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

This study investigated a heterogeneous photo-catalysis system by introducing a novel brick supported iron oxide (denoted as B1) for the heterogeneous photoassisted degradation of Reactive Black 5 (RB5) at pH value from 3 to 7 in a three-phase (gas-liquid-solid) fluidized bed reactor (3P-FBR). Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD) and N2 adsorption/desorption were used to characterize the B1 catalyst. The in situ formation of hydrogen peroxide and the depletion of oxalic acid by photochemical cycle of Fe(III)-oxalate complex under UVA light (λ = 365 nm) were studied. The effects of the solution pH and the concentration of oxalic acid on the degradation of RB5 are elucidated. About 90% decolourization was measured and 80% of the total organic carbon (TOC) was eliminated at pH 5.0 after 120 min for 20 mg/L RB5 in presence of 10 g/L B1 catalyst, 30 mg/L oxalic acid under 15 W UVA light. A mechanism for the photocatalytic degradation of RB5 over B1 catalyst is proposed. [ABSTRACT FROM AUTHOR]

Fenton technologies for wastewater treatment have demonstrated their effectiveness in eliminating toxic compounds. This study examines how hydrogen peroxide concentration and ultraviolet (UV) light affects oxidation processes. However, total mineralization through these Fenton technologies is expensive compared with biological technologies. Therefore, partial chemical oxidation of toxic wastewaters with Fenton processes followed by biological units may increase the application range of Fenton technologies. Using 2,6-dimethylaniline (2,6-DMA) as the target compound, this study also investigates oxidation intermediates and their biodegradable efficiencies after treatment by Fenton, electro-Fenton and photoelectron-Fenton processes. Analytical results show that the UV light-promoting efficiency, rPE-F/rE-F, was 2.02, 2.55 and 2.67 with initial hydrogen peroxide concentrations of 15, 20 and 25 mM, respectively. We conclude that UV irradiation promoted 2,6-DMA degradation significantly. The same tendency was observed for biochemical oxygen demand/total organic carbon (BOD5/TOC) ratios for each process, meaning that 2,6-DMA can be successfully detoxified using the electro-Fenton and photoelectro-Fenton processes. Some organic intermediates aminobenzene, nitrobenzene, 2,6-dimethylphenol, phenol and oxalic acid-were detected in different oxidation processes. [ABSTRACT FROM AUTHOR]

Abstract: A batch photo-fluidized bed reactor (photo-FBR) is designed for the mineralization of phenol and the minimization of iron species leached from an active immobilized iron oxide (denoted as SiG2). The hydroxyl radical (h is produced from the reaction of hydrogen peroxide (H2O2) and SiG2 under irradiation by a 400-W Hg-vapor lamp, was confirmed by electron paramagnetic resonance signals of 5,5-DIMETHYL-1-pyrroline-N-oxide (DMPO)-us solution). The mineralization of phenol was more efficient in the presence of light. In general, a decrease of solution pH is commonly ascribed to the formation of carboxylic acids (acetic acid, oxalic acid, formic acid etc.) during the degradation of phenol. However, in this study, an interesting phenomenon was observed. The solution pH first decreased and then rose during the reaction in the presence of light. Also, in this case, the variation of solution pH reflected the degree of mineralization in this study. The approximately 98% mineralization of phenol led to fewer iron species being leached from SiG2 in the photo-FBR. A savings of more than 40% of the H2O2 dosage required for the phenol mineralization process was confirmed. In a batch photo-FBR, the system loading reflects the ratio of catalyst weight to the reaction volume. About 96%, 86% and 11% of the total organic carbons were removed after 180min, resulting in catalyst weight to reaction volume ratios of 30:1, 20:1 and 13:1, respectively. The activity of SiG2 did not decline after six reactions. The reactions for photo-assisted SiG2 in the presence of hydrogen peroxide and phenol were summarized. [Copyright &y& Elsevier]

A two-stage oxidation (UV-Na2S2O8/H2O2-Fe(II,III)) process was applied to mineralize bisphenol A (BPA) at pHi (initial pH) 7. We take advantage of the high oxidation potential of sulfate radicals and use persulfate as the 1st-stage oxidant to oxidize BPA to less complex compounds (stoichiometric ratio: [S2O8 2−]0/[BPA]0 =1). Afterwards, the traditional photo-Fenton process was used to mineralize those compounds to CO2. To the best of our knowledge, this is the first attempt to utilize the two processes in conjunction for the complete degradation of BPA. During the 2nd-stage reaction, other oxidants (H2O2 and Iron alone) were also employed to observe the extent of enhancement of photo-Fenton. Further, qualitative identification of both hydroxyl and sulfate radicals was performed to evaluate their dominance under different conditions. The BPA degradation in this UV/persulfate process formulated a pseudo-first-order kinetic model well, with a rate constant of approximately 0.038min−1 (25°C), 0.057min−1 (35°C), and 0.087min−1 (50°C), respectively. The much lower activation energy (ΔE =26kJmol−1) was further calculated to clarify that the thermal-effect of an illuminated system differs from single heat-assisted systems described in other research. Final total organic carbon (TOC) removal levels of BPA by the use of such two-stage oxidation processes were 25–34%, 25%, and 87–91% for additional Fe(II,III) activation, H2O2 promotion, and Fe(II,III)/H2O2 promotions, respectively. [Copyright &y& Elsevier]

The photolysis and photo-catalysis of ferrioxalate in the presence of hydrogen peroxide with UV irradiation (UV/ferrioxalate/H2O2 process) for treating the commercial azo dye, reactive Black B (RBB), is examined. An effort is made to decolorize textile effluents at near neutral pH for suitable discharge of waste water. pH value, light source, type of initial catalyst (Fe3+ or Fe2+) and concentration of oxalic acid (Ox) strongly affected the RBB removal efficiency. The degradation rate of RBB increased as pH or the wavelength of light declined. The optimal molar ratio of oxalic acid to Fe(III) is three, and complete color removal is achieved at pH 5 in 2h of the reaction. Applying oxalate in such a photo process increases both the RBB removal efficiency and the COD removal from 68% and 21% to 99.8% and 71%, respectively. [Copyright &y& Elsevier]

Abstract: A novel organic–inorganic nanocomposite of methylene blue (MB) and silicon oxide was synthesized and characterized by TEM, FTIR, and UV–vis. The as-prepared material was able to transfer the electron of the MB to electrode and was different from other SiO2 spheres structurally. It can be used as mediator to construct a biosensor with horseradish peroxidase (HRP) coimmobilized in the gelatine matrix and cross-linked with formaldehyde. The resulting biosensor exhibited fast amperometric response and good stability to hydrogen peroxide (H2O2). The linear range for H2O2 determination was from 1×10−5 to 1.2×10−3 M, with a detection limit of 4×10−6 M based on S/N=3. Moreover, the lifetime is more than 3 months under dry conditions at 4°C. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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

Evaluates the performance of the circulating fluidized-bed reactor with the supported gamma-FeOOH catalyst. Proportion of homogeneous and heterogeneous catalysis; Effects of pH, hydrogen peroxide concentration and benzoic acid concentration on the oxidation of benzoic acid by the catalyst; Advantages of the use of benzoic acid.

Chemical oxo-precipitation (COP) is a facile method to remove boron by the precipitation of perborate salts with the aid of hydrogen peroxide. Despite that the COP using barium precipitant (Ba–COP) has been advanced to provide excellent boron removal, the production of hazardous sludge limits the implementation. This study aims to improve the COP using calcium precipitant (Ca–COP) to provide boron removal comparable to COP without the production of hazardous waste. In addition to the precipitation of calcium perborate, the formation of calcium carbonate and calcium peroxide played decisive roles in the Ca–COP. The instant precipitation of calcium perborates (CaPBs) at pH 11 could eliminate boron from 1000 to 30 mg-B/L in 15 min. The prominent uptake of atmospheric CO 2 induced the precipitation of calcium carbonate and consumed calcium ion, which resulted in the increment in boron level due to the incongruent dissolution of CaPBs. The formation of calcium carbonate and calcium perborate provided an additional route to remove boron through sorption. Accordingly, a multi-stage Ca–COP process was developed to remove precipitated CaPBs for preventing the incongruent dissolution and to dose calcium precipitant multiple times to induce the sorptive removal. The proposed process could eliminate boron from 1000 to 5 mg-B/L, which is comparable to the state-of-art Ba–COP process with 45% of its cost. [Display omitted] • Dissolution of calcium perborate was triggered by the calcium depletion by CaCO 3. • Formation of CaCO 3 and CaO 2 provided a sorptive route to remove boron. • Multi-step Ca–COP process attained 99.5% of boron removal from 1 g-B/L solution. • Ca–COP process was 45% cheaper than the Ba–COP process by avoiding hazardous sludge. [ABSTRACT FROM AUTHOR]

Chemical oxo-precipitation (COP) is a facile method to remove boron by the precipitation of perborate salts with the aid of hydrogen peroxide. Despite that the COP using barium precipitant (Ba–COP) has been advanced to provide excellent boron removal, the production of hazardous sludge limits the implementation. This study aims to improve the COP using calcium precipitant (Ca–COP) to provide boron removal comparable to COP without the production of hazardous waste. In addition to the precipitation of calcium perborate, the formation of calcium carbonate and calcium peroxide played decisive roles in the Ca–COP. The instant precipitation of calcium perborates (CaPBs) at pH 11 could eliminate boron from 1000 to 30 mg-B/L in 15 min. The prominent uptake of atmospheric CO 2 induced the precipitation of calcium carbonate and consumed calcium ion, which resulted in the increment in boron level due to the incongruent dissolution of CaPBs. The formation of calcium carbonate and calcium perborate provided an additional route to remove boron through sorption. Accordingly, a multi-stage Ca–COP process was developed to remove precipitated CaPBs for preventing the incongruent dissolution and to dose calcium precipitant multiple times to induce the sorptive removal. The proposed process could eliminate boron from 1000 to 5 mg-B/L, which is comparable to the state-of-art Ba–COP process with 45% of its cost. [Display omitted] • Dissolution of calcium perborate was triggered by the calcium depletion by CaCO 3. • Formation of CaCO 3 and CaO 2 provided a sorptive route to remove boron. • Multi-step Ca–COP process attained 99.5% of boron removal from 1 g-B/L solution. • Ca–COP process was 45% cheaper than the Ba–COP process by avoiding hazardous sludge. [ABSTRACT FROM AUTHOR]

This work investigated the effective precipitation recovery of boron by chemical oxo-precipitation (COP), which uses hydrogen peroxide (H 2 O 2 ) 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) 3 OOB(OH) 3 and Ba(B(OH) 3 OOH) 2 to BaB(OH) 2 (OO) 2 B(OH) 2 were proposed. [ABSTRACT FROM AUTHOR]

Chemical oxo-precipitation (COP), which combines treatment with an oxidant and precipitation using metal salts, was developed for treating boron-containing water under milder conditions (room temperature, pH 10) than those of conventional coagulation processes. The concentration of boron compounds was 1000 mg-B L-1. They included boric acid (H3BO3) and perborate (NaBO3). Precipitation using calcium chloride eliminated 80% of the boron from the perborate solution, but was unable to treat boric acid. COP uses hydrogen peroxide (H2O2) to pretreat boric acid, substantially increasing the removal of boron from boric acid solution by chemical precipitation from less than 5% to 80%. Furthermore, of alkaline earth metals, barium ions are the most efficient precipitant, and can increase the 80% boron removal to 98.5% at [H2O2]/[B] and [Ba]/[B] molar ratios of 2 and 1, respectively. The residual boron in the end water of COP contained 15 ppm-B: this value cannot be achieved using conventional coagulation processes. [ABSTRACT FROM AUTHOR]