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Caulerpa is a genus of green macroalgae that lives in tropical and subtropical coastal waters. It is an intriguing organism because, despite having plant-like structures, it is one giant cell – which, next to multiple nuclei, chloroplasts, and mitochondria, also contains endo- and epiphytic bacteria. The role of these bacteria is unknown, but they might impact the growth and development of the host, adaptation to environmental parameters, and, hence, the ecological success of these algae. We hypothesised that increased sulphide concentrations would trigger a significant shift in the microbial community composition associated with C. prolifera rhizoids, favouring sulphide-oxidizing bacteria. To test this hypothesis, we conducted a mesocosm experiment incubating C. prolifera in sediments with different sulphide concentrations and analysed the algal photosynthesis, growth, and microbiome composition. While photosynthesis was not affected, the Caulerpa weight-based growth rate decreased linearly with increasing sulphide concentration. To analyse the microbiome, we extracted DNA and RNA from the fronds, rhizoids, and the accompanying sediments and performed 16S amplicon sequencing. The microbiome of the fronds was unaffected in both the DNA and RNA samples. However, an increase in sulphide concentration coincided with a decrease in the relative abundance of sulphate-reducing bacteria associated with Caulerpa rhizoids, particularly from the family Desulfocapsaceae. In the RNA samples, potential sulphide oxidisers of the rhizoid-associated members of the Beggiatoaceae were detected. Our results suggest that the rhizobiome of Caulerpa plays a significant role in its adaptation to sulphide-rich environments, offering new insights into the complex interactions within marine holobionts. [ABSTRACT FROM AUTHOR]

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants due to improper utilization in past industrial activity. Anaerobic reductive dechlorination, where bacteria use CAHs as electron acceptors, is crucial for bioremediation. Environmental conditions, such as nutrient availability and electron donors (i.e., molecular hydrogen), can influence the effectiveness of bioremediation processes. Also, bioremediation strategies like bioaugmentation (i.e., the supply of the enriched dechlorinating consortium) and bio-stimulation (i.e., the supply of electron donor) can improve CAHs removal performances. Here, a microcosm study is presented to assess the effectiveness of bioaugmentation with an enriched dechlorinating consortium for groundwater remediation. Target contaminants used were tetrachloroethane (TeCA), trichloroethylene (TCE) and sulphate ion. Various conditions, including biostimulation and bioaugmentation approaches were tested to evaluate the feasibility of biological treatment. Operating conditions, i.e., mineral medium and lactate, facilitated the dechlorination of TCE into ETH, leading to an increase in the dechlorinating population (Dehalococcoides mccartyi) to 67% of the total bacteria, with reductive dechlorination (RD) rates up to 7 µeq/Ld. Conversely, the RD performance of microcosms with real contaminated groundwater was negatively affected by the combined presence of TeCA and sulphate, indicated by a low abundance of D. mccartyi (

Caulerpa is a genus of green macroalgae that lives in tropical and subtropical coastal waters. It is an intriguing organism because, despite having plant-like structures, it is one giant cell – which, next to multiple nuclei, chloroplasts, and mitochondria, also contains endo- and epiphytic bacteria. The role of these bacteria is unknown, but they might impact the growth and development of the host, adaptation to environmental parameters, and, hence, the ecological success of these algae. We hypothesised that increased sulphide concentrations would trigger a significant shift in the microbial community composition associated with C. prolifera rhizoids, favouring sulphide-oxidizing bacteria. To test this hypothesis, we conducted a mesocosm experiment incubating C. prolifera in sediments with different sulphide concentrations and analysed the algal photosynthesis, growth, and microbiome composition. While photosynthesis was not affected, the Caulerpa weight-based growth rate decreased linearly with increasing sulphide concentration. To analyse the microbiome, we extracted DNA and RNA from the fronds, rhizoids, and the accompanying sediments and performed 16S amplicon sequencing. The microbiome of the fronds was unaffected in both the DNA and RNA samples. However, an increase in sulphide concentration coincided with a decrease in the relative abundance of sulphate-reducing bacteria associated with Caulerpa rhizoids, particularly from the family Desulfocapsaceae. In the RNA samples, potential sulphide oxidisers of the rhizoid-associated members of the Beggiatoaceae were detected. Our results suggest that the rhizobiome of Caulerpa plays a significant role in its adaptation to sulphide-rich environments, offering new insights into the complex interactions within marine holobionts.

This work presents a biological remediation process for molybdenum-bearing wastewater which may lead to the fabrication of biogenic Mo chalcogenide particles with (photo)catalytic properties. The process is based on dissimilatory sulphate reduction, utilising sulphate-reducing bacteria (SRB), and reductive precipitation of molybdate which is the predominant species of molybdenum in oxygenated water/wastewater. The SRB culture was established in a biofilm reactor which was fed with synthetic solutions containing sulphate (17.7 mM), molybdate molybdenum (2 mM), divalent iron (1.7 mM) and ethanol as the carbon/electron donor. The performance of the bioreactor was monitored in terms of pH, sulphate and molybdenum (Mo(VI) and total) content. The presence of thiomolybdate species was studied by scanning UV-Vis absorbance of samples from the reactor outflow while the reactor precipitates were studied via electron microscopy coupled with energy dispersive spectrometry, X-ray diffractometry and laser light scattering. A molar molybdate/sulphate ratio of 1:12.5 proved effective for molybdate reduction and recovery by 76% in 96 h, whereas sulphate was reduced by 57%. Molybdenum was immobilised in the sulphidic precipitates of the bioreactor, presumably via two principal mechanisms: (i) microbially mediated reduction and precipitation, and (ii) thiomolybdate formation and sorption/incorporation into iron sulphides. [ABSTRACT FROM AUTHOR]

Electro-bioremediation offers a promising approach for eliminating persistent pollutants from groundwater since allows the stimulation of biological dechlorinating activity, utilizing renewable electricity for process operation and avoiding the injection of chemicals into aquifers. In this study, a two-chamber microbial electrolysis cell has been utilized to achieve both reductive and oxidative degradation of tetrachloroethane (TeCA). By polarizing the graphite granules cathodic chamber at −650 mV vs the standard hydrogen electrode and employing a mixed metal oxide (MMO) counter electrode for oxygen production, the reductive and oxidative environment necessary for TeCA removal has been established. Continuous experiments were conducted using two feeding solutions: an optimized mineral medium for dechlorinating microorganisms, and synthetic groundwater containing sulphate and nitrate anions to investigate potential side reactions. The bioelectrochemical process efficiently reduced TeCA to a mixture of trans-dichloroethylene, vinyl chloride, and ethylene, which were subsequently oxidized in the anodic chamber with removal efficiencies of 37 ± 2%, 100 ± 4%, and 100 ± 5%, respectively. The introduction of synthetic groundwater with nitrate and sulphate stimulated reductions in these ions in the cathodic chamber, leading to a 17% decrease in the reductive dechlorination rate and the appearance of other chlorinated by-products, including cis-dichloroethylene and 1,2-dichloroethane (1,2-DCA), in the cathode effluent. Notably, despite the lower reductive dechlorination rate during synthetic groundwater operation, aerobic dechlorinating microorganisms within the anodic chamber completely removed VC and 1,2-DCA. This study represents the first demonstration of a sequential reductive and oxidative bioelectrochemical process for TeCA mineralization in a synthetic solution simulating contaminated groundwater.

Uranium was extracted in the Königstein uranium mine by in-situ leaching with sulfuric acid until 1990. The originally anoxic conditions in the ore body became oxic due to the leaching process and the dewatering of the mine workings. Under these conditions, acid and metals continue to be mobilized. A field test was performed on how to restore reductive conditions in an area of the mine workings with low flow velocities. The aim was to test the immobilisation of contaminants as a prerequisite for further flooding of the mine. The field test showed that it is possible to re-establish and maintain rather reductive geochemical in-situ-conditions, which is necessary to precipitate sulphides as well as reduce acidity and metal concentrations. [ABSTRACT FROM AUTHOR]

Biogenic coalbed methane is produced by biological processes mediated by the synergistic interaction of microbial complexes in coal seams. However, the comprehensive ecological role of methanogenic archaea in biogenic coalbed methane production remains poorly understood. Here, we study the metagenome assembled genomes (MAGs) of Methanoculleus from coal seams, which were stimulated by minimal salts plus yeast media in anaerobic conditions. The Methanoculleus genus accounted for the highest proportion of archaea (80.4 ± 2.8%) once the CH4 concentration in the headspace increased to 15.0 ± 2.6% on the 50th day. The Methanoculleus MAGs were closely related to M. thermophiles; even so, 30 genes were detected in MAGs which were lacking in the genomes of M. thermophiles ATCC 33837. A deeper look at the metabolic pathway showed several metabolic pathways, including methanogenesis, glycolysis, urea cycle, TCA cycle and sulphur reduction. The CO2 and acetate were the primary carbon sources of these cells for the methanogenesis pathway. Glycolysis and sulphate reduction processes were the main processes for providing acetate. In addition, the cells had a variety of other functions, including nitrogen fixation and hydrogen production. Overall, this study enabled a better understanding of the ecological roles of Methanoculleus for biogenic methane in coal seams by combining bioinformatic techniques. [ABSTRACT FROM AUTHOR]

Sulphate (SO4) abundance in the earth's crust contributes largely to industrial wastewater contamination lowering the pH, which exuberates the dissolution of metals forming acidic drainages. Biological sulphate reduction as a remediation process can be affected by factors such as pH, temperature and high sulphide concentrations. In this study, sulphate-reducing bacterial community enriched from mine wastewaters was applied in semi-automated bio-reactors to assess the effects of these factors on microbial sulphate reduction capacities. Low pH (3.5) and temperature (10°C) were observed to promote the toxicity of sulphur-reduced species on the consortium while mesophilic temperature (25°C) and near neutral pH (6.2) were observed to induce optimum SO4 reduction attaining a maximum of 95% SO4 reduction. Obtained SO4 reduction dynamics data was then applied in formulating a unique non-competitive inhibition equation that models biogeochemical events during SO4 reduction under varied pH and temperature conditions and predicts the efficacy of a bioremediation system. [ABSTRACT FROM AUTHOR]

This study investigates the effect of micro aeration of Skim Latex Wastewater (SLW) in an ammonia-rich environment. SLW contains sulphate, ammonia, and protein at significant levels. Original SLW contains influent COD/SO4−2 and COD/TKN ratios of 2.7 and 10.1, respectively. Experiments were conducted in five phases by varying input O2/S ratios at 0, 0.5, 1, and 1.5 by feeding air into the bulk liquid. The COD/SO4−2 ratio was adjusted to 5 and 10 by adding ethanol to the original SLW into inflow. These experiments were performed in thoroughly mixed micro-aerated anaerobic digesters at 35 ± 1 °C and pH of 7.5–8.0 operated semi-batch-wise. This newly developed biodigester is called a Single-stage Sulphate-removal Micro-aerated Anaerobic Digester (SSMAD). Variations of sulphurous compounds in the SSMADs were monitored. It showed that the yield and stability of the generated elemental sulphur improved at an input O2/S ratio of 1.0–1.2 and COD/SO4−2 of 5. Although ethanol enhanced sulphate reduction, when the influent COD/SO4−2 was increased from 5 to 10, it adversely affected the generated elemental sulphur, degrading back to gaseous H2S, thereby reducing the elemental sulphur yield by 69%. The developed novel approach through SSMAD can successively recover sulphurous pollutants from ammonia-rich SLW. [ABSTRACT FROM AUTHOR]

An obligately anaerobic, spore-forming sulphate-reducing bacterium, strain SB140 T , was isolated from a long-term continuous enrichment culture that was inoculated with peat soil from an acidic fen. Cells were immotile, slightly curved rods that stained Gram-negative. The optimum temperature for growth was 28 °C. Strain SB140 T grew at pH 4.0-7.5 with an optimum pH of 6.0-7.0 using various electron donors and electron acceptors. Yeast extract, sugars, alcohols and organic acids were used as electron donors for sulphate reduction. SB140 T additionally used elemental sulphur and nitrate as electron acceptors but not sulphite, thiosulphate or iron(III) provided as ferrihydrite and fumarate. The 16S rRNA gene sequence placed strain SB140 T in the genus Desulfosporosinus of the phylum Bacillota . The predominant cellular fatty acids were iso-C 15 : 0 (52.6%) and 5,7 C 15 : 2 (19.9%). The draft genome of SB140 T (5.42 Mbp in size) shared 77.4% average nucleotide identity with the closest cultured relatives Desulfosporosinus acididurans M1 T and Desulfosporosinus acidiphilus SJ4 T . On the basis of phenotypic, phylogenetic and genomic characteristics, SB140 T was identified as a novel species within the genus Desulfosporosinus , for which we propose the name Desulfosporosinus paludis sp. nov. The type strain is SB140 T (=DSM 117342 T =JCM 39521 T ).

Significantly elevated U, Mo, Zn and Pb contents characterize the Early Ordovician black shales in the Sillamäe area, NE Estonia. The presence of silty interlayers with sulphidic mineralization and authigenic carbonates suggests unique physicochemical conditions for metal enrichment in this location. We investigated metallogenesis of these shallow-water black shales based on high-resolution mapping of element distribution in the Sõtke drill core and nearby Päite outcrop using X-ray fluorescence spectroscopy, inductively coupled plasma mass spectrometry and organic elemental analysis, complemented by optical microscopy and scanning electron microscopy of selected samples. Enriched metals in the black shales of the study area show dissimilar distribution trends with sharp vertical concentration gradients. The recorded variance ranges were 88â275 ppm for U, 70â2467 ppm for Mo, 85â1600 ppm for V, 21â17 283 ppm for Zn and 95â26 549 ppm for Pb, while total organic carbon varied from 0.5 to 13 wt%. In most cases, the metals showed no clear covariance with organic matter or other major compounds such as S or P. The development of a sulphate reduction zone near the sedimentâwater interface with a sharp decrease in Eh, production of H2S, elevated alkalinity and pH, and (re)distribution of phosphorus probably controlled the syngenetic capture of Mo and U. Enhanced transfer of fluids and solutes in coarse-grained permeable beds facilitated the accumulation of metals, while the deposit probably acted as a semi-open geochemical system throughout its geological evolution. Local Zn and Pb enrichment developed due to the intrusion of late diagenetic metal-bearing fluids and the entrapment of metals in beds that contained authigenic carbonates.

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Seagrass ecosystems are globally-significant 'blue carbon' sinks; however, there is concern that this capacity will decline if rising ocean temperatures accelerate microbial decomposition. Decomposition of plant litter is a key process in the global carbon cycle—it influences how much carbon is available for sequestration. Therefore, understanding the biogeochemistry underlying decomposition is essential to predicting the capacity of seagrass ecosystems to act as carbon sinks in the future. Here, we tracked the breakdown of standardised and natural litter of varying chemical recalcitrance (rooibos tea > seagrass leaves > green tea) combined with highly-sensitive microsensor technology to test (a) how elevated water temperatures affect short-term microbial turnover, and (b) provide novel information on how the decay dynamics of the tea litter compare to those of natural litter. We found that increased temperatures (+ 5–10 °C) boosted microbial activity for all substrates, exhibited as enhanced decay, oxygen consumption and sulphate reduction. Within the 1-month experiment, the green tea litter had a rapid Q10 response to the temperature increase, quickly exhausting the resources for microbes, while the response of the rooibos tea and seagrass litters became more apparent toward the end of the experiment. Our results suggest that the tea litters capture a range of decomposition traits and can be compared with natural litter using traditional exponential decay models. The enhanced temperature-driven organic matter turnover, even under anoxic conditions, highlights the vulnerability of fresh litter to microbial attack during the early stages of decay and the potential weakening of blue carbon accumulation rates under future climatic conditions. [ABSTRACT FROM AUTHOR]

Denitrifying woodchip bioreactors, natural treatment systems used for the reduction of nitrates in agricultural runoff or groundwater, may cause adverse side effects within receiving waters. One of the least studied but nonetheless still serious issues is the production of hydrogen sulphide, which occurs in bioreactors under operating conditions favourable to its creation. The aim of this paper is to elucidate the effect of process parameters on the production of sulphides and the proportion of hydrogen sulphide in a 1-year-long experimental study with four laboratory-scale denitrifying bioreactors. During the study, the strong dependence of sulphate reduction and the production of sulphides on the effluent oxidation-reduction potential (ORP) and nitrate-nitrogen (NO3-N) concentrations of bioreactors became evident. Sulphide formation occurred at concurrent effluent NO3-N concentrations below 3 mg/L and ORPs lower than − 100 mV. The tested hydraulic retention time of 1.7 days was sufficiently long to achieve these conditions. At an effluent pH of 7 or lower, the majority of the total sulphides present were in the form of hydrogen sulphide. It is suggested that in order to avoid the production of hydrogen sulphide, the production of total sulphides has to be minimised. [ABSTRACT FROM AUTHOR]

Natural anaerobic biogeochemical processes used for passive treatment of AMD were observed in the extensive shallow water zone of a polymictic pit lake in the former German lignite district of Upper Palatinate. Although continuously fed by acidic metalliferous groundwater, lake-pH increased from 3.5 to circumneutral over a little more than 10 years. The natural attenuation processes were studied and quantified using a regional surface- and groundwater flow model linked with hydrochemical monitoring datasets to establish a simple mass balance. The acidity inflow was estimated at ≈ 5900 kmol over the period 2014–2018, which corresponds to an average inflow of ≈ 1190 kmol/a. This estimate is in very good accordance with an acidity inflow rate for the period 2000–2014 estimated from acidity deposition in the sediment based on sediment core analyses plus the calculated cumulative acidity outflow based on extrapolation of pre-neutralisation acidity levels in the pit lake, together yielding a total acidity of ≈ 15,000 kmol, which corresponds to an inflow rate of ≈ 960 kmol/a. The results strongly indicate that the pit lake self-neutralised due to beneficial environmental and ecological conditions, amplified and potentially initialised by the circumneutral discharge from a chemical mine water treatment plant, and that well-known biogeochemical mechanisms such as natural microbial sulfate reduction were the driving force. The results give rise to perspectives concerning the potential development of pit lakes if ecological considerations are considered. [ABSTRACT FROM AUTHOR]

Industrial by-products and wastes from Portugal and Spain were tested for the first time as carbon sources/electron donors for sulphate-reducing bacteria. Cultures in mineral medium supplemented with the tested substrates were monitored, and sulphate reduction efficiency is discussed in light of substrates compositions, dosages and corresponding chemical oxygen demand/[SO42−] ratios. The results reveal the ability of those substrates to feed SRB and confirm that testing doses targeting ratios of 1.5 and values close to this was a good strategy to optimize sulphate reduction activity. As expected, this activity was faster for substrates that have in their composition simple compounds (such as low-chain alcohols and organic acids) and/or compounds that can be rapidly degraded (such as sugars), though it also occurred in a longer-term perspective with substrates composed mainly of slowly degradable compounds (such as cellulose and lignin). Thus, this work demonstrates the potential of new substrates and respective required doses to feed SRB bioreactors in long-term passive bioremediation processes or faster more active processes. That is, it opens the way for the use of such substrates in the treatment of sulphate-rich waters, as the acid mine drainage generated in some mines on the Iberian Pyrite Belt region, and it encourages further experiments to evaluate the use of SRB-based processes to treat the industrial wastewaters successfully tested in this work themselves, specially the olive mill wastewater which is still a problem for many small olive oil producers. [ABSTRACT FROM AUTHOR]

This study explores linkages between the microbial composition and hydrochemical variables of pristine groundwater to identify active redox conditions and processes. Two confined aquifers underlying the city of Qianjiang in the Jianghan Plain in China were selected for this study, having different recharge sources and strong hydrochemical gradients. Typical methods for establishing redox processes according to threshold concentration criteria for geochemical parameters suggest iron or sulphate reduction processes. High‐throughput 16S rRNA sequencing was used to obtain diversity and taxonomic information on microbial communities. Instead of revealing iron‐ and sulphate‐reducing bacteria, salt‐ and alkali‐tolerant bacteria, such as the phylum Firmicutes and the class Gammaproteobacteria, and in particular, the family Bacillaceae, were dominant in the downstream groundwater of the first aquifer that had high ion concentrations caused by the dissolution of calcite and dolomite; meanwhile, the heterotrophic microaerophilic families Comamonadaceae and Rhodocyclaceae prevailed in the upstream groundwater of the first aquifer. Sulphate‐reducing bacteria were extremely abundant in the upstream groundwater of the second aquifer, as the SO42− concentration was especially high. Methanogens and methanotrophs were predominant in the downstream groundwater of the second aquifer even though the concentration of SO42− was much higher than 0.5 mg L−1. The microbial communities, together with the geochemical parameters, indicated that the upstream region of the first aquifer was suboxic, that Fe(III) and Mn(IV) reductions were not the main redox processes in the downstream groundwater of the first aquifer with high Fe and Mn concentrations, and that the redox processes in the upstream and downstream regions of the second confined aquifer were SO42− reduction and methanogenesis, respectively. This study expands understanding of the linkages between microbial communities and hydrogeochemistry in pristine groundwaters and provides more evidence for identifying active redox conditions and processes. [ABSTRACT FROM AUTHOR]

Abstract Subsurface flow constructed wetlands with wood chips (SSF-CWs) have proven to effectively reduce the loss of nitrogen (N) from agricultural fields to surface water, however in some cases production of negative side effects such as methane and phosphate occur. We examined if these side effects can be avoided by decreasing the hydraulic retention time (HRT) from on average 82 h to 11 h during summer to autumn in two pilot SSF-CWs. Furthermore, we investigated the potential of the SSF-CWs to reduce phosphorus (P) loss from agricultural drainage systems. The influent and effluent concentration of total N (TN), nitrate-N, total P, phosphate-P, suspended sediment, and sulphate were monitored for five years (2013–2017). Methane concentrations were measured during two periods in 2014 and 2017. Flow was measured continuously by electromagnetic flow-meters. The nitrate-N removal was reduced from 98-100% to 27–32% and the sulphate reduction from 32-53% to 1–2% when decreasing HRT. Concurrently this resulted in a considerable decrease in the difference between the effluent and influent concentration of phosphate-P and methane concentration compared to similar periods in the preceding years. The SSF-CWs retained 67–85% of the annual loading of particulate P, but acted as both a sink and source of phosphate-P, thus further initiatives are therefore required to prevent phosphate-P release from SSF-CWs. Although during the entire monitoring period the SSF-CWs retained 29–33% of the total P loading. In summary, this study stresses how important a holistic approach is when implementing and designing new N mitigation measures. Graphical abstract Image 1 Highlights • Subsurface flow constructed wetlands (SSF-CWs) can have negative side effects. • In this study the side effects were methane and phosphate. • Seasonally lowering of hydraulic retention time reduced these side effects. • Over five years 41 and 31% of TN and TP load from drainage water was removed. • SSF-CWs design should be holistic rather than designed only for N removal. [ABSTRACT FROM AUTHOR]

Abstract The Mandovi Estuary, located along the tropical west coast of India, transforms from being a freshwater-dominated body during the monsoon season to a tide-dominated system during post-monsoon season, with a salinity gradient developing from the freshwater end to the estuarine mouth (∼0–33). The sulphate reduction (SR) rates were measured by the 35SO 4 2− radiotracer method in the estuarine sediments at three different sites. The porewater H 2 S concentrations were negligible at all the sites and SR rates did not exhibit any clear trend along the salinity gradient. Pyrite content (3.45–12.9 mg g−1) was the highest at the marine end and decreased towards the freshwater end. The SR rate (15.71 mmol m−2 d−1) and total Fe content (14–20%) were highest in sediments of mid-estuary with intermediate salinity and variable porosity. Organic carbon (OC) mineralization rate through SR also did not show any trend along the salinity gradient with intermediate salinity site having higher values (31.83 mmol C m2 d−1) compared to other sites (3.12–8.62 mmol C m2 d−1). SR was responsible for ∼8–50% of sedimentary OC mineralization implying that OC mineralization through Fe (III) and Mn (IV) reduction possibly played major role owing to their high concentrations in the estuarine sediments. [ABSTRACT FROM AUTHOR]

Abstract We have developed a new concept on the formation of diverse geochemical types of salt lakes, in particular for those in the Transbaikal region. This concept explains the nature of their different chemical composition under the close landscape-climatic and geological-geochemical conditions. The extensive hydrogeochemical field data and thermodynamic calculations demonstrate that in addition to evaporation, interactions with rocks play a substantial role in the formation of the composition of these salt lakes. Such processes are most widespread in soda lakes, which is confirmed by the highest pH values (9.0–10.7). These lakes provide evidence of the interaction of the lake waters with aluminosilicates; their hydrolysis provides a pH increase and consequently a high concentration of carbonate ions. These high pH and HCO 3 − and CO 3 2− contents in turn lead to the maximum precipitation of Ca, Mg and Fe carbonates. Soda lakes also contain high chloride ion concentrations, since a small portion of those ions evaporate under the lake conditions. If evaporation continues and the amount of carbonate ions in the lake does not increase, or increases slowly due to binding with carbonate minerals, the chlorine content becomes higher, the pH lowers to less than 9.0, and the lakes become chloride. Another fundamental process in these lake environments is sulphate reduction, which results in the production of hydrogen sulphide, fundamentally changing the geochemical environment from oxidizing to reducing. The presence of an oxidizing environment and sulphides in rocks gives additional sources for sulphates, which ensures the formation of sulphate-type lakes. Highlights • New concept on the formation of the geochemical composition of salt lakes. • The interaction between water and rocks plays a great role in the lake formation. • Waters are not in equilibrium with many minerals of endogenous genesis. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sulphidogenesis was optimal at 2.5 g SO 4 2−·L−1 and a COD:sulphate ratio of 2.4. • Sulphidogenesis was robust to transient feeding conditions at 2.5 g SO 4 2−·L−1. • Sulphate RE was ≥40% at 15 g SO 4 2−·L−1 influent sulphate concentration. • NH 4 + feast-famine conditions affected the sulphate reduction process. Abstract This work aimed to study the effect of transient feeding conditions on sulphidogenesis in 8 sequencing batch bioreactors (SBR). SBR L1 and H1, operated under steady-state conditions were used as the control reactors, while four SBR were tested under transient feeding conditions using moderate (L2 and L3, feast and famine: 2.5 and 0 g SO 4 2−·L−1) and high (H2 and H3, feast and famine: 15 and 0 g SO 4 2−·L−1) loads. The sulphate removal efficiency (RE) was ≥90% in SBR L2, L3 and H1. The NH 4 + famine conditions resulted in a higher sulphate RE (≥40% H3) compared to feast conditions (≤20% H2). Besides, the sulphidogenic first-order kinetic constant was 4% larger and the use of electron donor was 16.6% more efficient under NH 4 + famine conditions. Sulphidogenesis is robust to transient feeding conditions, but not when applying high loading rates (SBR H2 and H3). [ABSTRACT FROM AUTHOR]

Abstract Anaerobic sludge from a sewage treatment plant was used to acclimatize microbial colonies capable of anaerobic oxidation of methane (AOM) coupled to sulfate reduction. Clone libraries and fluorescence in situ hybridization were used to investigate the microbial population. Sulfate-reducing bacteria (SRB) (e.g. , Desulfotomaculum arcticum and Desulfobulbus propionicus) and anaerobic methanotrophic archaea (ANME) (e.g. , Methanosaeta sp. and Methanolinea sp.) coexisted in the enrichment. The archaeal and bacterial cells were randomly or evenly distributed throughout the consortia. Accompanied by sulfate reduction, methane was oxidized anaerobically by the consortia of methane-oxidizing archaea and SRB. Moreover, CH 4 and SO 4 2 − were consumed by methanotrophs and sulfate reducers with CO 2 and H 2 S as products. The H 3 CSH produced by methanotrophy was an intermediate product during the process. The methanotrophic enrichment was inoculated in a down-flow biofilter for the treatment of methane and H 2 S from a landfill site. On average, 93.33% of H 2 S and 10.71% of methane was successfully reduced in the biofilter. This study tries to provide effective method for the synergistic treatment of waste gas containing sulfur compounds and CH 4. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Biological reduction of sulphate at low hydraulic retention time (HRT) is presented in this paper. A sulphidogenic inverse fluidized-bed bioreactor (IFBB) was operated successfully at a progressively decreasing HRT from 1 to 0.125 days for a total of 155 days. Synthetic wastewater containing sulphate at a concentration of 745 (± 17) mg/L was used. COD was supplied as lactate in variable concentrations at COD/SO42− ratios of 1.2-2.4. The pH of the feed ranged between 5.2 and 6.2. The highest measured removal rates were 2646 and 4866 mg SO42−/L day at an HRT of 0.25 and 0.125 days, respectively, using a COD/SO42− ratio of 2.3. The biological sulphate reduction was limited by the influent COD concentrations at a COD/SO42− ratio < 2.3. The IFBB ensured biomass retention at a maximum liquid residence time of θ = 3.84 (± 0.013), according to the residence time distribution analysis. Hydrodynamic studies were carried out at recirculation rates of 0, 200, 300, 350, 400, and 500 L/h to measure the relative bed expansion, the mixing pattern, and the fluidization characteristics of the reactor. A dynamic model is also developed based on COD and sulphate as the two limiting substrates in a Monod-type kinetic equation describing the kinetics of lactate oxidation by SRB. A set of the following parameters YVSS/COD′ = 0.23 mg COD of VSS/mg lactate, µmax = 1.758 day− 1, KCOD = 956 mg COD of lactate/L, KSO4 = 316 mg SO42−/L, kd = 0.024 day− 1, tres = 5.7 days, and kexchange = 0.4 day− 1 simulated adequately the residual effluent COD and sulphate concentrations, the produced sulphide concentration as well as the pH of the IFBB effluent. Low HRT values, shown efficient in this study, are prerequisite for industrial applicability and economic feasibility of the sulphur reduction process. In addition, the developed model can be used for optimum experimental design and further process upscale and development. [ABSTRACT FROM AUTHOR]

The occurrence of sulphate reducing bacteria in bottom sediments of selected estuarine ecosystems of South Kerala, and their activities were analyzed in vitro. The study covered three estuaries viz., Poonthura, Veli and Kadinamkulam of Thiruvananthapuram District. SRB were enumerated using the roll tube technique (modified Hungate method) in Postgate medium. Morphologically distinct colonies were isolated and transferred to Postgate broth in serum vials capped with butyl rubber stopper and aluminium cap assembly. The isolated cultures were used for further characterization and sulphate reduction studies. The viable count of SRB corresponded to organic carbon and sulphate concentration of the sediment. Molecular characterization by phylogeny of 16SrRNA genes revealed that strain S4 was Citrobacter freundii and S5 was Bacillus tequilensis, the activity of the latter as SRB is hitherto unreported. Nevertheless, both the identified cultures did not belong to the traditional group of SRB (δ proteobacteria). The growth of SRB and sulphate reduction was tested in two carbon sources (ethanol, acetate) and electron acceptors (sulphite, sulphate). When ethanol was used as substrate, both sulphate and sulphite as electron acceptors showed similar range of sulphide production. However, when acetate was used as substrate, sulphate as electron acceptor showed more sulphide production than sulphite. Acetate provided continued growth of C. freundii throughout the incubation period and sulphate reduction was more during decline phase of growth. This study indicates the presence of extremely diverse SRB communities that exhibit geographic patchiness and warrants more research. [ABSTRACT FROM AUTHOR]

The aim of this work was to evaluate the feasibility of the use of different industrial and agricultural wastes as reactive materials in Permeable Reactive Barriers (PRB) for Acid Mine Drainage (AMD) remediation. Sugar foam (SF), paper mill sludge (PMS), drinking water sludge (DWS) and olive mill waste (OMW) were evaluated in terms of pH neutralization and metal removal from AMD. Laboratory batch tests and continuous pilot scale up-flow columns containing 82% of Volcanic Slag (VS), as porous fill material, and 18% w/w of one of the industrial and agricultural wastes previously indicated, were tested. From the batch tests it was observed that the reactive material presenting the best results were the SF and the PMS. The results obtained in all the PRB were accurately described by a pseudo-first order model, presenting coefficient of determination higher than 0.96 in all the cases. During the continuous operation of the PRB, the porosity and hydraulic retention time (HRT) of most of the up-flow columns strongly decreased due to chemical precipitation and biofilm growth. The SF presented a significant number of fine particles that were washed out by the liquid flow, generating an effluent with very high total suspended solid concentration. Despite SF was the material with the highest alkalinity potential, the reduction of the HRT limited its neutralization and metal removal capacity. PMS and DWS presented the best pollutant removal yields in the continuous operation of the PRB, ranging from 55 to 99% and 55–95% (except in the case of the Mn), respectively. These results allowed the metal removal from the AMD. Additionally, these wastes presented very good biological sulphate reduction. Based on these results, the use of PMS and DWS as reactive material in PRB would allow to simultaneously valorise the industrial waste, which is very interesting within the circular economy framework, and to remove metals from the AMD by means of a low-cost and environmentally sustainable procedure. [Display omitted] • Acid mine drainage remediation was studied using permeable reactive barriers. • Four wastes were tested for pH neutralization and dissolved metals removal. • Bed porosity and hydraulic retention times decreased during treatment. • The industrial wastes promoted chemical neutralization and biological sulphate removal. [ABSTRACT FROM AUTHOR]

Microorganisms in the deep biosphere are believed to conduct little metabolic activity due to low nutrient availability in these environments. However, destructive penetration to long-isolated bedrock environments during construction of underground waste repositories can lead to increased nutrient availability and potentially affect the long-term stability of the repository systems, Here, we studied how microorganisms present in fracture fluid from a depth of 500 m in Outokumpu, Finland, respond to simple carbon compounds (C-1 compounds) in the presence or absence of sulphate as an electron acceptor. C-1 compounds such as methane and methanol are important intermediates in the deep subsurface carbon cycle, and electron acceptors such as sulphate are critical components of oxidation processes. Fracture fluid samples were incubated in vitro with either methane or methanol in the presence or absence of sulphate as an electron acceptor. Metabolic response was measured by staining the microbial cells with fluorescent dyes that indicate metabolic activity and transcriptional response with RT-qPCR. Our results show that deep subsurface microbes exist in dormant states but rapidly reactivate their transcription and respiration systems in the presence of C-1 substrates, particularly methane. Microbial activity was further enhanced by the addition of sulphate as an electron acceptor. Sulphate- and nitrate-reducing microbes were particularly responsive to the addition of C-1 compounds and sulphate. These taxa are common in deep biosphere environments and may be affected by conditions disturbed by bedrock intrusion, as from drilling and excavation for long-term storage of hazardous waste.

Recently the formation of pyrrhotite and greigite is more often linked with sulfate-methane transit zones of modern sediments. The paper considers methane generations as one of the possible ways of forming ferromagnetic iron sulfides in sedimentary rocks of Bakchar deposit. The main aim of the study is to reconstruct the environmental conditions for formation of ferromagnetic sulphides in rocks of the Bakchar deposit for disclosure processes, which occurred in sediments of the ancient epicontinental West Siberian Sea at the PaleoceneEocene boundary and also for interpretation of the high magnetization of these rocks. The methods used in the work: mineralogical (scanning electron microscopy, X-ray diffraction analysis), geophysical (kappametry) and geochemical (X-Ray analysis, ICP-MS) studies of sediments (samples from core) which contain pyrrhotite and greigite to reconstructthe evolution of specific postdepositional processes within the shelf of ancient West-Siberian Sea at Paleocene-Eocene boundary. As a result of the investigation the authors advance the theory of ferromagnetic iron sulfides formation in Bakchar deposit sediments with the upward diffusing methane and limited amount of sulfide ion. This environment was enriched with paleoredox proxies (Mo, U, V) and paleoproductivity proxies (Ba[bio] and P). Sedimentary rocks containing pyrrhotite and greigite are characterized by high values of magnetic susceptibility (more than 80x10-5 SI) that is a useful property to identify analogical rocks in drill cores. Presence of ferromagnetic iron sulfides within sedimentary rocks might be used to detect ancient gas hydrate systems in the Paleocene-Eocene sequences of Western Siberia. Methane emissions within the ancient West Siberian Sea might probably triggering large submarine landslides and affecting the global climate change at the Paleocene-Eocene boundary.

Industrial wastewaters containing high concentrations of sulphate, such as those generated by mining, metallurgical and mineral processing industries, require electron donor for biological sulfidogenesis. In this study, five types of lignocellulosic biowastes were characterized as potential low-cost slow release electron donors for application in a continuously operated sulphidogenic inverse fluidized bed bioreactor (IFBB). Among them, natural scourer and cork were selected due to their high composition of volatile solids (VS), viz. 89.1 and 96.3%, respectively. Experiments were performed in batch (47 days) and in an IFBB (49 days) using synthetic sulphate-rich wastewater. In batch, the scourer gave higher sulphate reduction rates (67.7 mg SO42− L−1 day−1) in comparison to cork (12.1 mg SO42− L−1 day−1), achieving >82% sulphate reduction efficiencies. In the IFBB packed with the natural scourer, the average sulphate reduction efficiency was 24 (±17)%, while the volumetric sulphate reduction rate was 167 (±117) mg SO42− L−1 day−1. The long incubation time in the batch experiments (47 days) allowed higher sulphate reduction efficiencies in comparison to the short hydraulic retention time (24 h) in the IFBB. This suggests the hydrolysis-fermentation was the rate-limiting step and the electron donor supply (through hydrolysis of the lignocellulosic biowaste) was limiting the sulphate reduction.Lignocellulose as carrier material and slow release electron donor for sulphidogenesis [ABSTRACT FROM AUTHOR]

This study was designed to investigate the characteristics of bacterial communities in intertidal sediments along the Yangtze Estuary and their responses to environmental factors. The results showed that bacterial abundance was significantly correlated with salinity, SO 4 2 − and total organic carbon, while bacterial diversity was significantly correlated with SO 4 2 − and total nitrogen. At different taxonomic levels, both the dominant taxa and their abundances varied among the eight samples, with Proteobacteria being the most dominant phylum in general. Cluster analysis revealed that the bacterial community structure was influenced by river runoff and sewerage discharge. Moreover, SO 4 2 − , salinity and total phosphorus were the vital environmental factors that influenced the bacterial community structure. Quantitative PCR and sequencing of sulphate-reducing bacteria indicated that the sulphate reduction process occurs frequently in intertidal sediments. These findings are important to understand the microbial ecology and biogeochemical cycles in estuarine environments. [ABSTRACT FROM AUTHOR]

The leather industry transforms raw hides and skins into high-performance leather products. This transformation requires a high usage of chemicals. About 90% of all leather products are tanned by basic chromium sulphate tanning agents. The use of large quantities of tanning agent causes elevated chromium and sulphate concentrations in the wastewater of conventional tanneries. This article focuses on the reduction of tanning agent consumed by the chromium tanning procedure. Compressed carbon dioxide is used to intensify the process. Carbon dioxide-intensified tanning at 60 bar allows the production of high-quality leather by using about 50 wt% less of tanning agent compared to the conventional tanning process. The chromium and sulphate concentrations in the wastewater generated by the tanning process are highly reduced. Results of full skin tanning (bull skin; up to 10 square metre per skin) in a high-pressure reactor with a volume of 1700-L are presented for the first time. [ABSTRACT FROM AUTHOR]

Anaerobic microbial communities in the anoxic zones degrade organic matter in estuarine sediments. Thermodynamic energy yield for the oxidation reactions with various electron acceptors decreases in the order of O 2 > NO 3 - > Mn 4 + > Fe 3 + > SO 4 2- > CO 2 . The predominant terminal electron accepting (TEA) process has an influence on the biogeochemical cycles of nutrients as well as the production of important greenhouse gases such as nitrous oxide and methane from estuarine sediments. The research questions of this study were (1) what are the environmental factors (pH, salinity, organic carbon, sulphate, redox potential) explaining variability in TEA activities such as nitrate reduction rate (NRR), iron reduction rate (IRR), sulphate reduction rate (SRR) and methane production rate (MPR) and (2) which is the predominant TEA process during degradation of organic matter. To determine the TEA activities, sediment samples collected from 13 sampling stations of Ashtamudi estuary during monsoon 2014 and summer 2015 were incubated with sulphate depleted artificial seawater, under anaerobic conditions for 72 h, in microcosms. Spatial variations dominated temporal variations for environmental variables. Nevertheless, biogeochemical processes showed a distinct seasonal variation. Total TEA activity was higher during summer than monsoon, indicating the higher heterotrophic microbial activity favored by high temperature. Individually, SRR was the maximum during summer, while NRR, IRR and MPR were the maximum during monsoon. Sulphate reduction was observed to be the predominant electron accepting process in all sampling stations with cumulative values of 3125.79 and 4046.07 nmol cm -3 day -1 during monsoon and summer respectively. This was followed by NRR, IRR and MPR. Although thermodynamically more favorable, NRR could not predominate due to scarcity of nitrate in sediments. Nevertheless, two-fold and five-fold increase in methanogenesis and denitrification were observed respectively during monsoon in sampling stations, which cannot be ignored, owing to the importance of methane and nitrous oxide as a potent greenhouse gas. [ABSTRACT FROM AUTHOR]

The Watson River drains a portion of the SW Greenland ice sheet, transporting microbial communities from subglacial environments to a delta at the head of Søndre Strømfjord. This study investigates the potential activity and community shifts of glacial microbiota deposited and buried under layers of sediments within the river delta. A long-term (12-month) incubation experiment was established using Watson River delta sediment under anaerobic conditions, with and without CO/H enrichment. Within CO/H-amended incubations, sulphate depletion and a shift in the microbial community to a 52% predominance of Desulfosporosinus meridiei by day 371 provides evidence for sulphate reduction. We found evidence of methanogenesis in CO/H-amended incubations within the first 5 months, with production rates of ~4 pmol g d, which was likely performed by methanogenic Methanomicrobiales- and Methanosarcinales-related organisms. Later, a reduction in methane was observed to be paired with the depletion of sulphate, and we hypothesise that sulphate reduction out competed hydrogenotrophic methanogenesis. The structure and diversity of the original CO/H-amended incubation communities changed dramatically with a major shift in predominant community members and a decline in diversity and cell abundance. These results highlight the need for further investigations into the fate of subglacial microbiota within downstream environments. [ABSTRACT FROM AUTHOR]

Microbiological studies related to the geological disposal of radioactive waste have been conducted at the Mont Terri rock laboratory in Opalinus Clay, a potential host rock for a deep geologic repository, since 2002. The metabolic potential of microorganisms and their response to excavation-induced effects have been investigated in undisturbed and disturbed claystone cores and in pore- (borehole) water. Results from nearly 15 years of research at the Mont Terri rock laboratory have shown that microorganisms can potentially affect the environment of a repository by influencing redox conditions, metal corrosion and gas production and consumption under favourable conditions. However, the activity of microorganisms in undisturbed Opalinus Clay is limited by the very low porosity, the low water activity, and the largely recalcitrant nature of organic matter in the claystone formation. The presence of microorganisms in numerous experiments at the Mont Terri rock laboratory has suggested that excavation activities and perturbation of the host rock combined with additional contamination during the installation of experiments in boreholes create favourable conditions for microbial activity by providing increased space, water and substrates. Thus effects resulting from microbial activity might be expected in the proximity of a geological repository i.e., in the excavation damaged zone, the engineered barriers, and first containments (the containers). [ABSTRACT FROM AUTHOR]