ions were as high as 96.88% and 96.81%, respectively. The final pH values of both phosphorus and copper ions solutions changed slightly. The reuse of lime mud in the form of ceramsites is an effective strategy.

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

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

CeO2-covered nanofiber for highly efficient removal of phosphorus from aqueous solution

The lowering phosphorus concentration of lakes or rivers using adsorbents has been considered to be the most effective way to prevent water eutrophication. However, the development of an adsorbent is still challenging because conventional adsorbents have not shown a sufficient phosphorus adsorption capacity (0.3-2.0mmol/g) to treat industrial, agricultural or domestic wastewater at a large scale. Herein, a novel and effective strategy to remove phosphorus efficiently with a CeO2-covered nanofiber is shown. The CeO2-covered nanofiber was synthesized through (1) amine group immobilization onto an electrospun polyacrylonitrile nanofiber and (2) adsorption of Ce(3+) on it. The CeO2-covered nanofiber played a role in catching phosphate ions in an aqueous solution by the oxidation, reduction, and ion-exchange of adsorbed Ce(3+) on the nanofiber from CeO2 to CePO4, and enabled remarkable phosphate adsorption capacity of the nanofiber (ca. 17.0mmol/g) at the range of ca. pH 2-6. Our strategy might be the most feasible method to efficiently lower the phosphorus concentration in lakes or rivers owing to the easy and inexpensive preparation of CeO2-covered nanofiber at an industrial scale, with a high phosphate adsorption capacity.

Use of modified clays for removal of phosphorus from aqueous solutions

Phosphorus (P) removal from aqueous solutions was investigated using modified bentonite, calcite, kaolinite, and zeolite with FeCl3, CaCl2, and NaCl. The maximum sorption capacity of P was obtained by modified adsorbents with Fe(3+) ions (Fe-adsorbents). The results showed that P sorption capacity by Fe-adsorbents (bentonite (1.31 mg g(-1)), calcite (1.97 mg g(-1)), kaolinite (1.31 mg g(-1)), and zeolite (1.58 mg g(-1))) was improved by ∼467, 107, 409, and 427 %, respectively, compared to unmodified adsorbents (bentonite (0.28 mg g(-1)), calcite (1.82 mg g(-1)), kaolinite (0.32 mg g(-1)), and zeolite (0.37 mg g(-1))). Sorption isotherms were well described by the Freundlich model. Desorption experiments showed that the desorption capacity was in order of unmodified adsorbents > modified adsorbents with Na(+) ions (Na-adsorbents) > modified adsorbents with Ca(2+) ions (Ca adsorbents) > Fe-adsorbents. Effect of pH and ion strength was also investigated. At different pH, changes in the ionic strength had little effect on the adsorption. Results showed that double-layer model (DLM) could model P adsorption onto modified adsorbents over a wide range of pH and varying ionic strength. According to the scanning electron microscopy (SEM) images and saturation indices (SIs), high P removal by adsorbents was partly due to the P precipitation.

Phosphate removal from domestic wastewater using thermally modified steel slag

This study was performed to investigate the removal of phosphate from domestic wastewater using a modified steel slag as the adsorbent. The adsorption effects of alkalinity, salt, water, and thermal modification were investigated. The results showed that thermal activation at 800°C for 1 hr was the optimum operation to improve the adsorption capacity. The adsorption process of the thermally modified slag was well described by the Elovich kinetic model and the Langmuir isotherm model. The maximum adsorption capacity calculated from the Langmuir model reached 13.62 mg/g. Scanning electron microscopy indicated that the surface of the modified slag was cracked and that the texture became loose after heating. The surface area and pore volume did not change after thermal modification. In the treatment of domestic wastewater, the modified slag bed (35.5 kg) removed phosphate effectively and operated for 158 days until the effluent P rose above the limit concentration of 0.5 mg/L. The phosphate fractionation method, which is often applied in soil research, was used to analyze the phosphate adsorption behavior in the slag bed. The analysis revealed that the total contents of various Ca-P forms accounted for 81.4%-91.1%, i.e., Ca10-P 50.6%-65.1%, Ca8-P 17.8%-25.0%, and Ca2-P 4.66%-9.20%. The forms of Al-P, Fe-P, and O-P accounted for only 8.9%-18.6%. The formation of Ca10-P precipitates was considered to be the main mechanism of phosphate removal in the thermally modified slag bed.

Reduction of sediment internal P-loading from eutrophic lakes using thermally modified calcium-rich attapulgite-based thin-layer cap

We conducted a laboratory evaluation of a low-cost P-capping agent-700°C-heated natural calcium-rich attapulgite (NCAP700)-in terms of its ability to reduce internal P-loading in lake sediments. Batch studies indicated that NCAP700 could effectively reduce sediment mobile P (P mobile) in various types of lake sediment, and the dosage equation required to immobilize P mobile was developed accordingly. The equation was then applied to a laboratory incubation study on intact sediment cores. The results indicated that the NCAP700-based thin-layer cap can enhance the redox potential (Eh), pH and dissolved oxygen (DO) in surface sediment. However, this enhancing effect was decreased with increasing time. P fluxes and the concentration of P in overlying water and pore water from sediment could be effectively inhibited under anaerobic conditions. P fractionation analysis indicated that 34.5% of P mobile was bound in the upper 2 cm sediment layer during a 40-day remediation period, but this only exerted a minor influence on the P mobile in the 2-4 cm sediment layer. P immobilization by NCAP700 was mainly achieved through transformation of P mobile to stable Ca-P. These results indicate that NCAP700 can be used for lake eutrophication control by means of thin-layer capping.

The role of Mn oxide doping in phosphate removal by Al-based bimetal oxides: adsorption behaviors and mechanisms

This study investigated the behaviors and mechanisms of phosphate adsorbed onto manganese (Mn) oxide-doped aluminum (Al) oxide (MODAO). The isotherm results demonstrated that the maximum amount of phosphorus (P) adsorbed onto MODAO was 59.8 mg/g at T = 298 K (pH 6.0). This value was nearly twice the amount of singular AlOOH and could increase with rising temperatures. The kinetic results illustrated that most of the P was adsorbed onto MODAO within 5 h, which was shorter than the equilibrium time of phosphate adsorption onto AlOOH. The Elovich model effectively described the adsorption kinetic data of MODAO because of its heterogeneous surface. The optimal solution pH for phosphate removal was approximately 5.0 because of electrostatic interaction effects. Meanwhile, the decrease in P uptake with increasing ion strength suggested that phosphate adsorption occurred through an outer-sphere complex. Phosphates would compete for adsorption sites on the surface of MODAO in the presence of fluoride ion or sulfate. In addition, the spectroscopic analysis results of Fourier transform infrared spectroscopy and X-ray photoemission spectroscopy indicated that removal mechanisms of phosphate primarily include adhesion to surface hydroxyl groups and ligand exchange.