High Concentration Cr Research Articles

Precisely constructed core-shell organic/inorganic heterojunction for heightened photoreduction of Cr(VI): Synergy of reinforced interface interaction and high-speed carrier transfer

Photocatalysis technology has been widely studied for treating Cr(VI) pollution in water and constructing heterogeneous structures presents a compelling approach to enhance the efficiency of Cr(VI) treatment. Pitifully, solely utilizing heterostructure, especially random composites of heterogeneous photocatalysts, often falls short of effectively enhancing the separation efficiency of photogenerated carriers. Furthermore, most photocatalysts interact weakly with the Cr(VI) anions, greatly reducing the utilization efficiency of photogenerated carriers. Herein, pyridine-based conjugated imprinted polymer (CIP) photocatalyst was precisely coated on urchin-like TiO2 using an in-situ condensation approach, forming a compact core–shell structure of organic/inorganic heterojunction. On the one hand, the compact heterojunction structure of the core–shell effectively improved the separation efficiency of photogenerated carriers. On the other hand, CIP enhanced the adsorption between the photocatalyst and Cr(VI), effectively improving the utilization efficiency of photogenerated carriers. Due to the collaborative effects of selective adsorption and core–shell heterojunction photocatalysis, the photocatalyst demonstrated remarkable performance in eliminating Cr(VI). For high concentration Cr(VI) pollution of 100 ppm, complete elimination could be achieved within 90 min. This research presented an innovative and efficient approach for the precise synthesis of photocatalysts.

Inhibitory mechanism of Cr(VI) on sulfur-based denitrification: Bio-toxicity, bio-electron characteristics, and microbial evolution

Sulfur-based denitrification is a promising technology for efficient nitrogen removal in low-carbon wastewater, while it is easily affected by toxic substances. This study revealed the inhibitory mechanism of Cr(VI) on thiosulfate-based denitrification, including bio-toxicity and bio-electron characteristics response. The activity of nitrite reductase (NIR) was more sensitive to Cr(VI) than that of nitrate reductase (NAR), and NIR was inhibited by 21.32 % and 19.86 % under 5 and 10 mg/L Cr(VI), resulting in 10.12 and 15.62 mg/L of NO2--N accumulation. The biofilm intercepted 36.57 % of chromium extracellularly by increasing 25.78 % of extracellular polymeric substances, thereby protecting microbes from bio-toxicity under 5 mg/L Cr(VI). However, it was unable to resist 20–30 mg/L of Cr(VI) bio-toxicity as 19.95 and 14.29 mg Cr/(g volatile suspended solids) invaded intracellularly, inducing the accumulation of reactive oxygen species by 165.98 % and 169.12 %, which triggered microbial oxidative-stress and damaged the cells. In terms of electron transfer, S2O32- oxidation was inhibited, and parts of electrons were redirected intracellularly to maintain microbial activity, resulting in insufficient electron donors. Meanwhile, the contents of flavin adenine dinucleotide and cytochrome c decreased under 5–30 mg/L Cr(VI), reducing the electron acquisition rate of denitrification. Thermomonas (the dominant genus) possessed denitrification and Cr(VI) resistance abilities, playing an important role in antioxidant stress and biofilm formation. Environmental ImplicationSulfur-based denitrification (SBD) is a promising method for nitrate removal in low-carbon wastewater, while toxic heavy metals such as Cr(VI) negatively impair denitrification. This study elucidated Cr(VI) inhibitory mechanisms on SBD, including bio-toxicity response, bio-electron characteristics, and microbial community structure. Higher concentrations Cr(VI) led to intracellular invasion and oxidative stress, evidenced by ROS accumulation. Moreover, Cr(VI) disrupted electron flow by inhibiting thiosulfate oxidation and affecting electron acquisition by denitrifying enzymes. This study provided valuable insights into Cr(VI) toxicity, which is of great significance for improving wastewater treatment technologies and maintaining efficient and stable operation of SBD in the face of complex environmental challenges.

A novel quaternary ammonium structure of carbon dots modified TiO2 for fast reduction of Cr(VI) over a wide pH range under sunlight

Cr(VI) pollution in water caused by industrialization poses a serious threat to human health and ecosystems, necessitating a rapid reduction of Cr(VI) treatment method. Therefore, We have established a photocatalytic method for the rapid reduction of Cr(VI) by modifying TiO2 with carbon dots (CPC-CDs) that possess a quaternary ammonium structure in the first time. The CPC-CDs widens the band gap of TiO2 and increases the electrostatic interactions between CPC-CDs/TiO2 and Cr(VI), thus improving the reduction efficiency. CPC-CDs/TiO2 (0.1 g, 2 % CPC-CDs) exhibited excellent reduction performance and fully reduced Cr(VI) (50 mg/L) under neutral conditions within 150 min using a xenon lamp to simulate sunlight. Moreover, CPC-CDs/TiO2 achieved more than 95 % reduction efficiency over a wide pH range (pH = 3, 5, 7, and 9) and showed excellent reduction of Cr(VI) at various concentrations (10, 20, 30, 40 and 50 mg/L). CPC-CDs/TiO2 maintained high Cr(VI) reduction efficiency (93.57 %) after five cycles. Tests under real sunlight revealed that CPC-CDs/TiO2 thoroughly reduced Cr(VI) (10 mg/L) within 30 min, and exhibited excellent structural stability under conditions with interfering ions. Furthermore, CPC-CDs/TiO2 exhibited prominent antibacterial activity against Escherichia coli. In addition, free-radical trapping experiments verified that the superoxide radicals (•O2-) was the main active species. This study aims to overcome the limitations of photocatalytic reduction under conditions of high concentration Cr(VI), neutral and alkaline environments, and natural sunlight, thereby providing technical support for the rapid reduction of Cr(VI).

Enhanced reduction of Cr(VI) in UV/EKR system by organic acids: Focus on Cr(VI) desorption and Fe(III) catalysis

Reducing highly toxic and mobile Cr(VI) to environmentally less hazardous Cr(III) is vital research for remediating Cr-contaminated soil. In this study, a UV/EKR system, which combined electrokinetic remediation (EKR) technology with ultraviolet (UV) photoreduction, was employed to investigate the enhanced reduction of Cr(VI) in actual contaminated soil by oxalic, malic, and tartaric acids. The results demonstrated that the introduction of UV radiation resulted in the removal of 99.49% of Cr(VI) from the anolyte and further enhanced the removal efficiency of high-concentration Cr(VI) in the near-anode soil layer by 14.83% compared to traditional EKR. Among the three acids, malic acid exhibited superior performance, as it alleviated the clogging caused by precipitates, provided more photocatalyst Fe(III), and reduced the retention of the reduction product Cr(III) in the soil. This resulted in the removal rates of 90.38%, 83.82%, and 27.14% of water-soluble, weakly bound, and strongly bound Cr(VI), respectively in the near-anode soil layer. Therefore, the combination of organic acids and the UV/EKR technique shows high compatibility, offering a promising solution to the poor reduction efficiency of Cr(VI) in actual soil in the field of EKR. This approach provides new insights for the in-situ remediation of Cr-contaminated soil.

Synergistic effect of amorphous ZnO/crystalline N-TiO2 interface for photoreduction of high concentration Cr(VI)

Although the synthesis of amorphous/crystalline heterojunction is still difficult due to thermodynamic instability, the introduction of amorphous components not only avoids lattice mismatch but also triggers higher photoelectric activity at the interface, making it particularly attractive. Herein, a novel amorphous ZnO/crystalline N-TiO2 heterojunction (aZn/NT) was firstly synthesized by a simple one-pot synthesis process. Non-specific preparation conditions and inexpensive raw materials [e.g., zinc acetate, bis(ammonium lactate) titanium hydroxide (TALH) and citric acid] are significant indicators of this method. The systematic test shows that the hydrolysis of TALH is independent and precedes the substitution reaction of citric acid to form a composite spherical structure. Different testing methods have shown that the newly formed bonds (Ti-O-N-Zn or Ti-N-O-Zn) between the two components during the hydrothermal process are the basis of the heterostructure association. Moreover, the combination of positively charged surfaces, abundant oxygen vacancy defects, and transport channels accelerates the photoreduction of Cr(VI) on aZn/NT surface. The high catalytic rate [0.022 min−1 for 200 mg L−1 Cr(VI)] and low activity loss rate (∼2.3% within 5 cycles) under optimal conditions indicate that the synthesis of highly active heterogeneous materials can be achieved through a simple path.

Sensitive photocatalytic reduction of high concentration chromium-containing wastewater driven by one-step hydrothermal synthesis of bi-element modified TiO2

N-doped or carbon coated TiO2 often shows excellent visible light response activity and efficient catalytic performance, although its synthesis is usually cumbersome and requires specific conditions. In this paper, a very simple one-step synthesis strategy of N, C co-modified TiO2is firstly presented using only sucrose and titanium(IV) bis(ammonium lactato)dihydroxide (TALH) as raw materials. The hydrolysis of TALH is independent and prior to the carbonization of sucrose, which is the reason for the formation of the core@shell structure. Hydrothermal process promotes the formation of Ti-O-N-C/Ti-N-O-C bonding between core and shell. The directional movement of delocalized electrons in the carbon layer due to bond cooperation leads to the in-situ reduction of Ti4+. Systematic test data prove that the positive charge surface, abundant Ti3+/oxygen vacancy defects and transport channels together accelerate the reduction of Cr(VI) on the surface of N-TiO2-x@C nanocomposite. The optimized catalyst is suitable for high concentration Cr wastewater (0.20 g L-1) in terms of removal rate (0.0503 min−1) and sustainability (more than 90% removal efficient after 5 cycles). The synthesis strategy constructed is novel and valuable for the study of TiO2-based catalysts, because it ensures the treatment of high concentration toxic heavy metal wastewater during the provision of simple, sustainable, safe, and effective modification methods.

2D/2D Transition‐Metal‐Sulfide Self‐Assembly Enables a Huge Tolerance to High Concentration Cr(VI) and a Prominent Photocatalytic Reduction Performance

AbstractTwo‐dimensional (2D) transition‐metal‐sulfides always suffer from poor optical absorption ability, serious photogenerated carrier recombination, and lack of tolerance to high concentration Cr(VI), which limit their wide applications. Herein, 2D MoS2 nanosheets are in situ grown on 2D 5 % Cu‐doped ZnIn2S4 nanosheets to fabricate self‐assembly via a two‐step solvothermal method. The incorporation of Cu broadens the optical response range of self‐assembly and introduces an acceptor trap level that changes the valence band allocation of ZnIn2S4 nanocrystals, which improves the separation and migration of photogenerated electron‐hole pairs. As a result, complete photoreduction of Cr(VI) is surprisingly achieved for 2D/2D self‐assembly MoS2/Cu−ZnIn2S4 in 4 min under visible light irradiation (λ≥400 nm) without sacrificing any agents. Moreover, this self‐assembly is further indicated to have a strikingly huge tolerance to high concentration Cr(VI) (250 mg ⋅ L−1), and the photoreduction activity of Cr(VI) is almost not disturbed by high concentration inorganic ions in wastewater. All these merits demonstrate that 2D/2D transition‐metal‐sulfide self‐assembly may find many practical applications in water cleaning and environmental remediation.

Effects of microplastic combined with Cr(III) on apoptosis and energy pathway of coral endosymbiont.

The combined effect of polyethylene (PE) microplastics and chromium (Cr(III)) on the scleractinian coral Acropora pruinosa (A. pruinosa) was investigated. The endpoints analysed in this study included the endosymbiont density, the chlorophyll a + c content, and the activity of enzymes involved in apoptosis (caspase-1, caspase-3), glycolysis (lactate dehydrogenase, LDH), the pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G6PDH) and electron transfer coenzyme (nicotinamide adenine dinucleotide, NAD+/NADH). During the 7-day exposure to PE and Cr(III) stress, the endosymbiont density and chlorophyll content decreased gradually. The caspase-1 and caspase-3 activities increased in the high-concentration Cr(III) exposure group. Furthermore, the LDH and G6PDH activities decreased significantly, and the NAD+/NADH was decreased significantly. In summary, the results showed that PE and Cr(III) stress inhibited the endosymbiont energy metabolism enzymes and further led to endosymbiont apoptosis in coral. In addition, under exposure to the combination of stressors, when the concentration of Cr(III) remained at 1 × 10-2mg/L, the toxic effects of heavy metals on the endosymbiont were temporarily relieved with elevated PE concentrations. In contrast, when coral polyps were exposed to 5mg/L PE and increasing Cr(III) concentrations, their metabolic activities were seriously disturbed, which increased the burden of energy consumption. In the short term, the toxic effect of Cr(III) was more obvious than that of PE because Cr(III) exposure leads to endosymbiont apoptosis and irreversible damage. This is the first study to provide insights into the combined effect of microplastic and Cr(III) stress on the apoptosis and energy pathways of coral endosymbionts. This study suggested that microplastics combined with Cr(III) are an important factor affecting the apoptosis and energy metabolism of endosymbionts, accelerating the collapse of the balance between the coral host and symbiotic endosymbiont.

In-situ synthesis of CrOx(OH)3-2x for synchronous adsorption of Si and V from high concentration Cr (VI) solution and converted to excellent Cr2O3 pigment

Removing impurities from hexavalent chromium system without secondary pollution is the key to the successful development of green chromate production technology. Here, hydrated chromium oxide CrOx(OH)3-2x with lamellar cluster microsphere structure was prepared by in-situ hydrothermalmethod and used to simultaneously adsorb Si (IV) and V (V) in high concentration Cr (VI) solution. In the in-situ hydrothermal process of pH 7, 160 ℃ for 8 h, the Si (IV) and V (V) removal rates of the actual chromate production Na2Cr2O7-Na2SiO3-NaVO3-H2O solution can reach 92.27 % and 94.81 %, respectively, which is higher than the ex-situ removal efficiency of Si (IV) (62.88 %) and V (V) (63.16 %) under the same conditions. Further characterization of STEM-elemental mapping, XPS and FT-IR results indicate that during in-situ adsorption, Si (IV) and V (V) are mainly adsorbed on the surface of CrOx(OH)3-2X adsorbent by interacting with surface hydroxyl groups. More importantly, the simultaneous formation and adsorption of the adsorbent are more conducive to the full utilization of active adsorption sites on the adsorbent surface. After that, CrOx(OH)3-2x was converted into nano Cr2O3 with a purity of 97.87 % by simple desorption and calcination processes. In addition, the results of UV–vis DRS and SEM show that the residual Si and V elements in Cr2O3 unexpectedly increase the size of the particles to about 300 nm, which redshifts the absorption band of the blue region by 3.3 nm. This results in more red absorption and makes Cr2O3 more yellowish-green and exhibits excellent pigment properties. Thus, the in-situ synthesis, synergistic adsorption and green conversion of trivalent chromium adsorbent provide a promising and sustainable technology for the purification of high concentration Cr (VI) solution that avoids the discharge of Cr (VI) containing slag.

Bioreduction mechanisms of high-concentration hexavalent chromium using sulfur salts by photosynthetic bacteria

Eliminating “sulfur starvation” caused by competition for sulfate transporters between chromate and sulfate is crucial to enhance the content of sulfur-containing compounds and improve the tolerance and reduction capability of Cr(VI) in bacteria. In this study, the effects of sulfur salts on the Cr(VI) bioremediation and the possible mechanism were investigated in Rhodobacter sphaeroides SC01 by cell imaging, spectroscopy, and biochemical measurements. The results showed that, when the concentration of metabisulfite was 2.0 g L−1, and the initial OD600 was 0.33, the reduction rate of R. sphaeroides SC01 reached up to 91.3% for 500 mg L−1 Cr(VI) exposure at 96 h. Moreover, thiosulfate and sulfite also markedly increased the concentration of reduced Cr(VI) in R. sphaeroides SC01. Furthermore, the characterization results revealed that –OH, –CONH, –COOH, –SO3, -PO3, and -S-S- played a major role in the adsorption of Cr, and Cr(III) reduced by bacteria was bioprecipitated in the production of Cr2P3S9 and CrPS4. In addition, R. sphaeroids SC01 combined with metabisulfite significantly increased the activity of glutathione peroxidase and the content of glutathione (GSH) and total sulfhydryl while decreasing reactive oxygen species (ROS) accumulation and cell death induced by Cr(VI) toxic. Overall, the results of this research revealed a highly efficient and reliable strategy for Cr(VI) removal by photosynthetic bacteria combined with sulfur salts in high-concentration Cr(VI)-contaminated wastewater.

Remediation of high-concentration Cr(VI)-contaminated soils with FeSO4 combined with biostimulation: Cr(VI) transformation and stabilization

Efficient and sustainable technologies for cleaning up of hexavalent chromium (Cr(VI)) contaminated soil are under urgent demand. In this study, chemical reduction and biostimulation were combined to remediate contaminated soil with a high concentration of hexavalent Cr(VI) to compensate for the shortcomings of single-treatment technology. The Cr(VI) concentration, Cr speciation, and bacterial diversity of the contaminated soil were measured after combined remediation with ferrous sulfate (FeSO4) and different electron donors. The changes in various indexes in the soil after microbial death were also studied. The results indicated that the optimal reduction rate of Cr(VI) was as high as 95.20% when 10% FeSO4 was combined with lactic acid. The water-soluble fraction of Cr with the highest toxicity in the soil was almost completely converted into other stable fractions. Stabilization experiments proved that Cr(III) in the remediated soil did not revert to Cr(VI) after microorganism death, and had a good stabilization effect. The bacterial diversity results indicated that Acinetobacter spp. and Pseudomonas spp. were the dominant species during the biostimulation process and might be involved in the reduction of Cr(VI).

Acetate improves catalytic performance for rapid removal of Cr(VI) by sodium borohydride in aqueous environments

An efficient method of remediating Cr(VI) involves the conversion of Cr(VI) to Cr(III) using sodium borohydride (NaBH4). However, information regarding the role of organic substances in Cr(VI) remediation is limited. As such, in this study, we aimed to evaluate the role of common low-molecular-weight acetate in the rapid chemical reduction of Cr(VI) by NaBH4 and subsequent total chromium (TCr) removal. The results showed that acetate promoted the transformation of high-concentration Cr(VI) to Cr(III) by NaBH4. The presence of 0–4 mM acetate did not affect the subsequent precipitation of Cr(III). In the presence of 4 mM acetate, Cr(VI) conversion was 99.03%, and subsequent TCr removal was 95.87% within 15 min without adding precipitant. The addition of acetate reduced the requirement for a low initial pH to achieve high Cr(VI) reduction efficiency. In particular, in the presence of 10 mM acetate, the conversion of 100 mg/L Cr(VI) by NaBH4 at an initial pH of 4 was 99.26% compared with 36.89% in the absence of acetate. Regarding the promotion mechanism of acetate for the reduction of Cr(VI) by NaBH4, we did not observe direct electron transfer from acetate to Cr(VI) at the origin of the reduction, but the reduction of Cr(VI) was promoted by inhibiting the production of OH– through buffering. Cr in HCrO4- was the favorable site for nucleophilic reaction, which could be attacked by H- from BH4-. According to the results of qualitative and semiquantitative XPS, Fourier transform infrared spectroscopy, and elemental analyses of sediments, a small amount of Cr(VI) and approximately 3% of acetate was removed through precipitation adsorption by the precipitated Cr(III). This novel acetate–Cr(VI)–NaBH4 remediation technology, which is simple and easy to use, improves the removal of high-concentration Cr(VI) from wastewater.

In-Situ Synthesis of Crox(Oh)3-2x for Synchronous Adsorption of Si and V from High Concentration Cr (Vi) Solution and Converted to Excellent Cr2o3 Pigment

In-Situ Synthesis of Crox(Oh)3-2x for Synchronous Adsorption of Si and V from High Concentration Cr (Vi) Solution and Converted to Excellent Cr2o3 Pigment

Zeolitic imidazolate framework-67 nanocrystal for high concentration Cr(VI) adsorption: a self-sacrifice process

Zeolitic imidazolate framework-67 nanocrystal for high concentration Cr(VI) adsorption: a self-sacrifice process

High efficient adsorption and photocatalytic removal of hexavalent chromium over three-dimensional grapheneoxide aerogel under visible light

<p indent="0mm">Heavy metal ions such as hexavalent chromium (Cr(VI)) existed in wastewater have caused serious pollution problems.Cr(VI) is teratogenic and carcinogenic, while trivalent chromium (Cr(III)) is an essential nutrient for humans and animals. Adsorption method can transfer Cr(VI) from liquid phase to absorbent surface, but it needs follow-up treatment to remove Cr(VI). Photocatalysis technique can reduce Cr(VI) to Cr(III), so as to decrease its toxicity, but the adsorption capacity towards Cr(VI) is always small due to poor surface area of some traditional semiconductor oxide photocatalysts. Therefore, a new material with both good adsorption capacity and photocatalytic activity is needed for Cr(VI) removal. As an emerging kind of carbon materials, graphene oxide (GO) has attracted particular attention in the catalysis field. Graphene oxide aerogel (GOA), a three dimensional nanomaterial, possesses numerous adsorption sites and superior ability to accept and transport photogenerated electrons, would thus present good adsorption capacity and high photocatalytic performance simultaneously. So far, most studies on GO-base material are towards investigating its co-catalyst role (adsorption enhancement or electron shuttle) in improving efficiency of metal or semiconductor photocatalysts. Only a few studies have applied GO-base material as a sole photocatalyst. In this study, combined with the cross-linking method and the supercritical CO₂ fluid extraction method, three-dimensional porous and recyclable GOA with large specific surface area and defect sites was prepared by using GO as the precursor. The physicochemical properties were characterized by SEM, XRD, Raman spectroscopy and nitrogen adsorption methods. The adsorption behavior and photocatalytic reduction performance of GOA towards Cr(VI) under visible light were investigated. GO was hydrothermally reduced during the preparation process, and many defects were generated on GO sheets. Melamine and cyanuric acid were used as crosslinking agents to increase the interlayer spacing, and at the same time providing GOA a large specific surface area and a rich porous structure. When the mass ratio of GO, melamine, and cyanuric acid was 3:3:3 and the GO concentration was 6 mg L⁻¹, GOA exhibited the largest specific surface area and defect density. This kind of GOA, i.e., GOA_333-6 presented the best adsorption capacity and photocatalytic efficiency of Cr(VI). The adsorption behavior of GOA on Cr(VI) fits to the quasi-second-order kinetic model and the Langmuir adsorption isotherm model, indicating that the adsorption process was a single-layer chemical adsorption, in which the intra-particle diffusion in the initial adsorption stage was the rate-limiting step. The three-dimensional graphene oxide aerogel GOA obtained in this study exhibited large adsorption capacity, high photocatalytic removal efficiency for high concentration Cr(VI) under visible light, and good repeatability. Single GOA material has potential application in removing heavy metal ions from polluted wastewater.

Highly efficient removal of Cr(VI) from aqueous solution by pinecone biochar supported nanoscale zero-valent iron coupling with Shewanella oneidensis MR-1

Nanoscale zero-valent iron (nZVI) has been extensively used to remove various pollutants. However, the rapid deactivation due to aggregation and surface passivation severely limits its practical application. In this study, a novel composite with nZVI supported by pinecone biochar (nZVI-PBC) was successfully synthesized and used for the removal of high concentration Cr(VI) from aqueous solution in the presence of Shewanella oneidensis MR-1 (MR-1). The results showed that the nZVI-PBC coupling with MR-1 (nZVI-PBC/MR-1) exhibited an excellent removal performance for high concentration Cr(VI) compared to the nZVI-PBC alone. Under optimal conditions, 100 mg/L Cr(VI) could be removed completely by nZVI-PBC/MR-1 within 48 h, while only 39.50% of Cr(VI) was removed by nZVI-PBC alone. The improvement of Cr(VI) removal is due to the dissolution of the surface passivation layer of nZVI-PBC, formation of sorbed Fe(II) in the presence of MR-1, and an important role of extracellular polymeric substance (EPS) derived from MR-1. X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near-edge structure spectra (XANES) confirmed that most Cr(VI) was reduced to insoluble Cr(III) and formed Cr2O3, CrxFe1-x(OH)3 and FeCr2O4 precipitates, and a small amount of unreduced Cr(VI) was immobilized through adsorption and complexation. The results suggest that nZVI-PBC/MR-1 can effectively overcome the limitations of nZVI and achieve highly efficient removal of high concentration Cr(VI).

A near-zero-waste approach using simple physical-chemical methods recovery high concentrations of ammonia nitrogen, heavy metal, and sodium salts from hazardous vanadium-extracted solution

An integrated simple physical-chemical method was proposed to realize the comprehensive utilization of valuable resources from vanadium-extracted solution. The hazardous vanadium-extracted solution contains high concentrations of Cr(VI), ammonia nitrogen, sodium salt, and silicic acid. Firstly, a series of operations include reduction-precipitation, calcination, and leaching were used to recover high concentration Cr(VI), and 99.96% of Cr(VI) was recovered as chromium oxide with the purity of 97.24%. Optimum conditions for the reduction pH, amount of sodium sulfite, precipitation pH, and precipitation time were 2.0, 1.2 times theoretical, 7.3, and 15 min, respectively. Secondly, clean ammonia nitrogen recovery through waste heat distillation was realized. And the total recovery efficiency of ammonia nitrogen was 95.6% at pH = 11.0, distillation 50 min with 0.5M sulfuric acid as the absorption liquid. Also, the distillation residue sodium sulfate was concentrated and purified by distillation. Finally, all the resources were separated efficiently and could be reused back into the upstream vanadium extraction process, achieving resource recycling. Moreover, material balance, energy analysis and the flow chart of the near-zero-waste approach for resource recycling from the hazardous vanadium-extracted solution were concluded.

Photoinduced Fenton-simulated reduction system based on iron cycle and carbon dioxide radicals production for rapid removal of Cr(VI) from wastewater

For the harmless treatment of oxoanions, reduction approach is thought to be ideal. In this study, a Fenton mode-simulated advanced reduction system was conceived to directly produce highly reductive radical for the rapid removal of high concentration Cr(VI). Oxalate anions could be induced by Fe3+ under light excitation to generate reductive carbon dioxide anion radicals (CO2•-) and Fe2+. Both species could reduce Cr(VI), wherein CO2•- would produce environmentally friendly CO2 while Fe2+ is converted into Fe3+ for next catalytic cycle. Factor tests suggested that the concentration of Fe3+ and oxalate mainly determined the reduction rate and capacity of Cr(VI) respectively. The reduction efficiency could reach almost 100% even within 5 min at 1.0 mM Cr(VI) concentration. The molar ratio of reduced Cr(VI) over provided oxalate always maintained at about 0.35–0.4. More importantly, this system could operate at natural light with a respectable kinetic rate and degrade dye synchronously in Cr(VI) reduction. Furthermore, the continuous treatment of Cr(VI) was achieved through simply adding oxalate. The mechanism was confirmed by electron spin resonance (EPR) experiment and dissolved oxygen was revealed to participate reaction pathway. This system is economical, easy operated and efficient, showing a great practical application potential on oxoanions removal from wastewater.

Long-term adaptive evolution of Shewanella oneidensis MR-1 for establishment of high concentration Cr(VI) tolerance

Acclimation is the main method to enhance the productivity of microorganisms in environmental biotechnology, but it remains uncertain how microorganisms acquire resistance to high concentrations of pollutants during long-term acclimation. Shewanella oneidensis MR-1 was acclimated for 120 days with increasing hexavalent chromium (Cr(VI)) concentrations from 10 to 190 mg/L. The bacterium was able to survive from the highly toxic Cr(VI) environment due to its enhanced capability to reduce Cr(VI) and the increased cell membrane surface. We sequenced 19 complete genomes from 7 populations of MR-1, including the ancestral strain, the evolved strains in Cr(VI) environment on days 40, 80 and 120 and their corresponding controls. A total of 27, 49 and 90 single nucleotide polymorphisms were found in the Cr(VI)-evolved populations on days 40, 80 and 120, respectively. Nonsynonymous substitutions were clustered according to gene functions, and the gene mutations related to integral components of the membrane, including efflux pumps and transporters, were the key determinants of chromate resistance. In addition, MR-1 strengthened the detoxification of Cr(VI) through gene variations involved in adenosine triphosphate binding, electron carrier activity, signal transduction and DNA repair. Our results provide an in-depth analysis of how Cr(VI) resistance of S. oneidensis MR-1 is improved by acclimation, as well as a genetic understanding of the impact of long-term exposure of microorganisms to pollution.

Study on the DNA-protein crosslinks induced by chromium (VI) in SPC-A1

Objective: This study was designed to investigate the effect of chromium (VI) on DNA-protein crosslinks (DPC) of SPC-A1 cells. Methods: We exposed SPC-A1 cells were cultured in 1640 medium and treated with the SPC-A1 cells in vitro to different concentrations of Hexavalent chromium Cr(VI) for 2h, the KC1-SDS precipitation assay were used to measure the DNA-protein cross-linking effect. Results: All the different concentrations of Cr(VI) could cause the increase of DPC coefficient in SPC-A1 cells. But this effect was not significant (P>0.05) at low concentrations; while in high concentration Cr(VI) induced SPC-A1 cells could produce DNA-protein cross-linking effect significantly (P<0.05). Conclusions: chromium (VI) could induce DNA-protein crosslink.