TOC Removal Efficiency Research Articles

Persulfate activation for efficient degradation of norfloxacin by a rGO-Fe3O4 composite

Abstract An environmental friendly magnetic reduced graphene oxide nanosheet-iron oxide (rGO-Fe3O4) composite was synthesized by co-precipitation method. Unlike other methods, we only added ferric iron to form Fe3O4, and also used much less reduced graphene oxide during the synthesis. The prepared rGO-Fe3O4 could effectively activate persulfate (PS) for the degradation of norfloxacin (NOF) and be easily recovered through magnetic separation. The effects of catalyst dosage, PS dosage, initial NOF concentration and initial pH were evaluated. Degradation experiments showed that the removal efficiencies of NOF and TOC were 89.69% and 45.69% within 75 min, respectively. The degradation intermediates of NOF were identified by HPLC-MS and the degradation pathways were also proposed. The quenching experiments indicated that there were three reactive active species, sulfate radical (SO4•−), hydroxyl radical (•OH) and singlet oxygen (1O2) generated in rGO-Fe3O4/PS system, in which 1O2 was the dominant active species for the degradation of NOF. The recycling test shows that rGO-Fe3O4 composite has good stability, showing a promising application.

Waste control by waste: Fenton–like oxidation of phenol over Cu modified ZSM–5 from coal gangue

Coal gangue and phenol are two main pollutants in coal mining and processing. Using coal gangue as raw material, a series of Cu modified ZSM–5 (Cu/ZSM–5) catalysts were developed to remove phenol through heterogeneous Fenton–like reaction. This procedure implies the concept of waste control by waste. The characterization results showed that Cu modification had no obvious impact on the MFI (Mobile Five) structure of ZSM–5. Copper ions were presented as doping element (substitution of Na and Al ions) and copper oxides on ZSM–5 surface. The XPS spectra suggested the co–existence of Cu2+ and Cu+. As a consequence of well-defined experimental parameters, 7% Cu/ZSM–5 performed excellent activity and stability for the degradation and mineralization of phenol pollutant, which could degrade phenol completely within 30min and the TOC removal efficiency could reach 63% within 60min and 92% within 8h. ESR and radicals capturing experiments demonstrated that OH and 1O2 played the dominant roles in the Fenton–like reaction. In combination with XPS, ESR and catalytic tests, it's found that the redox cycling of Cu+/Cu2+ played critical roles in accelerating the active radical generation in this Fenton–like system.

Biological removal of phosphorus and diversity analysis of microbial community in the enhanced biological phosphorus removal (EBPR) system

AbstractAn anaerobic/aerobic sequencing batch reactor was used to test enhanced biological phosphorus removal (EBPR) in wastewater. In the present study, after 6 weeks of operation, the phosphorous and TOC removal efficiency reached to 97.8 and 97.5%, respectively. Our results suggest that phosphate‐accumulating organisms (PAOs) play a key role in the phosphorus removal in the EBPR system. Qualitative and quantitative measurements indicate the appear and changing trend of characteristic particles in activated sludge, which further illustrates the metabolic activity and mechanism of PAOs. Fluorescence in situ hybridization (FISH) images showed that PAOs gradually became the predominant bacteria in the EBPR system, aligning with the results of phosphorus removal rate. PCR‐DGGE profile demonstrated that with the operation of EBPR process, the composition of microorganisms became more and more abundant in the EBPR system over time. Further sequencing analysis indicated that these microbial populations belonged to α‐Proteobacteria, β‐Proteobacteria, γ‐proteobacteria, Rhodococcus sp. and Pseudomonas sp.

Visible-light-driven MIL-53(Fe)/BiOCl composite assisted by persulfate: Photocatalytic performance and mechanism

The novel semiconductor heterojunction of MIL-53(Fe)/BiOCl composite was first prepared through the solvothermal reaction. The prepared materials were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunner-Emmet-Teller (BET) and ultraviolet-visible diffuse reflectance spectroscopy (DRS). MIL-53(Fe)/BiOCl heterojunction is a kind of photoexcited materials and it accelerates the photoreactivity of BiOCl under the visible light irradiation. It was used to remove Rhodamine B (RhB) with the existence of persulfate (PS). The UV–vis spectrophotometer and the TOC detector show that the degradation rate and TOC removal efficiency of RhB (20 mg/L) are 99.5% and 69.4%within 30 min visible-light irradiation, respectively. Due to the proper band gap of material and the presence of electron acceptor, PS, the survival time of active radicals are increased. The active species h+, ·SO4− and ·OH are found to play the important roles during the reaction system. The possible mechanism for the RhB degradation of MIL-53(Fe)/BiOCl/PS is also proposed. Furthermore, the results of the material reusability for the degradation of RhB indicate that the MIL-53(Fe)/BiOCl has a good stability and can be used in the environmental water sample treatment.

Catalytic oxidation of various aromatic compounds in supercritical water: Experimental and DFT study

Abstract Catalytic supercritical water oxidation (CSCWO) has sprung up as a promising technique to eliminate refractory aromatic compounds, which are difficult to be removed by conventional wastewater treatment processes. Decompositions and degradation mechanisms of 18 aromatic compounds, including benzene, phenol, bisphenol A (BPA) etc., were investigated using CSCWO in this study. It was found that TOC removal efficiencies of the aromatic compounds were significantly enhanced, when CSCWO temperatures raised from 325 to 525 °C and reaction time prolonged from 0.5 to 6 min, with the addition of Cu(NO3)2. The correlationships among TOC degradation rates (kTOC), temperature at TOC removal rate of 90% (T90) and 19 molecular descriptors were studied. The results indicated that BOn and q(H)x could greatly impact the degradation behaviors. Fukui indices based density functional theory (DFT) method was applied to reveal the conceivable degradation pathway of BPA during CSCWO process.

Sol-gel synthesis of novel Li-based boron oxides nanocomposite for photodegradation of azo-dye pollutant under UV light irradiation

In the present study, Li2B4O7/LiBO2/Li3BO3 (LBO) nanocomposites were synthesized by a modified Pechini sol-gel route utilizing the mixture of different polybasic acids and gelling agents. This work demonstrated that by controlling the reaction variables including kind of polybasic acids and gelling agents, pH and mole ratio of polybasic acid to total metals, the LBO nanostructures with various morphologies and particle sizes were prepared. Furthermore, the LBO nanocomposites showed excellent TOC removal (70%) and photocatalytic efficiency (91%) in order to photodegradation of acid violet 7 azo dye as water pollutant under UV light irradiation. Moreover, compared to commercial P25 photocatalyst, the LBO heterostructures exhibited higher photodegradation activity for removal of acid violet 7 dye in 90 min under UV light irradiation, even after four times cycles. The excellent photocatalytic degradation of LBO photocatalyst can be ascribed to the strong photon absorption, high-efficiency charge carrier separation, uniform particle size and appropriate band gap energy of the nanocomposite. Also, radical trapping capability test exhibited that the photoinduced superoxide radicals (•O2−) and holes (h+) were the prevailing active species in the photocatalytic performance.

Application of electro-Fenton process for treatment of water contaminated with benzene, toluene, and p-xylene (BTX) using affordable electrodes

Electro-Fenton (EF) process was utilized for degradation of benzene (B), toluene (T), and p-xylene (X) (BTX) in aqueous solutions using different electrodes. The cathode was made from carbon felt, while different materials were used as anodes including carbon, stainless steel, and nickel. Complete degradation of BTX was attained within 30 min under favored conditions. However, TOC removal of BTX in the mixture was only 75% at early stages of the EF process due to the remaining organic by-products. The effects of operational conditions at different initial concentrations of BTX were assessed in-depth. The EF process was able to attain 95.4%, 88.7%, and 87.6% TOC removal efficiencies at an initial concentration of 150 mg/L using sacrificial stainless steel, carbon, and nickel anodes respectively in 60 min. The stainless steel anode in the mode of the sacrificial electrode was favored due to the continuous production of Fe2+ in the solution. The precipitated sludge during the EF process was treated and used to improve the degradation of BTX. A cost estimation study showed that treatment of one cubic meter of BTX contaminated water by electro-Fenton process costs $1.40 under certain conditions.

Novel Fenton-like system (Mg/Fe-O2) for degradation of 4-chlorophenol

A novel heterogeneous Fenton-like system (Mg/Fe-O2) which could directly convert oxygen (O2) to hydrogen peroxide/hydroxyl radicals (H2O2/•OH) was developed and used to degrade 4-chlorophenol. The Mg/Fe bimetallic particles were prepared by chemical displacement process and characterized by XRD, SEM and TEM. The in situ continuous production of H2O2/•OH and the effect of the mole ratio of Mg to Fe in the Mg/Fe bimetallic particles and the operating parameters on the degradation 4-chlorophenol in Mg/Fe-O2 system were investigated in detail. It was found that the Mg/Fe bimetallic particles with the mole ratio of Mg to Fe of 32:1 had the best performance for the 4-chlorophenol degradation and the maximum cumulative concentration of H2O2, the degradation efficiency of 4-chlorophenol and the removal efficiency of TOC in Mg/Fe-O2 system were 34.5 mg/L, 100% and 91.8%, respectively, at pH 3, O2 flow rate 400 mL/min, dosage of Mg/Fe bimetallic particles 2 g/L, 4-chlorophenol initial concentration 50 mg/L and reaction time 60 min. It was revealed by radical scavenging experiments that •OH, particularly the surface-bound •OH, were the predominant reactive oxygen species in Mg/Fe-O2 system for the degradation of 4-chlorophenol. The main intermediates of 4-chlorophenol degradation were detected by high-resolution liquid chromatography equipped with time-of-flight mass spectrometry (HRLC–ToF-MS) and ion chromatography (IC). Based the results of control experiments and the electrochemical tests, the possible pathway and mechanism of 4-chlorophenol degradation in Mg/Fe-O2 system were tentatively proposed.

The removal of cephalexin antibiotic in aqueous solutions by ultrasonic waves/hydrogen peroxide/nickel oxide nanoparticles (US/H2O2/NiO) hybrid process

ABSTRACTAntibiotics are non-biodegradable and can remain for a long time at aquatic environments and they have a big potential bio-accumulation in the environment. The antibiotics are broadly metabolized by humans, animals and plants and they or their metabolites, after metabolization, are entered into the aquatic environment. This study aimed to optimize the operational parameters by Taguchi design and to carry out the kinetic studies for removal of cephalexin antibiotic from aqueous solutions by US/H2O2/NiO hybrid process. This experimental study was performed on a laboratory scale in a 500 mL pyrex-made reactor. The main operational parameters to influence the US/H2O2/NiO process were identified as the initial concentration of CEX (20–80 mg/L), hydrogen peroxide (H2O2) (10–40 mL/L), NiO nanoparticle (2.5–10 mg/L) and reaction time (15–90 min) and therefore, the influence of these factors were studied. Under optimum conditions (pH = 3, reaction time = 90 min, CEX = 40 mg/L, NiO = 7.5 mg/L and H2O2 = 30 mL/L) and using the US/H2O2/NiO process, the removal efficiencies of CEX, COD and TOC were 93.86%, 72.46% and 54.55%, respectively. The percentage contribution of each factor was also determined. Results introduced the solution pH as the most powerful factor, and its percentage contribution value was up to 94% in the studied process. It was also identified that the removal of CEX antibiotic using the hybrid process obeys the pseudo-first-order kinetics.

A green strategy for simultaneous Cu(II)-EDTA decomplexation and Cu precipitation from water by bicarbonate-activated hydrogen peroxide/chemical precipitation

Classical chemical precipitation technology is inefficient for the removal of heavy metal-organic complexes from wastewater. In this study, a novel and green strategy of coupling bicarbonate-activated hydrogen peroxide (BHP) oxidation and alkaline precipitation was proposed for simultaneous decomplexation of Cu-ethylenediaminetetraacetic acid (Cu-EDTA) and Cu precipitation. The Cu-EDTA decomplexation efficiency reached 92.0% within 60 min of the BHP treatment, and the decomplexation process was spontaneous and endothermic. Reactive substances such as O2−, OH, and 1O2 were identified, and O2− was predominant in the Cu-EDTA decomplexation. The weak alkaline environment provided by bicarbonate favored the generation of the reactive substances and subsequent Cu-EDTA decomplexation. Relatively higher H2O2 dosage favored Cu-EDTA decomplexation, while excessive bicarbonate dosage inhibited the reaction. TOC removal efficiency and Cu removal efficiency reached 78.4% and 68.3% after 60 min treatment, respectively. The CuO and CuN bonds in Cu-EDTA were destroyed by the reactive substances, and a series of Cu-containing intermediates, small organic molecules such as ethanamine, ethylene glycol and butanediol, and NO3− were produced. The released Cu ions were precipitated as Cu2(OH)2CO3, CuCO3, Cu(OH)2, and CuO. Possible pathways of Cu-EDTA decomplexation in this system were proposed.

Simultaneous debromination and mineralization of bromophenol in an up-flow electricity-stimulated anaerobic system

Due to highly recalcitrant and toxicological nature of halogenated organic compounds, conventional anaerobic dehalogenation is often limited by low removal rate and poor process stability. Besides, the reduction intermediates or products formed during dehalogenation process, which are still toxic, required further energy-intensive aerobic post-treatment. In this study, an up-flow electricity-stimulated anaerobic system (ESAS) was developed by installing cathode underneath and anode above to realize simultaneous anaerobic debromination and mineralization of 4-bromophenol (4-BP). When cathode potential was −600 mV, high TOC removal efficiency (98.78 ± 0.96%), complete removal of 4-BP and phenol could be achieved at 4-BP loading rate of 0.58 mol m−3 d−1, suggesting debrominated product of 4-BP from cathode (i.e., phenol) would be utilized as the fuel by the bioanode of ESAS. Under high 4-BP loading rate (2.32 mol m−3 d−1) and low electron donor dosage (4.88 mM), 4-BP could be completely removed at acetate usage ratio as low as 4.21 ± 1.42 mol acetate mol−1 4-BP removal in ESAS, whereas only 13.45 ± 1.38% of 4-BP could be removed at acetate usage ratio as high as 31.28 ± 3.38 mol acetate mol−1 4-BP removal in control reactor. Besides, electrical stimulation distinctly facilitated the growth of various autotrophic dehalogenation species, phenol degradation related species, fermentative species, homoacetogens and electrochemically active species in ESAS. Moreover, based on the identified intermediates and the bacterial taxonomic analysis, possible metabolism mechanism involved in enhanced anaerobic debromination and mineralization of 4-BP in ESAS was proposed.

Hybrid coagulation, gamma irradiation and biological treatment of real pharmaceutical wastewater

The present study aimed towards the utilization of hybrid approaches for the effective treatment of real pharmaceutical industry wastewater. The focus was to treat pharmaceutical wastewater with low (LSW) and high organic strength (HSW), which was collected from the effluent treatment plant of the representative bulk pharmaceutical manufacturing unit. The hybrid approach included coagulation treatment, biological treatment and gamma irradiation which were employed individually and in sequence to determine the most appropriate treatment sequence for effective remediation of real pharmaceutical wastewater. To compare process performance, gamma-irradiation was employed as pre-treatment and post-treatment stage to biological treatment. To achieve the enhanced removal efficiency using gamma irradiation treatment, oxidant like H2O2 and persulfate ions S2O82- were used and optimized for LSW and HSW. Results indicated that use of H2O2 lead to enhanced COD and TOC removal efficiency when compared to S2O82-. The sequential approach of coagulation, gamma irradiation and biological treatment accounts for the synergistic degradation and detoxification of recalcitrant pharmaceutical wastewaters, and lead to overall 92.7% ± 2.3% and 90.2% ± 2.9% of COD removal of LSW and HSW, respectively. The pre-treatment using gamma-irradiation enabled effective treatment, achieving 58.7% ± 3.2% COD and 80.4% ± 2.1% TOC removal efficiencies for LSW; whereas 62.0% ± 2.9% COD and 71.0% ± 2.7% TOC removal efficiencies were achieved for HSW. Cytotoxicity assessment and cost analysis of the treatment process were examined and analyzed.

Synthesis of ternary CdS-G-LTO hybrids with enhanced photocatalytic performance for natural food pigment industrial wastewater

In this work, a series of CdS-G-LTO composites were fabricated and characterized using multiple methods, to determine their performance for degrading natural food pigments in industrial wastewater. The optimal composite for the degradation of MO was CdS-G-LTO-2 (20 wt% CdS), with degradation rate of 109 times and 50 times higher than that of LTO thin film and G-LTO. The photocatalytic performance of these composites with regard to gardenia yellow pigment and real wastewater was also investigated. The removal efficiency of chorma and TOC for gardenia yellow reached 83% and 75% respectively after 40 min; while for the wastewater, the removal efficiency of COD and TOC was 62% and 74.4% after 6 h. The enhanced photocatalytic activity was ascribed to the high separation and transfer rate of photo-excited charge carriers. The O2– radicals (as the main species) and h+ both participated in the photocatalytic degradation reaction of gardenia yellow.

Degradation of flumequine in water by pulsed discharge plasma coupled with reduced graphene oxide/TiO2 nanocomposites

Herein, pulsed discharge plasma (PDP) was coupled with reduced graphene oxide (rGO)/TiO2 nanocomposites to degrade flumequine (FLU) in water. The rGO/TiO2 nanocomposites were prepared by hydrothermal method, which were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM) and nitrogen adsorption apparatus. The characteristic results showed that the rGO/TiO2 nanocomposites could be synthesized successfully. The rGO/TiO2 nanocomposites had a larger specific surface area than pure TiO2. The degradation performance indicated that the removal efficiency could reach 99.4% with 60 min treatment in PDP-rGO/TiO2 system, which was higher than in sole PDP system (64.8%) and PDP-TiO2 system (75.7%). Moreover, compared to pure TiO2, the kinetic constant, TOC removal, synergistic factor and energy efficiency could be also improved when rGO/TiO2 nanocomposites were added into PDP system. Besides, the effect of catalyst dosage, peak voltage, air flow rate and solution pH on FLU removal efficiency was investigated. Subsequently, response surface methodology (RSM) was adopted to inspect the interactional influences between catalyst dosage, peak voltage, air flow rate and solution pH, and the optimal parameters based on the result of single factor experiments. No matter reaction system was PDP system or PDP-rGO/TiO2 system, the O3 and OH concentration in deionized water were higher than that in FLU solution, suggesting that O3 and OH played major role in degrading FLU. The addition of rGO/TiO2 could consume O3 and lead to more OH generation, which accelerated the degradation of FLU. The decline of pH value and the rise of conductivity deduced that many acid substances could be produced during FLU degradation, which could be mineralized into CO2 and H2O ultimately.

Morphology evolution effects on electrochemical activity of hierarchically stacking SnO2-Sb/TiO2-NTs electrode prepared by the hydrothermal method

Distinct three-dimensional hierarchically stacking SnO2-Sb/TiO2-NTs electrode with a good-adhesion TiO2-NTs@SnO2-Sb interlayer, a compact plate SnO2-Sb middle layer, and an apparent uniform microsphere layer was successfully prepared through the hydrothermal method. The evolution of micro-morphology and structure of electrode catalyst layer was realized so as to improve the catalytic performance of electrode through tuning the hydrochloric acid concentration. Experimental results show that SnO2-Sb/TiO2-NTs electrode prepared in 0.5 mol L−1 HCl condition possesses the optimal performance containing a low phenol oxidation potential of 1.2 V (vs. SCE), and a maximum current density of 3.8 mA cm−2 towards phenol degradation in phosphate buffered solution. The electrochemical phenol removal results show that the phenol degradation process coincides with the first-order kinetics and the corresponding optimal constant reaches 14.2 × 10−3 min−1. The TOC removal efficiency of optimal electrode reaches 62%.

Treatment of real pharmaceutical wastewater using combined approach of Fenton applications and aerobic biological treatment

The pharmaceutical wastewater of different organic loads i.e. high (HSW) and low strength wastewater (LSW) were collected from the bulk pharmaceutical industry and subjected to different applications of Fenton’s treatment followed by subsequent biological treatment. For both the HSW and LSW, applications of Fenton such as, dark-Fenton (DF), solar driven photo-Fenton (PF) and electro-Fenton (EF) were utilized as pre-treatment technologies to improve the biodegradability and reduce the organic load of wastewater by combine oxidation and coagulation. The operational parameters like pH, hydrogen peroxide dosage and iron concentration were optimized in case of DF and PF processes, whereas in case of EF process, applied voltage and hydrogen peroxide dosage were optimized to make water biocompatible for subsequent biological degradation. The use of Fenton applications as a pre-treatment resulted in a significant enhancement in the BOD5/COD ratio validating the production of easily degradable metabolites or secondary products. Overall results indicated that among the utilized Fenton technologies, pre-treatment of pharmaceutical wastewater with PF lead to better COD and TOC removal efficiency with subsequent biological degradation when compared to DF and EF pre-treatment. Overall COD removal efficiency of the combined PF and biological treatment was around 84% for LSW and 82% for HSW. Conclusively, it can be established that combined Fenton applications as pretreatment technology and biological treatment is more effective approach in comparison to single stage oxidation either by Fenton or biological treatment. Cytotoxicity assessment revealed that complete detoxification of wastewaters were achieved indicating that hybrid treatment technology of Fenton’s and biological treatment did not exhibited any toxicity against the selected microbes.

Enhanced catalytic ozonation by highly dispersed CeO2 on carbon nanotubes for mineralization of organic pollutants.

Heterogeneous catalytic ozonation, in which ozone is activated by various catalysts to produce reactive oxygen species (ROS), is an effective approach to degrade persistent organic pollutants in water. However, catalyst with high activity and good stability for catalytic ozonation still remains rare. In this work, a highly dispersed cerium oxide on oxidized carbon nanotubes (CeO2-OCNT) were prepared and characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction using hydrogen (TPR-H2) experiments. The as-synthesized CeO2-OCNT showed significantly enhanced catalytic performance for degrading organic pollutants during catalytic ozonation. The removal efficiency of optimized CeO2-OCNT for phenol mineralization was 2-3 times of pure CeO2 and OCNT, and was also better than that of a composite with the same composition, which demonstrated a synergic effect between OCNT and CeO2 on CeO2-OCNT for catalytic ozonation. The TOC removal efficiency exhibited no obvious reduction after five cycling experiments, indicating the synthesized CeO2-OCNT possessed good reusability. Moreover, electron paramagnetic resonance (EPR) and radicals quenching experiments revealed that hydroxyl radicals (OH) were the dominant ROS for organic pollutants degradation. The superior activity of CeO2-OCNT for catalytic ozonation could be attributed to the well-dispersed CeO2, the improved mass transfer, and the facilitated redox Ce3+/Ce4+ cycling.

Degradation of p-nitrophenol (PNP) in aqueous solution by mFe/Cu-air-PS system

In this study, batch experiments were conducted to investigate the performance of microscale Fe/Cu bimetallic particles-air-persulfate system (mFe/Cu-air-PS) for p-nitrophenol (PNP) treatment in aqueous solution. First, the optimal operating parameters (i.e., aeration rate of 1.0 L/min, theoretical Cu mass loading (TMLCu) of 0.110 g Cu/g Fe, mFe/Cu dosage of 15 g/L, PS total dosage of 15 mmol/L, feeding times of PS of 5, initial pH 5.4) were obtained successively by single-factor experiments. Under the optimal conditions, high COD and TOC removal efficiencies (71.0%, 65.8%) were obtained after 60 min treatment. Afterword, compared with control experiments (i.e., mFe/Cu, air, PS, mFe/Cu-air, mFe/Cu–PS, air-PS and mFe-air-PS), mFe/Cu-air-PS system exerted superior performance for pollutants removal due to the synergistic effect between mFe/Cu, air and PS. In addition, the results of control experiments and radical quenching experiments indicate this reinforcement by feeding of PS was greater than by aeration in mFe/Cu-air-PS system. Furthermore, the degradation intermediates of PNP in mFe/Cu-air-PS process were identified and measured by HPLC. Based on the detected intermediates, the degradation pathways of PNP were proposed comprehensively, which revealed that toxic and refractory PNP in aqueous solution could be decomposed effectively and transformed into lower toxicity intermediates. As a result, mFe/Cu-air-PS system with the performance of oxidation combined reduction can be also a potential technology for the treatment of toxic and refractory PNP contained wastewater.

Electrochemical Abatement of Analgesic Antipyretic 4‐Aminophenazone using Conductive Boron‐Doped Diamond and Sub‐Stoichiometric Titanium Oxide Anodes: Kinetics, Mineralization and Toxicity Assessment

AbstractThe oxidation ability of two prominent eco‐friendly electrochemical advanced oxidation processes (EAOPs), namely anodic oxidation with H2O2 generation (AO‐H2O2) and electro‐Fenton (EF) for complete abatement of acidic solution of 4‐aminophenazone (4‐APZ) has been investigated using conductive boron‐doped diamond (BDD) and sub‐stoichiometric titanium oxide (Ti4O7) anodes and carbon‐felt cathode. The higher performance of EF compared to AO‐H2O2 with either anode was demonstrated. In all trials, 4‐APZ was completely destroyed, following pseudo first‐order kinetics with the rate constant values increasing with applied current and higher values attained with BDD compared to Ti4O7 anode at similar conditions. The absolute rate constant for the reaction between 4‐APZ and hydroxyl radicals was found to be 3.9±0.2×109 L mol−1 s−1. Complete mineralization could be attained with BDD anode, whereas Ti4O7 anode only showed excellent mineralization up to 94 % TOC removal. Therefore, Ti4O7 anode can constitutes a promising anode material thanks to its lower manufacturing cost. Inorganic ions like NO3− and HCO3− at concentration up to 25 mM has no effect on mineralization efficiency during AO‐H2O2, but the presence of Cl− even at lower concentration of 10 mM significantly reduced the TOC removal efficiency. The toxicity of the solution sharply increased at initial stage of treatment, corresponding to the formation of cyclic by‐products but their conversion to carboxylic acids due to longer treatment time involved a sharp toxicity decrease, thus ensuring overall detoxification.

Optimization of Dyeing Wastewater Treatment with New Eco-friendly Polysilicate Ferromanganese

To improve the efficiency of the removal of dye wastewater, a new type of coagulant "polysilicate ferromanganese (PSFM)" has been synthesized using sodium silicate, ferrous sulfate, and potassium permanganate. Three dyes (direct red, disperse blue, and active yellow) were used for the coagulation tests. The effects of the alkalinity and turbidity on the performance of PSFM were studied. The experimental results show that PSFM performs well with respect to the coagulation of the direct red and disperse blue dyes. The color and TOC removal efficiencies reach 99.2%, 95.4% and 98.5%, and 93.8%, respectively. The coagulation performance is better than that of the conventional coagulants polysilicate iron (PSF), Al2(SO4)3, and FeCl3. The color and TOC removal rates of PSFM for the active yellow dye reach 56% and 51%, respectively. Turbidity has no significant effect on the coagulation efficiency of PSFM. The purification efficiency and alkalinity depend on the amount of dye to be removed. The best alkalinity for the direct red, disperse blue, and active yellow dyes is 50 mg·L-1, 0 mg·L-1, and 75 mg·L-1, respectively. In addition, PSFM has been characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The Zeta potentials of the mixed solutions and flocs during coagulation were also determined. The main indicators of PSFM coagulation are positively charged polynuclear complexes produced by hydrolysis of Fe+ and Mn+ and the bridging polymerization of polysilicon. The adsorption of hydrated manganese dioxide and hydroxyl oxide may also be included.