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Chemical oxo-precipitation (COP) is an enhanced precipitation method for boron removal with the conversion of boric acid to perborate anions. When using barium-based precipitant, the boron can be effectively precipitated as barium perborates (BaPBs). The phase transformation of BaPBs from amorphous (A-BaPB, Ba(B(OH) 3 OOH) 2) to crystalline (C–BaPB, BaB 2 (OO) 2 (OH) 4) form is crucial for effective boron removal. However, scaling up this phase transformation of BaPBs is hindered by poor diffusion. This study aims to promote the growth of C–BaPB through seed-induced crystal growth, eliminating the need for phase transformation. By examining the relationship between crystal growth rate and supersaturation, surface spiral growth was identified as the rate-limiting step of the growth of micron-sized seeds near pH pzc. To enable continuous crystal growth, granular seeds of C–BaPB were prepared and employed as the medium for fluidized-bed crystallization (FBC). The system reached steady state 3 hydraulic retention times, achieving 90% boron removal. The effect of surface loading, ionic strength, and dosages on steady-state crystal growth rate was studied, revealing a shift of the rate-limiting step in FBC to diffusion. Lastly, the system that constituted of two FBCs in-series for sequential crystallization of A-BaPB and C–BaPB was demonstrated. The integrated system provided 97.8% of boron removal from synthetic wastewater containing 500 mg-B/L, with 92.3% of boron crystallized on the granular seeds of BaPBs. [Display omitted] • Seed-induced crystal growth of C–BaPB enabled rapid boron removal. • Spiral surface growth was the rate-limiting step near pH pzc. • Continuous crystal growth of granular C–BaPB seeds removed 90% boron in FBC. • Two FBCs in-series eliminated boron from 500 to 8 mg-B/L, >92% on granular seeds. [ABSTRACT FROM AUTHOR]

Abstract In this study, iron is removed from aqueous solution using a fluidized-bed crystallizer. Homogeneous oxyhydroxide pellets (FeOOH) were recovered at various value of pH, surface loading (L), and initial ferrous concentration to assess the treatability of iron-containing water. The optimal conditions for treating initial ferrous concentrations of 100–300 mg/L were L = 0.6 kg/m2/h (with 29 m/h of upflow velocity), a bed expansion of 50% and pH = 6.5 yielding the total iron removal (TR) of more than 99% and a corresponding iron crystallization ratio (CR) of 85%. X-ray diffractometry (XRD) revealed that the pellets consisted of a mixture of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). Scanning electron microscopy (SEM) yielded images of pellets of up to 1 mm in diameter, which were assembled from FeOOH flakes with thicknessess of 0.2–0.4 µm. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Phosphate recovery from wastewaters is one of the major engineering challenges to securing the worldwide food production. Fluidized-bed heterogeneous crystallization of struvite has been one of the most considered technologies. Nevertheless, the recovery of other phosphate products could be of the major interest at industrial level. Thus, in this work we present the recovery of calcium phosphate salts as brushite by a novel fluidized-bed homogeneous crystallization (FBHC) process. The no requirement of seeds in FBHC reactor allows obtaining high-purity crystals. The operational parameters of the FBHC process have been optimized in order to achieve the higher degree of granulation and to obtain the most homogeneous distribution of granules sizes. Thus, the treatment of 1500 mg/L of phosphate at pH 9.0 with a ratio of 1.2:1.0 of [Ca 2+ ]:[PO 4 3− ] T leads to the obtaining of ca. 90% of granulation with crystals of 0.5 mm of diameter. The influence of electrolytes typically found in TFT-LCD industry has been further considered. The characterization of the spheroidal crystals obtained allowed identifying brushite (calcium hydrogenphosphate salt) as unique crystal phase. [ABSTRACT FROM AUTHOR]

This work demonstrates the recovery of phosphorus from a solution (150 mg-P/L) using ferrous salts (FeSO 4 ) and hydrogen peroxide (H 2 O 2 ) as precipitants through the fluidized bed crystallization (FBC) process. Jar-test experiments were conducted to investigate effective pH and molar ratios of H 2 O 2 /Fe(II) and Fe(II)/P in the removal of phosphate. The pure ferric phosphate crystal was then recovered using the FBC process and the effluent pH e and surface loading (L, kg-P/m 2  h) were tested. The results of XRD revealed that the FBC pellets were composed of the mixtures of rodolicoite and giniite, with a Fe/P molar ratio of approximately 1.1, based on elemental analysis. Under conditions pH e = 2.6, an H 2 O 2 /Fe(II) molar ratio of 0.6, an Fe(II)/P molar ration of 1.2, and L  = 0.3–0.89 kg/m 2  h, a crystallization ratio of 86% and a removal efficiency of 95% were achieved. [ABSTRACT FROM AUTHOR]

Calcium is one of the divalent ions contributing to the hardness level of the water. This work describes the removal of calcium ions from aqueous solution using carbonate salts as precipitants and the recovery of homogeneous calcium carbonate crystals via a fluidized-bed homogeneous crystallization (FBHC) process without a heterogeneous seed material. The considered parameters were effluent pH, initial molar ratio of carbonate salt to Ca, up-flow velocity, and cross-section loading. The removal efficiency of Ca hardness reached 95% at the optimal pH of 10–11 and the corresponding crystallization ratio was 88% for initial concentrations of Ca of 50–330 ppm. The FBHC process was effective with a cross-section loading of calcium in the water of up to 4.5 kg/m 2 /h. The efficiency of Ca immobilization as the crystal grew on the fluidized pellets was greatly improved by adjusting the degree of supersaturation in the range 2–3, resulting in the crystallization ratio (CR) and total removal of Ca (TR) of 88% and 92%, respectively. XRD analysis revealed that the formed crystals comprised two calcium carbonate (CaCO 3 ) phases—calcite and aragonite. SEM images of the surface morphology revealed that calcium carbonate particles (around 1–2 mm) were formed by the aggregation of fine crystals (around 5 µm). [ABSTRACT FROM AUTHOR]

This investigation studies the crystallization of alkaline earth metal phosphates (Me-PO 4 , Me = Mg, Ca, Sr, Ba) to recover phosphorus (1000 ppm-P) in a fluidized-bed reactor without the addition of seeds. Experimental results showed that the effluent pH e critically determined the phosphorus removal rate (PR%) and crystallization ratio (CR%). The PR%s that were achieved by the generation of Mg, Ca, Sr and Ba-phosphates with an inlet molar ratio [Me] in /[P] in of 2 were 77.8%, 99.4%, 97% and 98.9% at the pH e values exceeded 7.5, 6.6, 7.2 and 6.4, respectively. However, the CR% was strictly optimized by a pH e that transformed the crystalline phases of granular pellets (0.5–2 mm in diameter) from metal hydrogen phosphate (MeHPO 4 ) to hydroxyapatite (Me 5 (PO 4 ) 3 (OH)), and maximum CR%s of 54.5%, 78.8%, 79.0% and 89.0% were obtained by the generation of Mg, Ca, Sr and Ba-phosphates. According to estimates of aquatic chemistries and supersolubility behaviors in the effluent, a successful FBHC process operated under a supersaturation that was close to the metastable zone. Finally, a reasonable mechanism of the removal of phosphorus by converting the aqueous phosphorus into highly pure metal phosphate pellets was inferred. [ABSTRACT FROM AUTHOR]

The fluidized-bed crystallization (FBC) removes heavy metals onto the fluidized pellets, which is an outstanding alternative to the precipitation method. This study simultaneously recovers iron and copper as binary metal-oxide pellets (FeIII 0.66 CuI 0.33 @SiO 2) in a synthetic wastewater using FBC and silica as a seed material. The operating parameters for FBC include the Fe/Cu ratio, pH, cross-sectional loading (L, kg/m2.h) and bed height (H, cm) and these are optimized to maximize the crystallization efficiency of iron and copper. At pH = 8, an input Fe/Cu ratio = 2 at a total metal concentration of 3 mM, the crystallization ratio (CR) and the total respective metal removal (TR) for Fe and Cu is 90% and 99%. Precipitation rates of 0.88 and 0.38 mg-metal/ gr-seed•h were obtained at respective cross-sectional loadings of 0.25 kg m− 2•h and 0.15 kg m− 2•h for Fe and Cu. The crystal phases of FBC product are respectively characterized as FeOOH and Cu 2 O by XRD analysis. The high crystallization ratio and the recovery of crystal pellet product indicated that the quantity of the sludge has been reduced significantly in comparison to the traditional chemical precipitation. [Display omitted] • Mixed metal-containing wastewater was treated by fluidized-bed crystallization. • Fe and Cu were recovered in form of FeOOH/Cu 2 O composite on silica pellet. • 90% of metals were crystallized as oxides as to reduce sludge formation. • Removal efficiency of binary metal oxides achieved 99% under optimal conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] An iron oxide recovered from fluidized-bed Fenton reactor is used as adsorbent. [•] BT1 adsorbent composes of poorly crystallized Goethite. [•] High removal of Sr is achieved by BT1 with an adsorption capacity of near 40mg/g. [•] Kinetics and thermodynamics of Sr adsorption have been elucidated. [ABSTRACT FROM AUTHOR]

Abstract: This work demonstrates the synthesis of a novel KMnO4-modified form of iron oxide, MnBT-4, using a fluidized bed reactor (FBR) for the adsorptive removal of arsenic (III)/(V). Characterization by XRD, BET, and SEM indicated that the BT-4 support was poorly crystallized goethite (α-FeOOH) with a specific surface area of 229m2 g−1. In FBR experiments of synthesizing MnBT-4, the Fe and Mn salts were found to have an optimal dosage ratio of less than 4, which maximized the KMnO4 immobilization efficiency. The immobilized Mn compounds on MnBT-4 underwent an additional oxidation step of As (III), promoting arsenic adsorption. When applied MnBT-4 for As (III) removal from solution, the sorption isotherm was accurately fitted with Langmuir and Freundlich models, while the maximum adsorption capacity of 27.4mgg−1 exceeded those of other adsorbents in the literature. Batch experimental results revealed that both raw BT-4 and MnBT-4 could take up a large amount of As (V). However, the MnBT-4 provided a substantially higher As (III) removal efficiency than BT-4. [Copyright &y& Elsevier]

Abstract: SHRIMP zircon U–Pb dating, mineral chemical, element geochemical and Sr–Nd–Pb–Hf isotopic data have been determined for the Yulong monzogranite-porphyry in the eastern Tibet, China. The Yulong porphyry was emplaced into Triassic strata at about 39 Ma. The rocks are weakly peraluminous and show shoshonitic affinity, i.e., alkalis-rich, high K2O contents with high K2O/Na2O ratios, enrichment in LREE and LILE. They also show some affinities with the adakite, e.g., high SiO2 and Al2O3, and low MgO contents, depleted in Y and Yb, and enrichment in Sr with high Sr/Y and La/Yb ratios, and no Eu anomalies. The Yulong porphyry has radiogenic 87Sr/ 86Sr (0.7063–0.7070) and unradiogenic 143Nd/ 144Nd (ε Nd =−2.0 to −3.0) ratios. The Pb isotopic compositions of feldspar phenocrysts separated from the Yulong porphyry show a narrow range of 206Pb/ 204Pb ratios (18.71–18.82) and unusually radiogenic 207Pb/ 204Pb (15.65–15.67) and 208Pb/ 204Pb (38.87–39.00) ratios. In situ Hf isotopic composition of zircons that have been SHRIMP U–Pb dated is characterized by clearly positive initial ε Hf values, ranging from +3.1 to +5.9, most between +4 and +5. Phenocryst clinopyroxene geothermometry of the Yulong porphyry indicates that the primary magmas had anomalously high temperature (>1200 °C). The source depth for the Yulong porphyry is at least 100 km inferred by the metasomatic volatile phase (phlogopite–carbonate) relations. Detailed geochemical and Sr–Nd–Pb–Hf isotopic compositions not only rule out fractional crystallization or assimilation-fractional crystallization processes, but also deny the possibility of partial melting of subducted oceanic crust or basaltic lower crust. Instead, low degree (1–5%) partial melting of a metasomatized lithosphere (phlogopite–garnet clinopyroxenite) is compatible with the data. This example gives a case study that granite can be derived directly by partial melting of an enriched lithospheric mantle, which is important to understand the source and origin of diverse granites. [Copyright &y& Elsevier]

The mixture of copper and iron often results in materials with favorable properties. The material production processes involving these metals including electroplating produce hazardous wastewater. In this study, the Fluidized Bed Homogeneous Crystallization (FBHC) process was applied to treat iron and copper-containing wastewater. The initial iron copper particles were successfully recovered from synthetic wastewater with [Fe] 0 :[Cu] 0 of 2:1, the total metal concentration of 3 mM, at effluent pH = 7.75 ± 0.75, with the upflow velocity (U) of 1.76 m/h. The agglomerates hardening process is a crucial step for initial particle synthesis. The SEM analysis reveals the spherical particle's densified crust and porous core. The particle formation mechanism which includes the formation of the nucleus, attachment of precipitate flakes, and densification of particles was proposed after microscopic observation. The initial particles synthesized were used to initiate the treatment of synthetic wastewater at the operating condition pH = 7.75 ± 0.5, [Fe] 0 :[Cu] 0 of 2:1, the total metal concentration of 3 mM, [CO 3 2−] 0 :[M] 0 = 1.2:1, and U of 28.66 m/h which results in the total metal removal of 99% and crystallization ratio of 90% and 88% for iron and copper respectively. The conditions were then applied to treat electroplating wastewater and resulted in the total metal removal of 99% for both iron and copper and a crystallization ratio of 83% and 79% for iron and copper, respectively. The treatment provided advantages in terms of treating larger amounts of sludge while eliminating the need to provide seed thus yielding a higher purity of product. [Display omitted] • High-purity Fe–Cu particles were recovered from wastewater. • A total metal removal of 99% was achieved for both synthetic and real wastewater. • Cost reduction of up to 88% compared to conventional chemical precipitation. [ABSTRACT FROM AUTHOR]

This work demonstrated the removal of lead (Pb) from aqueous solution using fluidized-bed crystallization (FBC, using silica sand as seeds) and fluidized-bed homogeneous crystallization (FBHC, without seeds) systems. Synthetic lead wastewater with concentrations of 10, 40 and 200 ppm were treated. The results thus obtained indicated that effluent pH was an essential parameter in determining the efficiency of FBC and FBHC. A comparison between theoretical solubility and residual Pb in effluents revealed that FBHC in the predictable metastable region of pH 6.5–8.5 guaranteed 99% Pb removal and a crystallization ratio of 95% (CR%). XRD analysis suggested that the lead carbonate of FBHC products comprised either a cerussite (PbCO 3 ) or a hydrocerussite (Pb 3 (CO 3 ) 2 (OH) 2 ) phase, depending on pH. FBHC was proven to be effective in remediating lead wastewater under optimal hydraulic conditions (initial molar ratio of [Na 2 CO 3 ]/[Pb] > 1.2, upflow velocity = 25–35 m h −1 and pH e = 7.2 ± 0.4), which were all similar to those in FBC. The cross-section loading (L, kg m −2 L −1 ) depended on the input Pb level; L was controlled at 0.15 kg m −2 h −1 for treating 10 ppm-Pb and was increased to 5.73 kg m −2 h −1 for 40 and 200 ppm-Pb, optimizing the FBHC and FBC processes. Without the addition of seed materials, FBHC recovered purer lead carbonate than did FBC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfide-containing synthetic wastewater was treated by fluidized-bed homogeneous crystallization. • Fluidized bed homogeneous crystallization technology does not need to add the heterogeneous seeds. • The crystallization efficiency of sulfide recovered as zinc sulfide particles reached 97.8%. • Supersaturation is calculated to determine the optimum condition of sulfur crystallization. Sulfide wastewater that is anthropogenically generated from industrial activities is highly corrosive, hazardous, and harms the natural ecosystem. This study uses a novel fluidized-bed homogeneous crystallization (FBHC) method to remove sulfide ions from an aqueous solution. Zinc is used as a precipitant to crystallize ZnS homogeneously in the FBHC reactor to reduce the sludge, which is commonly produced in a conventional chemical precipitation process. The optimal pH value, [Zn2+] 0 /[S2-] 0 M ratio, sulfide cross-sectional surface loading (L, kg-S/m2.hr), and hydraulic retention time (HRT) for the system are established, to optimize the sulfur removal efficiency. The maximum crystallization ratio and the total removal efficiency for sulfur are 97.7% and 98.8%, respectively, at pH = 5.4, a [Zn2+] 0 /[S2-] 0 M ratio of 1, a cross-sectional surface loading of 2.2 kg-S/m2.hr, and an HRT number of 6 with an initial sulfur concentration of 320 mg/L. The solid products are collected and identified as zinc sulfide (wurtzite) using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

[Display omitted] • 85% of boron was crystallized as barium perborate granules within FBC. • Effluent boron levels were close to equilibrium solubility of barium perborate. • The sludge production rate increased drastically with supersaturation. • Algorithm based on supersaturation was developed to predict the performance of FBC. • The treatment cost of Ba-COP in FBC is 30% lower than in batch stirred-tank. The development of treatment process for boron removal is urgent to control the anthropogenic emission of boron to freshwater. Barium-based chemical oxo-precipitation (Ba-COP) is an effective method to treat boron-rich streams in ambient condition by the precipitation of barium perborate (BaPB), but it is limited to batch operation and mass production of sludge. This study aims to circumvent these drawbacks by performing Ba-COP in fluidized-bed crystallization system (Ba-COP@FBC) to immobilize BaPB on the surface of the fluidized granules continuously. When Ba-COP@FBC was operated at pH 10, 85% of total removal (TR) and 83% of crystallization ratio (CR) were attained from an input boron level of 600 mg-B/L, indicating that the homogeneous nucleation could be suppressed. Despite that both TR and CR varied greatly upon the dosage of H 2 O 2 and Ba, initial concentration and reflux ratio, the influence of these parameters can be summarized by supersaturation. TR was related to the supersaturation at the effluent (S E), which was fixed at 1.15 ± 0.04; the sludge production rate increased drastically with the supersaturation at the mixing zone (S M), which in turn reflects on CR. Accordingly, an algorithm based on the supersaturation ratio was developed to predict the performance of Ba-COP@FBC based on the initial concentration, hydraulic condition, dosages and ionic strength. The economic analysis reveals that Ba-COP@FBC is more competitive than the Ba-COP conducted in batch stirred-tank reactor in terms of solid disposal cost due to the difference of water content between granule and sludge. [ABSTRACT FROM AUTHOR]

• Extremely high concentrations form denser sludge instead of suspended particulates. • A preliminary experiment formed atypical flake-like CaF 2 particles. • Various flow regimes can be crucial to CaF 2 granulation. • A 2.0-mm glass-bead bed enhances the over-all granulation efficiency. • CaF 2 homogenous granulation is achieved with 98% removal and granulation. Excessive and industrial advances have increased fluoride quantity in the effluents. However, the environmental carrying capacity for fluoride is relatively slim immediately affecting both aquatic and terrestrial animals while its transport can further contaminate the water source. To protect the public and the environment, different environmental agencies globally set their respective effluent standard restricting F- concentration to 15 mg/L as the median value. However, various processes from previous investigations have mostly been limited in treating 100–1000 mg F-/L with secondary pollution commonly overlooked. Re-assessing the available defluoridation technologies, chemical precipitation has still been the most feasible among the technologies, especially extremely high fluoride concentrations. In this study, fluoride removal through chemical precipitation was investigated using conventional precipitation and fluidized-bed homogeneous crystallization. Parameters such as a wide range of initial concentrations from 100 to10,000 mg/L and pH 2.0–11.0 under conventional precipitation were varied and analyzed. To reduce high water content sludge, a 550-mL cylindrical glass was modified to simulate a fluidized-bed reactor to investigate homogenous crystallization varying influent concentration, bed-support size, and fluid flow. Results showed that chemical precipitation could effectively remove fluoride even at very high fluoride concentrations ranging from 1,000 to 10,000 mg/L. Alternatively in the fluidized-bed granulation process, an initial very low flow without recirculation flow was required to initiate particle formation. The predominant size of the recovered particle was < 0.2 mm which was relatively heavy atypically not reaching the upper region of the reactor. Under the observed optimum condition with an initial fluoride concentration of 450 mg/L, both total removal and crystallization ratio could reach ∼ 98% efficiency lowering fluoride concentration to < 15.0 mg F-/L within 7 days. [ABSTRACT FROM AUTHOR]

• Fluidized-bed homogeneous crystallization of iron in wastewater was developed. • 77% of iron was removed as crystallized magnetite granulate. • The recovery of iron oxide was dependent on index of supersaturation in effluent. • RB5 was degraded in three-phase photo reactor using the iron oxide catalyst. • The decolorization and mineralization efficiency reached 98% and 68%, respectively. Iron recovery from wastewater as magnetite (Fe 3 O 4) pellets was performed in a fluidized-bed homogeneous crystallization (FBHC) process. The catalytic effectiveness of magnetite in the heterogeneous degradation of RB5 azo dye was evaluated. The key parameters of FBHC, including effluent pH, cross-section loading (L, kg/m2.h), initial iron concentration ([Fe(II)], mg/L), and inlet supersaturation (S), were optimized to maximize the total iron removal (TR, %) and crystallization ratio (CR, %) from a fluidized-bed reactor. Under the conditions of pH = 8.5–9.5 and [Fe(II)] in = 100 – 500 mg/L, the TR and CR values reached 99% and 77%, respectively. The magnetization and coercivity of the recovered Fe 3 O 4 pellets were analyzed to confirm the magnetic characteristic. A Fenton-like degradation of RB5 azo dye was activated using the Fe 3 O 4 pellets under UVA irradiation, pH = 2.75 – 3.0, initial peroxide concentration of 10 mM, and catalyst loading of 2 g/L. The efficiencies of decolorization and mineralization reached about 98 – 99% and 60 – 68%, respectively. FBHC method benefited the recovery of high-purity metal oxides and the production of a low quantity of sludge. Magnetic pellets transformed from the dissolved iron in wastewater were promising materials to reuse as a photochemical reactant for organic pollutant degradation. [ABSTRACT FROM AUTHOR]

The crystallization of struvite in fluidized-bed crystallizer (FBC) was performed to treat synthetic wastewaters that contain phosphorous. Under optimal conditions (pH 9.5, molar ratio Mg/N/P = 1.3/4/1, struvite seed dose (53–297 μm) = 30 g L −1 , total flow rate = 12 ml min −1 , reflux = 120 ml min −1 ), the removal of phosphate (PR) and the crystallization ratio (CR) were 95.8% and 93.5%, respectively. Based on a thermodynamic prediction, the supersaturation, which was obtained from the difference between the theoretical solubility and phosphate concentration, predominated the crystallization efficiency and the properties of the struvite pellets, such as their morphology, particle size and apparent density. Coexisting ions NO 3 − (80, 160 ppm), CH 2 COOH − (260, 520 ppm), F − (650, 1300 ppm) and SO 4 2− (650, 1300 ppm), were utilized to prepare P-containing wastewaters. Of these ions, SO 4 2− (1300 ppm) remarkably reduced the capability of FBC to remove phosphate from solution. In the presence of NO 3 − and CH 3 COO − (for synthesizing TFT-LCD wastewater), and F − and SO 4 2− (for synthesizing semiconductor wastewater), CR% was lower than in pure water, although the ultimate PR% did not differ significantly. [ABSTRACT FROM AUTHOR]

• Phosphorus removals in the homogeneous and heterogeneous processes were studied. • The product was crystal Ca 3 (PO 4) 2 ·xH 2 O with the average size of 0.6 mm in FBC/FBHC system. • FBC has a greater performance than FBHC due to the active surface of dolomite. • Hydraulic optimization of FBC resulted in 92% phosphorus removal and 85% crystallization ratio. Fluidized-bed reactor technology was applied to recover phosphorus from solution via crystallization in a seeded (FBC, Fluidized-bed Crystallization) and unseeded (FBHC, Fluidized-bed Homogeneous Crystallization) system. Dolomite (CaMg(CO 3) 2) is applied as seed material to provide an existing surface in the seeded crystallization system. Under the optimum pH of 7.7, the presence of seed material in the FBC system enhanced the crystallization ratio of both phosphorus and calcium from 60% to 80%. The operating parameters, including - effluent pH e , up-flow velocity (U, m h−1), and cross-sectional loading (L, kg m−2 hr−1) were optimized in the FBC system. Under optimum conditions at pH 7.7, molar ratio of [Ca] 0 /[P] 0 =3.5/1, up-flow rate of 30 m h−1, and cross-sectional loading of 0.9 kg m−2 hr−1, the crystallization ratio (CR) and total removal (TR) of both phosphorus and calcium reached 85% and 92%, respectively. Based on the XRD and Raman pattern, it was confirmed the solid products consist of tricalcium phosphate (Ca 3 (PO 4) 2 ·xH 2 O) from both FBC and FBHC processes. An economic analysis shows that the disposal cost could be reduced from 0.92 US$ wastewater to 0.2 US$/m3. Phosphorus, encapsulated in a sparingly soluble crystalline form such as dolomite in the FBC system can be potentially used as a slow-release fertilizer and raw material for bio-ceramic and bioactive glass. [ABSTRACT FROM AUTHOR]

• Simultaneous recovery of phosphorus and potassium from urine was achieved. • Recovery of P and K reached 98.4% and 70.5%, respectively at low Mg:K ratio of 1.25. • K-struvite pellets recovered have low water content and high purity (>95%). • The fluidized bed homogeneous crystallization (FBHC) was performed without seeds. • FBHC recovery can help yield a profit of $0.26/m3-urine. Most of nutrients in municipal wastewater originate from human urine. In this study, a novel fluidized-bed homogeneous crystallization process was developed for the simultaneous recovery of phosphorus (P) and potassium (K) from synthetic human urine. The operational variables including pH, Mg:K ratios and up-flow velocity were tested in the laboratory. The total removal of P and K (TR%) reached 98.4% and 70.5%, respectively, and the crystallization ratios (CR%) were 86.5% and 62.3%, respectively, at conditions of pH 10 ± 0.2, molar ratio Mg:K = 1.25, initial concentrations 850 mg P/L and 1830 mg K/L. The SEM and XRD analyses showed that the fluidized bed homogeneous crystallization (FBHC) product was pure magnesium potassium phosphate (K-struvite) (average size = 0.85 mm; purity = 95 ± 3%). The modelling of minimum fluidization velocity (MFV) resulted in values of up-flow 1.5–2.0 times the MFV for the effective fluidization. The profit of the recovery of P and K from human urine via FBHC process could be $0.26/m3-urine. [ABSTRACT FROM AUTHOR]