Catalytic properties of nanofibrous carbon in selective oxidation of hydrogen sulphide

Nanofibrous carbonaceous materials (NFC) as a new class of materials having many applications, can catalyze the selective oxidation of H2S to sulfur. The correlation between NFC structure and its activity and selectivity in H2S oxidation was determined. It is demonstrated that selectivity can be improved if NFC with more ordered structure be synthesized and the portion of the original catalyst in carbon be reduced by increasing the carbon accumulated in the catalyst.

Gene profiling reveals hydrogen sulphide recruits death signaling via the N-methyl-D-aspartate receptor identifying commonalities with excitotoxicity

Recently the role of hydrogen sulphide (H₂S) as a gasotransmitter stimulated wide interest owing to its involvement in Alzheimer's disease and ischemic stroke. Previously we demonstrated the importance of functional ionotropic glutamate receptors (GluRs) by neurons is critical for H₂S-mediated dose- and time-dependent injury. Moreover N-methyl-D-aspartate receptor (NMDAR) antagonists abolished the consequences of H₂S-induced neuronal death. This study focuses on deciphering the downstream effects activation of NMDAR on H₂S-mediated neuronal injury by analyzing the time-course of global gene profiling (5, 15, and 24 h) to provide a comprehensive description of the recruitment of NMDAR-mediated signaling. Microarray analyses were performed on RNA from cultured mouse primary cortical neurons treated with 200 µM sodium hydrosulphide (NaHS) or NMDA over a time-course of 5–24 h. Data were validated via real-time PCR, western blotting, and global proteomic analysis. A substantial overlap of 1649 genes, accounting for over 80% of NMDA global gene profile present in that of H₂S and over 50% vice versa, was observed. Within these commonly occurring genes, the percentage of transcriptional consistency at each time-point ranged from 81 to 97%. Gene families involved included those related to cell death, endoplasmic reticulum stress, calcium homeostasis, cell cycle, heat shock proteins, and chaperones. Examination of genes exclusive to H₂S-mediated injury (43%) revealed extensive dysfunction of the ubiquitin-proteasome system. These data form a foundation for the development of screening platforms and define targets for intervention in H₂S neuropathologies where NMDAR-activated signaling cascades played a substantial role. J. Cell. Physiol. 226: 1308–1322, 2011.

A methodology for simulating hydrogen sulphide generation in sewer network using EPA SWMM

Predicting hydrogen sulphide concentration in sewer network through modelling tools will be beneficial for many stakeholders to design appropriate mitigation strategies. However, the hydrogen sulphide modelling in a sewer network is crucially dependent on the hydraulic modelling of the sewer. The establishment of precise hydrogen sulphide and hydraulic modelling however requires detailed and accurate information about the sewer network structure and the model parameters. This paper outlines a novel approach for the development of hydraulic and hydrogen sulphide modelling to predict the concentration of hydrogen sulphide in sewer network. The approach combines the calculation of wastewater generation and implementation of flow routing on the EPA SWMM 5.0 platform to allow hydrodynamic simulations. Dynamic wave routing is used for hydraulic simulations. It is considered to be the best approach to route existing/old sewer flow. The build-up of hydrogen sulphide model includes the empirical models of hydrogen sulphide generation and emission. Trial of the model was conducted to simulate a sewer network in Seoul, South Korea with some hypothetical data. Further analysis on the use of chemical dosing on the sewer pipe was also performed by the model. Promising results have been obtained through the model, however calibration and validation of the model is required. The presented methodology provides a possibility of the free platform SWMM to be used as a prediction tool of hydrogen sulphide generation. © 2014 © 2014 Balaban Desalination Publications. All rights reserved.

Mitigation strategies of hydrogen sulphide emission in sewer networks - A review

Hydrogen sulphide (H2S) gas emission in sewer networks is associated with several problems including the release of dangerous odour to the atmosphere and sewer pipe corrosion. The release of odour can endanger public health and corrode sewer pipe walls. Sewer corrosion has the potential to cost water utilities millions of dollars to maintain and rehabilitate the affected sewer pipes. Some chemical mitigation strategies to control hydrogen sulphide emission have been introduced. These include but are not limited to the injection of oxygen, magnesium and sodium hydroxide, calcium nitrate and iron salts. The optimisation of the dosing rate and location of each chemical mitigation strategy is required to achieve maximum hydrogen sulphide gas removal efficiency along with cost effectiveness. In this review paper, the five most popular chemical mitigation strategies that were previously mentioned have been investigated and discussed. The article is broken down into three main discussions. Firstly the sewer transformation processes and factors affecting the hydrogen sulphide generation and emission are highlighted. Secondly, comparisons and differences between each selected chemical mitigation strategy as well as its application covered. Finally, the review of the chemical efficiency and cost is conducted by comparing two case studies in controlling the formation of dissolved sulphide. It was found that the injection of oxygen is the cheapest mitigation strategy of hydrogen sulphide gas generation in sewers, but least effective.

Estimating hydrogen sulphide dissipation rate constant under the influence of different chemical dosing

Sewer odour and corrosion is caused by the reduction of sulphide ions and the release of hydrogen sulphide gas (H2S) into the sewer atmosphere. The reduction of sulphide is determined by its dissipation rate which depends on many processes such as emission, oxidation and precipitation that prevail in wastewater environments. Two factors that mainly affect the dissipation of sulphide are sewer hydraulics and wastewater characteristics; modification to the latter by dosing certain chemicals is known as one of the mitigation strategies to control the dissipation of sulphide. This study investigates the dissipation of sulphide in the presence of NaOH, Mg(OH)2, Ca(NO3)2 and FeCl3 and the dissipation rate is developed as a function of hydraulic parameters such as the slope of the sewer and the velocity gradient. Experiments were conducted in a 18m experimental sewer pipe with adjustable slope to which, firstly no chemical was added and secondly each of the above mentioned chemicals was supplemented in turn. A dissipation rate constant of 2×10^-6 for sulphide was obtained from experiments with no chemical addition. This value was then used to predict the sulphide concentration that was responsible for the emission of H2S gas in the presence of one of the above mentioned four chemicals. It was found that the performance of alkali substances (NaOH and Mg(OH)2) in suppressing the H2S gas emission was excellent while ferric chloride showed a moderate mitigating effect due to its slow reaction kinetics. Calcium nitrate was of little value since the wastewater used in this study experienced almost no biological growth. Thus the effectiveness of selected chemicals in suppressing H2S gas emission had the following order: NaOH ≥ Mg(OH)2 ≥ FeCl3 ≥ Ca(NO3)2.

Quantitative examination of carbide and sulphide precipitates in chemically complex steels processed by direct strip casting

A high strength low alloy steel composition has been melted and processed by two different routes: simulated direct strip casting and slow cooled ingot casting. The microstructures were examined with scanning and transmission electron microscopy, atom probe tomography and small angle neutron scattering (SANS). The formation of cementite (Fe3C), manganese sulphides (MnS) and niobium carbo-nitrides (Nb(C,N)) was investigated in both casting conditions. The sulphides were found to be significantly refined by the higher cooling rate, and developed an average diameter of only 100 nm for the fast cooled sample, and a diameter too large to be measured with SANS in the slow cooled condition (> 1.1 μm). Slow cooling resulted in the development of classical Nb(C,N) precipitation, with an average diameter of 7.2 nm. However, after rapid cooling both the SANS and atom probe tomography data indicated that the Nb was retained in the matrix as a random solid solution. There was also some evidence that O, N and S are also retained in solid solution in levels not found during conventional processing.

A sensitive procedure for the rapid determination of arsenic(III) by flow injection analysis and chemiluminescence detection

A novel chemiluminescence flow injection procedure for the determination of As(III) in aqueous samples is described. The method involves injection of As(III) samples into a 1% (m/v) sodium hexametaphosphate in 0.02 M H₂SO₄ carrier stream, which then merges at a Y-piece with a reagent stream consisting of potassium permanganate (5.0 × 10⁻⁵ M) made up in the acidic sodium hexametaphosphate carrier solution. The chemiluminescence intensity of the resulting reaction mixture was measured at a photomultiplier tube operated at a voltage of 0.93 kV. Under optimized conditions, the method is characterised by a linear range from 0.5 to 5.0 μg l⁻¹, a detection limit of 0.3 μg l⁻¹ and a sampling frequency of 150 h⁻¹. The effects of common anionic and cationic interferences were investigated, and it was found that the only ions to cause serious interference were those which react with potassium permanganate, namely sulphide, iodide and ferrous.