Presence Of Sulfur Compounds Research Articles

New methodology for heavy oil desalination

The salts present in petroleum interfere in the characterization of its physicochemical properties, and from the measurements of these properties is established the price of crude oil. Therefore the water and salt need to be removed before these analyses. A new desalting apparatus was developed for heavy crude oils desalination by using demulsifier with water. The desalination process is accomplished in several washing steps and the extracted oil salts are monitored by ionic conductivity. Operational conditions were studied before and after the desalting process and the following parameters were evaluated: density, kinematic viscosity, total salinity index, total sulfur, total acid number and ionic conductivity. Using the proposed process it was possible to reduce the chloride content in the crude oil to values lower than 43mgkg−1 of sodium chloride in petroleum with extraction efficiency about 99.87%. After the desalination process it was not observed significant changes in the intrinsic oil properties, and after the fourth wash of the oil there was a reduction of approximately 33% of total sulfur and total acid number content. These results indicate an improvement in oil quality, once the presence of sulfur compounds in the oil is undesirable because it increases the polarity of the oil, thereby increasing the polarity of the emulsions. These compounds are also responsible for the corrosivity of the petroleum products and produce harmful gases during combustion. Variations about 2% in API gravity and 3% in kinematic viscosity were not significant, indicating no change in the physical properties of the oils. The proposed procedure is faster (about 80min) than the salt extraction method given by ASTM D6470 (about 140min) for four washing cycles and it was possible to obtain a suitable condition for salt removal from heavy crude oil emulsions without toxic reagents.

Simultaneous N, C, S stable isotope analyses using a new purge and trap elemental analyzer and an isotope ratio mass spectrometer.

The evolution of stable isotope applications has demonstrated the increasing need for the determination of more than one isotopic signature from the same sample. Simultaneous determinations of (13)C/(12)C and (15)N/(14)N have become a widespread technique but up to now very few fully automated systems have offered the possibility of also measuring (34)S/(32)S from the same sample aliquot. This could be critical when sample amounts are limited, but it could also represent a significant gain of analytical time or cost. The technique that we are presenting provides these multiple isotopic signatures on small sample aliquots with high precisions, especially for sulfur determinations. A high-precision, easy and rapid method for the simultaneous measurement of carbon ((13)C/(12)C), nitrogen ((15)N/(14)N) and sulfur ((34)S/(32)S) ratios as well as elemental concentrations was employed, using a new combination of an elemental analyzer and an isotope ratio mass spectrometer. The elemental analyzer was based on 'purge and trap' technology rather than conventional packed-gas chromatography (GC) gas separation. Emphasis was put on the efficiency of the system to reliably combust sulfur-bearing compounds of both organic and inorganic origin with high conversion yields. High-quality measurement of (34)S/(32)S ratios was obtained using various international reference materials. A working calibrated material was also selected and characterized for all three isotopic signatures in order to fully use the capacities of the system in future work. The possibilities of such a system for the reliable measurement of S isotope ratios as well as N and C isotope ratios within the same aliquot of sample opens up new fields of investigation in many domains where multi-isotopic approaches are required.

Effect of sulfur and its compounds on the performance of graphite electrooxidation in molten carbonate

Direct carbon fuel cells are promising power sources with their performance significantly depending on the electrooxidation activity of carbon fuel. The impurities in the carbon fuel may affect the anode reactions. Sulfur and some of its inorganic compounds (CaSO4, K2SO3, K2S, FeS2) were added in molten carbonate and their effect on graphite electrooxidation was investigated. Cyclic voltammograms of gold electrode with addition of these sulfur compounds showed CaSO4 was stable and other compounds were electrochemically oxidized to high valence state sulfur compounds at operating voltage range. Linear sweep voltammetry of graphite with addition of sulfur compounds exhibited enhanced current density compared to pure graphite electrooxidation. Chronoamperometry was carried out to examine steady-state test of graphite electrooxidation in presence of sulfur compounds and the results indicated the enhanced current densities were caused by improved Boudouard reaction for CaSO4 and sulfur electrooxidation for other compounds, respectively. These inorganic sulfur compounds had no impact on electrooxidation process of graphite.

Treatment of a submerged anaerobic membrane bioreactor (SAnMBR) effluent by an activated sludge system: The role of sulphide and thiosulphate in the process

This work studies the use of a well-known and spread activated sludge system (UCT configuration) to treat the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) treating domestic wastewater. Ammonia, phosphate, dissolved methane and sulphide concentrations in the SAnMBR effluent were around 55 mg NH4–N L−1, 7 mg PO4–P L−1, 30 mg non-methane biodegradable COD L−1, and 105 mg S2− L−1 respectively. The results showed a nitrification inhibition caused by the presence of sulphur compounds at any of the solids retention time (SRT) studied (15, 20 and 25 days). This inhibition could be overcome increasing the hydraulic retention time (HRT) from 13 to 26 h. Among the sulphur compounds, sulphide was identified as the substance which caused the nitrification inhibition. When the nitrification was well established, removal rates of nitrogen and phosphorus of 56% and 45% were reached respectively. The sulphide present in the influent was completely oxidised to sulphate, contributing this oxidation to the denitrification process. Moreover, the presence of methanotrophic bacteria, detected by FISH technique, could also contribute to the denitrification.

Multiple sulfur and oxygen isotope compositions in Beijing aerosol

Multiple sulfur isotopes (32S, 33S, 34S, 36S) and oxygen isotopes (16O, 18O) in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The δ 34S values of Beijing aerosol samples range from 1.68‰ to 12.57‰ with an average value of 5.86‰, indicating that the major sulfur source is from direct emission during coal combustion. The δ 18O values vary from -5.29‰ to 9.02‰ with an average value of 5.17‰, revealing that the sulfate in Beijing aerosols is mainly composed of the secondary sulfate. The main heterogeneous oxidation of SO2 in atmosphere is related to H2O2 in July and August, whereas H2O2 oxidation and Fe3+ catalytic oxidation with SO2 exist simultaneously in September and October. Remarkable sulfur isotope mass-independent fractionation effect is found in Beijing aerosols, which is commonly attributed to the photochemical oxidation of SO2 in the stratosphere. In addition, thermochemical reactions of sulfur-bearing compounds might be also a source of sulfur isotope anomalies based on the correlation between Δ33S and CAPE.

Advanced Process Control of Nickel Electrodeposition for Packaging in Semiconductor Industry

Nickel deposit is valued for its barrier properties and is used to separate other deposition layers (i.e.Cu/Sn and Sn Alloys; Cu/Pd; Cu/Au) which would otherwise form intermetallics. It is widely employed in the semiconductor industry for different packaging schemes, e.g. under bump metallization, base layer under noble material for TSV wafer-level packaging. [1]. Semiconductor device must be able to survive extreme temperature swings during multiple cycles of operation. This favors the use of a nickel sulfamate formulation, known for its low deposit stress. The inherently low current efficiency of Ni electrodeposition leads to pitting due to hydrogen bubbles. Tools with horizontal wafer orientation can usually spin off bubbles by fast wafer rotation. Tools with vertical wafer orientation typically require the use of organic surfactants to reduce surface tension and promote the release of bubbles from the surface. Surfactant is removed from the process by drag-out and foaming which requires tight control. Not enough surfactant increases the potential for pitting, while too much can cause inclusion of organics into the deposit which can result in defects and reliability failures by a burn out during heat cycling [2]. One process control option is to measure surface tension. However, this property by itself is not highly selective. The same concentration of surfactant can cause different surface tensions depending on the concentrations of other components. Authors has developed a highly selective and accurate potentiometric titration method to address this process demand. Details of the method will be elaborated in the presentation. Type I Brighteners are typically used for nickel electro-deposition to fine-tune the stress level by incorporating sulfur-bearing compounds into the deposit. The process window for these chemicals is narrower than for surfactants with the potential for out-of- spec related to stress level, deposit purity, and reliability under heat cycling. Traditional metrology for brighteners employs long and hazardous methods such as polarography and HPLC.. A non-reagent, real-time, spectral analytical method was developed by ECI for this application. Sulfamate ion is known to decompose at the anode producing azodisulfonate which itself behaves as a “Type I Brightener” [3]. However, the generation of this compound depends on the type of anodes and whether a membrane is used to separate anode and cathode compartments. Figure 1 shows spectra of the same process solution after operation in different process tools. Acceptable deposition was obtained only in the process tool where azodisulfonate products were detected in the solution. It can be argued that use of these products as an additive is better than lengthy burn-ins to generate these products. The truly unique challenge of nickel deposition for semiconductor packaging is related to the presence of a lithographic photoresist mask on the surface. Ideal positive type photoresist should be fully resistant to solutions in unexposed form but quickly dissolves in developer following UV exposure. In reality, unexposed photoresist is slowly attacked by the hot nickel solution. The presence of photoresist has detrimental effects on the performance of Ni baths. The concentration of leached photoresist is a main limiting factor for electrolyte lifetime. Thus, its metrology becomes crucial to bath dump and/or bleed and feed adjustment. A non-reagent spectroscopy method has been developed by ECI to monitor the accumulation of photoresist (Figure 2). The presentation will show some examples of this method. In conclusion, a comprehensive array of metrology techniques was developed to monitor surfactant, stress controlling compound, and leached photoresist in the nickel electrodeposition processes used in the semiconductor industry.

Extending the analytical window for water-soluble organic matter in sediments by aqueous Soxhlet extraction

Dissolved organic matter (DOM) in marine sediments is a complex mixture of thousands of individual constituents that participate in biogeochemical reactions and serve as substrates for benthic microbes. Knowledge of the molecular composition of DOM is a prerequisite for a comprehensive understanding of the biogeochemical processes in sediments. In this study, interstitial water DOM was extracted with Rhizon samplers from a sediment core from the Black Sea and compared to the corresponding water-extractable organic matter fraction (<0.4μm) obtained by Soxhlet extraction, which mobilizes labile particulate organic matter and DOM. After solid phase extraction (SPE) of DOM, samples were analyzed for the molecular composition by Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry (FT-ICR MS) with electrospray ionization in negative ion mode. The average SPE extraction yield of the dissolved organic carbon (DOC) in interstitial water was 63%, whereas less than 30% of the DOC in Soxhlet-extracted organic matter was recovered. Nevertheless, Soxhlet extraction yielded up to 4.35% of the total sedimentary organic carbon, which is more than 30-times the organic carbon content of the interstitial water. While interstitial water DOM consisted primarily of carbon-, hydrogen- and oxygen-bearing compounds, Soxhlet extracts yielded more complex FT-ICR mass spectra with more peaks and higher abundances of nitrogen- and sulfur-bearing compounds. The molecular composition of both sample types was affected by the geochemical conditions in the sediment; elevated concentrations of HS- promoted the early diagenetic sulfurization of organic matter. The Soxhlet extracts from shallow sediment contained specific three- and four-nitrogen-bearing molecular formulas that were also detected in bacterial cell extracts and presumably represent proteinaceous molecules. These compounds decreased with increasing sediment depth while one- and two-nitrogen-bearing molecules increased, resulting in a higher similarity of both sample types in the deep sediment. In summary, Soxhlet extraction of sediments accessed a larger and more complex pool of organic matter than present in interstitial water DOM.

Removal of elemental mercury from gas stream using sulfur-functionalized silica microspheres (S-SMs)

Silica microspheres (SMs) was synthesized and modified through impregnation with elemental sulfur (S8) and carbon disulfide (CS2) to produce sulfur-functionalized silica microspheres (S-SMs). The morphology of SMs did not change after modification, however, its pore characteristics and sulfur content as expected did change significantly. The elemental mercury adsorption rate and capacity from synthetic gas stream increased with the presence of sulfur compounds in the SMs. For instance, at bed temperature of 50 °C, the adsorption capacity and rate of adsorbents (SMs, S8-SMs and CS2-SMs) were (5.71, 37.24, and 83.41 µg/g) and (0.319, 0.749, and 1.922 µg Hg°/g min), respectively. It was observed that the adsorption rate and the capacity increased with bed temperature only for the SMs, while decreasing for the S-SMs. This might be due to different governing adsorption mechanisms for both types of adsorbents.

Spectroscopic Detection and Structure of Hydroxidooxidosulfur (HOSO) Radical, An Important Intermediate in the Chemistry of Sulfur-Bearing Compounds

The rotational spectrum of hydroxidooxidosulfur, HOSO, an intermediate of particular interest in the combustion of sulfur-rich fuels, has been determined to high accuracy from gas-phase measurements. Detection of specific isotopic species using isotopically enriched gases suggests that HOSO is formed in our discharge nozzle via the reaction H + SO2 (+M) → HOSO (+M). A precise experimental r0 geometry has also been derived from the isotopic analysis; HOSO has a cis configuration, but the subtle structural question of its planarity remains unresolved. From the derived spectroscopic constants, in situ and remote sensing for this fundamental radical can now be undertaken in a variety of environments, including in combustion reactors, the troposphere of Earth, and Io, the innermost Galilean moon of Jupiter.

Gaseous byproducts from high‐temperature thermal conversion elemental analysis of nitrogen‐ and sulfur‐bearing compounds with considerations for δ2H and δ18O analyses

High-temperature, conversion-reduction (HTC) systems convert hydrogen and oxygen in materials into H2 and CO for δ(2)H and δ(18)O measurements by isotope ratio mass spectrometry. HTC of nitrogen- and sulfur-bearing materials produces unintended byproduct gases that could affect isotope analyses by: (1) allowing isotope exchange reactions downstream of the HTC reactor, (2) creating isobaric or co-elution interferences, and (3) causing deterioration of the chromatography. This study characterizes these HTC byproducts. A HTC system (ThermoFinnigan TC/EA) was directly connected to a gas chromatograph/quadrupole mass spectrometer in scan mode (m/z 8 to 88) to identify the volatile products generated by HTC at conversion temperatures of 1350 °C and 1450 °C for a range of nitrogen- and sulfur-bearing solids [keratin powder, horse hair, caffeine, ammonium nitrate, potassium nitrate, ammonium sulfate, urea, and three nitrated organic explosives (PETN, RDX, and TNT)]. The prominent HTC byproduct gases include carbon dioxide, hydrogen cyanide, methane, acetylene, and water for all nitrogen-bearing compounds, as well as carbon disulfide, carbonyl sulfide, and hydrogen sulfide for sulfur-bearing compounds. The 1450 °C reactor temperature reduced the abundance of most byproduct gases, but increased the significant byproduct, hydrogen cyanide. Inclusion of a post-reactor chemical trap containing Ascarite II and Sicapent, in series, eliminated the majority of byproducts. This study identified numerous gaseous HTC byproducts. The potential adverse effects of these gases on isotope ratio analyses are unknown but may be mitigated by higher HTC reactor temperatures and purifying the products with a purge-and-trap system or with chemical traps.

Influence of ozonization on the hydrocarbon composition of raw benzene at coke plants

The influence of ozonization on the composition of raw benzene produced at coke plants is studied. Preliminary ozonization reduces the quantity of unsaturated hydrocarbons and sulfur-bearing compounds and correspondingly the proportion of benzene increases.

Chemical species of sulfur in prostate cancer cells studied by XANES spectroscopy

The role of sulfur in prostate cancer progression may be significant for understanding the process of carcinogenesis. This work, based on X-ray Absorption Near Edge Structure (XANES) spectroscopy, is focused on determination of sulfur chemical species occurring in prostate cancer cell lines. The experimental material consisted of four commercially available cell lines: three from metastasized prostate cancer (PC3, LNCaP, and DU145) and one, used as a control, from the non-tumourigenic peripheral zone of the prostate (PZ-HPV-7). The experiment was performed at the SUL-X beamline of the synchrotron radiation source ANKA, Karlsruhe (Germany). The K-edge XANES spectra of sulfur were analyzed by deconvolution in order to establish sulfur species that occur in prostate cancer cells and to find out whether there are any differences in their content between various cell lines. Experimental spectra were fitted in two ways: with two Gaussian peaks and one arctangent step function, and additionally by a Linear Combination Fit with spectra of reference compounds in order to obtain quantitative chemical information. All fitting procedures were performed with the Athena code (Ravel and Newville, 2005) and the results of deconvolution were used to determine the fraction of each sulfur form. The results of data analysis showed that cell lines from different metastasis had different ratio of reduced to oxidized sulfur species. The LCF analysis demonstrated that the highest content of GSH, one of the most important sulfur-bearing compounds in cells, was observed in DU145 cells. These findings may confirm the hypothesis of changes in redox balance in case of cancer initiation and progression.

EXAFS studies of prostate cancer cell lines

Sulphur plays a vital role in every human organism. It is known, that sulphur-bearing compounds, such as for example cysteine and glutathione, play critical roles in development and progression of many diseases. Any alteration in sulphur's biochemistry could become a precursor of serious pathological conditions. One of such condition is prostate cancer, the most frequently diagnosed malignancy in the western world and the second leading cause of cancer related death in men. The purpose of presented studies was to examine what changes occur in the nearest chemical environment of sulphur in prostate cancer cell lines in comparison to healthy cells. The Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy was used, followed by theoretical calculations. The results of preliminary analysis is presented.

Methionine Metabolism: Major Pathways and Enzymes Involved and Strategies for Control and Diversification of Volatile Sulfur Compounds in Cheese

For economical reasons and to accommodate current market trends, cheese manufacturers and product developers are increasingly interested in controlling cheese flavor formation and developing new flavors. Due to their low detection threshold and diversity, volatile sulfur compounds (VSCs) are of prime importance in the overall flavor of cheese and make a significant contribution to their typical flavors. Thus, the control of VSCs formation offers considerable potential for industrial applications. This paper gives an overview of the main VSCs found in cheese, along with the major pathways and key enzymes leading to the formation of methanethiol from methionine, which is subsequently converted into other sulfur-bearing compounds. As these compounds arise primarily from methionine, the metabolism of this amino acid and its regulation is presented. Attention is focused in the enzymatic potential of lactic acid bacteria (LAB) that are widely used as starter and adjunct cultures in cheese-making. In view of industrial applications, different strategies such as the enhancement of the abilities of LAB to produce high amounts and diversity of VSCs are highlighted as the principal future research trend.

Gradual and stepwise pyrolyses of insoluble organic matter from the Murchison meteorite revealing chemical structure and isotopic distribution

To study the detailed structural and isotopic heterogeneity of the insoluble organic matter (IOM) of the Murchison meteorite, we performed two types of pyrolytic experiments: gradual pyrolysis and stepwise pyrolysis. The pyrolysates from the IOM contained 5 specific organic groups: aliphatic hydrocarbons, aromatic hydrocarbons, sulfur-bearing compounds, nitrogen-bearing compounds, and oxygen-bearing compounds. The release temperatures and the compositions of these pyrolysates demonstrated that the IOM is composed of a thermally unstable part and a thermally stable part. The thermally unstable part mainly served as the linkage and substituent portion that bound the thermally stable part, which was dispersed throughout the IOM. The linkage and substituent portion consisted of aliphatic hydrocarbons from C 4 to C 8, aromatic hydrocarbons with up to 6 rings, sulfo and thiol groups (the main reservoirs of sulfur in the IOM), and carboxyl and hydroxyl groups (the main reservoirs of oxygen). However, the thermally stable part was composed of polycyclic aromatic hydrocarbons (PAHs) containing nitrogen heterocycles in the IOM. Isotopic data showed that the aliphatic and aromatic hydrocarbons in the linkage and substituent portion were rich in D and 13C, while the thermally stable part was deficient in D and 13C. The structural and isotopic features suggested that the IOM was formed by mixing sulfur- and oxygen-bearing compounds rich in D and 13C (e.g., polar compounds in the interstellar medium (ISM)) and nitrogen-bearing PAHs deficient in D and 13C (e.g., polymerized compounds in the ISM).

Electrochemical Behavior of a Glassy Carbon Electrode Chemically Modified with Nickel Pentacyanonitrosylferrate in Presence of Sulfur Compounds

AbstractThe glassy carbon electrode was modified with a nickel pentacyanonitrosylferrate film by electrodeposition of Ni and subsequent derivatization with NaPCNF. The film was characterized by XPS and electrochemical methods. Cyclic voltammetry of the NiPCNF onto the GC shows a redox couple (FeIII/FeII) with E°′ of 538 mV (Ipa/Ipc around 1) and ΔEp of 93 mV in 0.5 mol L−1 KNO3, with a diffusion‐controlled process. There was a decrease of anodic peak currents of the film in the presence of sulfide and 2‐propanethiol due to a precipitation reaction on the film surface by nucleophilic attack.

Pt–Sn/γ-Al 2O 3 and Pt–Sn–Na/γ-Al 2O 3 catalysts for hydrogen production by dehydrogenation of Jet A-1 fuel: Characterisation and preliminary activity tests

The partial dehydrogenation of fuels like diesel or kerosene cuts to produce H 2 is an emerging idea of increasing interest. In the present work the study of the partial dehydrogenation of Jet A-1 fuel on Pt–Sn/γ-Al 2O 3 based catalysts to produce H 2 to feed an on-board (aircraft) proton exchange membrane fuel cell is presented. Extensive physico-chemical characterization of 5% wt.Pt-1% wt.Sn/γ-Al 2O 3 and 5%wt.Pt-1%wt.Sn-1%wt.Na/γ-Al 2O 3 pelleted materials has been performed. A gradient of the active metals from the edge to the centre of the pellet has been observed. A higher concentration of Pt 0 has been detected on the outer part of the pellet than in the inner part, whereas Sn has been detected only on the external part of the pellet. The investigated materials are active as catalysts for the partial dehydrogenation of normal and desulfurised Jet A-1 kerosene fuel. The presence of sulfur compounds and coke deposition strongly affects the H 2 productivity which decreases rapidly with time on stream. The presence of a Na cation addition contributes to give the highest and most sustained H 2 production. The condensed outlet liquid stream retains the fuel properties in the range of the Jet A-1 kerosene fuel. These are encouraging preliminary results, inviting further research; coking and sulfur poisoning as well as identification of appropriate reaction conditions are the main challenges to be overcome in the immediate future.

Prebiotic synthesis of methionine and other sulfur-containing organic compounds on the primitive Earth: a contemporary reassessment based on an unpublished 1958 Stanley Miller experiment.

Original extracts from an unpublished 1958 experiment conducted by the late Stanley L. Miller were recently found and analyzed using modern state-of-the-art analytical methods. The extracts were produced by the action of an electric discharge on a mixture of methane (CH4), hydrogen sulfide (H2S), ammonia (NH3), and carbon dioxide (CO2). Racemic methionine was formed in significant yields, together with other sulfur-bearing organic compounds. The formation of methionine and other compounds from a model prebiotic atmosphere that contained H2S suggests that this type of synthesis is robust under reducing conditions, which may have existed either in the global primitive atmosphere or in localized volcanic environments on the early Earth. The presence of a wide array of sulfur-containing organic compounds produced by the decomposition of methionine and cysteine indicates that in addition to abiotic synthetic processes, degradation of organic compounds on the primordial Earth could have been important in diversifying the inventory of molecules of biochemical significance not readily formed from other abiotic reactions, or derived from extraterrestrial delivery.

BIODESULPHURIZATION WITHIN NATURAL GAS IN OIL AND GAS FIELD

The presence of sulphur compounds in natural gas can interfere to the quality of natural gas. The decline of combustion gas capacity, metal instrument corrosion in gas piping, and the environmental pollution from gas emission can affect by their presence. Bio-filter is one of the methods that selected to reduce sulphur content in natural gas. A lab scale study of hydrogen sulphide reduction in natural gas had conducted in oil and gas field using bio-filter method. The bio-filter system (±1 L volume) contains an active carbon and thiosulphide medium as a substrate, Thiobacillus thioparus as a single culture of sulphur bacteria, and Thiobacillus thioparus with sludge as a mixed culture of sulphur bacteria. The study of hydrogen sulphide reduction was conducted with continuous flow line process. The gas flow rate approximately 1.5 L/min with a fluctuate presence of Hydrogen sulphide (approximately 40 – 70 mg/L). The bio-filter system contains active carbon, thiosulphide medium, and single culture of T. thioparus appear as a good filter for hydrogen sulphide reduction. During 24 hours, the hydrogen sulphide reduction obtains 93% to 16%. When culture media added, the hydrogen sulphide reduction will increase almost 60% and then the reduction decrease to 4% after 20 hours. It is concluded that the bio-filter have potential to develop for sulphur reduction in natural gas.

The behavior of nitrifying sludge in presence of sulfur compounds using a floating biofilm reactor

The tolerance, kinetic and oxidizing capability of a nitrifying sludge exposed to different initial concentrations of sulfide (1.7 to 18mg/L) was evaluated in batch experiments. A nitrifying sludge fed with ammonium and thiosulfate and produced in steady state conditions was used as inoculum. Sulfide induced a significant effect either on ammonium consumption rates or nitrite accumulation. In spite of the nitrifying kinetic was affected, the ammonium consumption efficiencies were close to 100%, with nitrate production yields around 1.0. The IC(50) value for ammonium oxidizing-process was 13mg/L of sulfide. Sulfide was oxidized in two steps: first sulfide was oxidized to elemental sulfur and afterward into sulfate. FISH oligonucleotide probes for Thiobacillusdenitrificans, Nitrosomonas spp., and Nitrobacter spp. were used in order to know if these bacteria were part of the microbial ecology. The obtained results showed that under nitrifying conditions are possible to carry out simultaneously two biological processes, nitrification and sulfur oxidation.