Elemental Sulfur Species Research Articles

Integrated co-cultured bacterial strains capabilities to aqueous sulfide and chemical oxygen demand mitigation from high-strength petroleum refinery wastewater

The heterogeneous nature of petroleum refinery based wastewater (PRW) couple with the documented paucity of the classical physicochemical mitigation approaches were behind the quest for a cost-effective and ecofriendly alternative with minimum negative effects. The toxic and inhibitory substances contained in PRW have made its treatment strenuous using a simple pure culture. A novel integrated bacterial mixed culture (BMC), Pseudomonas putida (ATCC 49128) and Bacillus cereus (ATCC 14579) with traceable imprints in biodegradation of high-strength PRW was proposed as a suitable alternative for sulfide oxidation and COD reduction with a potential alternative to classical physicochemical mitigation approaches. Comparative biodegradation potential of two acclaimed bacteria mixed-culture regimen was evaluated. The degree of inhibition cast was assessed based on the effectiveness of BMC to remove the targeted compounds (aqueous hydrogen sulfide and COD) within the assigned period of 8 hours hydraulic retention time (HRT). The PRW was found to contained initial concentration of 8,155 ppm COD, and 500 ppm sulfide, coupled with other refractory substances. The experiment was repeated batch-wise under defined optimal conditions of 0.25 L/min O2, the temperature of 30oC, agitation of 140 rpm at 8 hours retention time. The results obtained indicated 97.47±1.7 % (mg/L) COD reduction and 99.75±1.8 (ppm) sulfide removal efficiency (RE). In addition, the SEM analysis revealed further the potential of BMC to degrade sulfide from PRW to economically feasible elemental sulfur species, while EDXS demonstrated a proportionate elemental composition revealing appreciable sulfur content and high organic carbon accumulation. Despite the expected toxicity and inhibitory effect of the medium, an overwhelming biodegradation was achieved disproportionately, hence the model can be suggested for further research of repulsive wastewaters.Keywords: Biodegradation, petroleum refinery wastewater, mixed-culture, Batch culture

Enhanced elemental mercury removal by facile sulfurization of agrowaste chars

Facile sulfurization of char from agrowaste of coconut pith (CP) and elemental sulfur was developed towards producing cheaper adsorbents for elemental mercury (Hgº) adsorption. It was found that physicochemical properties of the sulfurized chars changed with the initial CP to elemental sulfur ratio (CPS) and sulfurization temperatures, that generally affected the Hgº adsorption. The CPS ratio of 1:1 and sulfurization temperature of 300 ºC (i.e. CPS300(1:1)) resulted in outstanding Hg° adsorption performance. Characterization of the char indicates the presence of the organic compounds, organic sulfur and elemental sulfur species onto the adsorbents were likely favoring the Hgº adsorption. The adsorption capacity of CPS300(1:1) was higher than 26077.7 μg/g, since the adsorbents still did not reach breakthrough time even after 80 d of adsorption process. The study on the effect of bed temperature found that the adsorbent was still effective in removing Hgº at any temperature (50 ºC to 200 ºC). The sulfurized-char however was non-regenerable.

Optical and structural analysis of ZnS core-shell type nanowires

ZnS core-shell type nanowires were grown by the hot filament chemical vapor deposition technique using ZnS powders as solid source and molecular hydrogen as reactant gas. The growth temperature was varied ranging from 200 to 400 °C. X-ray diffraction patterns and micro-Raman spectra show that the grown material is formed by hexagonal and cubic crystalline ZnS combined phases. Micrographs revealed the formation of nanostructures with a pyramidal morphology ending with long tips. The tip endings measurement gives 600 nm-length and 20 nm-diameter. High resolution images indicate the formation of the core-shell type nanostructures with metallic zinc core and polycrystalline ZnS shell. The photoluminescence spectra of the nanowires are caused by native defects, elemental sulfur species on the surface and structural defects in the nanostructures.

The surface evolution of La0.4Sr0.6TiO3+δ anode in solid oxide fuel cells: Understanding the sulfur-promotion effect

The ideal solid oxide fuel cells (SOFCs) can be powered by readily available hydrocarbon fuels containing impurities. While this is commonly recognized as a key advantage of SOFC, it also, together with the elevated operating temperature, becomes the main barrier impeding the in-situ or operando investigations of the anode surface chemistry. Here, using a well-designed quenching experiment, we managed to characterize the near-surface structure of La0.4Sr0.6TiO3+δ (LST) anode in SOFCs fuelled by H2S-containing methane. This new method enabled us to clearly observe the surface amorphization and sulfidation of LST under simulated SOFC operating conditions. The ∼1 nm-thick two dimensional sulfur-adsorbed layer was on top of the disordered LST, containing –S, –SH and elemental sulfur species. In SOFC test, such “poisoned” anode showed increased performances: a ten-fold enhanced power density enhancement (up to 30 mW cm−2) and an improved open circuit voltage (from 0.69 V to 1.17 V). Moreover, its anodic polarization resistance in methane decreased to 21.53 Ω cm2, a difference of 95% compared with the sulfur-free anode. Control experiments confirmed that once the adsorbed sulfur species were removed electrochemically, methane conversion slowed down simultaneously till full stop.

Comparative Study of Iron and Sulfur Speciation Transformation of Pyrite and Marcasite by Extreme Thermophilic Archaea <i>Acidianus manzaensis</i>

Differential utilization of isomers pyrite and marcasite by Acidianus manzaensis were comparatively studied, besides the iron and sulfur speciation transformation of the minerals was also investigated based on synchrotron radiation X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the biooxidation of pyrite was faster than marcasite. The bioleached surface of both pyrite and marcasite are serious corroded, and the Fe (III)-containing species as well as jarosite were gradually produced, and more elemental sulfur species were formed on the marcasite surface than that for pyrite. It demonstrates the mineral structure does affect the biooxidation of pyrite and marcasite, and the more precipitated elemental sulfur might be one of the reasons leading to lower oxidation rate of marcasite by A. manzaensis.

Differential utilization and speciation transformation of orthorhombic α-S8 and amorphous μ-S by substrate-acclimated mesophilic Acidithiobacillus ferrooxidans

The utilization and speciation transformation of α-S8 and μ-S by the typical mesophilic acidophilic strain Acidithiobacillus ferrooxidans ATCC 23270 were investigated. A. ferrooxidans cells first acclimated to the energy source α-S8 or μ-S, respectively. The results of cell growth and sulfur oxidation behavior showed that the strain grown on α-S8 entered slowly (about 1 d later) into the exponential phase, while grew faster in the exponential phase and attained higher maximal cell density and lower pH value than that on μ-S. After bio-corrosion, both of the two sulfur samples were evidently eroded and modified by A. ferrooxidans cells. After growth of A. ferrooxidans, the surface composition of amorphous μ-S became 63.1% μ-S and 36.9% α-S8, and that of orthorhombic α-S8 became 68.3% α-S8 and 31.7% μ-S, while the surface compositions of α-S8 and μ-S in sterile experiment were not changed, indicating that these two elemental sulfur species can be interconverted by A. ferrooxidans.

Green phosphorescence of zinc sulfide optical ceramics

In the present work, we report a novel luminescent characteristic of the ZnS ceramics. ZnS undoped nanopowders have been synthesized by a wet chemical precipitation method using Na2S as the source of sulfur. Spark plasma sintering (SPS) has been applied to the nanopowders to fabricate dense ZnS ceramics in the pure phase of zinc blende. Photoluminescence (PL) and fluorescence lifetime spectra have been utilized to characterize the luminescent properties of the ZnS ceramics, indicating that these materials exhibit green phosphorescence. In addition, elemental analysis has also been adopted to determine the elemental composition and valency of elements within the ceramic samples. It is concluded that the green phosphorescence results from the presence of elemental sulfur species and Na impurities.

Comparative study of sulfur utilization and speciation transformation of two elemental sulfur species by thermoacidophilic Archaea Acidianus manzaensis YN-25

The sulfur utilization and speciation transformation of two elemental sulfur species (orthorhombic α-S8 and amorphous μ-S) by thermoacidophilic Archaea strain Acidianus manzaensis YN-25 was comparatively studied. The results of cell growth and sulfur oxidation behavior showed that A. manzaensis cultured on μ-S grew faster (about 24h earlier to reach stationary phase than that on α-S8) and produced more H+ and SO42−. Results of scanning electron microscopy indicated that the surfaces of μ-S and α-S8 were differently bio-corroded by A. manzaensis into loose porosities and pits, respectively. Fourier transform-infrared spectroscopy analysis indicated both μ-S and α-S8 were adsorbed by the cells. X-ray diffraction and Raman spectra analysis indicated that μ-S was mostly converted into α-S8 after A. manzaensis cell growth while α-S8 was not transformed into a different allotrope. The fitted result of sulfur K edge XANES spectra further showed that the μ-S after growth of A. manzaensis were composed of 92.1% α-S8 and 7.9% μ-S, while no change in composition for α-S8 was found.

Sulfurization of a carbon surface for vapor phase mercury removal – II: Sulfur forms and mercury uptake

Sulfur forms deposited on carbonaceous surfaces after exposure to hydrogen sulfide were analyzed using XPS and XANES. Higher temperatures promote the formation of organic sulfur and the presence of H 2S during the cooling process increased elemental sulfur content. Temperatures between 400–600 °C were found to be optimal for producing effective mercury uptake sorbents. The increased amount of sulfur deposited during the cooling process in the presence of H 2S was very effective towards Hg uptake in nitrogen. Correlation of mercury uptake capacity and the content of each sulfur form indicated that elemental sulfur, thiophene, and sulfate are likely responsible for mercury uptake, with elemental sulfur species being the most effective.

Temperature-dependent photoluminescence from elemental sulfur species on ZnS nanobelts

We report the experimental study of the temperature-dependent photoluminescence from elemental sulfur species on zinc sulfide nanobelts. The green band emission shows an anomalous blueshift-redshift transition and the half-width undergoes a narrowing-broadening transition with decreasing temperature. We observed that the thermal quenching of the integrated intensity of the green band was suppressed. The anomalous behavior can be attributed to strong carrier localization in the unsaturated dangling orbitals of the elemental sulfur. In addition, the blue band in the undoped ZnS nanobelts is also related to the surface sulfur species that is different from the previously reported self-activation mechanism.

Origin of the green photoluminescence from zinc sulfide nanobelts

ZnS nanobelts with a pure wurtzite phase have been synthesized by a thermal evaporation method with the assistance of H2S in an Ar atmosphere. Photoluminescence band centered at about 535nm has been observed under excitation in the range of 250–480nm with decay rate as short as 860ps. The origin of this intense photoluminescence is related to elemental sulfur species on the surface of the ZnS nanobelts. This assignment is substantiated by structural analysis by high-resolution electron microscopy, x-ray photoelectron spectroscopy, and photoluminescence and excitation technique. ZnS nanobelts with intense surface photoluminescence could be used as effective green light emitters, humid sensors, and UV light detectors.

Effect of pH and Surface Chemistry on the Mechanism of H2S Removal by Activated Carbons

The performances of three wood-based activated carbons as adsorbents of hydrogen sulfide were evaluated by dynamic breakthrough testing. The subsequent products of H2S oxidation on the carbon surfaces were analyzed. The adsorbents were studied using sorption of nitrogen, thermal analysis, Boehm titration, FTIR, ion chromatography, and temperature programmed desorption. Based on the results, the effects of surface chemistry and structural features on the yield of water soluble products and on the regenerability of the exhausted carbons were evaluated. The results showed that the breakthrough capacity and the yield on regeneration depend on the average pH of the carbon surface related to the pH in local pore environment. When the surface is very acidic, the dissociation of H2S is suppressed resulting in a very small concentration of hydrogen sulfide ions and thus in the formation of highly dispersed sulfur. Such conditions are favorable for oxidation of sulfur to S4+ and S6+. When the surface is less acidic the degree of dissociation is higher and the creation of polymeric elemental sulfur species resistant to further oxidation is more favorable. A small increase in pH (half a unit) in the acidic range results in a 15-fold increase in hydrogen sulfide breakthrough capacity accompanied by only a one third decrease in the yield of sulfur oxides.

Evidence of bacterial activity from micrometer-scale layer analyses of black-smoker sulfide structures (Pito Seamount Site, Easter microplate)

We report the observation of an external layer, less than 20 μm thick, attached to hydrothermal chimney fragments of black smokers collected from the Pito Seamount site on the Easter microplate. Scanning electron microscope observations revealed bacterial imprints located on and within the layer, which was associated with underlying layers of thin jarosite deposits and iron sulfides displaying corrosion features. X-ray, electron microprobe, DRIFT and HPLC measurements were used to determine the precise chemical composition and nature of compounds in the layer. The external layer was composed mainly of a combination of hydrated ferric sulfate, ferrous sulfate, iron oxi-hydroxide and elemental sulfur species. A jarosite-like mineral was found deeper in the layer. We suggest that this layer may not be the result of an abiotic thermochemical precipitation, but instead, was formed chemically by bacterial processes. These processes were (1) elemental sulfur oxidation which represents major energetic exchanges within the external layer and (2) bioleaching processes inducing iron oxidation. Originally, elemental sulfur probably resulted from thermochemical precipitation. The results of this study give new insight on the possible role and impact of related acidophilic microorganisms living in hot vent environments of the deep sea.