Partial Oxidation Of Sulfide Research Articles

Recovery of bio‑sulfur and metal resources from mine wastewater by sulfide biological oxidation-alkali flocculation: A pilot-scale study

Mine wastewater treatment using bio-sulfate reduction technology forms sulfur-containing wastewater that comprises sulfides (HS− and S2−) and metal ions. Bio‑sulfur generated by sulfur-oxidizing bacteria in such wastewater is usually negatively charged hydrocolloidal particles. However, bio‑sulfur and metal resource recovery are difficult using traditional methods. In this study, the sulfide biological oxidation-alkali flocculation (SBO-AF) method was investigated to recover the above resources, and to provide a technical reference for mine wastewater resource recovery and heavy metal pollution control. Specifically, the performance of SBO in forming bio‑sulfur and the key parameters of SBO-AF were explored and then applied in a pilot-scale process to recover resources from wastewater. Results show that partial sulfide oxidation was achieved under a sulfide loading rate of 5.08 ± 0.39 kg/m3·d, dissolved oxygen of 2.9–3.5 mg/L and temperature of 27–30 °C. The average sulfide oxidation rate and sulfur selectivity ratio were 92.86 % and 90.22 %, respectively. At pH 10, metal hydroxide and bio‑sulfur colloids co-precipitated through the precipitation catching and adsorption charge neutralization effect. The average manganese, magnesium and aluminum concentrations and turbidity in the wastewater were 53.93 mg/L, 522.97 mg/L, 34.20 mg/L and 505 NTU, respectively, and decreased to 0.49 mg/L, 80.65 mg/L, 1.00 mg/L and 23.33 NTU, respectively, after treatment. The recovered precipitate mainly contained sulfur, along with metal hydroxides. The average sulfur, manganese, magnesium and aluminum contents were 45.6 %, 29.5 %, 15.1 % and 6.5 %, respectively. Economic feasibility analysis and the above results show that SBO-AF has obvious technical and economic advantages in the recovery resources from mine wastewater.

Elemental sulphur recovery from a sulphate-rich aqueous stream in a single hybrid linear flow channel reactor is mediated through microbial community dynamics and adaptation to reactor zones.

The coupled application of biological sulphate reduction (BSR) and partial sulphide oxidation to treat sulphate-rich wastewater is an effective strategy to mitigate pollution and recover elemental sulphur for repurposing. The recent development of the hybrid linear flow channel reactor (LFCR) achieves simultaneous BSR and partial sulphide oxidation with biosulphur recovery via a floating sulphur biofilm (FSB). Here, we explore the microbial community zoning and dynamics facilitating the process. A total of three continuous LFCRs were used to evaluate the effect of reactor zones, hydraulic residence time (HRT), carbon source, namely lactate and acetate, as well as reactor geometry and scale on process performance and microbial community dynamics. Community composition of sessile and planktonic microbial consortia were resolved at a 5- and 2-day HRT through 16S rRNA amplicon sequencing. Preferential attachment and prevalence of specific phylotypes within the sessile and planktonic communities revealed clear adaptation of key microorganisms to different microenvironments. Key microbial taxa affiliated with sulphate reduction and sulphide oxidation as well as those implicated in fermentation and syntrophic metabolism, fluctuated in response to changes in HRT and process performance. Through understanding the relationship between microbial community dynamics and process performance, this research will inform better process design and optimization of the hybrid LFCR.

Effect of temperature change on the performance of the hybrid linear flow channel reactor and its implications on sulphate-reducing and sulphide-oxidising microbial community dynamics

Semi-passive bioremediation is a promising strategy to mitigate persistent low volume mine-impacted wastewater containing high sulphate concentrations. Building on the proof of concept demonstration of the hybrid linear flow channel reactor (LFCR), capable of simultaneous biological sulphate reduction and partial sulphide oxidation with elemental sulphur recovery, the impact of key operating parameters, such as temperature, on process performance is critical to real-world application. Temperature fluctuates seasonally and across the diurnal cycle, impacting biological sulphate reduction (BSR) and partial sulphide oxidation. The process is reliant on the metabolic activity and synergistic interactions between sulphate-reducing (SRB) and sulphide-oxidising (SOB) microbial communities that develop within discrete oxic and anoxic microenvironments within the hybrid LFCR. In this study, the impact of operating temperature on process performance was evaluated by decreasing temperature with time from 30 to 10°C in each of three laboratory-scaled hybrid LFCR units operating in pseudo-steady state at 1 g/L sulphate. Using lactate as a carbon source, two reactor sizes (2 and 8 L) were considered, while the impact of lactate vs. acetate as carbon source was evaluated in the 2 L reactors. On incremental decrease in temperature from 30 to 10°C, a decrease in volumetric sulphate reduction rate was observed: from 0.144 to 0.059 mmol/L.h in the 2 L lactate-fed reactor; from 0.128 to 0.042 mmol/L.h in the 8 L lactate-fed reactor; and from 0.127 to 0.010 mmol/L.h in the 2 L acetate-fed reactor. Similarly, sulphate conversion efficiency decreased (2 L lactate-fed: 66% to 27%; 8 L lactate-fed: 61% to 20%; 2 L acetate-fed: 61% to 5%). A decrease in temperature below the critical value (15°C) led to considerable loss in metabolic activity and overall BSR performance. Sessile and planktonic microbial communities were represented by bacterial phyla including Proteobacteria, Synergistetes, Bacteroidetes, and Firmicutes. A diverse group of putative SRB (Deltaproteobacteria) and SOB, including Alpha, Beta, Gamma, and Epsilonproteobacteria phylotypes, were prevalent and shifted in relative abundance and community composition in response to decreasing temperature. Specifically, the decrease in the relative abundance of Deltaproteobacteria with decreasing temperature below 15°C corresponded with a loss of BSR performance across all three reactors. This study demonstrated the impact of low temperature on the physiological selection and ecological differentiation of SRB and SOB communities within the hybrid LFCR and its implications for real-world process performance.

Evaluating and modeling biological sulfur production in the treatment of sulfide‐laden streams containing ammonium

AbstractBACKGROUNDBiological treatment of effluents containing H2S and ammonium are of great interest as both can trigger serious environmental problems when disposed of. The aim of this study was to optimize the production of biosulfur from the partial oxidation of sulfide in sulfide‐ and ammonium‐containing streams. Biological performance was evaluated under various aerating conditions and key kinetic parameters were adjusted based on an existing mathematical model adapted to this system.RESULTSAn optimal conversion of sulfide to S0 of 86% (w/w) was found at an oxidation–reduction potential (ORP) of −380 ± 10 mV and at an O2/S2− molar ratio of 0.44. Partial nitrification was observed at ORP higher than −200 mV and in excess of oxygen supply. Sulfide‐oxidizing bacteria (SOB) outcompeted ammonium‐oxidizing bacteria (AOB) in the competition for dissolved oxygen. In a modeling effort, the maximum specific growth rate for SOB, the sulfur shrinking kinetic constant, the maximum specific growth rate for AOB and the AOB oxygen half‐saturation constant were adjusted to 10.1 day−1, 0.3 mg2/3 VSS mg−2/3 S, 1.75 day−1 and 1.5 mg L−1, respectively, during model calibration.CONCLUSIONSOptimal S0 production was found under limiting O2 conditions in which AOB were not able to outcompete SOB. The mathematical model described satisfactorily the experimental profiles for ammonium, nitrite, sulfide and sulfate as a function of the aeration flow rate. © 2020 Society of Chemical Industry (SCI)

Effects of reactor geometry and electron donor on performance of the hybrid linear flow channel reactor

Semi-passive sulphate reducing bioreactors show potential to play an important role in remediation of persistent, low volume acid or neutral rock drainage, characterised by high sulphate concentration. The hybrid linear flow channel reactor (LFCR) integrates biological sulphate reduction and partial sulphide oxidation within a single operating unit, allowing elemental sulphur recovery. Here, the impact of reactor geometry and scale-up of the hybrid LFCR was evaluated. In addition, the use of acetate as an alternative carbon source and electron donor to lactate was investigated. Scale up from 2 to 8 L did not significantly affect process performance over the range of hydraulic residence times tested. A decrease in HRT from 4 to 2 days resulted in an increase in VSRR (2 L: 0.068 to 0.113 mmol/L/h; 8 L: 0.070–0.132 mmol/L/h), coupled with a small decrease in sulphate conversion (2 L: 63–52%; 8 L: 65–61%) in the lactate-fed reactors. This confirmed the consistency of performance across the reactor configurations. On using acetate as a carbon source and electron donor, under optimal conditions, a sulphate conversion efficiency of 64% and a VSRR of 0.069 mmol/L/h was comparable to its lactate-fed equivalent. Unlike the lactate-fed system, disruption or harvesting of the biofilm resulted in a significant decrease in sulphate reduction performance in the acetate system and an extended recovery time.

Effect of hydraulic residence time on biological sulphate reduction and elemental sulphur recovery in a single-stage hybrid linear flow channel reactor

Biological sulphate reduction and partial sulphide oxidation, occurring simultaneously within the hybrid linear flow channel reactor (LFCR) were evaluated, under controlled conditions at laboratory scale, as a function of hydraulic residence time (HRT) using a synthetic media containing 1 g/L sulphate. The hybrid LFCR comprises a rectangular channel containing carbon microfibers as a support matrix for attachment of sulphate-reducing bacteria and an exposed air-liquid interface to facilitate the formation of a floating sulphur biofilm. Exposure to decreasing HRT, from 3 days to 12 h, resulted in an increase in the volumetric sulphate reduction rate (0.14 to 0.63 mmol/L.h), achieving levels typically associated with active reactors. Sulphate conversion was highest (97 %) at a 3 day HRT, decreasing to 73 % at 12 h. The highest sulphide removal efficiency (82 %) and accompanying sulphur recovery through harvesting of the floating sulphur biofilm (FSB) was observed at a 2 day HRT. The sulphur fraction not recovered through the biofilm was predominantly released within the effluent as colloidal elemental sulphur and fragments of the sulphur-rich biofilm, with minimal re-oxidation to sulphate occurring in the reactor. The hybrid LFCR technology was able to achieve high rates of sulphate reduction and effective sulphide removal within a single, semi-passive reactor unit.

Mechanisms of sulfur selection and sulfur secretion in a biological sulfide removal (BISURE) system

Biological desulfurization technology is a sustainable process for the sulfide removal from biogas, which has multiple advantages. In this study, a biological sulfide removal (BISURE) system was established to investigate the working performances and process mechanisms. The results showed that the sulfide removal rate was 2.30 kg-S/(m3 d), the sulfide removal efficiency was higher than 98%, the sulfur production rate was 1.76 kg-S/(m3 d), the sulfur selectivity was 75.02 ± 3.63% and the main form of products (sulfur compounds) was Rosickyite-S and S8. The performance of BISURE system was supported by the dominant genus (abundance more than 60%) of sulfur-oxidizing bacteria (SOB) which shifted to Thiovirga at the high SLR. The sqr and dsrA genes could serve as the indicators for the pathway of two-step sulfide oxidation, i.e. “partial sulfide oxidation (PSO, sulfide → sulfur)” and “complete sulfide oxidation (CSO, sulfur → sulfate)”. The sulfur selectivity was improved by enhancing PSO and inhibiting CSO with the indication of two genes. The cellular sulfur secretion was revealed, and the “outer-membrane vesicles (OMVs)-dependent” sulfur-secreting hypothesis was proposed to explain the transportation of elemental sulfur from inside to outside of SOB cells. The findings of this work provide a new perspective to understand the sulfur selection of sulfide bio-oxidation and the sulfur secretion of SOB cells so as to promote the development of biological desulfurization technology.

Demonstration of simultaneous biological sulphate reduction and partial sulphide oxidation in a hybrid linear flow channel reactor

Semi-passive remediation systems have the potential to treat low-volume, sulphate-rich, mining impacted waters in a sustainable way. This paper describes the “proof of concept” evaluation of a hybrid linear flow channel reactor, capable of efficient biological sulphate reduction and partial oxidation of the sulphide to elemental sulphur. Key elements include a sulphate-reducing microbial community, immobilised onto carbon fibres and the rapid development of a floating sulphur biofilm at the air-liquid interface. The biofilm impedes oxygen mass transfer, creating a suitable pH-redox microenvironment for partial sulphide oxidation. Demonstration of the concept was successful, with near complete sulphate reduction (1 g/L feed), effective sulphide management (95–100 % removal) and partial recovery of sulphur by harvesting the biofilm. The biofilm re-formed within 24 h, with no decrease in volumetric sulphate reduction rate during this period. Colonisation of the carbon microfibers ensured biomass retention, suggesting the reactor could remain effective at high volumetric flow rates.

Generation of zero valent sulfur from dissimilatory sulfate reduction under methanogenic conditions

Dissimilatory sulfate reduction mediated by sulfate-reducing microorganisms (SRMs) has a pivotal role in the sulfur cycle, from which the generation of zero valent sulfur (ZVS) represents a novel pathway. Nonetheless, information on ZVS production from the dissimilatory sulfate reduction remains scarce. This study successfully showed the ZVS production from the dissimilatory sulfate reduction both in a bioreactor and batch experiments under the methanogenic condition. The ZVS was produced in the form of polysulfide and largely located at extracellular sites. In the bioreactor, interestingly, ZVS could be generated first from partial sulfide oxidation mediated by sulfide-oxidizing bacteria (e.g., Thiobacillus) and later from the dissimilatory sulfate reduction in SRMs when changing the reactor operation from anoxic to obligate anaerobic and black condition. In batch experiments, increasing sulfate concentration was shown to enhance ZVS production. Based on these results, together with thermodynamic calculations, a scenario was proposed for the ZVS production from dissimilatory sulfate reduction, in which SRMs might utilize sulfate-to-ZVS as an alternative pathway to sulfate-to-sulfide to increase the thermodynamic favorability and alleviate the inhibitive effects of sulfide. This study expands our understanding of the SRMs-mediated dissimilatory sulfate reduction and may have important implications in environmental bioremediation.

Recovery of elemental sulfur with a novel integrated bioelectrochemical system with an electrochemical cell

Several industrial activities produce wastewater with high sulfate content that can cause significant environmental issues. Although bioelectrochemical systems (BESs) have recently been studied for the treatment of sulfate contained in this wastewater, the recovery of elemental sulfur with BESs is still in its beginnings. This work proposes a new reactor configuration named BES-EC, consisting of the coupling of a BES with an electrochemical cell (EC), to treat this type of wastewater and recover elemental sulfur. The reactor consisted of four electrodes: i) an abiotic anode, ii) a biocathode for the autotrophic sulfate reduction, iii) an anode of an electrochemical cell (EC) for the partial oxidation of sulfide to elemental sulfur (the biocathode and the EC anode were placed in the same chamber) and iv) an abiotic EC cathode. Several cathode potentials and sulfate loads were tested, obtaining high sulfate removal rates (up to 888 mg SO42−-S L−1 d−1 at −0.9 V vs. SHE with a specific energy consumption of 9.18 ± 0.80 kWh kg−1 SO42−-S). Exceptionally high theoretical elemental sulfur production rates (up to 498 mg S0-S L−1 d−1) were achieved with the EC controlled at a current density of 2.5 A m−2. Electron recovery around 80% was observed throughout most of the operation of the integrated system. In addition, short experiments were performed at different current densities, observing that sulfate removal did not increase proportionally to the higher applied current density. However, when the BES was controlled at 30 A m−2 and the EC at 7.5 A m−2, the proportion of elemental sulfur produced corresponded to 92.9 ± 1.9% of all sulfate removed.

Treatment of real flue gas desulfurization wastewater in an autotrophic biocathode in view of elemental sulfur recovery: Microbial communities involved

Sulfur oxide emissions can lead to acidic precipitation and health concerns. Flue gas desulfurization (FGD) systems treat these emissions generating a wastewater with high-sulfate content. This work is the first attempt to treat this effluent with bioelectrochemical systems (BES) in order to recover elemental sulfur, a technology that allows the treatment of several wastewaters that lack of electron donor. The sulfate treatment and elemental sulfur recovery have been studied in a biocathode with simultaneous sulfate reduction to sulfide and partial sulfide oxidation, comparing the performance obtained with synthetic and real wastewater. A decrease of the sulfate removal rate (SRR) from 108 to 73mgS-SO42−L−1d−1 was observed coupled to an increase in the elemental sulfur recovery from 1.4 to 27mgS-S0L−1d−1. This elemental sulfur recovered as a solid from the real wastewater represented a 64% of the theoretical elemental sulfur produced (the elemental sulfur corresponded to a 72% of the solid weight). In addition, microbial communities analysis of the membrane and cathode biofilms and planktonic biomass showed that the real wastewater allowed a higher growth of sulfur oxidizing bacteria (SOB) adapted to more complex waters as Halothiobacillus sp. while decreasing the relative abundance of sulfate reducing bacteria (SRB).

Sulfate reduction processes in salt marshes affected by phosphogypsum: Geochemical influences on contaminant mobility

Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, which suggest partial sulfide oxidation, but marsh may have capacity to buffer potential release of contaminants. The importance of sulfur species was quantitatively confirmed by XANES, which also supports the accuracy of selective extraction schemes. Accordingly, managing pore-water quality through organic carbon-rich amendments over phosphogypsum stacks could lead to a decrease in contaminant loading of leakages resulting from weathering.

Horizontal-flow anaerobic immobilized biomass (HAIB) reactor for organic matter and sulfate removal from paper recycling plant wastewater with simultaneous conversion of sulfide into elemental sulfur

Recycling helps reduce organic matter and sulfur content in effluents from the paper industry, as well as minimize large volumes usually generated, making the anaerobic process a feasible alternative to treat such waste. The objective of this paper is to evaluate simultaneous sulfate and organic matter removal in a bench-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor continuously fed with diluted wastewater from a full paper recycling plant. The reactor was filled with wood charcoal matrices containing immobilized anaerobic sludge. The tested wastewater contained Chemical Oxygen Demand (COD) of 1745 mg L−1 and concentrations of sulfate ranging from 220 (phase 1) to 585 mg L−1 (phase 2). The anaerobic process from paper recycling effluent was followed by partial oxidation of sulfide to elemental sulfur. Sulfate reduction, methanogenesis and effluent desulfurization occurred in the same reactor and were spatially segregated by the plug-flow regime. The investigated HAIB reactor anaerobically removed organic matter and sulfate at high removal efficiencies (>90%), converting about 30% of the inconvenient dissolved sulfide to elemental sulfur. Therefore, integrated sulfate reduction and elemental sulfur production, as presented herein, can be considered an attractive component for sustainable wastewater treatment.

A hybrid membrane gas absorption and bio-oxidation process for the removal of hydrogen sulfide from biogas

A study was conducted on hydrogen sulfide (H2S) removal from biogas using a novel hybrid polydimethylsiloxane (PDMS) membrane bioscrubber. The effect of absorption liquid pH, biogas flowrate and DO concentration on H2S selectivity, removal efficiency and sulfide oxidation were investigated. The process performance at pH 7 was better than pH 8.5 in terms of H2S removal capacity and selectivity. Desulfurization selectivity of H2S/CO2 and H2S/CH4 increased along with the increase of gas flowrate (32 l/d) and reached 3.5 and 63, respectively. The calorific value of the biogas significantly increased due to the raising of CH4 content by 21%. During the long-term operation, air diffusion through the membrane into the biogas was not observed. Almost complete H2S removal (>97%) and high conversion ratio to So (>74%) were achieved when volumetric loading rate and DO concentration were kept below 148 g H2S/m3d and 1 mg/l, respectively. Partial oxidation of sulfide to So (1 mg/l) rather than sulfate (4 mg/l) reduced the caustic consumption by half. Even though So and inorganics were detected on membrane surface with SEM-EDS analysis, fouling and wetting problems were not observed. The novel hybrid process developed in this study is a cost-effective and robust alternative to conventional biogas desulfurization.

Sulfide-oxidizing bacteria establishment in an innovative microaerobic reactor with an internal silicone membrane for sulfur recovery from wastewater.

A novel bioreactor, employing a silicone membrane for microaeration, was studied for partial sulfide oxidation to elemental sulfur. The objective of this study was to assess the feasibility of using an internal silicone membrane reactor (ISMR) to treat dissolved sulfide and to characterize its microbial community. The ISMR is an effective system to eliminate sulfide produced in anaerobic reactors. Sulfide removal efficiencies reached 96% in a combined anaerobic/microaerobic reactor and significant sulfate production did not occur. The oxygen transfer was strongly influenced by air pressure and flow. Pyrosequencing analysis indicated various sulfide-oxidizing bacteria (SOB) affiliated to the species Acidithiobacillus thiooxidans, Sulfuricurvum kujiense and Pseudomonas stutzeri attached to the membrane and also indicated similarity between the biomass deposited on the membrane wall and the biomass drawn from the material support, supported the establishment of SOB in an anaerobic sludge under microaerobic conditions. Furthermore, these results showed that the reactor configuration can develop SOB under microaerobic conditions and can improve and reestablish the sulfide conversion to elemental sulfur.

Sulfur Recovery from Wastewater Using a Micro-aerobic External Silicone Membrane Reactor (ESMR)

Sulfide, found in some wastewaters and industrial off-gases, is a toxic and highly corrosive pollutant, especially in wastewater applications. Sulfide removal was studied in a new sulfide-oxidizing reactor (External Silicone Membrane Reactor—ESMR) that employs a tubular silicone rubber membrane for micro-aeration. The chemical and biological sulfide oxidation at pH 8.0, 9.0, and 10.0 were investigated. The applied velocity (V s) in the membrane was also investigated as a system control parameter. The local overall mass transfer coefficient (R) was estimated for the tubular silicone rubber membrane and had an average value of 0.153 m.h−1. Oxygen mass transfer was found to not be influenced by the applied velocity. The sulfide oxidation to sulfate could be partially avoided and the biotic tests showed larger sulfur aggregates deposited in the silicone membrane, which could easily be washed away upon flushing. By contrast, colloidal sulfur formation observed in the chemical oxidation assays was harder to separate from the liquid phase. This study reveals that the ESMR is a suitable reactor design to promote partial sulfide oxidation because it provides an adequate oxygen supply with minimized aeration costs.

Factors affecting crystallization of copper sulfide in fed-batch fluidized bed reactor

This work has assessed factors affecting crystallization of copper sulfide (CuS) under batch conditions and in fed-batch fluidized bed reactor (FBR) using calcium-coated sands as a seed material. Compared with using sodium sulfide nonahydrate as a sulfidation reagent, larger CuS crystals were produced from sodium sulfide pentahydrate, most likely because of the lower surface charge. Due to the partial oxidation of sulfide in the pentahydrate form, the optimum molar ratio of Cu2+ to S2− was found to be 1:2, higher than the theoretical ratio. Crystal growth and aggregation were further increased by using calcium ion as a cross-linker among the CuS fines (<100nm), resulting in an additional 30% decrease in Cu2+ concentrations from the effluent of fed-batch FBR. The efficacy of CuS crystallization was also remarkably dependent on the operating factors, i.e., the resting height of the seed material and recirculation rate. Under optimal conditions, >95% of the initial Cu2+ (100mgCu2+/L) was successfully transformed to CuS crystals within 120min. The size and crystallinity of the star-shaped CuS crystals were confirmed by FEG–SEM and XRD analyses, respectively. Principal component analysis indicated that the resting height and the seed type were the primary parameters affecting CuS crystallization in the fed-batch FBR.

Microbiological analysis of the population of extremely haloalkaliphilic sulfur-oxidizing bacteria dominating in lab-scale sulfide-removing bioreactors

Thiopaq biotechnology for partial sulfide oxidation to elemental sulfur is an efficient way to remove H2S from biogases. However, its application for high-pressure natural gas desulfurization needs upgrading. Particularly, an increase in alkalinity of the scrubbing liquid is required. Therefore, the feasibility of sulfide oxidation into elemental sulfur under oxygen limitation was tested at extremely haloalkaline conditions in lab-scale bioreactors using mix sediments from hypersaline soda lakes as inoculum. The microbiological analysis, both culture dependent and independent, of the successfully operating bioreactors revealed a domination of obligately chemolithoautotrophic and extremely haloalkaliphilic sulfur-oxidizing bacteria belonging to the genus Thioalkalivibrio. Two subgroups were recognized among the isolates. The subgroup enriched from the reactors operating at pH 10 clustered with Thioalkalivibrio jannaschii–Thioalkalivibrio versutus core group of the genus Thioalkalivibrio. Another subgroup, obtained mostly with sulfide as substrate and at lower pH, belonged to the cluster of facultatively alkaliphilic Thioalkalivibrio halophilus. Overall, the results clearly indicate a large potential of the genus Thiolalkalivibrio to efficiently oxidize sulfide at extremely haloalkaline conditions, which makes it suitable for application in the natural gas desulfurization.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-008-1598-8) contains supplementary material, which is available to authorized users.

Sulfide-induced nitrate reduction in the sludge of an anaerobic digester of a zero-discharge recirculating mariculture system

The anaerobic digester is a vital component in a zero-discharge mariculture system as therein most of the organic matter is mineralized and nitrogen-containing compounds are converted to gaseous N 2. Although denitrification is a major respiratory process in this nitrate-rich treatment stage, also sulfate respiration takes place and may cause undesirable high sulfide concentrations in the effluent water. To examine the effect of sulfide on nitrate reduction, in situ depth profiles of inorganic nitrogen and sulfur compounds were determined. Additionally, nitrate reduction was examined as a function of ambient sulfide concentrations in sludge collected from different locations in the anaerobic reactor. Depth profiles showed high concentrations of nitrate and low concentrations of sulfide and ammonia in the aqueous layer of the reactor. A sharp decrease of nitrate and an increase in sulfide and ammonia concentrations was measured at the water–sludge interface. Nitrate reduction was highest in this interface zone with rates of up to 8.05 ± 0.57 μmol NO 3 − h −1 g (sludge) −1. Addition of sulfide increased the nitrate reduction rate at all sludge depths, pointing to the important role of autotrophic denitrification in the anaerobic reactor. Dissimilatory nitrate reduction to ammonia (DNRA) was found to be low in all sludge layers but was enhanced when sludge was incubated at high sulfide concentrations. Although nitrate reduction rates increased as a result of sulfide addition to sludge samples, no differences in nitrate reduction rates were observed between the samples incubated with different initial sulfide concentrations. This as opposed to sulfide oxidation rates, which followed Michaelis–Menten enzymatic kinetics. Partial oxidation of sulfide to elemental sulfur instead of a complete oxidation to sulfate, could explain the observed patterns of nitrate reduction and sulfide oxidation in sludge incubated with different initial sulfide concentrations.

Pressure oxidation leaching of chalcopyrite: Part II: Comparison of medium temperature kinetics and products and effect of chloride ion

Pressure oxidation reaction kinetics and products are compared for the recovery of copper from a chalcopyrite concentrate under medium temperature conditions at 125–150 °C, as patented and promoted by various commercial operations, normally referred to as the Anglo/UBC, CESL and NSC (nitrogen species catalysed) processes. The main aim was to compare the effect of additives on the dispersion of molten sulfur and recovery of copper, and develop a better understanding of the role of chloride ion. Greater than 94% copper was extracted from the concentrate under all process conditions (except NSC) within 30 min. The extraction of the remaining copper in some instances took substantially longer due to poor dispersion of sulfur and agglomeration of the sulfide minerals. The partial oxidation of sulfide to elemental sulfur was about 70–80% at 150 °C and was greater in the presence of chloride ion and at higher initial acidity. Iron was leached and re-precipitated forming a number of different phases depending upon the acidity and salinity. These phases including hematite, jarosite and goethite were characterised using Quantitative X-ray Diffraction (QXRD) analysis. Hematite formation was favoured at higher temperatures (≥ 150 °C), low acidity and low to moderate salinity. Goethite formation was favoured at lower temperatures (< 150 °C) and by low acidity and low salinity. Jarosite was formed under conditions of moderate to high acidity and its formation was enhanced/stabilised in the presence of sodium ions. It was demonstrated that the basic copper salt, antlerite, could be produced under conditions of low acidity. Chloride ion addition and high acid concentrations enhanced copper extraction kinetics and recovery, and inhibited the oxidation of sulfur to sulfate. This suggests that chloride ion is adsorbed on the sulfur surface to restrict direct oxygen reaction. Chloride ion also enhances the anodic oxidation of mineral sulfides and the dispersion of molten sulfur.