Search

Municipal and industrial wastewater can be a potential source of magnesium. Therefore, the development of magnesium recovery technology can both release the burden of wastewater treatment and help ...

A bimetallic Fe-Cu catalyst was applied as a catalyst for heterogeneous Fenton reaction. Fluidized-bed crystallization of bimetallic catalyst supported by a silica seed (FeIII0.66CuI0.33 @SiO2) was conducted at specific hydraulic conditions. The deposited state of copper and iron of FeIII0.66CuI0.33@SiO2 were identified as Cu(I) and Fe(III), which could effectively catalyze H2O2 to form hydroxyls radical for the abatement and mineralization of benzoic acid under blue light irradiation (436 nm). The cupric species as an electron donor enabled the reductive dissolution of the deposited iron to drive a Fenton reaction. The blue light irradiation promoted the regeneration of Fe(III) to Fe(II) through the photoreduction mechanism. Operating parameters included Fe to Cu ratio (0.5–4), dose of H2O2 (0–4 mM), initial pH (3–7) and light intensity (0–10 mW/cm2). The photo Fenton process using FeIII0.66CuI0.33@SiO2 catalyst resulted in 86% of benzoic acid mineralization in 3 h.

Given the potential shortage of critical nutrients (e.g., nitrogen, phosphorus, and potassium) predicted in the near future, nutrient recovery technologies have attracted wide attention from the sc...

The environment is affected by agricultural, domestic, and industrial activities that lead to drastic problems such as global warming and wastewater generation. Wastewater pollution is of public concern, making the treatment of persistent pollutants in water and wastewater highly imperative. Several conventional treatment technologies have been applied to water and wastewater remediation, but each has numerous limitations. To address this issue, treatment using bimetallic systems has been extensively studied. Synergistic effects between the two metals are highly desirable because they usually offer enhanced activity, selectivity, and stability relative to their monometallic counterparts. In this study, a novel method to fabricate bimetallic Fe-Co catalyst supported on waste silica was investigated for the treatment of methylene blue dye as model pollutant. Under the optimum conditions of pHi 3.0, 3.0 mM H2O2, 1.0 g L-1 Fe-Co/SiO2 catalyst, and 20 mg L-1 initial dye concentration, the maximum response for the decoloration and mineralization efficiencies of methylene blue were 100% and 64.57%, respectively. Superoxide radical was unveiled to be the dominant reactive oxygen species in the photo-Fenton-like system over Fe-Co/SiO2 catalyst. Compared to the contrastive catalyst, the Fe-Co/SiO2 synthesized using fluidized-bed crystallization exhibited comparable decoloration and mineralization efficiencies, and relatively lower metal leaching.

Acid mine drainage (AMD) released from gold and coal mining contains a large quantity of heavy metals, thus being a threat to the surrounding ecosystem. The recovery of metals from AMD can both address the potential contamination and bring more economic profits. In this study, the sequential selective precipitation and fluidized bed homogeneous crystallization (FBHC) were integrated to recover iron(II) and Al(III) from real AMD wastewater. The selective precipitation of Fe was optimized by adjusting pH. The FBHC recovery of Al performed its best at pH 9.25 ± 0.2, molar ratio of [H2O2]/[Al(III)] = 2.0 and up-flow velocity (U) = 30.5 m/h. Iron(II) and Al(III) were recovered in the form of iron hydroxide (Fe(OH)3) and bayerite (α-Al(OH)3) pellets. Removal efficiencies were as high as 99.7% and 99.3% for Fe(II) and Al(III), respectively. A brief cost-benefit estimation was performed and showed that the estimated profit gained from field-scale recovery of Fe(II) and Al(III) would be $1.31/m3-AMD.

Advanced oxidation process is a promising technology for the treatment of azo dye wastewater, owing to its high degradation performance and less secondary contamination. Herein, the mineralization of azo dye Reactive Black 5 (RB5) by the heterogeneous photo-Fenton process was investigated in a three-phase fluidized bed reactor. The waste iron oxide (denoted as BT) obtained from tannery wastewater process with Fenton’s reagent was selected as a heterogeneous catalyst. The introduction of BT to the UV/H2O2 process (UV/H2O2/BT) shows obviously higher mineralization efficiency because ferric complexes of carboxylic acid, the degradation intermediates of RB5, could be readily decomposed by UV irradiation. The decolorization was achieved by homogenous photo-Fenton reaction induced by leached iron, while the mineralization was contributed to heterogeneous oxidation. Under the conditions of 254 nm UV irradiation, 19.00 mM H2O2, 2.0 g L–1 catalyst loading and natural pH0 of 5.0, 90.2% TOC removal of RB5 could be achieved. The catalyst indicated an acceptable stability and reusability after four cycles. The proposed heterogeneous photo-Fenton process with stable performance is environmental-friendly for the mineralization of RB5.

Wastewater containing cobalt and copper comprised of plating wash water, plant wash water, and equipment cooling and wash water is generated in the electroplating industry. These metals can be detrimental to humans, animals, plants, and the environment. Thus, it is necessary to treat electroplating wastewater to remove these toxic metals. Carbonate and hydroxide precipitation were utilized for the removal of Co(II) and Cu(II) from synthetic electroplating wastewater by jar tests in this work. The effects of solution pH, precipitant-to-metal ratio, and type of precipitant on the precipitation efficiency of cobalt and copper from the single- and co-contaminated systems were investigated. Carbonate precipitation achieved higher removal efficiency for both target metals in the single- and co-contaminated wastewater streams. Furthermore, it can operate at relatively low pH range of about 7.0-8.0. Cobalt in both pollutant systems was almost completely removed at pH 10.0 using both precipitant systems. Copper was found to be easily removed which was possibly brought about by precipitation-adsorption mechanism. The extent of the co-removal of cobalt with copper is significantly pH dependent. The effect of precipitant-to-metal ratio for cobalt and copper treatment varied in single- and co-contaminated streams. Carbonate precipitation led to lower sludge density than that of hydroxide precipitation.

An electrode made of loofah sponge derived activated carbon supported on nickel foam (AC/Ni) was successfully fabricated and used to remove ammonium ion (NH4+) from aqueous solution. A multilayer adsorption isotherm was used to describe ammonium electro-sorption on AC/Ni electrodes at different temperature, initial NH4+ concentration, and electrical field. The cyclic voltammetry (CV) results suggested that the electrical capacitance of AC/Ni electrodes, with the AC being prepared without preheating (OAC) or with low temperature heating (i.e., 300 AC), were higher than those prepared at high preheating temperature (i.e., 400 AC and 500 AC). Increasing the electro-sorption temperature from 10 to 50 °C decreased the monolayer NH4+ adsorption capacity from 5 to ca. 2–3 mg-N g−1, respectively. Background electrolyte, namely, sodium sulfate, exhibited significant competitive effect on the adsorption of ammonium ion at sodium ion concentration > 10−2 M. The activation energy and heat of adsorption were 9–23.2 kJ mol−1 and −3.7–−10.7 kJ mol−1, respectively, indicating a physisorption and exothermic adsorption characteristics. Based on the kinetics and thermodynamics analysis, there was slight increase in the activation energy with elevating preheating temperature, which increased the quantity of micro-pores and surface heterogeneity of the AC materials. Overall, results clearly demonstrated that carbon pyrolysis played a role on the capacitive charging behaviors of electrodes and the efficiency of NH4+ electro-sorption on the AC/Ni electrodes.

Tetrafluoroborate anion (BF4−) is found in the streams of flue-gas desulfurization and borosilicate glasses etching which deteriorates water quality through slow hydrolysis into boric acid and fluoride. Decomposition and electrocoagulation (EC) of BF4− were studied using metallic aluminum as the sacrificial electrode. The dissolved Al(III) from the anode could efficiently decompose BF4− in forms of fluoroaluminate complexes, and the derived boric acid and fluoride ion were removed by sweep flocculation. Major variables were investigated to optimize EC, including the reaction pH, initial concentration of BF4−, current density and electrolyte type. The mechanism of EC process was elucidated with the kinetics of consecutive reactions. Experimental results suggested that the removal of BF4− and total fluoride were less influenced by pH, and that of total boron reached a maximum at pH 8 which favored the surface complexation between borate species and EC precipitates. Under the conditions: [BF4−]0 = 9.3 mM, [NaCl] = 10 mM, pH = 8.0, current density = 5 mA/cm2, 98.3% of BF4− was decomposed and the removal of total fluoride and boron attained 98.2% and 74.1%, respectively within 3 h. EC using the Al electrode outperformed the conventional chemical coagulation and reduced the levels of BF4 , B(OH)3 and F− in aqueous solution synergically.

The anthropogenic emission of boron to river has become a serious problem that deteriorates the water quality and endangers the ecosystem. Although boron is a micronutrient, it is toxic to plants, animals and humans upon exposure. In this review, we first present the sources of the boron-containing streams and their composition, and then summarize the recent progress of boron removal methods based on adsorption and coagulation systematically. The boron-spiked streams are produced from coal-fired and geothermal power plants, the manufacturing and the activities of oil/gas excavation and mining. The adsorbents for boron removal are classified into the ones functionalized by chelating groups, the ones on the basis of clays or metal oxide. Three subgroups reside in the coagulation approach: electrocoagulation, chemical precipitation and chemical oxo-precipitation. The hybrid technology that combines membrane process and adsorption/coagulation was covered as well. To provide a comprehensive view of each method, we addressed the reaction mechanism, specified the strength and weakness and summarized the progress in the past 5 years. Ultimately, the prospective for future research and the possible improvement on applicability and recyclability were proposed.

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 molar 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 molar 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).

Magnetically separable spinel ferrites were created in an electrocoagulation (EC) process for removing boron from aqueous solution. Coprecipitates of NiFe2O4, CoFe2O4 and CuFe2O4 were obtained using sacrificial iron anodes (EC-Fe) in an electrolyte that contained transition metal salts (Ni, Co, Cu). The use of nickel chloride (NiCl2) as the supporting electrolyte yielded the highest boron removal since the maximum adsorption capacity of the resulting sludge was 28.9 mg-B/g. An EC that used iron and nickel as anodes (EC-Fe/Ni) in NaCl electrolyte was then employed to form nickel ferrite by electrochemical dissolution of ferrous (Fe(II)) and nickel (Ni(II)) ions, providing comparable removal efficiency but minimizing the residual level of Ni(II) in the treated water. The saturation magnetization of the precipitate that was produced in the EC-Fe/Ni system was 50.3 emu/g which exceeded that in the EC-Fe system with nickel chloride – 21.8 emu/g, indicating its outstanding magnetic separability. EC-Fe/Ni was optimized to remove 95% of boron from solution in 60 min with an initial boron concentration of 10 ppm at pH 8 and a current density of 3.75 mA/cm2.

The imidacloprid was mineralized by heterogeneous photo-Fenton process in a three-phase fluidized bed reactor using waste iron oxide as catalyst. The effects of catalyst loading, dosage of H2O2 and...

A nickel foam-supported Ni(OH)2/NiOOH electrode, synthesized in-situ at a specific electrode overpotential, was used to study the oxidation of ammonia in aqueous solution. Results of voltammetric analysis showed the formal potential of Ni(OH)2/NiOOH transition at +0.6 V (vs. Hg/HgO, pH 11) at which the current profile was improved by electron transfers of NH3 in the electrolyte. Selectivity of NH3 conversion to NO3− and N2 was evaluated by batch constant current experiments. Electrochemical parameters, including solution pH (6–12), temperature (20–40 °C), current density (0.2–3 mA cm−2), and initial NH3-N concentration (20–450 mg-L−1), that may affect ammonia oxidation toward nitrogen selectivity were studied. At constant current density of 1.5 mA cm−2A, ammonia removal reached 98.5% and NO3− was the major product at initial NH3-N concentration of 50 mg-L−1 in 7 h. By contrast, N2 evolution dominated at low current density ( 100 mg-L−1). A surface steady-state approach, with NH3 deprotonation as the rate-limiting step, provided the reaction pathways of NH3 conversion to molecular nitrogen byproduct.

Chemical oxo-precipitation (COP) is a modified precipitation process in which hydrogen peroxide is used to transform boric acid to perborate anions, which are precipitated with calcium salt under ambient conditions. To minimize the production of sludge, chemical oxo-precipitation was performed in a fluidized-bed reactor to reclaim boron as unseeded calcium perborate pellets. Several major experimental parameters, including effluent pH, calcium dosage, and surface loading that affected the degree of supersaturation and the efficiency of boron removal, were tested. A crystallization ratio of around 60% was attained under the following conditions: initial boron concentration = 1000 ppm, molar ratios of [Ca]/[B] = 0.6 and [H2O2]/[B] = 2, effluent pH = 10.6, bed height = 80 cm, and hydraulic retention time = 18 min. On the basis of the characterization of XRD, SEM, and Raman spectroscopy, the granules recovered were amorphous calcium perborates Ca(B(OH)3OOH)2 and CaB(OH)3OOB(OH)3.

Direct electrocatalytic oxidation of ammonia was carried out using an open-pore structured nickel foam electrode via electrochemical formation of Ni(OH)2/NiOOH nano-flowers (theophrastite phase) on the nickel substrate at specific overpotentials. The electrode surface was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectrometer (RS), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammograms gave information on the nature of electron transfer between nitrogen species and nickel foam electrode and revealed the potential dependence nature of ammonia oxidation over the potential window of +0.7 V to +0.85 V (vs. Hg/HgO). Batch controlled potential experiments using nickel foam as the working anode in a three-electrode system were conducted to study the oxidation of ammonia in solution containing 0.1 M of Na2SO4 electrolyte, at pH 11 and temperature of 25 °C. Based on the current efficiency and reaction kinetics, it was possible to establish the mechanism of selective ammonia conversion to gaseous nitrogen and nitrate.

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 [Ca2+]:[PO43−]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.

A commercial polyvinyl alcohol (PVA)/polyacrylonitrile (PAN) hybrid membrane (B3 membrane) was tested to evaluate its ability to dehydrate waste cutting oil by pervaporation (PV). The major material and the water content of the waste cutting oil were analyzed by TGA, NMR, and Karl Fisher titrator. A preliminary PV experiment that involved treatment with 15 wt% aqueous diethylene glycol (DEG) was carried out at various temperatures, and 85 °C was found to be the optimal temperature. The separation factor increased from around 530 to 1140 and the total flux decreased from approximately 0.88 to 0.01 kg/m2/h as the water concentration in the feed solution decreased. Then, a PV experiment that involved treating the waste cutting oil was carried out at 85 °C and the obtained results were almost the same as those in the preliminary experiment, indicating that PV is an effective method for recycling waste cutting oil.

Due to heterogeneous morphological and immunophenotypic features, approximately 50% of peripheral T-cell lymphomas are unclassifiable and categorized as peripheral T-cell lymphomas, not otherwise specified. These conditions have an aggressive course and poor clinical outcome. Identification of actionable biomarkers is urgently needed to develop better therapeutic strategies. Epigenetic alterations play a crucial role in tumor progression. Histone modifications, particularly methylation and acetylation, are generally involved in chromatin state regulation. Here we screened the core set of genes related to histone methylation (KMT2D, SETD2, KMT2A, KDM6A) and acetylation (EP300, CREBBP) and identified 59 somatic mutations in 45 of 125 (36.0%) patients with peripheral T-cell lymphomas, not otherwise specified. Histone modifier gene mutations were associated with inferior progression-free survival time of the patients, irrespective of chemotherapy regimens, but an increased response to the histone deacetylase inhibitor chidamide. In vitro, chidamide significantly inhibited the growth of EP300-mutated T-lymphoma cells and KMT2D-mutated T-lymphoma cells when combined with the hypomethylating agent decitabine. Mechanistically, decitabine acted synergistically with chidamide to enhance the interaction of KMT2D with transcription factor PU.1, regulated H3K4me-associated signaling pathways, and sensitized T-lymphoma cells to chidamide. In a xenograft KMT2D-mutated T-lymphoma model, dual treatment with chidamide and decitabine significantly retarded tumor growth and induced cell apoptosis through modulation of the KMT2D/H3K4me axis. Our work thus contributes to the understanding of aberrant histone modification in peripheral T-cell lymphomas, not otherwise specified and the stratification of a biological subset that can benefit from epigenetic treatment.

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 H2O2 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 (SE), which was fixed at 1.15 ± 0.04; the sludge production rate increased drastically with the supersaturation at the mixing zone (SM), 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.

Graphite-supported α- and β-PbO2 electrodes (PbO2@G) were prepared by electrochemical deposition at appropriate potentials with regard to Pb(II)/PbO2 redox couple under alkaline and acidic conditions, respectively, for studying the direct electro-oxidation of ammonia in aqueous solutions. Results of surface characterization including scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) indicated the presence of polymorphs of PbO2@G. Cyclic voltammetry (CV) of the electrolyte containing NH3 indicated mediation of electron transfer by PbO2. At the onset potential of ca. +1.0 to +1.45 V (vs. Hg/HgO), a pathway of NH3 oxidation to nitrogen byproducts, namely, N2, NO2−, and NO3− was proposed. The removal efficiency and selective conversion of ammonia (0.1 M Na2SO4, pH 11, 25 °C) on PbO2@G was determined based on controlled potential experiments.

Fluoride is commonly an unwanted by-product in industrial processes becoming highly concentrated at the effluent reaching 1,000 to 50,000 ppm F–. However, most of the defluoridation studies focused on the treatment of low concentrations of fluoride Fe > Al > Zr > Mg). Meanwhile, among the discarded and recovered materials use for ballast CaCO3 demonstrated the highest defluoridation efficiency (CaCO3 > Al2O3 > CaHPO4 > SiO2 > Fe2O3). Calcite did not only act as ballast but also a precipitant by providing additional calcium ions through leaching. The defluoridation by ballasted precipitation could efficiently remove fluoride by 99% and reduced turbidity >90%. Moreover, the parameter correlation could be fitted in a quadratic equation (r2 from 0.8763 to 0.9999). The coefficients were used to estimate the significance of each parameter (showing pH > Ca/2F ratio > ballast dosage).

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

Resource recovery in wastewater treatment is the major challenge for achieving sustainable development. Further than only treatment, the recovery and reuse of nitrogen (N) and phosphorus (P) as a slow release fertilizer from actual swine wastewater (SW) was performed in this study. The development of a novel technique of converting soft sludge into hard particles using homogeneous granulation process in a fluidized bed reactor helps address the recovery. Under conditions of pH 8.5 ± 0.2, an Mg:P ratio of 1.2, total suspended solids (TSS)

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.

Chemical oxo-precipitation (COP) has become a promising method for treating boron wastewater at room temperature; it uses hydrogen peroxide to convert boric acid to perborate species, which are precipitated using alkaline earth metals. In this work, solubility models of barium perborates were established to predict residual boron levels from COP. The solubility product constants (pKsp) of two major barium perborates - amorphous Ba(B(OH)3OOH)2 (A-BaPB) and crystalline BaB(OH)2(OO)2B(OH)2 (C-BaPB) - were experimentally estimated (8.335±0.109 and 9.190±0.057, respectively) to define the solubility curves of BaPBs at given pH, ionic strength and concentrations of barium and peroxide species. The characterization of precipitates that were formed by COP confirmed that the boron levels in aqueous solution were governed by the phase transformation of A-BaPB to C-BaPB. The predictive solubility models of barium perborates can perfectly predict the residual concentration of boron after COP treatment and can be used to optimize the process for reducing boron concentrations in wastewater.

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).

The use of a porous PTFE membrane (pore size = 0.2 μm) in the dehydration of diethylene glycol (DEG) by a vacuum membrane distillation (VMD) method was studied. Experiments on VMD for the treatment of 85 wt. % aqueous DEG were carried out at temperatures from 70 to 90 °C, with stirring from 600 to 1700 rpm and vacuum degrees from 650 to 715 torr. The water contents in the feed and the permeate solution were detected by Karl Fisher titration. VMD for 100 min reduced the water content in the feed solution from 15 wt. % to 2 wt. % at 90 °C, 1500 rpm and 715 torr. The separation factor increased from 2500 to 9500 and the total flux declined from 18.5 to 1 kg/m 2 h.

The electrocoagulation (EC) using metallic Ni foam as electrodes was studied for the removal of boron from solution. The electrolytic parameters were pH (4-12), current density (0.6-2.5 mA cm-2), and initial concentration of boron (10-100 mg L-1). Experimental results revealed that removal efficiency was maximized at pH 8-9, and decreased as the pH increased beyond that range. At particular onset potentials (0.5-0.8 V vs. Hg/HgO), the micro-granular nickel oxide that was created on the surface of the nickel metal substrate depended on pH, as determined by cyclic voltammetry. Most of the crystallites of the precipitates comprised a mixed phase of β-Ni(OH)2, a theophrastite phase, and NiOOH, as revealed by XRD and SEM analyses. A current density of 1.25 mA cm-2 was effective in the EC of boron, and increasing the concentration of boric acid from 10 to 100 mg L-1 did not greatly impair removal efficiency. A kinetic investigation revealed that the reaction followed a pseudo-second order rate model. The optimal conditions under which 99.2% of boron was removed from treated wastewater with 10 mg L-1-B, leaving less than 0.1 mg L-1-B in the electrolyte, were pH 8 and 1.25 mA cm-2 for 120 min.

Spent ion exchange resins have become a crucial radioactive solid waste from the nuclear industry. Developing effective and safe disposal methods as alternatives to the present cementation method remains challenging. This investigation demonstrates the treatment of a mixed resin (sulfonated and quaternary ammonium polystyrene beads with a weight ratio of 40%:60%) by the electro-Fenton process. Mesh-type titanium metal that was coated with IrO 2 /RuO 2 (Ti-DSA) was used as the anode and a stainless steel net was used as the cathode. The conversion of resins to soluble fragments and the removal of total organic carbon reached 92% and 99.4%, respectively, under conditions of solid loading = 40g L −1 , pH 2, applied current = 2 A, H 2 O 2 flow rate = 1.2 mL min −1 , FeSO 4 = 20 mM at 85 °C. A pseudo first-order kinetic model of consecutive reactions specified that the efficacy of the electro-Fenton depended strongly on the slowly generated styrene in the aqueous phase by H 2 O 2 and strong acid, which was rapidly mineralized by the hydroxyl radicals. The electro-Fenton process with reused iron catalyst was effective for treating ion exchange resin for at least for three runs, greatly reducing the volume of waste resin liquid.

In this investigation, fluidized bed crystallization (FBC) is utilized to treat phosphorus wastewater that is produced by the manufacture of thin film transistor-liquid crystal displays (TFT-LCD). TFT-LCD wastewater contains 500 ± 10 ppm phosphorus. The pH and molar ratio of Fe/P for removing phosphorus was initially examined by performing a jar-test. The parameters of the FBC – effluent pHe, Fe/P ratio and the upflow velocity (m h−1) – were tested to recover phosphorus from wastewater as ferrous phosphate pellets, characterized using an X-ray diffractometer (XRD) and scanning electron microscopy (SEM), and silica sand was used as the seed material. The experimental results revealed that the control of effluent pHe was an essential parameter in maximizing the phosphorous removal (PR%) and crystallization ratio (CR%). At pHe 5–6, the supersaturation of phosphate precipitation by conditioning the molar ratio of Fe/P to 1.5 and the upflow rate was adjusted within the range of 30.56–68.76 m h−1 in the metastable zone at a cross-section loading of 0.72 kg per P per h per m2, leading to a phosphorus removal (PR) of 95% and a crystallization ratio (CR) of 63%. Under optimal hydraulic conditions, the treatment of real wastewater in a FBC process was viable by converting the pollutant into crystals with a high-purity phase of vivianite (Fe3(PO4)2·8H2O).

Ruthenium (Ru) is a rare-earth metal, which is employed widely in metal-processing industries. This study recovered Ru from the wastewater of an IC foundry by cementation using metallic aluminum (Al) powder as the sacrificial agent. Ru ions were efficiently reduced to the metal and coagulated with the derived aluminum hydroxide flocs. Experimental parameters included the particle size of Al, molar ratio of Al to Ru, initial Ru concentration and operation temperature. The recovery rate reached 99% under these conditions: particle size Al powder = 88–128 μm, Al/Ru molar ratio = 2.0, initial Ru = 200 mg L−1, temperature = 338.16 K, reaction time = 120 min, stirring speed = 150 rpm. The cemented Ru over Al powder was spherical with a rough surface. Kinetic modelling suggested that the diffusion of Ru through the ash layer of Al powder controlled the reaction rate with an activation energy of 40.75 kJ mol−1. A brief cost analysis demonstrated that the cementation of Ru yielded a profit of $0.180 per 0.1 m3-wastewater.

In this study, a fluidized bed reactor was used to compare heterogeneous and homogeneous crystallization for recovering magnesium ammonia phosphate (MAP) from the dewatering filtrate at a municipal water resource recovery facility. Investigating the factors affecting crystallization revealed that pH exerted a greater effect than the Mg/P molar ratio. The results of a heterogeneous crystallization experiment showed that removal efficiency of phosphate (RP%) and crystal efficiency of phosphate (CP%) were 68% and 66%, respectively, at a PO4-P concentration of 200 mg/L, pH of 8.0, and Mg/P molar ratio of 1.0 for 3 h. The reaction rate of heterogeneous crystallization was markedly higher than that of homogeneous crystallization. Those pellets produced through the heterogeneous crystallization exhibited a dense surface (particle size 0.5-1.0 mm; water content 8.7%). Through scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD) examination, the crystallized patterns of the needle-shaped pellets were identified as MgNH4PO4·6H2O.

High levels of fluoride, though, naturally occurring (which can reach as high as 2,800 mg F−/L) in the environment can be toxic to various living organisms. Moreover, it can be transported by water and by its confluences and exacerbated by anthropogenic activities making it an environmental and public health concern. World Health Organization has set the standard for drinking water at 1.5 mg F−/L while the average national effluent standard is 15 mg F−/L. Hence, different defluoridation techniques of aqueous solutions were developed in the past years. This study provides an overview of the popular methods in defluoridation (i.e. adsorption, ion-exchangers, precipitation, membrane, electrocoagulation, and electro-dialysis). The mechanisms, critical operational conditions, and research progress are presented. The results further reveal that adsorption, regarded as the primary technique for defluoridation, still needs further development and mostly on its bench-scale and is only proven effective at low initial concentrations. In this study, sorption techniques are also estimated to be 10 to 20 times more expensive in operational costs relative to the other treatments. Furthermore, the majority of the examined literature demonstrated defluoridation at limited initial concentration

The environment is affected by agricultural, domestic, and industrial activities that lead to drastic problems such as global warming and wastewater generation. Wastewater pollution is of public concern, making the treatment of persistent pollutants in water and wastewater highly imperative. Several conventional treatment technologies (physicochemical processes, biological degradation, and oxidative processes) have been applied to water and wastewater remediation, but each has numerous limitations. To address this issue, treatment using bimetallic systems has been extensively studied. This study reviews existing research on various synthesis methods for the preparation of bimetallic catalysts and their catalytic application to the treatment of organic (dyes, phenol and its derivatives, and chlorinated organic compounds) and inorganic pollutants (nitrate and hexavalent chromium) from water and wastewater. The reaction mechanisms, removal efficiencies, operating conditions, and research progress are also presented. The results reveal that Fe-based bimetallic catalysts are one of the most efficient heterogeneous catalysts for the treatment of organic and inorganic contamination. Furthermore, the roles and performances of bimetallic catalysts in the removal of these environmental contaminants are different.

Electrocoagulation (EC) using metallic aluminum as anode and cathode for boron removal from solution was studied. The electrolytic parameters included pH, current density, and initial boron concentration for optimizing the EC process. Experimental results showed that removal efficiency was increased by elevating pH from 4.0 to 8.0, and then decreased at higher pH. The electrolytic efficacy was increased with increasing current density from 1.25 to 5.0 mA cm−2. With respect of energy consumption, 2.5 mA cm−2 of current density was acceptable for an effective EC of boron, while increasing boric acid from 10 to 100 ppm-B did not impair removal efficiency. NaCl as a supporting electrolyte promoted more anodic dissolution of aluminum from the electrode surface than that predicted by the Faraday's law. The optimal conditions under which 95% of boron was removed and less than 5 ppm-B remained in the electrolyte would be pH 8, four pairs of electrodes, and 2.5 mA cm−2 in 180 min as treating wastewaters containing 10–100 ppm-B. X-ray powder diffractometer and scanning electron microscope were used and results suggested that the irregular crystallites of hydroxide precipitates were composed of bayerite and boehmite phases simultaneously.

Li 4 Ti 5 O 12 /hierarchical porous carbon matrixes composites are successfully prepared by a facile and fast polymers assisted sol–gel method, aiming to promote both electronic and ionic conductivity. As indicated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis, three less expensive cost and available water soluble polymers (e.g. PAA, CMC, and SA) can homogeneously react with Li–Ti–O precursor to incorporate into interior of nano-scale lithium titanate and provide a continues conductive network after pyrolysis. In addition, the results of scanning electron microscopy and transmission electron microscopy also prove that the Li 4 Ti 5 O 12 nanoparticles are firmly embedded in porous carbon matrix with no obvious agglomeration. EIS measurement and cyclic voltammetry further reveal that the facilitated electrode kinetics and better ionic transport of Li 4 Ti 5 O 12 /hierarchical porous carbon matrixes composites than that of Li 4 Ti 5 O 12 . The c-CMC-LTO exhibits a superior capacity of 92 mAh g −1 and retains its initial value with no obviously capacity decay over 200 cycles under an ultra-high C rate (50 C).

Fly ash that was enriched with lead (Pb), formed as an intermediate in waste lead-acid battery (WLAB) smelting, was recycled by the hydro-electrometallurgy. Characterization of fly ash thereof indicated that the Pb was in the forms of PbSO4 (anglesite) and Pb2OSO4 (lanarkite). Nitric acid and sodium hydroxide were firstly used to study the leaching of the fly ash sample, which was affected by leachant dosage and solid-to-liquid ratio (S/L). At an S/L of 60 g L−1, the leachability of Pb was 43% and 67% in 2 M acidic and basic solutions, respectively, based on an average 70 wt% of Pb in the original fly ash. Anglesite was completely soluble in NaOH and lanarkite was mildly soluble in HNO3. Pb was recovered from the pregnant leach solution within an electrolytic cell constructed with graphite or RuO2/IrO2-coated titanium (Ti-DSA) anodes and a stainless steel cathode. Properties of anodes deposited with lead dioxides were analyzed by cyclic voltammetry. The optimized parameters of electrowinning were 2 M NaOH leachant, a current density of 0.75 A dm−2 and an electrolytic process duration of 120 min, which yielded a Pb removal of higher than 99% and a specific energy consumption of 0.57 W h g−1. This process constitutes an eco-friendly and economic alternative to the presently utilized secondary pyrometallurgy for treating lead-containing fly ash.

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.

This work investigated the effective precipitation recovery of boron by chemical oxo-precipitation (COP), which uses hydrogen peroxide (H2O2) to transform aqueous boron to easy-precipitating perborates at room temperature. By using barium hydroxide (Ba(OH)2) as a precipitant, the boron removal enhanced with treatment time and the boron level was eventually reduced from 1000 ppm to 3 ppm in four hours. The transformation of the precipitates from amorphous to crystalline was assumed to be responsible for such high boron removal. The aqueous data and the characterization of the precipitates, including elemental analysis, dissolved oxygen, XRD and Raman microscopy, reveal that the phase transformation of perborate species in the precipitates carried out with time during the COP. Mechanisms of COP that describe the precipitates transformation from BaB(OH)3OOB(OH)3 and Ba(B(OH)3OOH)2 to BaB(OH)2(OO)2B(OH)2 were proposed.

A breakthrough Si ultranano particle (SiUP, size d ≤ 10 nm) inserted nitrogen-doped graphene nanosheet (SiUP@N-GNS) is designed as an anodic material for lithium-ion batteries. In this contribution, a continuous manufacturing process, including top-down dispersion followed by bottom-up synthesis, is addressed incorporated with facile and cost-effective strategies to realize industrial feasibility. Within this specially designed architecture, the volumetric variation induced by high capacitive SiUPs during lithiation/delithiation processes is mitigated effectively by means of several strain-released functions to extend the cycling lifetime. The intrinsic properties, including particle size, compositional configuration, and the spatial distribution demonstrated by SiUPs will alleviate the drastic volume change and local expansion within the nanostructure during cycling. Furthermore, in addition to establishing conductive networks, extended 2D-folded N-GNSs enclosed with SiUP nanoclusters provide mechanical supports to buffer structural variations and to further stabilize active electrodes. As a leading high capacity graphene-based anode material, this state-of-the-art design exhibits long cycling performance up to 600 cycles at a current density of 0.5 A g−1 with the initial specific capacity higher than 1200 mA h g−1 and a low capacity fading of less than ca. 0.09% per cycle.

How to effectively activate oxidants like hydrogen peroxide (H2O2), peroxydisulfate (PDS) and peroxymonosulfate (PMS) is the focus of advanced oxidation processes (AOPs). In this study, we have found that PMS can directly decolorize cationic dyes without activation in a wide pH range (2.0–12.0). In addition, the presence of Cl− results in the formation of free available chlorine species and thus improves the degradation efficiency as well as broadening the scope of target pollutants. The first-order rate constant increased by 4.3 times when 2.5 mM Cl− was added as observed by an increase from 0.021 to 0.089 min−1, which further rose to 1.371 min−1 when Cl− was present at a level of 50 mM. Furthermore, it was found that only PMS has such an amazing effect while H2O2 and PDS do not. Radical quenching experiments and electron paramagnetic resonance (EPR) studies show that the decolorization of cationic dyes by PMS does not rely on the formation of sulfate radicals. A plausible mechanism is that cationic dyes (i.e., RhB+) first form a complex with the active component of PMS (HSO5−) owing to their electrical interaction. Subsequently, direct electron transfer from cationic dyes to HSO5− may occur and probably this is responsible for the bleaching of cationic dyes.

Iron recovery from wastewater as magnetite (Fe3O4) 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 Fe3O4 pellets were analyzed to confirm the magnetic characteristic. A Fenton-like degradation of RB5 azo dye was activated using the Fe3O4 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.

Surfactants, namely, cetyltrimethylammonium chloride, polydiallyldimethylammonium chloride, and benzethonium chloride were used to control the crystal growth of metallic Cu nanoparticles supported on stainless steel mesh electrodes as to improve the selective electrochemical conversion of NO3− to non-toxic N2. Results showed that the Cu(200)/Cu(111) ratio controlled the selectivity of N2, NO2−, and NH4+. The Kd value increased from 10% to 30% when the Cu(200)/Cu(111) intensity ratio was decreased 60% to 30%, meaning increase Cu(111) increased N2 production. Furthermore, the presence of a second metal, namely, Pd increased the N2 selectivity. The best N2 yield (XN2 = 22%), occurring on monometallic Cu, synthesized with BZT at 1-time CMC was further increased to XN2 = 65% over bimetallic Pd0.27Cu0.73/SS. The selectivity of nitrite (SNO2-) and ammonium (SNH4+) on Cu/SS were 33.1 and 43.5%, respectively, which were decreased to 0.30 and 34.0%, respectively, on bimetallic Pd0.27Cu0.73/SS.

Wet oxidation processes such as Fenton and Fenton-like have been considered to treat radioactive ion exchange resins. This investigation demonstrates the oxidative dissolution of cation exchange resin beads by using a fluidized bed Fenton process. The cation exchange resin beads were firstly saturated with catalyst (Fe(II)) in the tubular reactor with a temperature control jacket, and then initiated the oxidation with injecting the H2O2 into the fluidized bed reactor. By means of adjusting a suitable amount of ferrous ions saturated on the cation IER, the reaction can be aimed on the IER destruction rather than homogeneous oxidation. The conversion of resins to gas and soluble fragments reached 91.6% under conditions of solid loading = 117.6 g/L, 25 mL H2O2 dosage (50 wt%), FeSO4 = 10 mM at 75 °C. The fluidized bed Fenton process is efficient and ready to control for the oxidation of cation exchange resin beads in heterogeneous catalysis.

Atmospheric carbon dioxide (CO2) imbalance due to anthropogenic emissions has direct impact in climate change. Recent advancements in the mitigation of industrial CO2 emissions have been brought about by a paradigm shift from mere CO2 capture onto various adsorbents to CO2 conversion into high value products. The present study proposes a system which involves the conversion of CO2 into high purity, low moisture, compact and large CaCO3 solids through homogeneous granulation in a fluidized-bed reactor (FBR). In the present study, synthetic solutions of potassium carbonate (K2CO3) and calcium hydroxide (Ca(OH)2) were used as sources of carbonate and precipitant, respectively. The effects of the degree of supersaturation (S) as chemical loading and influx flow rate (QT) as hydraulic loading on CaCO3 granulation efficiency were investigated. In the study, S was varied from 10.2 to 10.8 and QT from 40 to 80 mL min−1 while the operating pH and calcium-is-to-carbonate molar ratio ([Ca2+]/[CO32−]) were set at 10 ± 0.2 and 1.50, respectively. Results showed that carbonate ions end product distribution had a highest carbonate granulation efficiency at [Carbonate]G of 95–96% using S of 10.6 and QT of 60 mL min−1. Characterization of the granules confirmed high purity calcium carbonate. Overall, the transformation of industrial CO2 emissions into a valuable solid product can be a significant move towards the mitigation of climate change from anthropogenic emissions.

Activated carbon (AC), prepared from dried loofah sponge, was supported on nickel foam to fabricate AC/Ni electrodes. The characteristics of ammonium electrosorption on AC/Ni electrodes was studied. Results showed that AC prepared in one-step activation (without pre-pyrolysis), i.e., OAC, had relatively low crystallinity, high mesoporosity, and high specific capacitance compared to those made in two-step carbonation followed by activation. Adsorption and desorption density of NH4+ were measured at constant potential of −1.0 V (vs. Hg/HgO) and +0.1 V (vs. Hg/HgO), respectively. Non-faradaic charging contributed to the electrochemical storage and adsorption of ammonium ions on the AC surface with a maximal charge efficiency of 80%, at an applied potential of −1.0 V (vs. Hg/HgO). Multiple-layer adsorption isotherm better described the electrosorption of ammonium ion on OAC/Ni electrodes yielding a maximum adsorption capacity of 6 mg-N g−1, which was comparable with other similar systems. Overall, results clearly demonstrated the effect of synthesis strategy on the capacitive charging behaviors of AC/Ni electrodes and its relationship to NH4+ electrosorption.

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.

The granulation of calcium carbonate (CaCO3) exhibited high industrial demand due to its wider application and importance in cement, paper, glass and steel manufacturing. This paper investigated the granulation kinetics of CaCO3 through the fluidized-bed homogeneous granulation (FBHG) process during the homogenous nucleation stage. The CaOH solution was used as source of Ca2+ reactant, while K2CO3 solution as source of CO32− precipitant. The mechanism followed the pseudo-second order kinetics. The calcium cation attracts the carbonate anion to form CaCO3 through a double displacement chemical reaction. The calcium-is-to-carbonate molar ratio ([Ca2+]/[CO32−]) was varied into 1.25 to 2.50, with constant values of pH = 10 ± 0.2, influent carbonate concentration = 10 mM and total influx flow rate = 60 mL min−1. The ideal [Ca2+]/[CO32−] condition was found to be at 1.50 that means the precipitation of CaCO3 grew and stayed inside the reactor. At the same condition, granules of diameter size of 1 mm to 2 mm were collected with a subrounded shape and smooth surface as shown by its surface morphology. The characterization analysis also verified the high purity of CaCO3-aragonite granules precipitated through the FBHG process.

Fluorine is the most reactive elements among the halogen group and commonly and ubiquitously occurs as fluoride in nature. The industrial processes produce fluoride by-products causing the increase of unwanted environmental levels and consequently posing risk on human and environmental health worldwide. This review gives a fundamental understanding of fluoride networks in the industrial processes, in the geological and hydrological transport, and in the biological sphere. Numerous biological pathways of fluoride also increase the risk of exposure. Literature shows that various environmental levels of fluoride due to its chemical characteristics cause bioaccumulation resulting in health deterioration among organisms. These problems are aggravated by emitted fluoride in the air and wastewater streams. Moreover, the current waste disposal dependent on incineration and landfilling superpose to the problem. In our analysis, the fluoride material flow model still follows a linear economy and reuse economy to some extent. This flow model spoils resources with high economic potential and worsens environmental problems. Thus, we intend a shift from the conventional linear economy to a circular economy with the revival of three-dimensional objectives of sustainable development. Linkages between key dimensions of the circular economy to stimulate momentum for perpetual sustainable development are proposed to gain economic, environmental and social benefits.