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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.

The strong oxidant, persulfate (PS, S

Spent lithium ion batteries (LIBs) can be of great environmental concern because of the generation of heavy metal pollution in such wastes in huge quantities, mainly from the fast-growing mobile phone market. In this research, acidic leaching coupled with microwave and ultrasonic heating is integrated with oxidative precipitation and solvent extraction to reclaim and purify the metals in the cathode material of batteries. To optimize the leaching process, the effects of the concentrations of acids and reductant (H2O2), solid loading, and temperature, as well as heating with microwaves and ultrasound, on Co, Li, Mn, Ni, Cu, and Al dissolution are systematically tested. KMnO4 is first applied to remove Mn as MnO2 precipitate from the leachate, and most of the Li can be selectively collected in the aqueous phase by solvent extraction using di-(2-ethylhexyl) phosphoric acid. At the end of the process, the majority of Co and minor amounts of Ni, Cu and Al are reversely extracted using HCl. An effective purification process is proposed to obtain more than 90% of the valuable metals in each of the leaching, precipitation and extraction steps.

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.

Effects of Pd nanoclusters in PdxSn100-x/Ni electrodes with preferred diffraction planes of Sn(101) and Sn(200) plated on a nickel foam were studied on electrochemical reduction reaction of nitrate (NO3-). NO3- converted to NO2-, N2 and NH4+ by surface Hads was assessed at different Pd to Sn ratio through the electroanalysis and batch electrolysis at constant current mode. Pd loading obviously enhanced the current density of proton diffusion-controlled Sn0/Sn(II) transition. NO3- reduction was much more efficient on PdSn(200) than on PdSn(101); 53% of N2 yield on Sn(200)/Ni could increase up to 79% on Pd5Sn(200)95/Ni, while further increasing Pd loading would gradually increase NH4+ yield. The steady-state kinetics proposed a scheme of adsorption and deoxygenation of NO3- on Sn(200) and hydrogenation of NO2- to N2 on Pd NPs beside the Sn crystals.

Dyes are hazardous compounds commonly found in industrial wastewaters. Efficient and inexpensive removal of dye molecules from the water matrix has been demonstrated by adsorption processes. Magnetic nano-adsorbents, such as metal ferrites, can be efficiently recovered from the reaction mixture after treating the pollutant. Herein, MFe2O4@GO (M = Cu, Co or Ni) was synthesized via solution combustion method for the removal of dye molecules from aqueous solutions. The characteristics of the MFe2O4@GO, including surface area and pore diameter, surface functional groups, and elemental composition, were examined. Methylene blue was used as representative dye pollutant. Batch adsorption results conformed to the Langmuir isotherm. Maximum adsorption capacities of the MFe2O4@GO (M = Cu, Co or Ni) were 25.81, 50.15 and 76.34 mg g−1, respectively. Kinetics of methylene blue adsorption fitted the pseudo-second-order model. Overall, NiFe2O4@GO exhibited the highest adsorbent performance among the graphene-metal ferrites investigated, primarily because of its high specific surface area and presence of mesopores.

An electrode made of activated carbon that had high-specific-surface area and low pHzpc supported on graphite sheet was fabricated. The electrode, NSA/G, was used to study the effect of reversible surface charge on the adsorption of simple electrolyte, i.e., NaCl, on polarizable electrode. Polarizable surface charge is originated from externally applied potential whereas reversible surface charge is derived from change of activity of potential-determining ions, i.e., H+ or OH– owning to hydrous surface, which undergoes protonation and deprotonation of surface hydroxyl groups. Ion adsorption density was obtained from direct analytical measurement of corresponding ion studied instead of conductivity measurement. Langmuir adsorption isotherm was applied to estimate the monolayer ion adsorption density. Electrosorption/desorption kinetics was fitted well by the first-order rate law. In the applied potential range of −0.3 to −1.0 V (vs. SCE) and pH of 3 to 10, the pH-determining surface, i.e., reversible charge, accounted for Na+ sorption intensity was estimated based on the Gouy-Chapman version of electrical double layer theory. Results revealed that the two major surface charges, i.e., polarizable (σE) and reversible (σpH), contributed equally to the total charge density (σT). At high pH (pH 10) and low applied voltage (-0.3 V vs. SCE), the fraction of pH-determining contribution to total surface charge with respect to Na+ sorption, i.e., σpH/σT, was around 0.50. Results reaffirmed the importance of reversible surface charge together with polarizable surface charge on the design and operation of CDI system for electrosorption of ions from water.

In-situ chlorine generation has high disinfection potential for small to medium scale water treatment systems. Electrodes were prepared by coating Pt-, Ni-, Co-oxides on graphite substrate using electrodeless deposition method and characterized with SEM, EDS, XRD, XPS and cyclic voltammetry. Results showed that the molar ratio of Ni- and Co-oxides on graphite surface influenced surface structure and in-situ chlorine generation capacity. Pt0.01Ni0.24Co0.75 electrode exhibited a unique surface structure and the highest in-situ chlorine generation capability. The Pt0.01Ni0.24Co0.75-G electrode exhibited highly porous 3D structure and high oxygen deficit, which significantly promoted the formation of M-Cl− binding on electrode surface and enhanced chlorine generation. The onset of chlorine evolution potential was lower than that of oxygen on Pt0.01Ni0.24Co0.75-G electrode. Moreover, the transfer coefficient of chloride oxidation was smaller than that of water oxidation, which would enhance chloride oxidation current efficiency. The in-situ chlorine generation capability increased with NaCl concentration. The kinetics of chlorine generation was well described by the Langmuir-Hinsheldwood mechanism. The in-situ disinfection rate decreased with the increase in initial E. coli density. A 7.5-log disinfection was achieved in 15 min in the presence of 0.01 M NaCl under 5 mA/cm2 current density at room temperature. The lipid peroxide, morphology changes and destruction of E. coli cell membrane were observed in the in-situ disinfection process, indicating that reactive species such as chlorine radical in addition to free chlorine played the main role of in-situ disinfection.

Mesoporous zirconium pyrophosphate(ZPP) adsorbents were synthesized, with six quaternary ammonium salts (Quats), namely, Octyltrimethylammonium (OTMA, C8), Decyltrimethylammonium (DCTMA, C10), Dodecyltrimethylammonium (DDTMA, C12), Tetradecyltrimethylammonium (TDTMA, C14), Hexadecyltrimethylammoium (HDTMA, C16), and Octadecyltrimethylammonium (ODTMA, C18), as template for studying fluoride adsorption. Quats of long carbon chain length significantly affected the specific surface area of mesoporous ZPP adsorbents. C18-ZPP exhibited the largest specific surface area and fluoride adsorption density. Fluoride adsorption density remained constant at pH 10–11. Langmuir adsorption isotherm described fluoride adsorption characteristics well. Results showed that mesoporous ZPP synthesized with C18 at Zr to C18 molar ratio of 0.57:1 exhibited the best fluoride adsorption capacity (32 mmol/g) among all ZPP adsorbents prepared at various Zr to C18 molar ratios. C18-ZPP exhibited two-fold increase in fluoride removal capacity compared to plain ZPP. The reusability of C18-ZPP was assessed by running fluoride removal at least five cycles. Mesoporous ZPP is a promising adsorbent for fluoride removal from water with much enhanced adsorption capacity, regenerability, and reusability.

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.

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.

The capability of manganese dioxide (MnO2) supported on loofah-derived activated carbon (AC) in the electrosorptive removal of common inert ions was studied in constant potential mode. Four MnO2 polymorphs were prepared by redox chemical precipitation and characterized by XRD, SEM, BET and XPS. The pseudocapacitance property of the MnO2/AC electrode, significantly affected by the surface- and diffusion-controlled charge storage mechanism, was assessed via voltammetry and modified Langmuir adsorption isotherm. Batch electrosorption experiments were then performed at constant potential in the range of −1.5 V to + 1.5 V (vs. Ag/AgCl) using AC and α-MnO2/AC electrodes in the presence of common simple electrolytes, including NaNO3, Li2SO4, and Ca(ClO4)2. Consequently, the applied working potential (Eapp) positively affected the ion electrosorption rate and capacity. Faradaic processes occurred on MnO2, i.e., Mn(III)/Mn(IV) transition, increased the diffusion capacitance of AC, thus enhancing the first-order rate and monolayer capacity, mainly for the electrosorption of cations. Results showed that ion solvation, controlled by the ionic radius and valence of an ion, which impacted ion intercalation in MnO2 and affected ion adsorption characteristics. The cation sorption capacity of α-MnO2/AC followed the order of Na+ (2.8 × 10-4 mol g−1) > Ca2+ (2.1 × 10-4 mol g−1) > Li+ (0.76 × 10-4 mol g−1) at Eapp = -1.5 V. The differential capacitance as affected by polarized potential and the shift of zero net charge or IEP toward more positively charging potential further highlighted the contribution of pseudocapacitance to ion adsorption on α-MnO2/AC electrode.

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 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.

Ammonia oxidation and selectivity of nitrogen conversion were investigated over an Ni foam-supported NiCo oxide electrode synthesized using chemical precipitation and calcination. Characterization using XRD, SEM, and XPS determined the crystal phase and oxdiation state of the nano-textured particulate metal oxides. A voltammetry analysis showed that a M(II)/(III) (M = Ni and Co) redox reaction couple mediated the direct electron transfer of the nitrogen species. Batch electrochemical parameters, including the initial concentration of NH3 and the current density, were studied to evaluate the performance of the tested electrodes in the absence of chloride ions. The best N2 selectivity (40%) was obtained on the oxyhydroxide anode (H-Ni50Co50/Ni); further, as paired with an electroless Cu/Ni cathode, the total nitrogen (TN) loss in terms of gaseous nitrogen evolution was 76%. Consecutive kinetics was derived to assess the pathways of the NH3 conversion and the rates of the nitrogen cycle on different electrode pairs, such as Ni – Ni, Ni – Cu/Ni, and H-NiCo/Ni – Cu/Ni sets.

The characteristics of nanoparticles (NPs) uptake may fundamentally alter physicochemical effects of engineered NPs on aquatic organisms, thereby yielding different ecotoxicology assessment results. The adsorption behavior of nano-TiO2 (P-25) on zebrafish embryos in Holtfreter's medium (pH 7.2, I ∼ 7.2 × 10(-2) M) and the presence of sodium alginate (100 mg/L) as dispersant was investigated. Zebrafish embryos (total 100) were exposed to nano-TiO2 at different concentrations (e.g., 0, 10, 20, 60, 120 mg/L) in batch-mode assay. The adsorption capacity of nano-TiO2 on fish eggs was determined by measuring the Ti concentration on the egg surface using ICP-OES analysis. Results showed that the adsorption capacity increased rapidly in the first hour, and then declined to reach equilibrium in 8 h. The adsorption characteristics was visualized as a three-step process of rapid initial layer formation, followed by break-up of aggregates and finally rearrangement of floc structures; the maximum adsorption capacity was the sum of an inner rigid layers of aggregates of 0.81-0.84 μg-TiO2/#-egg and an outer softly flocculated layers of 1.01 μg-TiO2/#-egg. The Gibbs free energy was 543.29-551.26 and 100.75 kJ/mol, respectively, for the inner-layer and the outer-layer aggregates. Adsorption capacity at 0.5-1.0 μg-TiO2/#-egg promoted egg hatching; but hatching was inhibited at higher adsorption capacity. Results clearly showed that the configuration of TiO2 aggregates could impact the hatching efficiency of zebrafish embryos.

Various chemical oxidation techniques, such as potassium permanganate (KMnO4), sodium persulfate (Na2S2O8), Fenton (H2O2/Fe(2+)), and the modified persulfate and Fenton reagents (activated by ferrous complexes), were carried out to treat marine sediments that were contaminated with polycyclic aromatic hydrocarbons (PAHs) and dredged from Kaohsiung Harbor in Taiwan. Experimental results revealed that KMnO4 was the most effective of the tested oxidants in PAH degradation. Owing to the high organic matter content in the sediment that reduced the efficiencies of Na2S2O8 and regular Fenton reactions, a large excess of oxidant was required. Nevertheless, KH2PO4, Na4P2O7 and four chelating agents (EDTA, sodium citrate, oxalic acid, and sodium oxalate) were utilized to stabilize Fe(II) in activating the Na2S2O8 and Fenton oxidations, while Fe(II)-citrate remarkably promoted the PAH degradation. Increasing the molecular weight and number of rings of PAH did not affect the overall removal efficiencies. The correlation between the effectiveness of the oxidation processes and the physicochemical properties of individual PAH was statistically analyzed. The data implied that the reactivity of PAH (electron affinity and ionization potential) affected its treatability more than did its hydrophobicity (Kow, Koc and Sw), particularly using experimental conditions under which PAHs could be effectively oxidized.

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.

Various surfactants, such as nonionic Triton X-100 and Simple Green™ (SG), and anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) were utilized to remove polycyclic aromatic hydrocarbons (PAHs) from heavily contaminated harbor sediments dredged from Kaohsiung Harbor in Taiwan. Desorption/re-sorption equilibrium, kinetics, and washability of PAHs using the selected surfactant were evaluated under different critical micelle concentrations (CMC). Experimental results revealed that the desorption rate of high molecular weight PAHs was greater than those of low molecular weight PAHs, and the anionic SDS was relatively effective in the removal of total PAHs (>50%) compared to the other surfactants. The correlation between the effectiveness of the surfactant washing processes and the physicochemical properties of individual PAH was statistically analyzed. The resulting data suggested that hydrophobic factors (Kow, Koc and Sw) affected PAH treatability more than the reactivity of PAH (electron affinity and ionization potential). Since the adsorption of anionic surfactant altered the hydrophobicity of organic matter in the sediment, PAHs preferred transferring from the sediment to the hydrophobic core of micelles in aqueous solution. Nevertheless, the nonionic surfactant enhanced the PAH partition in the aqueous phase, thus increasing the micellar solubilization of PAH.

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 accumulation of halogenated organic contaminants in estuaries near harbor areas has been receiving increasing attention. This work demonstrates the reductive treatment of trichloroethene (TCE) within seawater and freshwater using a polymeric surfactant (polyvinyl alcohol-co-vinyl acetate-coitaconic acid) modified nanoscale zero-valent iron (GnZVI). Experimental parameters included the ratio of seawater to freshwater, reaction pH, dosage of GnZVI and initial TCE concentration. It was found that the rate of TCE reduction decreased with increasing weight ratio of seawater to freshwater (ka = 0.075 min−1 in freshwater and 0.01 min−1 in seawater); however, the rate substantially improved by increasing the dosage of GnZVI. A consecutive reaction model of adsorption/desorption and reductive dechlorination was established to assess the chemical kinetics of TCE and the intermediates over the GnZVI. The experimental results suggested that both the amount of free sites on the reductant and reactivity of iron to TCE dominated the degradation efficiency. Desorption was a rate-limiting step for the intermediates that evolved (DCE, VC and ethene) in the bulk solution. Under conditions: GnZVI = 5 g/L, reaction pH around 8 and initial TCE = 10 mg/L, the removal efficiency attained 95%, while the decline in the removal rate of TCE from the seawater could be simply improved by increasing GnZVI dosage (10 g/L). As a role of electron donor for water and TCE, ZVI might passivate with contact time, leading to formation of the main crystalline phase magnetite (Fe3O4) by the coprecipitation of oxidized iron (Fe(II)/Fe(III)) over the surfaces of ZVI particles.

Effects of ferrite materials as supports (CoFe 2 O 4 , NiFe 2 O 4 , and Fe 3 O 4 ) on nano-TiO 2 were elucidated by their use in the oxidation of methylene blue. These photocatalysts, which were synthesized by co-precipitation, were characterized by XRD, SEM, EDS and VSM. The crystalline phase of TiO 2 onto magnetic MFe 2 O 4 was formed by anatase and rutile. TiO 2 /CoFe 2 O 4 exhibited the strongest magnetic property of the prepared catalysts, and the photocatalytic efficiencies followed the order TiO 2 /CoFe 2 O 4 > TiO 2 /NiFe 2 O 4 > TiO 2 /Fe 3 O 4 . MB decolorization was enhanced with the amount of TiO 2 on the photocatalyst, and was moderately affected by the extent of structural distortion of ferrite supports.

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 (PbCO3) or a hydrocerussite (Pb3(CO3)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 [Na2CO3]/[Pb] > 1.2, upflow velocity = 25–35 m h−1 and pHe = 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.

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.

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 NO3− (80, 160 ppm), CH2COOH− (260, 520 ppm), F− (650, 1300 ppm) and SO42− (650, 1300 ppm), were utilized to prepare P-containing wastewaters. Of these ions, SO42− (1300 ppm) remarkably reduced the capability of FBC to remove phosphate from solution. In the presence of NO3− and CH3COO− (for synthesizing TFT-LCD wastewater), and F− and SO42− (for synthesizing semiconductor wastewater), CR% was lower than in pure water, although the ultimate PR% did not differ significantly.

This work demonstrates the combination of UV/persulfate and adsorption processes for treating 2,2,3,3-tetrafluoro-1-propanol (TFP) wastewater. Under the optimum conditions, 20 mM persulfate ( S 2 O 8 2 - ) , 254 nm UV–C, and pH 3, 99.7% of TOC removal from an initial TFP solution of 1.39 mM was achieved. The photolysis of persulfate ( S 2 O 8 2 - ) by UV irradiation yielded the sulfate radical ( SO 4 - ) with high activity, which mineralized most of the TFP in 2 h. The released fluoride ions were then removed by using a waste iron oxide, BT-4 adsorbent. 20 g L−1 BT-4 adsorbed 95% of the fluoride that was produced by mineralization of 1.39 mM TFP. The kinetics and isotherms of adsorption were examined to determine the fluoride removal efficiency of BT-4 which co-existed with the sulfate ions from the consumed sulfate radicals. Accordingly, the kinetics of adsorption was described by a pseudo-second-order rate model, while the adsorption isotherms were well fitted with the Langmuir model. BT-4 had a high adsorption capacity of 26.4 mg g−1 (25 °C) in removing the fluoride from TFP mineralization, suggesting that the co-existing sulfate ions never significantly affected the fluoride removal efficiency.