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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: In order to generate powerful radicals as oxidizing species for the complete decolorization and degradation of azo dye Reactive Black B (RBB) at near neutral pH (pH 6), homogeneous activation of peroxymonosulfate (Oxone: PMS) by the trace Co2+-catalysts was explored. We not only took advantage of the high oxidation–reduction potential of produced hydroxyl and sulfite radicals but also an opportunity to oxidize RBB to less complex compounds with extremely low dosages, especially the ppb level of the Co2+-catalyst (stoichiometric ratio: [Co2+]0/[RBB]0 =1.7×10−6–1.7×10−5; [PMS]0/[RBB]0 =8–32). Anion effects and pH effects were also carried out and discussed to simulate an actual application such as that of a textile waste stream. Both the degradations of RBB and its derivative aromatic fragments were illustrated successfully at UV–visable absorptions of 591 and 310nm, respectively, and the possible relationships between them were also proposed and discussed, based on the experimental results. The RBB degradation in this Co2+/PMS oxidative process successfully formulated a pseudo-first-order kinetic model at an isothermal condition of 25°C with or without different anions present. The initial rate and rate constant were calculated under different comparative conditions, and the results indicate that the activity of both RBB decolorization and its degradation are not obviously dependent on the PMS concentration, but rather are related to the Co2+ dosage. [Copyright &y& Elsevier]

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

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 (pK sp ) of two major barium perborates – amorphous Ba(B(OH) 3 OOH) 2 (A-BaPB) and crystalline BaB(OH) 2 (OO) 2 B(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. [ABSTRACT FROM AUTHOR]

This work demonstrates a novel chloride photo-electrochemical method for mineralizing citric acid. The electrolytic reactor with a length of 12 cm, a width of 12 cm and a height of 30 cm held 2.5 L of solution, which was involved in the batch reaction. Both anode and cathode were made of titanium coated with RuO2/IrO2. The results revealed that the solution pH dominated the production of hypochlorous acid (HOCl) oxidant in the presence of NaCl as direct current electricity was used. The chloride electrochemical process at pH 5.5 removed 59% of total organic carbon (TOC) in 4 h (NaCl = 200 mM, current = 5 A). UV irradiation (254 nm) in the reactor induced the photo-electrochemical reaction, increasing the TOC removal from 59% to 99.4%. Finally, the reaction pathway for citric acid mineralization was discussed with reference to the detection of intermediates using a liquid chromatography–mass spectrometry (LC–MS). [Copyright &y& Elsevier]

Abstract: Electroless nickel plating wastewaters commonly contain the citrate chelating complex and the coexisting hypophosphite, which is a scavenger of hydroxyl radicals, typically lowers the catalytic efficiency of H2O2 by Fe2+ in Fenton reaction. Hence, in this work, the Fered-Fenton method was adopted to remediate the citrate, and then alkaline precipitation was utilized to remove the freed nickel ions. The chemical oxidation demand (COD) of citric acid could be efficiently reduced by approximately 95% using 1080mM H2O2 (dosed in continual mode) and 20mM ferrous ions at a current density of 190Am−2 ([citric acid]=100mM and [Ni]=100mM). Meanwhile, 99.9% of the nickel that was liberated from the chelation of citric acid was removed by the cathodic deposition and the sequential precipitation. The hypophosphite did not significantly influence the COD or nickel removal efficiency. Finally, those optimal conditions for the successful management of simulated electroless plating wastewater consisted of citric acid and nickel ions coexisting with hypophosphite were then used to demonstrate the treatment of real wastewater (45,000ppm COD and 8000ppm nickel ions). The high COD removal, 93%, from the effluents of the electroless nickel plating process verified that the Fered-Fenton process can be practically applied. [Copyright &y& Elsevier]

Abstract: This study focuses on the effects of different carbon supplements on biological phosphorus removal in the optonics and semiconductor industrial wastewater treatment. Experimental results demonstrate that the addition of a carbon source (glucose, acetate, and digester supernatant) improved phosphorus removal effectively. When the COD/P ratios were controlled in the range of 18–20 (using glucose and supernatant as supplement), the acclimated sludge showed more than 98% removal of phosphorus. In addition, different organic carbons induce dissimilar behavior in anaerobic release and aerobic uptake of phosphorus. The glucose supplement induces significant phosphorus release in anaerobic phase and then an increased phosphorus uptake in aerobic phase. The released phosphorus descended in anaerobic phase when acetate and supernatant were added. There was a good linear relationship of first order reaction between initial COD concentration and specific substrate utilization rate in anaerobic phase. [Copyright &y& Elsevier]

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

This study aims to explore the reusability of wastewater treatment by-product for photo-Fenton process to treat an organic pollutant model. The optimal condition, reactive oxygen species (ROS), and kinetic approach in photo-Fenton process was discussed. The Metal oxide crystal pellets from are a by-product of the Fluidized-Bed Crystallization (FBC) process and can be used as a catalyst in the Photo-Fenton process. Electroplating wastewater containing iron and copper was treated via the FBC process using granulated Al(OH) 3 as carrier seeds. The binary oxide of FeOOH and Cu 2 O on the Al(OH) 3 surface (Fe 0.66 Cu 0.33 @Al(OH) 3) was identified as the FBC by-product after characterization using FTIR and XPS analysis. In the photo-Fenton process, visible light from a fluorescence lamp with a wavelength of 400–610 nm was chosen as an irradiation source. Oxalic acid was added as chelating agent to form photosensitive iron oxalate species and hydrogen peroxide was applied as oxidant to generate active radical to decolorize and mineralize RB5 synthesized solution (100 mg/L). The operating conditions including the oxalic acid to pollutant ratio ([OA] 0 /[RB5] 0) of 4.5–13.0, reaction pH (pHr) of 3–7 and initial to theoretical hydrogen peroxide molar ratio [H 2 O 2 ] 0 /[ H 2 O 2 ] theoretical of 35%–120% were optimized. Under the optimal conditions, pH r = 5.0; [H 2 O 2 ] 0 /[RB5] 0 at 75% stoichiometric and [OA] 0 /[RB5] 0 = 9, the RB5 is almost completely decolorized after 210 min of operation and the mineralization efficiency is 58%. The contribution of •OH, O 2 •-, and O 2 1 to the Photo-Fenton system was determined using ESR analysis with the addition of DMPO and TEMP as spin trap agents. The kinetic analysis reveals the observed rate constants k RB5 , k OA and k R from fitting are 0.0120, 0.0054 and 0.0001 M−1s−1, respectively. [Display omitted] • The binary oxide of by-product from FBC process is useful for organics treatment. • Treatability of azo dye RB5 by visible light-assisted photo-Fenton was investigated. • RB5 was completely degraded and mineralized of 55% using a 75% stoichiometric dosage of H 2 O 2 with the addition of oxalic acid at pH 5. • Up to 55% of TOC was mineralized mainly by O 2 •- and O 2 1. • Rate modeling of RB5 and TOC removal were explained using consecutive kinetics. [ABSTRACT FROM AUTHOR]

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 <100 mg F−/L. In contrast, industrial effluents may reach 250–1,000 mg F−/L (up to ∼10,000 mg F−/L at extreme cases). Inadequate removal of fluoride in water by single treatment also compels researchers to explore hybrid treatments. In addition, due to the lack of wastewater treatment facilities requiring high capital cost, bioremediation, a commonly overlooked alternative, is presented for temporarily alleviating fluoride levels. Finally, challenges such as limited literature for disposal of secondary pollution and cost evaluation along with other potential research perspectives are further discussed. Image 1 • Fluoride level in natural waters can be exceedingly high reaching 2,800 ppm F-. • Contaminated water and diseases caused by fluoride are prevalent worldwide. • Recent fluoride removal studies are mostly on the bench-scale phase. • Investigated techniques usually omit high F- concentration wastewater (>100 ppm). • Life cycle assessment and cost evaluation for defluoridation are deemed vital. [ABSTRACT FROM AUTHOR]

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. Image 1 • Bimetallic catalysts possess different physicochemical properties than those of monometallic catalysts. • Bimetallic catalysts have remarkable catalytic properties and functions, and exhibit high reducibility. • Organic and inorganic pollutants in water and wastewater can be treated using bimetallic systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both waste nutrients include swine slurry and swine wastewater could be recycled. • Utilizing swine slurry reduces magnesium and phosphorus additions. • 82.7% of nitrogen was removed and nutrient wastes were converted into green fertilizer. Struvite (MgNH 4 PO 4 ·6H 2 O) precipitation is widely used for nutrient recovery from swine wastewater. Additional magnesium source is required to produce struvite for nitrogen recovery due to the limited magnesium content in swine wastewater. The present study investigated the optimized condition for treating swine wastewater and producing struvite crystals using swine slurry, commercial MgCl 2 , and seawater as magnesium sources. The results showed that swine slurry as an alternative source is feasible both technically and economically. The struvite precipitation process using swine slurry at pH 9.0 and [P] 0 / [Mg] 0 / [N] 0 M ratio = 1.2/1.0/1.0 achieved removal efficiencies of 82.7 %, 83.1 %, and 92.7 % for nitrogen, phosphorus, and magnesium, respectively. X-ray diffraction analysis validated the solid product consisted of struvite. Further investigations revealed the harvested precipitate had a struvite content of 72.7 % with low heavy metal impurity, which could be used as fertilizer. Nutrient recovery from swine manure is a future driver for the economic and environmental sustainability of agricultural and wastewater treatment processes. [ABSTRACT FROM AUTHOR]

Heavy metal removal is a significant task that protects our water resources. Fluidized-bed homogeneous granulation process (FBHGP) was used to treat nickel containing wastewaters by recovering nickel in the form of nickel carbonate hydroxide granules with low moisture content rather than soft sludge. This study investigated nickel removal and recovery through HFBGP by determining the effects of varying influent nickel concentrations, [CO 3 2− : Ni 2+ ] molar ratios, and pH of the precipitant. This was conducted in a continuous process using a laboratory scale fluidized-bed reactor that determined the effects driven by supersaturation. The best operating conditions that resulted in a 98.8% nickel removal and 97.8% granulation efficiency were 200 mg L −1 influent nickel concentration, 2.0 M R of [CO 3 −2 :Ni +2 ], and 10.7 pH of precipitant. Based on SEM analysis, the granules formed have sizes between 0.50 mm and 0.15 mm. EDS results showed that the atomic percentages of nickel carbon, and hydrogen were ∼50%, ∼9–12%, and ∼35% respectively, representing the nickel carbonate compound. The XRD results showed the low symmetry of the granules formed that confirmed the characteristics of nullaginite mineral of Ni 2 (CO 3 )(OH) 2 . [ABSTRACT FROM AUTHOR]

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

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]