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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.

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.

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.

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.

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.

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 manufacture of products for the growing population results in large volume of wastewater that needs treatment. Advanced oxidation processes (AOPs) are popular for low cost, high efficiency and being eco-friendly in the degradation of toxic pollutants in the wastewater using the generated non-selective hydroxyl radical (•OH) for oxidation. Among the many AOPs, the Fenton process has been proven to be effective for treating recalcitrant organic compounds by using Fe2+ and H2O2 to produce the •OH. One disadvantage is the production of a large amount of sludge that needs further treatment and disposal. The fluidized-bed Fenton (FBF) process uses carriers that reduce the production of sludge by crystallizing the target pollutant onto the carrier surface. This paper is a comprehensive review of the recent development on FBF process application to industrial wastewater treatment. FBF process was used to treat industrial wastewaters like thin film transistor liquid crystal display manufacturing effluents, pharmaceutical products, textile, phenol and phenol derivatives-containing wastewater and other refractory organics in wastewater. This review highlights the advantages of FBF process over other technologies that are based on Fenton oxidation in terms of performance, operating conditions and factors affecting the removal efficiency. Included in this review are the reaction kinetics and mechanism involved and the carriers that were used. Finally, full-scale applications are collected and described. This review has shown the potential applicability of FBF technology to reduce the levels of recalcitrant organic contaminants in wastewater effluents.

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.

A waste iron oxide (labelled as BT4), which was a by-product of the fluidized-bed Fenton treatment of the bio-treated tannery wastewater, was utilized as the catalyst for the mineralization of bisphenol A (BPA) by a heterogeneous photo-Fenton process in a three-phase fluidized bed reactor. The main constituent of BT4 was identified as α-FeOOH, while BT4 exhibited higher catalytic activity than pure α-FeOOH. The effects of catalyst loading, H2O2 concentration and initial pH on the mineralization of BPA were elucidated. With 2 g/L catalyst loading, 0.74 mmol/L H2O2 and initial pH 3, 90% TOC of 0.05 mmol/L BPA was removed after 180 min reaction. The result of the catalyst reuse experiment indicated that BT4 showed a good stability.

To remove strontium (Sr) efficiently from aqueous solutions is important as Sr-90 is a radionuclide and could be a serious threat to the environment. This study examines the feasibility of Sr-90 removal using BT9, generated from a FBR-Fenton facility that was utilized in treating tannery wastewater. A rapid increased of Sr adsorption was detected when the solution pH increased from 7.11 to 11.22. A maxima adsorption capacity was estimated to be 29.85 mg Sr/g BT9 at 323 K and pH 11.22. Additionally, Sr adsorption decreases with the increase of the M/Sr from 0 to 100, indicating that the outer-sphere mechanism was importantly involved in the Sr adsorption. This Sr adsorption is spontaneous and endothermic, supported by the negative changed standard free energy with temperatures (Δ G ° = −5.75, −6.26, −6.72 kJ/mol at 288, 303, and 323 K, respectively) and the positive Δ H ° values (2.14 kJ/mol). The positive Δ S ° (27.49 J/mol K) further indicates that the randomness increased at solid-solution interface during Sr adsorption.

This investigation demonstrates an indirect chloride photo-electrochemical method for mineralizing the organic acids (5 mM), including acetic, maleic, malonic, citric, oxalic, and succinic acids. The electrolytic reactor (12 cm × 12 cm × 30 cm) held 2.5 L solution, in which both anode and cathode were the titanium-based dimensionally stable anode (Ti-DSA) that was coated with RuO2/IrO2. Different active chlorine species with various redox potentials, including OCl−, HOCl, and Cl2, produced in NaCl medium were the major oxidants depending on the pH of the electrolysis. The results revealed that a pH in the range 2.5–7 maximized the removal rate of total organic carbon (TOC) of citric acid solution. The UV-254 nm light was then utilized in the NaCl electrolysis to support a photo-electrochemical reaction. The substantial improvement in the mineralization efficiency for all organic acids was attributed to the hydroxyl radicals ( OH) and chlorine radicals (Cl ) from HOCl upon activation by the UV irradiation.

An iron oxide, BT1, recovered from a real fluidized-bed Fenton reactor, was studied to determine its effectiveness in the adsorptive removal of strontium ions (Sr2+) from water. Millimeter-scale BT1 (0.2–0.5 mm) mostly consisted of a poorly crystallized goethite phase (α-FeOOH), with a specific surface area of 185 m2/g. Batch jar-testing experiments were conducted at an initial Sr2+ level of 10 ppm to determine the effect of pH, the adsorption isotherms, the desorption process, and the kinetics of adsorption. The effectiveness of BT1 as an adsorbent for the removal of Sr2+ depended strongly on pH; at an equilibrium pH of 10.5, 5 g BT1 removed almost 100% of Sr2+. Sr2+ was desorbed by a solution of nitric acid at pH 3 with a relatively low rate, and the recycled BT1 maintained its high adsorption efficiency after at least three adsorption–desorption tests. The isotherms were accurately described using both Langmuir and Freundlich models, and the maximum adsorption capacity was found to be 38.46 mg/g. The thermodynamic parameters revealed the endothermic and spontaneous nature of the adsorption process at 20–45 °C. Kinetic studies revealed that the adsorption of Sr2+ ions on BT1 was a second-order reaction.

The photo-activated persulfate oxidation technology for efficient mineralization of 2,2,3,3-tetrafluoro-1-propanol (TFP) was investigated. The chemical bonds of TFP molecule could be efficiently broken by the sulfate radicals (SO4− ) with high redox potential (E0 = 2.6 V) produced from persulfate (S2O82−) photolysis. The initial pH value insignificantly influenced the treatment's efficiency, while the UV intensity and oxidant dosage which affected the generation of sulfate radicals could greatly enhance the TOC removal. Under UV irradiation (254 nm, 13 W × 3 lamps) and with an initial persulfate/TFP molar ratio about 4, above 99.5% TOC was reduced in 60 min. All sulfur species in the reaction solution were eventually transformed to sulfate ions. According to the fluoride ion releasing in advance of TOC removal, UV/persulfate was supposed to initially decompose TFP into intermediates with lower fluorinated forms, which were then mineralized in following reactions.

In this study, phenol was degraded by the photo-Fenton process at pH 3, 5 mg/L Fe(III), 1080 mg/L H2O2 using 3 UV lamps (365 nm). In the UV/H2O2 system, the degradation of phenol is inefficient, and only around 25% of the phenol is degraded in 1 h. The efficiency of the photo-Fenton system considerably exceeded that in UV/H2O2 and Fenton-like systems. The removal efficiency of COD by the photo-Fenton process was 98% respectively, but only 63% in the Fenton-like system. The effect of oxalate on the degradation of phenol was also investigated. The removal efficiency of phenol was highest at a molar concentration ratio of oxalic acid to ferric ions ([Ox]/[Fe3+]) of 2. Increasing the amount of dissolved oxygen promoted the degradation of phenol. Even when concentration of added ferric ions in the photo-Fenton system was low, the COD removal efficiency was still satisfactory. The intermediate organic acids during the degradation of phenol were formic acid, acetic acid, oxalic acid and succinic acid. The pathway of phenol degradation in the photo-Fenton process is proposed from experimental results and the literature.