Chromium Cr Research Articles

Assessment of the toxic effect of hexavalent chromium on the hematological indices in Nile tilapia, Oreochromis niloticus

The presence of heavy metals, which are typically released into water bodies as a result of fast industrialization, causes the aquatic environment to become extremely contaminated. Chromium is one of the most common heavy metal in the environment and is used in several types of industries. The effect of sublethal toxicity of hexavalent chromium Cr(VI) on hematological indices of the Nile tilapia, Oreochromis niloticus has been analyzed following exposure of concentration 9.349 mg/L and 18.698 mg/L (10% & 20% of LC50 value ) of potassium dichromate (K2Cr2O7) as hexavalent chromium for 7, 15, 30 days. Hematological parameters are the most important indicators of fish health status. The aim of this study was to determine the effect of Cr(VI) toxicity on hematological parameters in O. niloticus. The results show that hemoglobin percentage (Hb%), red blood cell (RBC), mean corpuscular volume (MCV), and platelet count level were significantly (P > 0.05) decreased and the total count of white blood cell (WBC) was significantly (P > 0.05) increased with increasing time of exposure at a concentration of 9.349 mg/L of K2Cr2O7 in the test groups compared to the control group. At the concentration of 18.69 mg/L, Hb%, RBC, MCV, mean corpuscular hemoglobin concentration (MCHC), and platelet count level were significantly (P > 0.05) decreased and the total count of WBC and erythrocyte sedimentation rate (ESR) value were significantly (P > 0.05) increased with the increasing time of exposure in the test groups compared to the control group. To study the R2 value of the linear regression equation, we found that the trend of the chronic toxic effect of hexavalent chromium at 60 and 90 days of both the sublethal concentrations 9.349 mg/L and 18.69 mg/L of K2Cr2O7, where the value of Hb, RBC, packed volume cell (PCV), MCV are found to drastically decreased and the value ESR and WBC are found to drastically increased in the experimental groups compared to the control group. The investigation recommended that the presence of hexavalent chromium in the aquatic medium has a strong impact on the hematological indices in O. niloticus.

Assessment of the Toxic Effect of Hexavalent Chromium on the Hematological Indices in Nile Tilapia, Oreochromis Niloticus

The presence of heavy metals, which are typically released into water bodies as a result of fast industrialization, causes the aquatic environment to become extremely contaminated. Chromium is one of the most common heavy metals in the environment and is used in several types of industries. The effect of sublethal toxicity of hexavalent chromium Cr (VI) on hematological indices of the Nile tilapia, Oreochromis niloticus has been analyzed following exposure of concentration 9.349 mg/L and 18.698 mg/L (10% & 20% of LC50 value) of potassium dichromate (K2Cr2O7) as hexavalent chromium for 7, 15, 30 days. Hematological parameters are the most important indicators of fish health status. The aim of this study was to determine the effect of Cr (VI) toxicity on hematological parameters in O. niloticus. The results show that hemoglobin percentage (Hb%), red blood cell (RBC), mean corpuscular volume (MCV), and platelet count level were significantly (P > 0.05) decreased and the total count of white blood cell (WBC) was significantly (P > 0.05) increased with increasing time of exposure at a concentration of 9.349 mg/L of K2Cr2O7 in the test groups compared to the control group. At the concentration of 18.69 mg/L, Hb%, RBC, MCV, mean corpuscular hemoglobin concentration (MCHC), and platelet count level were significantly (P > 0.05) decreased and the total count of WBC and erythrocyte sedimentation rate (ESR) value were significantly (P > 0.05) increased with the increasing time of exposure in the test groups compared to the control group. To study the R2 value of the linear regression equation, we found that the trend of the chronic toxic effect of hexavalent chromium at 60 and 90 days of both the sublethal concentrations 9.349 mg/L and 18.69 mg/L of K2Cr2O7, where the value of Hb, RBC, packed volume cell (PCV), MCV are found to drastically decreased and the value ESR and WBC are found to drastically increased in the experimental groups compared to the control group. The investigation recommended that the presence of hexavalent chromium in the aquatic medium has a strong impact on the hematological indices in O. niloticus.

Effect of hexavalent chromium on growth performance and metabolism in broiler chicken.

Hexavalent chromium Cr (VI) is one of the most hazardous heavy metals in the environment and is toxic to living organisms causing tissue damage, disruption of the intestinal microbiota and cancer. However, there is little information on the relationship between the Cr (VI) and broiler chickens. The current study was performed to investigate the effect of Cr (VI) on growth performance, serum biochemical analysis, histopathological observations, and metabolomics analysis in broilers. Results show that Cr (VI) exposure significantly decreased the body weight (p < 0.01) and caused liver damages in broilers. With the extension of Cr (VI) action time, the liver appeared obvious pathological changes, including hepatic cord disorder, incomplete hepatocyte additionally, decreased serum biochemical indices of calcium (Ca), phosphorus (P), total protein (TP), phosphatase (ALP), and globin (GLB) significantly (p < 0.01). Moreover, metabolomics analysis indicated that 29 differential metabolites were identified, such as phytosphingosine, L-Serine, 12, 13-DHOME, Alpha-dimorphecolic acid, L-Methionine, L-Phenylalanine, 3-Dehydroshikimate, L-Tyrosine, and N-Acetyl-L-phenylalanine were significantly decreased under the action of Cr (VI) (p < 0.05). These 29 differential metabolites are mainly involved in 35 metabolic pathways, such as aminoacyl-tRNA biosynthesis, phenylalanine metabolism, sphingolipid, and linoleic metabolism. The study revealed that exposure to Cr (VI) resulted in a decrease in growth performance and metabolism, with the hazards and toxicity in broiler chicken. The findings provided new insight and a comprehensive understanding of the relationship between Cr (VI) and broiler chickens.

Elucidating the impact of sulfur precursors on the reactivity, toxicity, and colloidal stability of post-sulfidized nanoscale zerovalent iron

The sulfur precursor-induced sulfidation effectively enhances the nanoscale zerovalent iron (nZVI) reactivity. However, due to the batch-to-batch variation in synthesis and reaction conditions, the sulfur precursor that confers superior reactivity to sulfidized nZVI (S-nZVI) and its application potential are undetermined. This study evaluated the impact of six sulfur precursors (Na2S, Na2S2O4, S0, Na2S2O3, K2S6, and sulfate reduction effluent [a sulfide-containing effluent]) on the reactivity, toxicity, and colloidal stability of S-nZVI. The reactivity enhancement induced by sulfidation of the different sulfur precursors was inconsistent and dependent on the contaminant. In the removal of trichloroethylene (TCE) and hexavalent chromium Cr(VI) in aqueous solution, S-nZVI, with a high Fe0 content, hydrophobicity, and electron transfer properties (i.e., S-nZVINa2S and S-nZVINa2S2O3), yielded relatively high capacities. In the removal of tetracycline (TC) by S-nZVI, the performance was relatively unaffected by the sulfur precursors. The toxicity evaluation demonstrated that S-nZVIs showed a limited toxicity (less than 0.35-log) to Escherichia coli (E. coli) in simulated groundwater. Despite sulfidation marginally improving the colloidal stability of nZVI—by reducing the interparticle forces—, the S-nZVI particle settling was observed, within 60 min, at the bottom of the vial containing the suspension. Overall, none of the sulfur precursors was manifestly preferable to the others. Na2S, Na2S2O3, and SR-effluent were recommended for use in low sulfur content post-sulfidation processes considering the material performances and costs. These findings contribute to the understanding of the effect of the sulfur precursors on the reactivity and application potential of S-nZVI, thereby providing guidance for tuning S-nZVI properties and selecting suitable sulfur precursors for specific in situ remediation scenarios.

New PCBs-degrading and hexavalent chromium-resistant bacteria isolated from Lake Mariout, Egypt

Polychlorinated biphenyls (PCBs) are persistent organic pollutants. They were widely used and distributed in the environment causing endocrine disruption, carcinogenicity, and immunotoxicity. The toxic heavy metal, Hexavalent chromium Cr(VI), co-exists with PCBs leading to ecological deterioration and health problems. Thus, bioremediation of the coexisting PCBs and Cr(VI) is essential for the environment and public health. In this study, three bacterial strains identified as Bacillus safensis, Bacillus cereus, and Bacillus vietnamenesis, were isolated. As revealed, various strains belonging to the genus Bacillus degraded PCBs. However, this study can be considered the first report on isolated strains as PCB-degraders that resist Cr(VI) as co-contaminants. All strains had the biphenyl dioxygenase (bphA) gene and grew on PCBs as the sole carbon and energy source and completely remediated 5 mg/l Cr(VI) individually within 24 h. The three isolates showed different response mechanisms to Cr(VI) that enabled Bacillus safensis and Bacillus cereus to grow on PCBs and Cr(VI) as co-contaminants. Bacillus vietnamensis recorded the highest growth on PCBs, but could not grow on PCBs with Cr(VI). Therefore, Bacillus safensis and Bacillus cereus are concluded to be good candidates for bioremediation of PCBs and Cr(VI) as co-contaminants, while Bacillus vietnamensis is more suitable for bioremediation of either PCBs or Cr(VI) individually.

The roles of different Fe-based materials in alleviating the stress of Cr(VI) on anammox activity: Performance and mechanism

Hexavalent chromium Cr(VI) is widely present in industrial wastewater, which can inhibit anammox performance significantly. Iron is a critical element of anammox metabolism and also has the capacity to remove Cr(VI). In this study, batch experiments were conducted to investigate the effects of commercial zero-valent iron (Fe0) and ferroferric oxide (Fe3O4) in the nano-(n) and micron-(m) scales (mFe0, nFe0, mFe3O4, and nFe3O4, respectively) on recovering anammox activity with inhibition of Cr(VI). Their recovery efficiencies on the anammox process were in the order of mFe0, mFe3O4, nFe0, and nFe3O4 at their minimum effective dosages, with specific anammox activities being promoted by 95.2%, 57.0%, 45.0%, and 15.8%, respectively, in comparison to the control. More hydroxyl groups in extracellular polymeric substances (EPS) were observed with mFe0, and the electron transport performances of soluble and loosely-bound EPS were particularly enhanced. By contrast, Fe3O4 stimulated more production of EPS than mFe0, which helped remove Cr(VI) outside the cell membrane. Moreover, the contents of heme c and cytochrome c were improved most with mFe3O4 by 10.9% and 41.3%, respectively, and hydrazine dehydrogenase activity was enhanced by 47.7% with mFe0, at their optimal dosages. In addition, cytochrome c showed a significant positive correlation with recovery performance for all four materials (R2 > 0.82, P < 0.05), indicating its pivotal role in alleviation effectiveness. More FeOOH was found on the two micron-scale materials detected by X-ray diffractometry and Fourier transform infrared spectroscopy, which would help electron transfer between materials and anammox bacteria. In contrast, the fast corrosion and adsorption processes and biological toxicity of nanoscale materials may lead to their poor performance.

Efficient removal of hexavalent chromium Cr (VI) using magnesium-iron layered double hydroxide supported on orange peel (Mg-Fe LDH@OPP): A synthetic experimental and mechanism studies

Herein, a series of meticulously designed batch and continuous mode sorption experiments were conducted to compare removal affinity of raw orange peel powder (OPP) and magnesium-iron layered double hydroxide impregnated OPP (Mg-Fe LDH@OPP) composite for the elimination of Cr (VI) ions from aqueous media. The relatively greater particle size, irregular pore distribution, effective surface area, and higher point of zero charge (pHpzc) of Mg-Fe LDH@OPP as compared to OPP were principally responsible for its superior Cr (VI) sorption from aqueous media. It was observed that highest Cr (VI) removal (OPP: 81.84 %; Mg-Fe LDH@OPP: 100 %), was achieved at optimum conditions of pH (2), adsorbent dosage (2 g/L), contact time (180 min) and temperature (25 °C) for suspension containing 20 mg/L initial Cr (VI) concentration. The sorption data was adequately fitted with Freundlich and pseudo-second order model using both biosorbents. The FT-IR and XRD analysis further confirmed the reduction pathway followed by complexation reactions as major sorption mechanisms using Mg-Fe LDH@OPP. However, in the case of OPP, ligand exchange played a critical role in removing Cr (VI) ions from water. Furthermore, continuous mode column studies suggested applicability of Mg-Fe LDH@OPP compared to raw OPP. The results indicated breakthrough times of up to 366 min and 60 min, and exhaustion times of up to 800 min and 350 min, for Mg-Fe LDH@OPP and OPP, respectively. In general, Mg-Fe LDH@OPP was found to be a promising material with strong Cr (VI) sorption potential from polluted water.

Aggregation-induced emission-based versatile 3D hierarchical porous nanoprobe for electrochemiluminscence-fluorescence dual-mode detection of Cr(VI)

Owing to the built-in cross reference correction function, dual-mode monitoring platform is conducive to perform the highly precise pollution surveillance and traceability analysis in complicated environmental media. Herein, a novel aggregation induced emission (AIE)-based 3D hierarchical porous nanoprobe COP-TPEN2 was successfully synthesized, as to design a electrochemiluminscence (ECL)-fluorescence dual-mode sensing platform for Cr(VI) detection in environmental water samples. Equipped with many -NH groups, COP-TPEN2 can reduce hexavalent chromium Cr(VI) to low-toxicity trivalent chromium Cr(III). Moreover, different valence states of Cr ions were discovered to consume portions of the reactive intermediates of S2O82- (i.e., SO4-), and the electrons during the reduction of COP-TPEN2 were captured due to the strong oxidation property of Cr2O72-, leading to a decrease in the ECL intensity for COP-TPEN2. Moreover, COP-TPEN2 with AIE properties could be applied for Cr(VI) detection in fluorescence channel through the joint action of inner filter effect and static quenching. On account of the different signal generation mechanisms, two independent signals were selectively triggered by Cr(VI), achieving efficient detection of Cr(VI) with LODs of 0.18 nM and 0.29 nM, respectively. This dual-mode sensor was successfully used to determine Cr(VI) in environmental samples with satisfactory results, thereby showing great potential in environmental monitoring.

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Deleterious reactive evaporation of chromium from stainless steels commonly used in solid oxide electrochemical systems is well-documented; however, interactions between Cr vapor species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between Cr vapor species and downstream components during operation is critical for improving system performance and safeguarding environmental, health and safety, as many condensed Cr compounds contain toxic and carcinogenic hexavalent chromium Cr(VI). Furthermore, the interactions between volatilized Cr species and surrounding interfaces are dependent upon dynamic chemical environments. The objective of this study is to systematically investigate and report on condensation pathways of Cr vapors within representative system environments with variable water concentrations. To accomplish this objective, an experimental platform was designed to generate Cr vapor species from the reactive evaporation of chromia (Cr2O3) powder with high-temperature (>1100 K) air/H2O mixtures, and expose downstream ceramic insulation materials (e.g., aluminosilicate fibers) at reduced temperatures (<600 K). Insulation material chemical compositions investigated include pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg, Sr). Materials are studied as a function of exposure conditions using complementary materials characterization tools such as SEM-EDX, XPS, and diphenyl carbazide reactions to assess Cr(VI) concentrations. Reactive evaporation of Cr from chromia occurs in the presence of oxygen and/or water vapor to form various Cr-containing vapor species. Thermodynamic data reveals an equilibrium partial pressure increase of several orders of magnitude at elevated (>500 K) temperatures for all Cr vapor species. In the presence of water vapor, the partial pressure of Cr oxyhydroxide (CrO2(OH)2(g)) is greater by many several orders of magnitude and becomes the dominant species up to ~1500 K. The research objective is to explore effects of water vapor in air on Cr condensation and speciation on different ceramic insulation materials. The experimental setup thus far has exposed aluminosilicate fibers to volatilized Cr species from Cr oxide powder at 1100 K for 150 hours under varying water vapor conditions: 0 vol%(dry), 3 vol%, and 10 vol% H2O. Preliminary results show an increase in Cr(VI) formation on fibers exposed to volatile Cr species as water vapor content increases. See Figure 1 for an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on water vapor. Analyses of these results will be presented and discussed in context of potential implications for SOFC/SOEC systems. Figure 1

Novel template free synthesis of high surface area mesoporous ceria and adaptive neuro fuzzy interference system (ANFIS) modelling for Cr(VI) adsorption

The search for sustainable and ecofriendly mesoporous materials with high surface area is intensively desired for catalytic applications. Herein, we explore a template-free hydrothermal method for synthesizing mesoporous Cerium Oxide (meso-CeO2) nanoparticles as an adsorbent, for the removal of toxic hexavalent chromium Cr(VI) from water. The morphology and structure of synthesized nanomaterials were characterized using various techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), UV–visible spectrophotometer (UV–Vis), Fourier transform infrared spectroscopy (FTIR), and Brunauer, Emmett, and Teller(BET) analysis. The BET analysis confirmed CeO2 possess a high surface area of 270 m2/g, a 4.5 nm pore diameter, 0.22 cm3/g pore volume, and a stable mesoporous structure. The synthesized meso-CeO2, exhibited efficient removal (99.8% at pH 5) of Cr (VI) from water within 60 min at room temperature. The meso-CeO2 material demonstrated reusability for up to 5 cycles. The removal of Cr (VI) using meso-CeO2 followed Pseudo-second order kinetics (R2 > 0.99) and showed a good fit with the Freundlich isotherm model. Moreover, adaptive neuro fuzzy inference system (ANFIS) models were employed on 320 experimental data sets to predict the adsorption process accurately. Overall, this study highlights the potential of meso-CeO2 nanoparticles as a promising adsorbent for effective water remediation of heavy metal contaminants like Cr (VI).

Co/S co-doped Mn3O4-based sulfur-oxide nano-flakes catalyst for highly efficient catalytic reduction of organics and hexavalent chromium pollutants

Co/S co-doped Mn3O4 bimetal sulfur-oxide nano-flakes catalyst, Co/S-Mn3O4 or MnCoOS, with excellent catalytic reducing performance, was successfully prepared via a feasible method and characterized by different testing techniques. The existence of heterovalent Co2+/Co3+ and Mn2+/Mn3+ states in Co/S-Mn3O4 enhances the electron lifetime and facilitates fast electron transfer, which speeds up the chemical pollutant reduction reaction. Likewise, the valence transition between Co2+/Co3+ and Mn2+/Mn3+ makes the Co/S co-doped in Mn3O4 catalyst increase its electrochemically active surface sites. The MnCoOS catalyst labeled as MnCoOS-3 exhibits good long-term stability and electrochemical performance. The Co/S-Mn3O4 catalytic performance was also tested for the reduction of 4-nitrophenol (4-NP), methyl orange (MO), rhodamine (RhB), methylene blue (MB), and hexavalent chromium Cr(VI). The results exhibited that the MnCoOS-3 catalyst prepared with n(Mn):n(Co):n(C2H5NS) = 1:1:1 had the best catalytic activity, with 10 mg it ultimately reduced 100 ml of 10 ppm 4-NP, 20 ppm MO, RhB, and MB, and 50 ppm Cr(VI) within 12, 10, 10, 20, and 24 min, respectively. Therefore, Co/S co-doped Mn3O4 catalysts have excellent catalytic potential application merits in reducing chemical pollutants.

Sorption enhancement of Cr(VI) from aqueous solution by polyaniline confined in three-dimensional network of composite porous hydrogel.

Hexavalent chromium Cr(VI) is a typical harmful pollutant, which is carcinogenic or mutagenic to aquatic animals and humans. In this study, sepiolite/humic acid/polyvinyl alcohol@ polyaniline (SC/HA/PVA@PANI) composite porous hydrogel adsorbent was synthesized by Pickering emulsion template in situ chemical oxidative polymerization for adsorption of Cr(VI) from aqueous solution. The in situ polymerization of aniline at the Pickering emulsion interface and the unique three-dimensional network structure of the hydrogel act as an effective "confinement" for the growth of the polymer. The porous structure of the material acts as a water channel, which effectively accelerates the binding of the adsorbate to the adsorption sites, and significantly improves the adsorption rate and adsorption capacity. The adsorption capacity of PANI for Cr(VI) confined in three-dimensional network of composite porous SC/HA/PVA@PANI hydrogel reached 1180.97 mg/g-PANI, which increased about 27-fold compared the adsorption capacity of pure PANI (43.48 mg/g). It is shown that the experimental design effectively avoids the agglomeration of PANI and improves its potential adsorption performance. In addition, the analysis of FESEM-EDX, FT-IR, and XPS spectra before and after adsorption confirmed that the main adsorption mechanisms of Cr(VI) on SC/HA/PVA@PANI included ion exchange, electrostatic attraction, and redox reaction. In conclusion, SC/HA/PVA@PANI has good stability and excellent adsorption performance, which is a new type of Cr(VI) ion adsorbent with great potential.

Enhancing the Immobilization of Hexavalent Chromium by the Interlayer Anion Adsorption of the Brucite-Transformed LDH in the Presence of Aluminum Ions

Current studies of chromium adsorption kinetics at the solid–liquid interface often neglect the influence of coexisting ions in complex wastewaters. Thus, it is critical to explore the hexavalent chromium Cr(VI) adsorption kinetics of solid-phase brucite (Mg(OH)2) in liquid-phase wastewater containing coexisting aluminum ions (Al(III)). This paper reveals that the presence of Al(III) significantly enhanced the Cr(VI) adsorption efficiency onto Mg(OH)2, with a peak of up to 91% compared to 5% for the absence of Al(III). The main reason for this enhancement was the initial surface ternary complexation of Mg(OH)2 and the cationic (Al(III)) isomorphic substitution to form Mg(II)-Al(III) layered double hydroxides (LDH), which also indicates a solid-phase transition on the surface of Mg(OH)2, which led to electrostatic adsorption in the gallery and made Cr(VI) immobilized and not readily released. Further calculation and analysis of the adsorption energy confirmed the mechanism of Cr(VI) adsorption. It was also concluded that Cr(VI) migration in Mg(OH)2-containing minerals was affected by the phase transformation of solids in the presence of Al(III). Hence, this study not only reveals the adsorption mechanism during the treatment of composite pollutant wastewater but also provides the methodological reference for brucite synergistic adsorption to remove heavy metal ions and purify and treat complex polluted wastewater.

Removal of Cr6+ from Synthetic Polluted Water using Fe Modified Sugarcane Bagasse &amp; Peanut shell Powder

Unprocessed waste is dumped in lakes and rivers which possess a severe environmental risk through heavy metal’s contamination within the food chain, especially chromium Cr6+. It applies for sustainable development goals by using green solid waste as a precursor. This research mainly focuses upon the analysis of time effect for Cr6+ removal by FeCl3 modified biochar using sugarcane bagasse and peanut shell powder as biomass. Adsorbent preparation was done using Bench-Scale Fixed Bed Reactor (B-SFBR) and Cr6+ was found using the calorimetric method. Characterization was done by BET, SEM-EDX, and FTIR. The highest Cr6+ percentage removal was achieved by Modified Peanut shell Powder with 99.97% removal upon pH 2, shaking time 180 mints, speed = 150 rpm, dosage 0.3 g, Cr6+ conc 20 mg/L. Percentage Removal by Modified SB was 98.96% with Cr6+ conc 20 mg/L, dosage 0.3 g, pH 2, shaking speed 150 rpm, time 180 mints. Hence, the present experimental research concludes that FeCl3 modified peanut shell powder shows greater Cr6+ removal efficiency up to 99.97 %.

Comparative study of the effective removal of hexavalent chromium via calcium alginate and calcium alginate/Ulva fasciata composite

The present study revealed for the first time the removal of hexavalent chromium Cr(VI) with a high efficiency using an eco-friendly composite beads of alginate with the green alga Ulva fasciata compared to calcium alginate beads. This conclusion was reached in this study from the comparison of the removal efficiency of Cr(VI) by the well-known biosorbent material, calcium alginate (CA) with the studied calcium alginate/Ulva fasciata (CA/UF) biocomposite beads. The characterization of the prepared beads was achieved using several techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray (EDAX). The Brunauer, Emmett, Teller (BET) and Barrett, Joyner, Halenda (BJH) analyses were also employed which indicated a three-fold increase in the surface area, a mean pore diameter of 2.3-fold and a total pore volume of 14-fold for calcium alginate/Ulva fasciata composite compared to calcium alginate beads. The results of batch experiments demonstrated the fast complete removal of Cr(VI) by the CA/UF composite compared to the maximum removal (75%) by CA. The Dubinin–Radushkevich isotherm model reflected the physical pore volume filling of Cr(VI) rather than adsorption on the pore walls, giving an adsorption mean free energy (2.24 kJ/mol) for CA/UF greater than that of CA (0.13 kJ/mol). Furthermore, Brunauer–Emmett–Teller isotherm reflected the multilayer adsorption for CA and CA/UF. Flory–Huggins isotherm model showed the more spontaneous adsorption for CA/UF than CA, with negative Gibbs free energy ΔG0 values of − 4.76 and − 6.91 kJ/mol, respectively. Whereas, Temkin isotherm model showed a higher adsorption binding energy of Cr(VI) on CA/UF than CA beads. In this study, the Langmuir model of Cr(VI) adsorption on CA/UF beads was the least applied among all studied adsorption isotherm models, which also revealed the multilayer adsorption mechanism of Cr(VI) ions. The Intra-particle diffusion model was applied for CA/UF composite beads, and this application suggested that the intra-particle diffusion is a part of the rate-limiting steps. The regeneration study showed a decrease in the adsorption efficiency of CA/UF composite from 97.4 to 82.3% for three consecutive cycles.

Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator

Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator

Use of iron oxide nanomaterials as adsorbents for wastewater treatment

The dissemination of chemical components into the environment might provoke harm to human health, animal species and the ecosystem. In order to reduce the negative effects of those pollutants, physico-chemical treatment procedures, namely the adsorption technique has been implemented. This study seeks to synthesize manufactured nanomaterials throughout a co-precipitation process such as nanoparticles (Ferrihydrite (Fh)) and nanocomposite magnetic iron (magnetite / activated carbon) capable of adsorbing certain inorganic species (heavy metals) such as hexavalent chromium Cr (VI). The prepared supports were characterized by IRTF analysis. The influence of the various experimental parameters (the initial concentration and the contact time) have been studied. Various isothermal models have been applied, namely Langmuir, Freundlich, Temkin and BET. The study of those absorption isotherms has shown that Langmuir’s model describes better Cr (VI) adsorption. It has been also noticed that the adsorption process on the Fh follows a pseudo 2nd order kinetics for the hexavalent chromium. The experimental results have proved that equilibrium is reached after 15 minutes with a better yield of 99.511% and a maximum retention capacity of 40.9157 mg / g.

Contrast between a mathematical model and the bioreduction process of Cr(VI) by consortia of bacteria isolated from wastewater of the Pasto River

Introduction. The versatile metabolism of microorganisms allows biodegradation of a wide variety of contaminants; however, the increasing scale of the industry exceeds its pollutant processing capacity. Due to its high toxicity, hexavalent chromium Cr(VI) is one of the heavy metals with the greatest global dissemination and concern. There are numerous investigations focused on proposing treatments to purify the different ecosystems affected with this metal; however, knowledge about various microorganisms from the same source that could help solve this problem is restricted. Objective. To evaluate the efficiency in the reduction of Cr(VI) of bacterial consortia (B. thuringiensis, B. amyloliquefaciens and Paenibacillus sp.) in a Batch type treatment, using municipal wastewater from Río Pasto as a substrate. Methodology. A mathematical model was formulated that reliably predictedthe behavior of the consortia, in relation to their growth and reduction percentage, the results of the simulations were compared with experimental data to select the consortium with the best Cr(VI) reduction results). Subsequently, its efficiency in the reduction of Cr(VI) was determined, using unsterilized residual river water as a substrate. Results. The statistical analyzes highlighted the absence of statistically significant differences in the reduction percentages between the consortia. However, with the selected culture, a reduction percentage of 91% was presented in 156 hours. Conclusion. The results found in this research are promising for their application in the improvement of treatment practices for Cr(VI) bioremediation.

Removal of Hexavalent Chromium from Water by Chitosan-Enhanced Ultrafiltration

Polymer-enhanced ultrafiltration has gained increasing attention as a selective separation process to remove small solutes, such as metal ions, from water or wastewater. Hexavalent chromium Cr(VI) is one of the metal ions in wastewater that has received considerable attention because of its toxicity. Chitosan was used in this study as the polymer to bind Cr(VI) to enhance its removal by ultrafiltration. The effects of chitosan-to-Cr(VI) ratio on Cr(VI) rejection and permeate flux were investigated. In addition, the fouling tendency was evaluated. Results showed that the addition of chitosan with a mass ratio of 12.5 increased the Cr (VI) rejection from 28% to 75% with a slight reduction in permeate flux from 12.5 L.m−2.h−1 to 9.3 L.m−2.h−1. Moreover, the reduced flux after 100 min of operation could be recovered using the backwash procedure by 89% compared to the initial flux.

Hydrochar effectively removes aqueous Cr(VI) through synergistic adsorption and photoreduction

Photoreduction is recognized as a desirable treatment method for hexavalent chromium Cr(VI) because of the advantages of high efficiency, energy-saving, and environmentally friendly. Herein, three kinds of hydrochars were synthesized by one-step hydrothermal carbonization of agricultural and forestry residuals for synergistic adsorption and photoreduction of Cr(VI). All of them showed relatively strong adsorption capability to Cr(VI). Without illumination, the maximum adsorption capacities of bamboo hydrochar (BHC), cornstalk hydrochar (CHC), and pine wood hydrochar (PHC) were 177.0, 164.2, and 156.5 mg/g, respectively. Moreover, the hydrochars also had excellent photocatalytic properties as indicated by various characterization techniques. Under light irradiation, they created synergistic effects between adsorption and photoreduction to effectively remove Cr(VI) under various conditions. The synergistic removal of Cr(VI) by adsorption and photoreduction in ultrapure water, tap water, and lake water on BHC all reached almost 100% in 40 min. Besides, the photoreduction of Cr(VI) was almost unaffected with various coexisting ions (Cl-, SO42-, PO43-), and the removal rate of Cr(VI) remained above 90% within 60 min after 5 runs of synergistic adsorption-photoreduction. The photocatalytic mechanism suggests that the BHC had suitable band energies which can reduce Cr(VI) to Cr(III) by photo-induced electron. Findings of this study demonstrate that hydrochar is a promising dual-functional material for the treatment of Cr(VI) contaminated water.