Investigation of the Degradation of Chelate Complexes in Liquid Redox Desulfurization Processes

Metal complexes such as Fe‐EDTA, which are used as pseudo‐catalysts or oxygen carriers in wet oxidative desulfurization processes, are subject to a degradation mechanism that significantly influences the economics of such processes. Therefore, this study presents a methodology for determining the degree of degradation during the reactive hydrogen sulfide absorption in a Fe‐EDTA solution within a continuously operating semi‐batch reactor system. For this purpose, the reactive conversion of H2S in the liquid phase was used as a reference, and a clear dependence of the degradation on the pH could be shown. In addition, indicators are introduced that evaluate the observed pH dependency of the degradation and distinguish pH‐induced effects such as the pH‐dependent absorption performance of H2S.TU Berlin, Open-Access-Mittel - 202

Evaluation of the Kinetics of Biologically Catalyzed Treatment and Regeneration of NOX Scrubbing Process Waters

A prototype apparatus was configured and operated to evaluate the efficacy of a process that integrates the absorption of nitric oxide in an aqueous solution of ferrous ethylenediamintetraacetic acid (Fe(II)EDTA) with biological treatment and regeneration of spent scrubber water. In addition to operation of a continuous-flow, closed-loop prototype process, a series of batch reactor tests were conducted to investigate the kinetics of microbially-catalyzed reduction of the nitrosyl adduct of ferrous EDTA and microbially-catalyzed reduction of oxidized ferric EDTA. Denitrifying and strictly anaerobic biomass from a municipal wastewater treatment process was cultivated using ethanol as the primary electron donor and nitrate and ferric EDTA as electron acceptors. Following 42-days of bioreactor start-up, nitric oxide (NO) scrubbed from a counter-current absorption tower replaced nitrate. After 27 days of aclimation, an 80-day period of steady state operation was observed. During steady state operation, mean NO scrubbing efficiency of 97.9% was achieved, process water oxidation/reduction potential (ORP) remained between -75 and -140 mV (vs. Ag/AgCl ref.), and generated biogas was 91% N2, by volume. Biomass in the prototype reactor was flocculent, and traveled throughout the closed-loop process. Because of the constant recirculation of washed-out biomass and low observed biomass yield (0.0393 g VSS/g COD), mass balance showed the prototype process sludge age to be 75.9 days. During steady state operation, biomass was extracted for kinetic batch analyses. Batch reactor kinetic tests revealed that both ferric EDTA and NO reduction proceed as a result of microbially-catalyzed reactions. Microbially-catalyzed reduction of ferric EDTA proceeds according to the Monod kinetic model, while strong inhibition of the microbially-catalyzed reduction of NO•Fe(II)EDTA was observed at ethanol concentrations above 0.33 g COD/l. Based on observed population parameters, including biomass yield, endogenous decay, and substrate utilization rate, the critical mean cell retention time below which wash out of a continuously-stirred bioreactor would occur was found to be 11.7 days and 51.4 days for NO reducers and ferric EDTA reducers, respectively. Experimental results provide insight into conditions required for the successful operation of a process for the biological treatment and regeneration of spent scrubber solution from a NOX absorption process

การดูดซึมทางเคมีและจนพลศาสตร์ของการเสื่อมสภาพของไอรอนคีเลทในกระบวนการกำจัดไฮโดรซัลไฟด์

Thesis (Ph.D., Chemical Engineering)--Prince of Songkla University, 201

A review: biological technologies for nitrogen monoxide abatement

David Cubides is a fellow of Eurecat's “Vicente López” PhD grant program. This work was financially supported by the Catalan government through the funding grant ACCIÓ-Eurecat (Project PRIV 2020/21-AIRECAT). The authors acknowledge the Spanish Government, through project RTI 2018-099362-B-C21 MINECO/FEDER, EU, for the financial support provided to perform this research.Peer ReviewedPostprint (published version

Subsurface interactions of actinide species and microorganisms: Implications for the bioremediation of actinide-organic mixtures

We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is a member of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f^1_5/2 and 4f^1_7/2 states. Also, we find that the Fermi surface has a strongly three-dimensional topology, in agreement with density-functional theory calculations.Comment: 7 pages, 4 figure

Innovative Fe(III)-dosed Anaerobic Biological Treatment System: From Fe and S Biogeochemical Reactions to Engineering Process

In moving toward more sustainable wastewater management, anaerobic treatment is gaining increasing popularity due to its simplicity, low energy requirement, low sludge production and less emission of greenhouse gases compared to typical aerobic wastewater treatment systems. Electron acceptors such as nitrate, sulfate, and CO2 have been used in various anaerobic processes for removal of organic matters from wastewater under anoxic or anaerobic environments. In energy producing regions, ferric iron, Fe(III), is a predominant element in iron containing wastes such as acid mine drainage (AMD) and coal ash, which can potentially be used as a source of iron in novel anaerobic wastewater treatment. Such an iron-based treatment approach can offer multi-faceted benefits over existing treatment methods including use of iron-containing wastes, no aeration, unique reaction mechanisms for coagulation, sulfide control, organic micropollutant removal, and useful sludge byproducts. The overall goal of this research was to develop an innovative Fe(III)-dosed anaerobic wastewater treatment process through incorporating known and novel biogeochemical reactions of iron in an engineered biological system. The major research objectives include (1) identifying the critical factors and investigating their effects on the treatment performance of Fe(III)-dosed wastewater treatment; (2) developing a continuous Fe(III)-dosed anaerobic biological treatment system and examining its technical feasibility and potential issues in long-term operations; (3) developing a method for transforming the sludge materials from the Fe(III)-dosed bioreactor into magnetic byproducts; and (4) exploring the applicability of this Fe(III)-dosed treatment method for nutrient removal and recovery. A detail literature review was first conducted to evaluate the suitability of using iron reduction for wastewater treatment and identify critical factors affecting the treatment. Several factors were identified that affect organics oxidation coupled to iron reduction, including the types of the ferric compound, microorganisms, ferric bioavailability and availability of substrate. Amorphous iron materials (e.g. iron sludge from AMD) with large surface areas and high ferric dissolution rates have great potential to be used in Fe(III)-dosed wastewater treatment process to enhance ferric bioavailability to iron reducers. Given the significant levels of sulfate (SO42-) in wastewater, sulfate reduction is expected to be co-occurring with iron reduction in the iron-dosed anaerobic treatment. Shift in microbial composition in relation to ferric and sulfate concentrations (expressed as Fe/S ratio) and their effects on organics removal are important knowledge gaps for developing such treatment technology. In particular, there is a need to understand the nature of the relationships between iron reducing bacteria (IRB) and sulfate reducing bacteria (SRB) (i.e., symbiotic or competitive) to identify optimal operating conditions for this type of wastewater treatment. Batch experiments on iron-dosed anaerobic biological treatment of wastewater under three different molar Fe/S ratios (1, 2 and 3) showed positive correlation between organics (chemical oxygen demand, COD) oxidation rate and Fe/S ratio. Microbiological analysis suggested that both iron reducers and sulfate reducers contributed to this organic oxidation. Maximum COD oxidation rate, Vmax estimated from Michaelis-Menten model ranged from 0.47 mg/L×min to 1.09 mg/L×min as Fe/S ratio increased from 1 to 3. A positive correlation was also observed between COD oxidation rate and the relative abundance of iron reducers, and both increased with the Fe/S ratio. Long-term continuous wastewater treatment using an anaerobic bioreactor dosed with ferric iron showed satisfactory COD removal of 84 ± 4%, 86 ± 4% and 89 ± 2% under Fe/S molar ratio 0.5, 1 and 2 respectively. Fe/S ratio was also observed to regulate the effluent quality by removing excess sulfide from aqueous phase with increasing quantity of ferrous through ferrous sulfide precipitation. The sludge materials contained both biomass (20-40 w/w%) and inorganic precipitates (80-60 w/w%) with the inorganic fraction increasing with Fe/S ratio. Spectroscopic and chemical elemental analyses indicated that the inorganic fraction of the sludge materials mainly contained FeS and FeS2. Microbiological analyses of the sludge materials identified Geobacter sp., Geothrix sp. and Ignavibacteria sp. as putative iron reducers, and Desulfovibrio sp., Desulfobulbus sp., Desulfatirhabdium sp., Desulforhabdus sp. and Desulfomonile sp. as putative sulfate reducers. A simple thermal treatment method was applied to transform the iron sulfide sludge from the bioreactor into magnetic particles. Sludge samples were treated at five different temperatures (300, 350, 400, 450, and 500°C) to evaluate the transformation of iron sulfide sludge into different magnetic phases of iron oxide particles. X-ray Diffraction (XRD) analysis and magnetization measurements showed successful transformation of the sludge to magnetic byproducts and indicated the presence of ferromagnetic magnetite and maghemite phases at different temperatures. The magnetic sludge byproducts have potential applications in biomedicine sector and wastewater treatment (e.g. coagulant, adsorbent). Crystallinity and crystallite size of the thermally derived particles were observed to play a noteworthy role in regulating the magnetization of the byproducts. Adsorption study revealed that both samples baked at 350°C and 500°C had high adsorption capacities to remove phosphate from aqueous solutions. A study to explore applicability of this Fe(III)-dosed treatment process for nutrient removal and recovery was conducted with synthetic wastewater containing typical concentrations of COD (420 mg/L), phosphate (10 mg/L), SO42- (50 mg/L) and ammonium (50 mg/L). Average removal efficiencies of COD, phosphate, SO42- and ammonium were 97 ± 2%, 99.7 ± 0.5%, 87.1 ± 3% and 20.3 ± 9% respectively. The results showed in addition to organics oxidation, significant phosphate and ammonium removals were achieved in the bioreactor. Potential removal mechanisms include chemical precipitation as ferric phosphate (FePO4) or ferrous ammonium phosphate (FAP). SEM-EDS and XPS analysis suggested the presence of FAP in the sludge materials. This innovative treatment process has shown consistent treatment performance and long-term stability under different operating conditions, suggesting its potential for large scale applications. Pilot-scale applications of this treatment approach using iron-containing wastes will give better understanding on the functionality of this process in a field scale environment. Utilizing iron wastes in this novel wastewater treatment process along with recovery of useful sludge byproducts not only can create new avenues to alleviate iron waste disposal, but also improve the sustainability of wastewater treatment

A revised scheme for the reactivity of iron (oxyhydr)oxide minerals towards dissolved sulfide

The reaction between dissolved sulfide and synthetic iron (oxyhydr)oxide minerals was studied in artificial seawater and 0.1 M NaCl at pH 7.5 and 25°C. Electron transfer between surface-complexed sulfide and solid phase Fe(III) results in the oxidation of dissolved sulfide to elemental sulfur, and the subsequent dissolution of the surface-reduced Fe. Sulfide oxidation and Fe(II) dissolution kinetics were evaluated for freshly precipitated hydrous ferric oxide (HFO), lepidocrocite, goethite, magnetite, hematite, and Al-substituted lepidocrocite. Reaction kinetics were expressed in terms of an empirical rate equation of the form: R-i = k(i)(H2S)(t=0)(0.5)A where Ri is the rate of Fe(II) dissolution (RFe) or the rate of sulfide oxidation (RS), ki is the appropriate rate constant (kFe or kS), (H2S)t=0 is the initial dissolved sulfide concentration, and A is the initial mineral surface area. The rate constants derived from the above equation suggest that the reactivity of Fe (oxyhydr)oxide minerals varies over two orders of magnitude, with increasing reactivity in the order, goethite < hematite < magnetite << lepidocrocite ≈ HFO. Competitive adsorption of major seawater solutes has little effect on reaction kinetics for the most reactive minerals, but results in rates which are reduced by 65-80% for goethite, magnetite, and hematite. This decrease in reaction rates likely arises from the blocking of surface sites for sulfide complexation by the adsorption of seawater solutes during the later, slower stages of adsorption (possibly attributable to diffusion into micropores or aggregates). The derivation of half lives for the sulfide-promoted reductive dissolution of Fe (oxyhydr)oxides in seawater, suggests that mineral reactivity can broadly be considered in terms of two mineral groups. Minerals with a lower degree of crystal order (hydrous ferric oxides and lepidocrocite) are reactive on a time-scale of minutes to hours. The more ordered minerals (goethite, magnetite, and hematite) are reactive on a time-scale of tens of days. Substitution of impurities within the mineral structure (as is likely in nature) has an effect on mineral reactivity. However, these effects are unlikely to have a significant impact on the relative reactivities of the two mineral groups

Protein folding, metal ions and conformational states: the case of a di-cluster ferredoxin

Dissertation presented to obtain the PhD degree in Biochemistry at the Instituto de Tecnologia Química e Biológica, Universidade Nova de LisboaMetal ions are present in over thirty percent of known proteins. Apart from a well established function in catalysis and electron transfer, metals and metal centres are also important structural elements which may as well play a key role in modulating protein folding and stability. In this respect, cofactors can act not only as local structural stabilizing elements in the native state, contributing to the maintenance of a given specific structural fold, but may also function as potential nucleation points during the protein folding process...Fundação para a Ciência e Tecnologia is acknowledged for financial support, by awarding a PhD Grant SFRH/BD/18653/2004. This work has been funded by the projects POCTI/QUI/37521; POCTI/QUI/45758 and PTDC/QUI/70101 all to Cláudio M. Gomes

Adsorption of Gold from Thiosulfate Leaching Solutions using Polyethylenimine Functionalised Magnetic Nanoparticles

In this research polyethylenimine coated iron oxide magnetic nanoparticles (PEI-MNPs), as a novel adsorbent, was evaluated for the adsorption of gold from thiosulfate leaching solutions that contain gold, copper and calcium thiosulfate. This novel adsorbent can simply be separated from the solution using an external magnetic field, followed by gold adsorption. Gold elution from the adsorbent was simple and rapid