Sulfide Generation Research Articles

Natural occurrence of microbial sulphur oxidation by long-range electron transport in the seafloor

Recently, a novel mode of sulphur oxidation was described in marine sediments, in which sulphide oxidation in deeper anoxic layers was electrically coupled to oxygen reduction at the sediment surface. Subsequent experimental evidence identified that long filamentous bacteria belonging to the family Desulfobulbaceae likely mediated the electron transport across the centimetre-scale distances. Such long-range electron transfer challenges some long-held views in microbial ecology and could have profound implications for sulphur cycling in marine sediments. But, so far, this process of electrogenic sulphur oxidation has been documented only in laboratory experiments and so its imprint on the seafloor remains unknown. Here we show that the geochemical signature of electrogenic sulphur oxidation occurs in a variety of coastal sediment environments, including a salt marsh, a seasonally hypoxic basin, and a subtidal coastal mud plain. In all cases, electrogenic sulphur oxidation was detected together with an abundance of Desulfobulbaceae filaments. Complementary laboratory experiments in intertidal sands demonstrated that mechanical disturbance by bioturbating fauna destroys the electrogenic sulphur oxidation signal. A survey of published geochemical data and 16S rRNA gene sequences identified that electrogenic sulphide oxidation is likely present in a variety of marine sediments with high sulphide generation and restricted bioturbation, such as mangrove swamps, aquaculture areas, seasonally hypoxic basins, cold sulphide seeps and possibly hydrothermal vent environments. This study shows for the first time that electrogenic sulphur oxidation occurs in a wide range of marine sediments and that bioturbation may exert a dominant control on its natural distribution.

A sulfate control on marine mid-depth euxinia on the early Cambrian (ca. 529–521 Ma) Yangtze platform, South China

Given the high oxygen demands of complex metazoans, a sound understanding of marine redox conditions is essential to reconstruct the factors that lead to the dramatic increases in ecosystem complexity and biological diversity in the early Cambrian. In this study, we report new Fe–Mo–C–S geochemical data from black shale-rich strata of the early Cambrian continental margin Yangjiaping section in the Yangtze platform, South China. Integrated Fe speciation and Mo abundance data from the Yangjiaping section, in combination with previously reported data from Shatan (inner shelf), Songtao (slope) and Longbizui (basinal) sections, suggest mid-depth euxinic waters coexisting with ferruginous deep waters and oxic surface waters. This redox structure is similar to conditions previously suggested for the Ediacaran Yangtze platform and other Proterozoic marine basins, indicating that Proterozoic layered ocean redox structure in some basins persisted into the early Cambrian. Furthermore, the Fe–Mo data demonstrate that the mid-depth euxinia was widespread during a marine transgression but shrank gradually along with widespread shelf oxygenation when the basin evolved into subsequent regression.Excess highly reactive iron (FeHR) in deep water with a hydrothermal origin may have had a control on the mid-depth euxinia, given geochemical and geological evidence for basinal hydrothermal activities. On the other hand, a sulfate limitation on bacterial sulfate reduction (BSR) and sulfide generation was suggested by a weak correlation (R2≤0.22) between pyrite iron versus FeHR and total organic carbon (TOC) form anoxic deep-water sections and high TOC (averagely 6%) in the deepest-ferruginous-water Longbizui section. Furthermore, a spatial gradient was observed in sulfur isotopic composition of pyrite (averagely from 0.2‰ to 21.0‰), consistent with a lateral gradient of sulfate in concentration or/and in isotope from shore to distal waters on the transgressive Yangtze platform. We accordingly proposed that two distinct sources – riverine input and ocean reservoir provided sulfate for BSR dominantly in near shore and distal areas, respectively, and the euxinic retreat observed for the regression can be explained as a response to the progressive sulfate consumption of the ocean reservoir by intensive BSR and pyrite formation during preceding transgression. Therefore, our results support a sulfate control on the spatiotemporal distribution of mid-depth marine euxinia on the Yangtze platform in early Cambrian when complex metazoans rapidly evolved.

Clostridia Initiate Heavy Metal Bioremoval in Mixed Sulfidogenic Cultures

Sulfate reducing bacteria (SRB) are widely used for attenuating heavy metal pollution by means of sulfide generation. Due to their low metal tolerance, several SRB species depend on associated bacteria in mixed cultures to cope with metal-induced stress. Yet the identity of the SRB protecting bacteria is largely unknown. We aimed to identify these associated bacteria and their potential role in two highly metal-resistant mixed SRB cultures by comparing bacterial community composition and SRB activity between these cultures and two sensitive ones. The SRB composition in the resistant and sensitive consortia was similar. However, whereas the SRB in the sensitive cultures were strongly inhibited by a mixture of copper, zinc, and iron, no influence of these metals was detected on SRB growth and activity in the resistant cultures. In the latter, a Gram-positive population mostly assigned to Clostridium spp. initiated heavy metal bioremoval based on sulfide generation from components of the medium (mainly sulfite) but not from sulfate. After metal levels were lowered by the Clostridium spp. populations, SRB started sulfate reduction and raised the pH of the medium. The combination of sulfite reducing Clostridium spp. with SRB may improve green technologies for removal of heavy metals.

Abatement of sulfide generation in sewage by glutaraldehyde supplementation and the impact on the activated sludge accordingly

Hydrogen sulfide emission in sewer systems is associated with toxicity, corrosion, odour nuisance and high costs treatment. In this study, a novel method to inhibit sulfide generation from sewage by means of glutaraldehyde supplementation has been suggested and evaluated under anaerobic conditions. Different concentrations of glutaraldehyde at 10, 15, 20, 30 and 40 mg·L−1 have been investigated. Besides, the possible impacts of glutaraldehyde supplementation on an activated sludge system and an appraisal of the economic aspects are presented as well. As observed from the experimental results, a dosage of 20 mg·L−1 glutaraldehyde resulted in a significant decrease of the sulfide production by 70%–80% in the simulated sewage. Moreover, the impacts of additional glutaraldehyde at 20 mg·L−1 on activated sludge, in terms of chemical oxygen demand removal and oxygen uptake rates, were negligible. From an economical point of view, the cost of the commercial glutaraldehyde products required in the operation, which was calculated on the basis of activated sulfide removal avoidance, was around €3.7–4.6 S·kg−1. Therefore it is suggested that glutaraldehyde supplementation is a feasible technique to abate the sulfide problems in sewer systems. Yet further research is required to elucidate the optimum “booster” dosage and the dosing frequency in situ accordingly.

Generation of hydrogen sulfide in the deepest part of a reservoir under anoxic water conditions

The generation of hydrogen sulfide in a reservoir can be characterized by a massive influx of organic matter, manifest thermal stratification, and an extreme anoxic state specifically at the hypolimnion layer in summer. It has been reported that in this deep layer of a thermally stratified water body, where dissolved oxygen is depleted and redox potential falls sharply below the value of zero, the prolonged oxygen-free period and negative redox potential may potentiate the production of toxic hydrogen sulfide. The main aim of this study was to simulate the varying concentration of hydrogen sulfide at the deepest part of the reservoir based on intensive monitoring of water quality parameters. A one-dimensional hydraulic ecosystem model was applied to simulate vertical distribution of dissolved oxygen (DO) continuously in time. Based on the simulated DO, the length of continuous oxygen-free state in the deepest layer was specified and then utilized to estimate the temporal changes of oxidation–reduction potential (ORP) using a polynomial regression model. Finally, a linear regression model for hydrogen sulfide was fitted from the observed ORP, based on which, the temporal changes of hydrogen sulfide concentration were modeled using the simulated ORP. The introduction of several calculations gave good simulated results of hydrogen sulfide concentration, and this approach can be considered useful for predictive and explanatory purposes in further research investigating toxic hydrogen sulfide at the hypolimnion of the reservoir.

Sulphur springs of the Craven Basin, NW England: indicators of natural methane leakage?

Sulphidic springs are a common feature of the Craven Basin and have long histories, indicating that they are natural phenomena, and not a result of recent anthropogenic contamination of groundwater. This study identified several extant sulphur springs and these were sampled and analysed for hydrochemistry and isotopic composition (δ 34 S of sulphate and sulphide, δ 18 O of sulphate and δ 13 C of total dissolved inorganic carbon (TDIC)). The springs are associated with limestone units and are located in anticlinal crests that are sometimes faulted. Sulphide concentrations at these ‘sulphur springs’ range from <0.5 to 96 mg l −1 and light sulphide isotopic compositions indicate that sulphide originates by microbial sulphate reduction. One site, ‘Stinky Bottoms’, with high sulphide concentration (46 mg l −1 ) also has very low δ 13 C-TDIC (–25.3‰ V-PDB) characteristic of a significant component of TDIC generation via methane oxidation. Other sites have δ 13 C-TDIC more typical of shallow groundwaters (−14.2 to −16.3‰ V-PDB) and two sites with highest Cl concentration and elevated Sr:Ca have heavier δ 13 C-TDIC (−11.3 and −6.8‰ V-PDB), indicative of a more evolved, long residence-time brine component. At Stinky Bottoms a strong case can be made that generation of sulphidic groundwater is related to subsurface methane. At other sites, sulphide generation may also be related to hydrocarbon or methane seeps (in some cases associated with a brine component) but the δ 13 C-TDIC values are more equivocal.

廃石膏の硫化水素発生条件に共存する酸化亜鉛，酸化カドミウム，酸化水銀の挙動に関する研究

廃石膏の硫化水素発生条件に共存する酸化亜鉛，酸化カドミウム，酸化水銀の挙動に関する研究

Fe(III) oxides protect fermenter–methanogen syntrophy against interruption by elemental sulfur via stiffening of Fe(II) sulfides produced by sulfur respiration

Thermosipho globiformans (rod-shaped thermophilic fermenter) and Methanocaldococcus jannaschii (coccal hyperthermophilic hydrogenotrophic methanogen) established H2-mediated syntrophy at 68°C, forming exopolysaccharide-based aggregates. Electron microscopy showed that the syntrophic partners connected to each other directly or via intercellular bridges made from flagella, which facilitated transfer of H2. Elemental sulfur (S(0)) interrupted syntrophy; polysulfides abiotically formed from S(0) intercepted electrons that were otherwise transferred to H(+) to produce H2, resulting in the generation of sulfide (sulfur respiration). However, Fe(III) oxides significantly reduced the interruption by S(0), accompanied by stiffening of Fe(II) sulfides produced by the reduction of Fe(III) oxides with the sulfur respiration-generated sulfide. Sea sand replacing Fe(III) oxides failed to generate stiffening or protect the syntrophy. Several experimental results indicated that the stiffening of Fe(II) sulfides shielded the liquid from S(0), resulting in methane production in the liquid. Field-emission scanning electron microscopy showed that the stiffened Fe(II) sulfides formed a network of spiny structures in which the microorganisms were buried. The individual fermenter rods likely produced Fe(II) sulfides on their surface and became local centers of a core of spiny structures, and the connection of these cores formed the network, which was macroscopically recognized as stiffening.

Disturbance of endogenous hydrogen sulfide generation and endoplasmic reticulum stress in hippocampus are involved in homocysteine-induced defect in learning and memory of rats

Homocysteine (Hcy) is a risk factor for Alzheimer's disease (AD). Hydrogen sulfide (H2S) acts as an endogenous neuromodulator and neuroprotectant. It has been shown that endoplasmic reticulum (ER) stress is involved in the pathological mechanisms of the learning and memory dysfunctions and that H2S exerts its neuroprotective role via suppressing ER stress. In the present work, we explored the effects of intracerebroventricular injection of Hcy on the formation of learning and memory, the generation of endogenous H2S, and the expression of ER stress in the hippocampus of rats. We found that intracerebroventricular injection of Hcy in rats leads to learning and memory dysfunctions in the Morris water maze and novel of object recognition test and decreases in the expression of cystathionine-β-synthase, the major enzyme responsible for endogenous H2S generation, and the generation of endogenous H2S in the hippocampus of rats. We also showed that exposure of Hcy could up-regulate the expressions of glucose-regulated protein 78 (GRP78), CHOP, and cleaved caspase-12, which are the major mark proteins of ER stress, in the hippocampus of rats. Taken together, these results suggest that the disturbance of hippocampal endogenous H2S generation and the increase in ER stress in the hippocampus are related to Hcy-induced defect in learning and memory.

Auxin-induced hydrogen sulfide generation is involved in lateral root formation in tomato

Similar to auxin, hydrogen sulfide (H2S), mainly produced by l-cysteine desulfhydrase (DES; EC 4.4.1.1) in plants, could induce lateral root formation. The objective of this study was to test whether H2S is also involved in auxin-induced lateral root development in tomato (Solanum lycopersicum L.) seedlings. We observed that auxin depletion-induced down-regulation of transcripts of SlDES1, decreased DES activity and endogenous H2S contents, and the inhibition of lateral root formation were rescued by sodium hydrosulfide (NaHS, an H2S donor). However, No additive effects were observed when naphthalene acetic acid (NAA) was co-treated with NaHS (lower than 10 mM) in the induction of lateral root formation. Subsequent work revealed that a treatment with NAA or NaHS could simultaneously induce transcripts of SlDES1, DES activity and endogenous H2S contents, and thereafter the stimulation of lateral root formation. It was further confirmed that H2S or HS−, not the other sulfur-containing components derived from NaHS, was attributed to the stimulative action. The inhibition of lateral root formation and decreased of H2S metabolism caused by an H2S scavenger hypotaurine (HT) were reversed by NaHS, but not NAA. Molecular evidence revealed that both NaHS- or NAA-induced modulation of some cell cycle regulatory genes, including the up-regulation of SlCDKA;1, SlCYCA2;1, together with simultaneous down-regulation of SlKRP2, were differentially reversed by HT pretreatment. To summarize, above results clearly suggested that H2S might, at least partially, act as a downstream component of auxin signaling to trigger lateral root formation.

Biocatalysed acidification and metal leaching processes in sediments of polluted urban streams

Sediments of fluvial streams are a sink for pollutants such as heavy metals and organic recalcitrant compounds. In anoxic conditions, sulphide generation and alkalinisation cause precipitation of heavy metals. The redox potential of the system could change to higher values, mainly owing to oxygen exposition generated by anthropogenic disturbances of the sediment such as dredging operations. Knowledge about the mechanisms involved is fundamental to assess the risk of acid generation and rise in heavy metals bioavailability. In this paper, the characterisation and assessment of acidification risk of sediments of a contaminated stream near Buenos Aires was carried out by static and kinetic assays. Speciation of heavy metals was determined after metal sequential extraction procedure. Also, re-suspension of sediments assay in batch mode, with and without Acidithiobacillus ferrooxidans inoculum, was carried out to assess the chemical changes that occur at oxygen exposure, verifying the acidification and heavy metal release processes.

Distribution of Sulfide in an Oil-water Treatment System and a Field Test of Treatment Technology in Daqing Oilfield

In recent years, the sulfide in oil-water treatment system of Daqing Oilfield has brought serious problems, to induce electric dehydrator trip and waste oil recycle difficultly and eventually so severe as to prevent further oil productions. The treatment difficulty of wastewater with sulfide will increase, the oily wastewater after treatment will be deteriorated and induce the formation plugging. Meanwhile, the equipments and pipelines will also be seriously corroded. The authors studied the generation and distribution of sulfide in oil water treatment system in Daqing Oilfield and the field test was conducted in the dewatering and wastewater treatment system based on microbiological method. The results showed that the dynamic microcontrol technology could effectively prevent the generation and accumulation of aging oil, avoid frequent electric dehydrator trip, and decrease the labor quantity to ensure the normal production and meet the dehydration standards. The application of this method would bring better profit and environmental benefits for Daqing Oilfield.

Paragenesis and geochemistry of ore minerals in the epizonal gold deposits of the Yangshan gold belt, West Qinling, China

Six epizonal gold deposits in the 30-km-long Yangshan gold belt, Gansu Province are estimated to contain more than 300 t of gold at an average grade of 4.76 g/t and thus define one of China's largest gold resources. Detailed paragenetic studies have recognized five stages of sulfide mineral precipitation in the deposits of the belt. Syngenetic/diagenetic pyrite (Py0) has a framboidal or colloform texture and is disseminated in the metasedimentary host rocks. Early hydrothermal pyrite (Py1) in quartz veins is disseminated in metasedimentary rocks and dikes and also occurs as semi-massive pyrite aggregates or bedding-parallel pyrite bands in phyllite. The main ore stage pyrite (Py2) commonly overgrows Py1 and is typically associated with main ore stage arsenopyrite (Apy2). Late ore stage pyrite (Py3), arsenopyrite (Apy3), and stibnite occur in quartz ± calcite veins or are disseminated in country rocks. Post-ore stage pyrite (Py4) occurs in quartz ± calcite veins that cut all earlier formed mineralization. Electron probe microanalyses and laser ablation-inductively coupled plasma mass spectrometry analyses reveal that different generations of sulfides have characteristic of major and trace element patterns, which can be used as a proxy for the distinct hydrothermal events. Syngenetic/diagenetic pyrite has high concentrations of As, Au, Bi, Co, Cu, Mn, Ni, Pb, Sb, and Zn. The Py0 also retains a sedimentary Co/Ni ratio, which is distinct from hydrothermal ore-related pyrite. Early hydrothermal Py1 has high contents of Ag, As, Au, Bi, Cu, Fe, Sb, and V, and it reflects elevated levels of these elements in the earliest mineralizing metamorphic fluids. The main ore stage Py2 has a very high content of As (median value of 2.96 wt%) and Au (median value of 47.5 ppm) and slightly elevated Cu, but relatively low values for other trace elements. Arsenic in the main ore stage Py2 occurs in solid solution. Late ore stage Py3, formed coevally with stibnite, contains relatively high As (median value of 1.44 wt%), Au, Fe, Mn, Mo, Sb, and Zn and low Bi, Co, Ni, and Pb. The main ore stage Apy2, compared to late ore stage arsenopyrite, is relatively enriched in As, whereas the later Apy3 has high concentrations of S, Fe, and Sb, which is consistent with element patterns in associated main and late ore stage pyrite generations. Compared with pyrite from other stages, the post-ore stage Py4 has relatively low concentrations of Fe and S, whereas As remains elevated (2.05∼3.20 wt%), which could be interpreted by the substitution of As− for S in the pyrite structure. These results suggest that syngenetic/diagenetic pyrite is the main metal source for the Yangshan gold deposits where such pyrite was metamorphosed at depth below presently exposed levels. The ore-forming elements were concentrated into the hydrothermal fluids during metamorphic devolatilization, and subsequently, during extensive fluid–rock interaction at shallower levels, these elements were precipitated via widespread sulfidation during the main ore stage.

Hierarchical nanostructures of PbS obtained in the presence of water soluble polymers

This study presents the generation of lead sulfide (PbS) nanocrystalline structures in the presence of water soluble polymers with different chemical structures. The PbS films were obtained by electrochemical deposition process on ITO glass substrate. The scanning electron microscopy (SEM) analysis revealed two types of PbS crystalline morphologies that form simultaneously, depending on the chemical structure of the polymer inducing the modification of the crystal growth mechanisms. The X-ray diffraction (XRD) analyses showed that PbS structures presented cubic crystallographic pattern.

Hydrogen sulfide: A multifunctional gaseous molecule in plants

Hydrogen sulfide (H2S), a gaseous transmitter, has long been considered as a phytotoxin, but nowadays as a small molecule with multiple functions fulfilled at low concentrations. H2S has many positive effects on plant growth, development, and the acquisition of plant stress tolerance. The focus of this review is to summarize the generation and properties of hydrogen sulfide and its potential physiological functions, including mediating stomatal movements; mediating the responses to abiotic stressors, such as heavy metals, salt, drought, and heating; involving in organogenesis and growth; regulating senescence; priming seed germination; and enhancing photosynthesis. Future prospects are also presented.

The effects of aerobic/anoxic period sequence on aerobic granulation and COD/N treatment efficiency

The effects of period sequence (anoxic-aerobic and aerobic-anoxic) on aerobic granulation from suspended seed sludge, and COD, N removal efficiencies were investigated in two sequencing batch reactors. More stable granules with greater sizes (1.8-3.5mm) were developed in R1 (anoxic-aerobic sequence). Yet, no significant difference was observed between the reactors in terms of removal efficiencies. Under optimum operational conditions, 92-95% COD, 89-90% TAN and 38-46% total nitrogen removal efficiencies were achieved. The anoxic-aerobic period sequence (R1) resulted in almost complete denitrification during anoxic periods while aerobic-anoxic sequence (R2) led to nitrate accumulation due to limited-carbon source and further granule disintegration. NH3-N concentration of 15-28 mg/L was found to inhibit COD removal up to 30%. This study also revealed the inhibitory sulfide production during anoxic periods. Sulfate concentration of 52.6-70.2mg/L was found to promote sulfate reduction and sulfide generation (0.24-0.62 mg/L) which, together with free-ammonia, inhibited TAN oxidation by 10-50%.

OP09 Sulfide regulates autophagy in Arabidopsis thaliana

In recent years, much progress has been made in understanding the most abundant enzymes involved in the metabolism of cysteine, but little attention has been put on the minor proteins. This is the case of the l -Cysteine desulfhydrase 1 (DES1) located in the cytosol recently identified in Arabidopsis thaliana [1] . DES1 is the only enzyme unequivocally established to be involved in the degradation of cysteine, and therefore responsible for generation of sulfide in this cellular compartment. Although plants have an available source of sulfide within chloroplast, it is present predominantly in the charged form due to the basic stromal pH, and is therefore unable to be released into the cytosol. Mutations of the DES1 gene impede sulfide generation in the cytosol and strongly affect plant metabolism. Detailed characterization of the null mutants has provided insight into the role of sulfide generated from cysteine in the cytosol as a signaling molecule regulating the process of autophagy. This process is an evolutionarily conserved and highly regulated mechanism for recycling intracellular constituents, vital for the growth and development of the plants like other eukaryotic organisms. The most remarkable feature of the autophagy is the formation of vesicles called autophagosomes that engulf the material to be degraded. From all AUTOPHAGY (ATG) proteins that are involved in the autophagy process, ATG8 has been used to monitor autophagic activity because ATG8 is covalently conjugated to a lipid molecule and its lipidation is required for autophagosome formation. DES1 deficiency promotes the accumulation and lipidation of the ATG8 protein, associated with the process of autophagy [2] . In addition, the transcriptional profile of the DES1 null mutant confirms its autophagy-induction phenotype, in which different ATG genes are upregulated. Because mutation of the DES1 gene disrupts sulfide generation in the Arabidopsis cytosol, restoring the capacity of sulfide generation, through exogenous sources or by genetic complementation, eliminates the phenotypic differences of the null mutants from wild-type plants. Interestingly, sulfide is also able to reverse ATG8 protein accumulation and lipidation, even in wild-type plants when autophagy is induced by carbon starvation. Moreover, sulfide inhibits as well the accumulation of GFP-ATG8-tagged vesicles that resemble autophagosomes in Arabidopsis roots after nitrogen starvation. These findings suggest a general effect of sulfide on autophagy regulation that is unrelated to sulfur or nitrogen limitation stress. Therefore, we suggest that cysteine-generated sulfide in the cytosol acts as a negative regulator of the process of autophagy in Arabidopsis and that DES1 is the responsible for modulating this sulfide generation for signaling purposes. To our knowledge this is the first report that show sulfide as a regulator of autophagy in a eukaryotic organism.

OP10 Proteomic analysis of endogenous S-sulfhydration in Arabidopsis thaliana

Hydrogen sulfide has emerged as one of the gaseous transmitter family of signalling molecules and appears to play an important regulatory role in a large array of physiological an pathological processes in mammals [1] . In plants, hydrogen sulfide has been found to mediate increases in tolerance and protection against certain plant stresses and alleviates the inhibitory effects of copper, aluminum and boron stress on wheat germination and cucumber root elongation. Moreover, sulfide treatment improves heat tolerance in tobacco and increases plant resistance against fungal pathogens. In addition, sulfide has been recently discovered as a component of the abscisic acid signalling network in guard cells [2] , [3] . We have recently demonstrated that sulfide exerts a general effect on autophagy through negative regulation, in a way unrelated to nutrient deficiency, and has an important impact on the transcriptional regulation in Arabidopsis. These observations have been genetically linked through the analysis of null mutant alleles of Arabidopsis defective of the cytosolic l -cysteine desulfhydrase DES1 involved in the degradation of cysteine and the generation of hydrogen sulfide in this cellular compartment [4] , [5] . Protein S-sulfhydration of the thiol residue of cysteines has been proposed as a mechanism for transforming the sulfide signal into a biological response in analogy with S-nitrosylation. Selective detection of protein S-sulfhydryl modification has been addressed in mammalian systems by using a modification of the biotin switch technique [6] . By using this method, we have been able to identify 176 S-sulfhydrated proteins (FDR [6] . The effect of sulfide on several enzyme activities is currently under investigation but preliminary data show that sulfide inhibits the enzymatic activity of the glutamine synthetase and this effect can be reverted by reducing agents such as DTT. On the contrary, glyceraldehyde 3 phosphate dehydrogenase increases its activity after sulfide treatment.

In-situ caustic generation from sewage: The impact of caustic strength and sewage composition

Periodic caustic dosage is a commonly used method by the water industry to elevate pH levels and deactivate sewer biofilms responsible for hydrogen sulfide generation. Caustic (NaOH) can be generated in-situ from sewage using a divided electrochemical cell, which avoids the need for transport, handling and storage of concentrated caustic solutions. In this study, we investigated the impact of caustic strength in the cathode compartment and the impact of sodium concentration in sewage on the Coulombic efficiency (CE) for caustic generation. The CE was found to be independent of the caustic strength produced in the range of up to ∼3 wt%. Results showed that a caustic solution of ∼3 wt% could be produced directly from sewage at a CE of up to 75 ± 0.5%. The sodium concentration in sewage had a significant impact on the CE for caustic generation as well as on the energy requirements of the system, with a higher sodium concentration leading to a higher CE and lower energy consumption. The proton, calcium, magnesium and ammonium concentrations in sewage affected the CE for caustic generation, especially at low sodium concentrations. Economical assessment based on the experimental results indicated that sulfide control in sewers using electrochemically-generated caustic from sewage is an economically attractive strategy.

Microcosm assessment of the biogeochemical development of sulfur and oxygen in oil sands fluid fine tailings

Bitumen recovery from Alberta oil sands generates fluid fine tailings, which are retained in tailings ponds where solids settle and release process water. The recovered water is recycled for bitumen extraction, while the resulting tailings are incorporated into various landforms for reclamation, with one option being conversion of tailings basins to viable end pit lakes. Tailings ponds commonly host diverse microbial communities, including SO4-reducing prokaryotes. The highly reducing nature of the hydrogen sulfide produced by these prokaryotes may impact the biogeochemical cycling of key nutrients. However, the behavioral dynamics of hydrogen sulfide production in ponds containing fluid fine tailings remain to be clearly explained. In this study, microcosms are used as analogues of the sediment–water interface of a tailings pond undergoing reclamation to determine sulfide generation patterns and the behavior of O2. In the microcosms, hydrogen sulfide fluxes correlated positively with biotic activity, reaching levels of over 2×103nmolcm−2s−1, leading to Fe sulfide formation. Depth-related hydrogen sulfide profiles in the microcosms were comparable to those encountered in situ, in Syncrude’s West In-Pit, an active tailing pond. Oxygen diffusion across the fluid fine tailing sediment–water interface was controlled to different degrees by both biotic and abiotic processes. The results have implications for quantitatively estimating the impact of hydrogen sulfide production, O2 availability, and biogeochemical cycling of key nutrients important for the success of life in fluid fine tailings-affected ecosystems. This paper shows that this production of hydrogen sulfide may be a self-limiting process, which will begin to decrease after a period of time.