Treatment Of Contaminated Wastewater Research Articles

Adsorptive Removal of Dyes: A Comparison of Graphene Oxide to Granular Activated Carbon and Zeolite NaY

Synthetic carbon-based compounds are a prevalent wastewater contaminant that can adversely impact water resources due to their potential carcinogenic and toxic effects on aquatic biota and human health. This research investigates the versatility of graphene oxide (GO) as an alternative to commonly used adsorbents (zeolite NaY (NaY) and granular activated carbon (GAC)) for removal of synthetic cationic dyes. Rhodamine B (RhB) and methylene blue (MB), were selected as the target contaminants to represent cationic synthetic dyes with differing molecular sizes and structural compositions. Batch experiments using GO, NaY, and GAC as adsorbents were used to assess both physicochemical interactions between adsorbent surfaces and contaminants, and removal efficiency. GO demonstrated the highest removal efficiency for both target contaminants—at 99% and 86%, respectively—while the lowest removal efficiency was observed for NaY. Langmuir, Freundlich, Temkin, and BET isotherm models were used to describe the adsorption isotherms. Overall, GO demonstrated a more robust and higher removal efficiency of cationic dyes compared with GAC and NaY, indicating the potential of graphene oxide for the removal of complex structured organic contaminants in wastewater treatment.

Using flow-through reactor to enhance ferric ions electrochemical regeneration in electro-fenton for wastewater treatment

Electrochemical regeneration of ferric ions catches more and more attention since it could decrease iron sludge to avoid the sludge problem while it could simultaneously obtain similar robust removal efficiency to refractory organic contaminants in wastewater treatment as the normal Fenton agent method. However, the electrochemical regeneration of ferric ions in aqueous solution was very slow. In this paper, the mass transfer limit of ferric ions in electro-Fenton reaction was evaluated. Koutecky-Levich equation reveals an extremely low diffusion coefficient (D0) value of ferric ions since its complex coordination of [Fe(HO)x(H2O)6-x]3-x. The D0 value was only 2.70 × 10−6 cm2·s−1. Flow-through reactor was therefore introduced in which the ferric ions was designed to penetrate through the 73.1 μm porous holes in the graphite fiber electrode. The μm-scaled confinement of ferric ions diffusion inside the holes was proved to successfully enhance the reduction current of ferric ions by more than 200 % since the diffusion distance of the ferric ions was significantly decreased in the flow-through reactor. However, besides the benefit of the flow-through reactor, the ferric ions reduction electro-Fenton (FeRR electro-Fenton) in flow-through still faces both the pH limit and H2O2 decomposition problems. Hydrogen evolution reaction (HER) could also cause the decrease of pH which exceeded the optimal pH window for Fenton and therefore destroyed the electro-Fenton reaction consequently although the electrochemical reaction of FeRR was 770 mV prior to HER reaction. The regeneration of Fe (II) process simultaneous destruction of H2O2 since H2O2 e-reduction was 120 mV prior to FeRR reaction, which resulted in only very low H2O2 concentration suitable for FeRR electro-Fenton. Even using stepwise addition of H2O2 in electro-Fenton, the decomposition of H2O2 still could not be avoided. Although the decomposition of H2O2 quite limited the application of FeRR electro-Fenton in real application, FeRR electro-Fenton still supports the enhancement removal efficiency of the refractory organic contaminants under low organic contaminants application.

Effective strategy for Cr(VI) removal from water in evolution process of ferroan brucite by redox and intercalation

Cr(VI)-contaminated wastewater treatment is of great significance to ecological environment and human health. In this work, ferroan brucite with different Fe2+ doping amounts (Mg1-XFeX(OH)2, x = 0.1–0.8) were synthesized for the removal of Cr(VI) from wastewater. The effect of Fe content, initial concentration of Cr(VI), reaction time, co-existing ions and pH for Cr(VI) removal performance were examined. As Fe2+ content increased, the removal efficiency initially increased and then decreased, Mg0.4Fe0.6(OH)2 exhibited the maximum removal amount of 494.63 mg/g. Kinetic studies showed Cr(VI) removal well fitted pseudo-second-order model and achieved equilibrium at approximately 40 min. Isotherm data was well described by Langmuir model. The coexisting ions except CO32− had negligible effect, while pH had a significant influence on Cr(VI) removal since different dominated form of Cr(VI) existed at different pH. The removal mechanism towards Cr(VI) under different pH values was explored. At acidic environment, most Cr(VI) in Cr2O72− was reduced to Cr(III) by Fe2+ resulting in the precipitation of (Fe,Mg)(Cr,Fe)2O4, the remaining part was immobilized by interlayer of reaction product LDHs, and the intercalation amounts of Cr2O72− were 114.05 mg/g and 106.78 mg/g at pH of 3 and 6. While under alkaline conditions, most CrO42− entered the interlayer of LDHs with amounts of 262.3 mg/g at pH = 11, and the rest was absorbed on the surface. Furthermore, the reaction product could be recovered as chromite with recovery rate of 83.94 %. The excellent removal performance suggested a promising strategy in sewage water remediation.

Iron minerals enhance Fe(II)-mediated abiotic As(III) oxidation

The abiotic oxidation of As(III) is simultaneously mediated by the oxidation of Fe(II) in microaerobic environment, but the role of Fe minerals in the Fe(II)-mediated As(III) oxidation have been neglected. This work mimicked the microaerobic environment and examined the mechanisms of Fe(II) mediated the As(III) oxidation in the presence of Fe minerals using a variety of iron minerals (lepidocrocite, goethite, etc.). The results indicated the Fe(II) and As(III) oxidation rate were improved with Fe minerals, while As(III) oxidation efficiency increased by 1.3–1.8 times in comparison to that without minerals. Fe(II) mediated the As(III) oxidation happened on Fe minerals surface in the presence of Fe minerals. The As(III) oxidation efficiency increased with increasing Fe mineral concentrations (from 0.5 to 2 g L−1) but decreased with increasing pH values. Reactive oxygen species (ROS) that play a crucial role in As(III) oxidation were Fe(IV) and ·O2−, accounting for 42.7%–47.9% and 24.1%–29.8%, respectively. The Fe minerals facilitated the oxidation of As(III) by ROS and stimulated the release of ROS through the adsorbed-Fe(II) oxidation, both of which favored As(III) oxidation. This work highlighted the potential mechanisms of Fe minerals in promoting Fe(II) mediated the As(III) oxidation in microaerobic environment, especially in terms of As(III) oxidation efficiency, shedding a valuable insight on optimization of arsenic contaminated wastewater treatment processes.

A parametric optimization for leveraging the potential of ammonia modified magnetic pine cone hydrochar for Cr (VI) contaminated wastewater treatment

The present study evaluated the biosorption potential of magnetic pine cone hydrochar (MPHC) for chromium removal from wastewater. Initially, three different methodologies were followed for the synthesizing magnetic hydrochar and were tested for chromium removal and with a maximum removal of 91.3%, ammonia-modified MPHC showed its tremendous potential for Cr (VI) removal. Further, the hydrochar was characterized physically, chemically, magnetic, and morphological and a Box-Behnken experimental design was used for examining the effect of all the five parameters for Cr (VI) removal from the simulated wastewater system. Ammonia-modified MPHC showed a removal efficiency of 98.46% under the optimized batch shake flask system with the initial chromium concentration (55 mg/L), MPHC dose (550 mg/L), temperature (40 °C) and reaction time (120 min) and iron-MPHC ratio (30%). Here, the maximum Cr (VI) adsorption capability (qe) was found to be 154 mg/g. Further, the effect of different bed height, inlet pollutant flow rate, and inlet pollutant concentration during the continuous packed bed biosorption study showed a significant removal. The breakthrough curves for Cr (VI) removal obtained via the continuous flow-through column study confirmed that MPHC in the fixed-bed column suits Cr (VI) removal.

Reactive species identification in KCl activated biochar/persulfate system under different pH condition: Theoretical calculation and column experiments

The challenges of remediating polluted water in mine areas are exacerbated by low emission dispersion and long-lasting pollution, particularly the significant fluctuations in pH value. Notably, the treatment of flotation reagent polluted water with variable pH scenarios remains a challenge. In this study, metal-free biochar-based materials (KBBC)/persulfate system was used for flotation reagent contaminated wastewater treatment with a wide pH range. Regarding the intrinsic nature of the biochar-based materials, ball milling enhanced the degree of graphitization, while introducing a hard template of KCl increased the proportion of carbonyl functional groups on their surface, thereby facilitating persulfate activation. Experimental findings revealed that the KBBC/PS system displayed efficient degradation of aniline aerofloat (AAF) as a representative flotation reagent across a wide pH range (pH = 3.6–10.4 with buffer). Investigations on the mechanism indicated that, under acidic and neutral conditions, superoxide radicals and direct electron transfer processes constituted primary pathways for pollutant degradation. Meanwhile, various active species contributed under alkaline conditions with increased involvement of free radicals (•OH and SO4•−) and singlet oxygen. Furthermore, continuous flow experiments were set up to prove the potential applicability of the KBBC/PS process. This study not only deepens the understanding of persulfate activation by metal-free carbon-based materials across a wide pH range but also expands their potential applications in mine-polluted water purification.

Surface engineered recombinant Escherichia coli for the potential application of the cobalt contaminated wastewater treatment and the photocatalytic dye degradation

The novel recombinant Escherichia coli strain was construct through cell surface display for the treatment of cobalt contaminated wastewater and dye contaminated wastewater. First, structural analysis of known cobalt binding peptide was conducted and core binding sites were figured out which showing better cobalt binding ability. The cobalt peptides were attached to OmpC to construct cobalt adsorbing recombinant Escherichia coli. The recombinant strain efficiently absorbed and retrieved cobalt from cobalt wastewater by adsorbing 1895 µmol/g DCW of cobalt. Following adsorption, cobalt nanoparticles were synthesized through thermal decomposition of cobalt adsorbed recombinant strain at 500˚C. The nanoparticles exhibited noteworthy photocatalytic properties, demonstrating a substantial capacity for degrading dyes when used as a catalyst at a concentration of 10 mg/dl. These results presenting potential solutions for effective and environmentally friendly approaches to address cobalt and dye contaminated wastewater treatment process.

Методы и применение интенсификации фиторемедиации сточных вод горнодобывающей промышленности

The article presents the latest results of research on the biological treatment of mining and metallurgical industrial wastewater using higher aquatic plants: Eichhornia (Eichhornia crassipes Solm) and Pistia (Pistia stratiotes L). The features of these plants detected during contaminated wastewater treatment have been identified. The primary results of experiments are based on single-stage treatment processes that ensure efficient wastewater treatment upon completion of plant adaptation to these waters. However, the duration of the process is long, i.e., 15–30 days; therefore, the process intensification experiments have been conducted. Experiments conducted within a week have achieved significant reductions in calcium, magnesium, sulfate, and chlorine ions. During the first days of the experiments, the plants continued to grow and develop, but due to high salt concentrations, some of the plants (approximately 50–60 %) died due to insufficient time for adaptation. The remaining plants were slowly recovering and continued vegetation. These plants have demonstrated high cumulative and treatment effects as they are considered most adapted to the chemical composition of wastewater. The use of such plants, however, will require longer periods for wastewater treatment, namely around a month, which does not comply with the production requirements. Therefore, a decision to experiment during 24 hours has been made. The results of the analysis have shown that the plants completely absorb calcium, magnesium, chlorine, nitrates, zinc, and cobalt already on the first day of planting; bicarbonates and sodium are absorbed on the second day; and iron on the third day. Potassium, manganese, arsenic, and thiocyanates are neutralized during 7–10 days. The average efficiency of wastewater treatment per day is 51% on the condition of frequent renewal of the plant biomass. Based on the results obtained, a biotechnology built on a multi-stage biological wastewater treatment system of industrial scale has been developed.

Identification and quantification of electron-generated atomic hydrogen through in-situ electron spin resonance and density functional theory

Electro-generated atomic hydrogen (H*) plays a crucial role in the electrochemical reduction process, serving as the key species that mediates the electrocatalytic hydrogenation reduction of stubborn contaminants in wastewater treatment. However, precisely identifying and quantifying transient atomic H* presents a significant challenge due to its limited lifespan and its existence solely within the boundary layer at the electrode/solution interface. Herein, we developed the electrodeposition of palladium nanoparticles onto carbon cloth and assessed its effectiveness as a cathode for generating and stabilizing atomic H*. The environmental application of atomic H* was validated through the dechlorination of 2, 4-dichlorophenol wastewater and the reduction of antimonite wastewater. Additionally, the identification of atomic H* was verified by electrochemical measurements, high-resolution mass spectra, and density functional theory. Moreover, introducing an excess of a spin trapping agent (5,5-dimethyl-1-pyrroline-N-oxide) and fast in-situ spin trapping facilitated creating favorable conditions for efficient trapping of atomic H* and subsequent electron spin resonance (ESR) spectroscopy quantification analysis. Subsequently, the quantification of atomic H* was achieved by double integration of the ESR signal of spin adduct and comparison with the external standard agent (4-hydroxy-2,2,6,6-tetramethyl-1-piperidine 1-oxyl). This study introduces a novel method for in-situ spin trapping and quantification of atomic H*, facilitating the advancement of electrochemical reduction technology and its application in wastewater treatment.

A comprehensive study of artificial neural network for sensitivity analysis and hazardous elements sorption predictions via bone char for wastewater treatment

Using bone char for contaminated wastewater treatment and soil remediation is an intriguing approach to environmental management and an environmentally friendly way of recycling waste. The bone char remediation strategy for heavy metal-polluted wastewater was primarily affected by bone char characteristics, factors of solution, and heavy metal (HM) chemistry. Therefore, the optimal parameters of HM sorption by bone char depend on the research being performed. Regarding enhancing HM immobilization by bone char, a generic strategy for determining optimal parameters and predicting outcomes is crucial. The primary objective of this research was to employ artificial neural network (ANN) technology to determine the optimal parameters via sensitivity analysis and to predict objective function through simulation. Sensitivity analysis found that for multi-metals sorption (Cd, Ni, and Zn), the order of significance for pyrolysis parameters was reaction temperature > heating rate > residence time. The primary variables for single metal sorption were solution pH, HM concentration, and pyrolysis temperature. Regarding binary sorption, the incubation parameters were evaluated in the following order: HM concentrations > solution pH > bone char mass > incubation duration. This approach can be used for further experiment design and improve the immobilization of HM by bone char for water remediation.

Synergistic effect of silver nanoparticle-embedded calcite-rich biochar derived from Tamarindus indica bark on 4-nitrophenol reduction

Calcite-biochar composites are attractive materials with outstanding adsorption capabilities for removing various recalcitrant contaminants in wastewater treatment, however, the complexity of their synthesis limits their practical applications. In this work, we have prepared calcite-rich biochar (Ca-BC) from a single precursor (Tamarindus indica bark), which simplifies the synthetic route for preparing calcite-biochar composite. The as-synthesized composite is utilized to make a heterogeneous catalytic system containing the supported silver nanoparticles (Ag@Ca-BC) formed by the reduction of Ag+ ions on the surface of the composite. The formation of Ag@Ca-BC is confirmed by various characterization techniques such as PXRD, FT-IR, UV–Vis, cyclic voltammetry, impedance measurement, SEM, and TEM analyses. Especially, the TEM analysis confirms the presence of Ag nanoparticles with size ranging between 20 and 50 nm on the surface of Ca-BC composite. The nano-catalyst Ag@Ca-BC efficiently promotes the conversion of 4-nitrophenol to 4-aminophenol using NaBH4 as the reductant in water within 24 minutes at room temperature, suggesting that Ag@Ca-BC can be an efficient catalyst to remove nitroaromatics from the industrial effluents. The straightforward synthesis of Ca-BC from a single precursor along with its utility as a catalytic support presents a compelling proposition for application in the field of materials synthesis, catalysis, and green chemistry.

Non-polyamide nanofiltration membranes with low MWCO prepared by combining the catechol-amine chemistry and the chemistry of amino-silane coupling agents

The present work provides an efficient strategy to prepare mussel-inspired nanofiltration membranes with lower MWCO, via combining the catechol-amine chemistry and the chemistry of amino-silane coupling agents. The membranes were synthesized by stepwise depositing tannic acid (TA) and pre-hydrolyzed 3-aminopropyltriethoxysilane (APTES) on the PSF support. TA adsorbed on the polysulfone (PSF) support via hydrogen bonding. The pre-hydrolyzed APTES self-polymerized and reacted with TA, forming a crosslinked network through the Michael addition/Schiff base reactions. The membrane performance was tailored by controlling the hydrolysis degree of APTES. At optimal conditions, the APTES-TA/PSF membrane with MWCO of 200 Da and water permeance of 11 Lm−2h−1bar−1 was fabricated. The salt rejections toward Na2SO4 and NaCl were around 90% and 20% respectively. The continuous prolonged filtration showed the membrane had good filtration stability. Compared with previously reported mussel-inspired and polyphenol membranes, the present membrane had a much lower MWCO and higher permeance. The membrane can efficiently remove typical pharmaceuticals with molecular weight from 200 to 400 Da, indicating this type of membrane has promising prospects in trace-organic contaminated wastewater treatment.

Construct durable, antifouling double network hydrogel coatings on PTFE hollow fiber membranes via silane grafting

Polytetrafluoroethylene (PTFE) hollow fiber membranes are a promising candidate in highly contaminated wastewater treatment and management because PTFE is intrinsically chemically inert and hydrophobic. However, low water flux and fouling (contamination due to protein attachment and accumulation), both associated with low surface energy, pose great limits in filtration efficiency and the long-term use of PTFE hollow fiber membranes. Here we report a surface engineering strategy of coating PTFE hollow fiber membranes with polyvinyl alcohol/oxidized sodium alginate (PVA/OSA) double network (DN) hydrogels via N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTS) hydrolysis and grafting. The as-prepared PVA/OSA DN hydrogel coated PTFE hollow fiber membranes exhibited high efficiency in oil-water separation and excellent antifouling performance due primarily to the favorable interfacial electrostatic interaction and the hydration coating layer on the membrane surfaces. Moreover, the PVA/OSA DN hydrogel coatings remained high hydrophilicity and structural intergrity and operation stability after extensive time of soaking in strong acidic and alkaline solutions, all in great favor of the performance they were initially designed and intended for.

Visible-light boosted photocatalytic performance of sulfonated polypyrrole-coated ZIF-8 hybrids for pollutants degradation

Enhancing the charge transfer through the cooperative effect of various materials is a promising solution to overcome the limitations of low photocatalytic efficiency with single photocatalysts. Conductive polymers have gained attention as metal free photocatalysts in recent years due to their excellent electronic and optical properties. In this work, the construction and description of sulfonated polypyrrole (SPPy) coated Zn-zeolitic imidazole framework (ZIF-8) has been reported. The synthesized SPPy/ZIF-8 heterostructures have been characterized by XRD, FESEM, BET surface area, EDX, UV–visible DRS, ELS, and PL analyses. The photocatalytic performance of the synthesized composites has been tested for degradation two types of organic pollutants, Congo red (CR) dye and antibiotic Amoxicillin (AMX) under visible-light (LED) irradiation. Significantly enhanced photocatalytic efficiency of ZIF-8 for pollutants degradation was obtained after SPPy conjunction. 2 wt%SPPy/ZIF-8 heterojunction was the optimum photocatalyst, showing highest degradation efficiency (98.5% in 90 min and 92.7% in 150 min for CR and AMX, respectively). The potential photocatalytic mechanism was proposed and supported by trapping experiments. The •O2− radicals were the main reactive specie involved in the process. This study provides the basis for the application of organic/inorganic (SPPy/ZIF-8) heterostructure as photocatalysts for decomposition organic and emerging contaminants in wastewater treatment.

Unveiling the structure–activity relationships of ofloxacin degradation by Co3O4-activated peroxymonosulfate: From microstructures to exposed facets

As a fluoroquinolone antimicrobial agent, ofloxacin (OFX) has been widely used, consequently causing serious damage to the ecological environment. Advanced oxidation processes based on persulfate activation (SR-AOPs) are widely applied to degrade stubborn organic contaminants in wastewater treatment. Co3O4 is being extensively investigated as a promising persulfate catalyst in SR-AOPs. In this work, four Co3O4 polycrystals with specific morphologies were synthesized and used to activate peroxymonosulfate (PMS) for OFX degradation. The obtained samples and corresponding precursors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and N2 adsorption/desorption isotherms. Experimental results showed that 30 mg·L-1 OFX could be completely removed in the lamella-like Co3O4/PMS system within 30 min under ordinary conditions. The underlying degradation mechanism was elaborated by high-resolution TEM (HRTEM) combined with density functional theory (DFT) calculations. Based on quenching experiments and the electron paramagnetic resonance (EPR) technique, sulfate radicals were identified as the dominant reactive oxygen species (ROS) in the lamella-like Co3O4/PMS system, and superoxide radicals, hydroxyl radicals, and singlet oxygen made minor contributions to the degradation of OFX. Possible degradation pathways were proposed based on DFT calculations and Fukui theory and confirmed by ultrahigh-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UHPLC-QTOF/MS). Furthermore, quantitative structure–activity relationship (QSAR) prediction was used to evaluate the developmental toxicity of the corresponding intermediates.

Effect of Ag modification on TiO2 and melem/g-C3N4 composite on photocatalytic performances

Here, the comparison of two different semiconductor materials is demonstrated, TiO2 and melem/g-C3N4 composites—modified with balls of approximately 5 nm Ag nanoparticles (NPs) as photocatalysts for the degradation of the model dye acid orange 7 (AO7). The melem molecule synthesized here is one of a series of organic compounds consisting of triazine ring compounds with a structure similar to that of melam and melamine. The photodegradation process of AO7 was carried out to examine all powder materials as a potential photocatalyst. Additionally, two different lamps of wavelengths 368 nm (UV light) and 420 nm (VIS light) were applied to compare the photodegradation tests. A new synthesis route for the acquisition of Ag NPs (Ag content 0.5, 1.0 and 2.5 wt%), based on a wet and low temperature method without the use of reducing reagents was proposed. The best photocatalytic performances under UV and VIS light were obtained for both, TiO2 and melem/g-C3N4 materials (new synthesis route) modified with a very low Ag content—0.5 wt%. The photodegradation activities using UV lamp (3 h, 368 nm irradiation) for samples with 0.5 wt% of Ag: TiO2 and melem/g-C3N4, in excess of 95 and 94%, respectively, were achieved. The highest photoactive materials melem/g-C3N4 with 0.5 and 1 wt% Ag revealed 98% of activity under the VIS lamp after 3 h long irradiation. Our work demonstrates a novel, environmentally acceptable, and cost-effective chemical strategy for preparation of photocatalysts suitable for degradation of organic contaminants in wastewater treatment.

Recent Application Prospects of Chitosan Based Composites for the Metal Contaminated Wastewater Treatment.

Heavy metals, known for their toxic nature and ability to accumulate and magnify in the food chain, are a major environmental concern. The use of environmentally friendly adsorbents, such as chitosan (CS)-a biodegradable cationic polysaccharide, has gained attention for removing heavy metals from water. This review discusses the physicochemical properties of CS and its composites and nanocomposites and their potential application in wastewater treatment.

A coupled photocatalytic system using niobium oxide and microalga: Cr (VI)-contaminated wastewater treatment

The increasing development of industries has caused unusual exploitation of natural resources, associated with the unregulated discharge of wastewater into the environment. Heavy metals, such as chromium, are among the pollutants known for their toxicity, non-biodegradability, durability in nature, and tendency to bioaccumulate. Cr contamination has intensified, and alternative processes, such as bioremediation and heterogeneous photocatalysis, are emerging as an option to traditional methods. The current work aimed to investigate the synergetic photocatalytic process in the reduction and removal of Cr (VI) using two independent phases: the initial addition of niobium oxide (Nb2O5) in a photoreactor under UV-C light, and the application of green alga Chlamydomonas reinhardtii, under another condition and time/space as a polish process. The synthetic wastewater was prepared with Cr (VI) concentrations of 10, 30, and 50 mg/L and introduced into the photoreactor under UV-C light, along with Nb2O5 at concentrations of 0.5 and 1.0 g/L; pH 3; recirculation of Cr (VI) solution at a continuous flow rate of 800 mL/min for 72 h. Aliquots were withdrawn at specific times and the remaining concentration of Cr (VI) was measured using a colorimetric method with 1,5-diphenylcarbohydrazide reagent, and the total Cr concentration was determined by flame atomic absorption spectrometry. Cr (VI) reduction results found for 1.0 g/L Nb2O5 were 51 %, 13 %, and 11 % in 10, 30, and 50 mg/L Cr (VI), respectively. The synthetic wastewater from the photoreactor was collected, centrifuged, and submitted to a batch reactor where C. reinhardtii was added at 1.0 g/L with pH 7 for 120 h, alternating 12/12 h in light/dark conditions. The efficiency of C. reinhardtii was verified by the analysis of cell density, Cr (VI) concentration, and total Cr concentration, as well as morphological analysis using SEM and EDS. Results of Cr (VI) reduction using microalgae were 50 % and 18 % for the concentration of 10 mg/L and 50 mg/L of Cr (VI) respectively; 81 % of reduction for 0.5 g/L and 39 % for 1.0 g/L of Nb2O5, both at a concentration of 30 mg/L of Cr (VI). In the end, the two processes provided, on average, results of 71 %, 31 %, and 18 % total removal of the heavy metal Cr at initial concentrations of 10, 30, and 50 mg/L of Cr (VI), respectively. Thus, the new proposed model, associating agents with distinct characteristics in two processes, an initial heterogeneous photocatalysis using Nb2O5 and subsequent biosorption by microalgae C. reinhardtii, proved to be a suitable new model for reducing and removing Cr.

Regulating the reaction pathway of nZVI to improve the decontamination performance through magnetic spatial confinement effect

Nanoscale zero-valent iron (nZVI) shows high effectiveness in the catalyzed removal of contaminants in wastewater treatment. However, the uncontrolled interfacial electron transfer behavior and formation of surface iron oxide (FeOx) layer led to severe electron wasting and occasionally form highly toxic intermediates. Here, we constructed magnetic mesoporous SiO2 shell on surface of nZVI to stimulate a magnetic spatial confinement effect and regulate the electron transfer pattern. Therein, Fe atom facilely spread out from the nZVI core, orderly release electron to surface adsorbed H2O molecule, which is efficiently transformed into active hydrogen (H*). Meanwhile, in-situ Raman revealed that Fe atoms were involved in the formation of penetrable γ-FeOOH rather than FeOx layer, enabling the continuous inward diffusion of H2O and outward diffusion of H* . Employing the catalyzed removal of halogenated phenols as demo reaction, the presence of magnetic mesoporous SiO2 shell utilized the reaction between electrons and H2O to switch the reaction pathway from the reduction/oxidation hybrid process to hydrodehalogantion, and increased the conversion of halogenated phenols-to-phenols by 5.53 times. This study shows the forehand of improving the decontamination performance of nZVI through sophisticated designed surface coating, as well as fine regulating the environmental behavior of magnetic material via micro-magnetic field.

Highly efficient activation of peroxymonosulfate by novel CuO-Chrysotile catalytic membrane for degradation of p-nitrophenol

A novel CuO-Chrysotile thin membrane catalyst was prepared by simple impregnation-calcination route, which provided new insights of catalytic membranes by natural mineral fiber for the degradation of organic contaminants in wastewater treatment. Through intermittent and continuous catalytic degradation experiments, peroxymonosulfate (PMS) was efficiently activated by the membrane to degrade p-nitrophenol (PNP), and the effects of experimental parameters (including initial solution pH value, PMS dosage, catalyst dosage, reaction temperature, membrane mass and flow rate) on PNP degradation were systematically studied. The results showed that the catalytic membrane had great catalytic performance and long-term stability, it could completely degrade 10 mg/L of PNP within 60 min and its degradation ratio could remain above 90 % after 5 cycles. Meanwhile, it was worth noting that 0.15 g of CuO-Chrysotile catalytic membrane used as fixed bed could continuously degrade 12.5 L of PNP solution with gratifying performance, which proved that the catalytic membrane had convenient use method and great application effect. The mechanism study found that 1O2 produced in this process played a key role in the degradation of PNP. From the aspects of manufacturing cost, catalytic performance and service life, the novel CuO-Chrysotile catalytic membrane has excellent industrial application potential.