scholarly journals Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

2021 ◽  
Vol 11 ◽  
Author(s):  
Zeeshanur Rahman ◽  
Lebin Thomas
Keyword(s):  
Reduction Rate ◽  
Reduction Process ◽  
Electron Donors ◽  
Main Process ◽  
Redox Mediators ◽  
Treatment Practices ◽  
Inorganic Substances ◽  
Comprehensive Information ◽  
High Valence State ◽  
Biological Organisms

Chromium (Cr) (VI) is a well-known toxin to all types of biological organisms. Over the past few decades, many investigators have employed numerous bioprocesses to neutralize the toxic effects of Cr(VI). One of the main process for its treatment is bioreduction into Cr(III). Key to this process is the ability of microbial enzymes, which facilitate the transfer of electrons into the high valence state of the metal that acts as an electron acceptor. Many underlying previous efforts have stressed on the use of different external organic and inorganic substances as electron donors to promote Cr(VI) reduction process by different microorganisms. The use of various redox mediators enabled electron transport facility for extracellular Cr(VI) reduction and accelerated the reaction. Also, many chemicals have employed diverse roles to improve the Cr(VI) reduction process in different microorganisms. The application of aforementioned materials at the contaminated systems has offered a variety of influence on Cr(VI) bioremediation by altering microbial community structures and functions and redox environment. The collective insights suggest that the knowledge of appropriate implementation of suitable nutrients can strongly inspire the Cr(VI) reduction rate and efficiency. However, a comprehensive information on such substances and their roles and biochemical pathways in different microorganisms remains elusive. In this regard, our review sheds light on the contributions of various chemicals as electron donors, redox mediators, cofactors, etc., on microbial Cr(VI) reduction for enhanced treatment practices.

scholarly journals Reduction Mechanism of Fine Hematite Ore Particles in Suspension

2021 ◽  
Author(s):  
Zhiyuan Chen ◽  
Christiaan Zeilstra ◽  
Jan van der Stel ◽  
Jilt Sietsma ◽  
Yongxiang Yang
Keyword(s):  
Particle Size ◽  
Temperature Drop ◽  
Reduction Rate ◽  
Reduction Process ◽  
Reciprocal Relationship ◽  
Drop Tube ◽  
Surface Nucleation ◽  
Order Of Magnitude ◽  
Relationship Of ◽  
Kinetics Of

AbstractIn order to understand the pre-reduction behaviour of fine hematite particles in the HIsarna process, change of morphology, phase and crystallography during the reduction were investigated in the high temperature drop tube furnace. Polycrystalline magnetite shell formed within 200 ms during the reduction. The grain size of the magnetite is in the order of magnitude of 10 µm. Lath magnetite was observed in the partly reduced samples. The grain boundary of magnetite was reduced to molten FeO firstly, and then the particle turned to be a droplet. The Johnson-Mehl-Avrami-Kolmogorov model is proposed to describe the kinetics of the reduction process. Both bulk and surface nucleation occurred during the reduction, which leads to the effect of size on the reduction rate in the nucleation and growth process. As a result, the reduction rate constant of hematite particles increases with the increasing particle size until 85 µm. It then decreases with a reciprocal relationship of the particle size above 85 µm.

Microbial Perchlorate Reduction in Groundwater with Different Electron Donors

2013 ◽  
Vol 295-298 ◽  
pp. 1402-1407
Author(s):  
Rui Wang ◽  
Ming Chen ◽  
Jia Wen Zhang ◽  
Fei Liu ◽  
Hong Han Chen
Keyword(s):  
Removal Efficiency ◽  
Electron Donor ◽  
Electron Acceptor ◽  
Reduction Rate ◽  
Electron Donors ◽  
Monod Equation ◽  
Hydrogen Addition ◽  
Perchlorate Reduction ◽  
Perchlorate Removal

Effects of different electron donors (acetate and hydrogen), acetate and perchlorate concentrations on microbial perchlorate reduction in groundwater were studied. The results showed that acetate and hydrogen addition as an electron donor can significantly improve perchlorate removal efficiency while a longer period was observed for hydrogen (15 d) than for acetate (8 d). The optical ratio of electron donor (acetate)-to-electron acceptor (perchlorate) was approximately 1.65 mg COD mg perchlorate-1. The highest specific reduction rate of perchlorate was achieved at the acetate-to-perchlorate ratio of 3.80 mg COD mg perchlorate-1. The perchlorate reduction rates corresponded well to the theoretical values calculated by the Monod equation and the parameters of Ks and Vm were determined to be 15.6 mg L-1 and 0.26 d-1, respectively.

scholarly journals Electrochemical Removal of Chromium (VI) from Wastewater

2019 ◽  
Author(s):  
Hao Peng ◽  
Yumeng Leng ◽  
Jing Guo
Keyword(s):  
Reaction Temperature ◽  
Current Density ◽  
Reduction Rate ◽  
Reduction Process ◽  
Order Equation ◽  
First Order ◽  
Chromium Vi ◽  
Reduction Efficiency ◽  
Pseudo First Order ◽  
Electrochemical Removal

Removal of hexavalent chromium had attracted much more attention as it was a hazardous contaminant. Electrochemical reduction technology was applied to removal chromium (VI) from wastewater. The mechanism and parameters affect the reduction process were investigated. The results showed that the reduction efficiency was significantly affected by the concentration of H2SO4, current density and reaction temperature. And the reduction efficiency was up to 86.45% at concentration of H2SO4 of 100g/L, reaction temperature of 70 ℃, current density at 50 A/m2, reaction time at 180 min and stirring rate of 500 rpm. The reduction process of chromium (VI) was followed pseudo-first-order equation, and the reduction rate could be expressed as Kobs = k [H2SO4]1• [j] 4•exp-4170/RT.

Influence of Redox Mediators and Electron Donors on the Anaerobic Removal of Color and Chemical Oxygen Demand from Textile Effluent

2013 ◽  
Vol 41 (9) ◽  
pp. 928-933 ◽  
Author(s):  
Sandra M. Amorim ◽  
Mario T. Kato ◽  
Lourdinha Florencio ◽  
Sávia Gavazza
Keyword(s):  
Chemical Oxygen Demand ◽  
Oxygen Demand ◽  
Electron Donors ◽  
Textile Effluent ◽  
Redox Mediators

Experimental process and kinetic behavior of carbothermal reduction of lithium cobaltate as a cathode for waste lithium batteries

2021 ◽  
Vol 11 (12) ◽  
pp. 1988-1996
Author(s):  
Cao Zhi-Kang ◽  
Li Ji-Dong ◽  
Li Zhen ◽  
Wang Xue-Lian ◽  
Yue Ling-Feng
Keyword(s):  
Cathode Material ◽  
Lithium Ion Batteries ◽  
Calcination Temperature ◽  
Carbothermal Reduction ◽  
High Efficiency ◽  
Diffusion Mechanism ◽  
Reduction Rate ◽  
Reduction Process ◽  
Lithium Ion ◽  
Lithium Cobaltate

Lithium cobaltate as a cathode material has great recycling value in the recycling process of spent lithium-ion batteries, To promote the thermal reduction process of lithium cobaltate and recover high-value cobalt and lithium metals, we studied the process of lithium cobaltate reduction by carbon under different conditions and its thermal reaction kinetics. The effects of calcination temperature, raw material ratio, pelletizing pressure and holding time on the reduction rate of lithium cobaltate were investigated by controlling variables. The results showed that the optimum experimental conditions were as follows: mass ratio of carbon and lithium cobaltate was 1:1, pelletizing pressure was 45 MPa, calcination temperature was 800 °C, and calcination time was 6 h. Under these conditions, lithium cobaltate could be converted into cobalt and lithium carbonate, and the recovery rate of cobalt and lithium was 97% and 95%, respectively. A kinetic study on the carbothermal reduction reaction of LiCoO2 showed that the average activation energy of the carbothermal reaction of LiCoO2 under nitrogen protection was 280.6851 kJ/mol, and the mechanism model of the thermal decomposition reaction of LiCoO2 was controlled by chemicals, showing a deceleration curve. The corresponding process conforms to the threedimensional diffusion mechanism of the inverse Jander equation, which lays a theoretical foundation for the high-efficiency separation and recovery of LiCoO2 cathode material for waste lithium-ion batteries.

Enhanced Biotransformation of Dinitrotoluene by Mediator-Functionalized Polypyrrole Composites

2012 ◽  
Vol 610-613 ◽  
pp. 129-132
Author(s):  
Jing Wang ◽  
Guang Fei Liu ◽  
Hong Lu ◽  
Ji Ti Zhou ◽  
Lihua Li
Keyword(s):  
Reduction Rate ◽  
Order Reduction ◽  
Water Soluble ◽  
Redox Mediators ◽  
Globular Structure ◽  
First Order ◽  
Pyrrole Monomer ◽  
Good Catalytic Activity ◽  
Secondary Contamination ◽  
Continuous Dosing

The continuous dosing and discharge of water soluble redox mediators such as biologically recalcitrant compounds will result in the secondary contamination. The immobilized redox mediator prepared by incorporation of anthraquinonedisulphon-ate (AQDS) during the electropolymerization of pyrrole monomer on active carbon felt (ACF), AQDS/PPy/ACF, was used for catalyzing bioreduction of 2,4-dinitrotoluene(2,4-DNT) in this study. The results showed that the morphology of the PPy films deposits on ACF are characterized by some globular structure; AQDS/PPy/ACF exhibited good catalytic activity and stability for 2,4-DNT, the enhanced reduction rates obtained in the incubations with AQDS/PPy/ACF was about 5 times that without AQDS/PPy/ACF, the corresponding first-order reduction rate constant k reached 0.045 h-1; 2,4-DNT was reduced to be 2,4-diaminotoluene via 2-amino-4-nitrotoluene and 4-amino-2-nitrotoluene in the system.

scholarly journals Effect of ionophores on carrier-mediated electron translocation in ferricyanide-containing liposomes

1979 ◽  
Vol 184 (1) ◽  
pp. 125-131 ◽  
Author(s):  
Mette Miller ◽  
Lars Chr. Petersen ◽  
Finn B. Hansen ◽  
Peter Nicholls
Keyword(s):  
Reduction Rate ◽  
Electron Donors ◽  
Oxidation Products ◽  
Ph Gradient ◽  
Ferricyanide Reduction ◽  
Electron Carrier ◽  
Carbonyl Cyanide ◽  
Biochemical Systems ◽  
Stimulation Of

Ferricyanide-containing liposomes were used as a system to compare the electron- and proton-translocating properties of six redox reagents commonly used as electron donors for biochemical systems. The effects of different ionophore combinations on the ferricyanide-reduction rate were generally consistent with the expected proton- and electron-translocating properties of the mediators. The transmembrane pH gradient produced by hydrogen carriers was demonstrated. Nigericin or valinomycin plus carbonyl cyanide p-trifluoromethoxyphenylhydrazone are capable of collapsing this gradient and of stimulating ferricyanide reduction mediated by this type of carrier. No pH gradient is produced with the electron carrier 1,1′-dibutylferrocene. In the presence of tetraphenylboron anion, which is needed for this carrier to act as an efficient mediator, addition of valinomycin alone is sufficient to obtain full stimulation of ferricyanide reduction. NNN′N′-Tetramethyl-p-phenylenediamine does not behave as a simple electron carrier. During NNN′N′-tetramethyl-p-phenylenediamine-mediated ferricyanide reduction protons are translocated across the membrane and accumulated in the vesicles. This is not due to the presence of demethylated impurities in the NNN′N′-tetramethyl-p-phenylenediamine sample, but may be the result of an accumulation of oxidation products other than the Wurster's Blue radical. These results suggest a reconsideration of studies on protonmotive forces across membranes where NNN′N′-tetramethyl-p-phenylenediamine is used as a mediator.

Metallurgical Behavior of Adjusted Converter Slag in Reduction Process

2011 ◽  
Vol 299-300 ◽  
pp. 310-313
Author(s):  
Min Chen ◽  
Zhen Tian ◽  
Qing Xian Yu ◽  
Zhen Feng Gao
Keyword(s):  
Mass Fraction ◽  
Slag Composition ◽  
Converter Slag ◽  
Reduction Rate ◽  
Selective Reduction ◽  
Reduction Process ◽  
Reducing Agent ◽  
Metal Phase ◽  
Reduction Temperature

The metallurgical behavior of adjusted converter slag components during the selective reduction process were investigated by thermodynamic calculating with different modified slag composition, addition of reducing agent and reduction temperature. The activities of main slag components were drawn from the calculated values. The results showed that the activity of SiO2increased with increment of its mass fraction in slag. The solubility of SiO2increased with increment of temperature. The selective reduction was promoted by selecting the appropriate amount of modifier. Reduction order was elucidated in this paper, Fe was reduced from the slag followed by P, Mn and Si and the reduction rate of Si could reach about 51%. The metal phase was rich in Fe, Si, Mn and P as a result of the selective reduction.

scholarly journals Selecting the best electron donor and operational temperature for the rapid biotransformation of the insensitive munitions compound 2,4-dinitroanisole (DNAN) by anaerobic sludge

2021 ◽  
Author(s):  
Natanna Melo ◽  
Osmar Menezes ◽  
Matheus Paraiso ◽  
Lourdinha Florêncio ◽  
Mário T. Kato ◽  
...  
Keyword(s):  
Reduction Rate ◽  
Anaerobic Treatment ◽  
Electron Donors ◽  
Anaerobic Sludge ◽  
Amino Groups ◽  
Manufacturing Plants ◽  
Insensitive Munitions ◽  
Operational Temperature ◽  
Abiotic Controls ◽  
The Military

Abstract 2,4-Dinitroanisole (DNAN) is a toxic compound increasingly used by the military that can be released to the environment on the soil of training fields and in the wastewater of manufacturing plants. DNAN's nitro groups are anaerobically reduced to amino groups by microorganisms when electron donors are available. Using anaerobic sludge as inoculum, we tested different electron donors for DNAN bioreduction at 20 and 30 °C: acetate, ethanol, pyruvate, hydrogen, and hydrogen + pyruvate. Biotic controls without external electron donors and abiotic controls with heat-killed sludge were also assayed. No DNAN conversion was observed in the abiotic controls. In all biotic treatments, DNAN was reduced to 2-methoxy-5-nitroaniline (MENA), which was further reduced to 2,4-diaminoanisole (DAAN). Ethanol or acetate did not increase DNAN reduction rate compared to the endogenous control. The electron donors that caused the fastest DNAN reductions were (rates at 30 °C): H2 and pyruvate combined (311.28 ± 10.02 μM·d−1·gSSV−1), followed by H2 only (207.19 ± 5.95 μM·d−1·gSSV−1), and pyruvate only (36.35 ± 2.95 μM·d−1·gSSV−1). Raising the temperature to 30 °C improved DNAN reduction rates when pyruvate, H2, or H2 + pyruvate were used as electrons donors. Our results can be applied to optimize the anaerobic treatment of DNAN-containing wastewater.

NOx Removal Process by Injection of NH3 and H2O2 in Gas Turbine Exhaust Gas

1979 ◽  
Author(s):  
Y. Hishinuma ◽  
F. Nakajima ◽  
H. Akimoto ◽  
Y. Uchiyama ◽  
S. Azuhata ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Nox Reduction ◽  
Reduction Rate ◽  
Reduction Process ◽  
Heterogeneous Reactions ◽  
High Rate ◽  
Exhaust Gas ◽  
Reduction Of Nox ◽  
Gas Turbine Exhaust ◽  
Turbine Exhaust

For the removal of NOx in a gas turbine exhaust gas, the reduction of NOx with NH3 and H2O2 was studied. It was found that the addition of H2O2 very effectively lowers the reduction temperature of NO with NH3 and that more than 90 percent NOx reduction could be attained at 550 C in the absence of O2. However, the NOx reduction rate decreased with increases in the concentration of O2, and NOx reduction was about 40 to 60 percent under gas turbine exhaust gas condition (15 percent O2). In order to attain a high rate of reduction of NOx, a combined reduction process, which consisted of homogeneous gas phase and the catalytic heterogeneous reactions, was also developed. The efficiency of the new process was proved in a pilot plant using half a size model of a 25-MW gas turbine combustor.

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