Enhancing phosphorus recovery from sewage sludge using anaerobic-based processes: Current status and perspectives

Anaerobic-based processes are green and sustainable technologies for phosphorus (P) recovery from sewage sludges economically and are promising in practical application. However, the P release efficiency is always not satisfied. In this paper, the P release mechanisms (regarding to different P species) from sewage sludge using anaerobic-based processes are systematically summarized. The obstacles of P release and the updated achievements of enhancing P release from sewage sludges are analyzed and discussed. It can be concluded that different P species can release from sewage sludge via different anaerobic-based processes. Extracellular polymeric substances and excessive metal ions are the two main limiting factors to P release. Acid fermentation and anaerobic fermentation with sulfate reduction could be two promising ways, with P release efficiencies of up to 64% and 63%. Based on the summarization and discussion, perspectives on practical application of P recovery from sewage sludge using anaerobic-based processes are proposed.

Release characteristics and mechanisms of sediment phosphorus in contaminated and uncontaminated rivers: A case study in South China

Phosphorus (P) cycling present in sediments associated with iron (Fe), manganese (Mn) and sulfur (S) geochemical processes may cause secondary pollution in overlying water. Understanding the mechanisms of P release from sediments should help to restore water quality. This study used the diffusive gradients in thin film (DGT) technique to investigate the seasonal variation in the lability, remobilization mechanisms, and release characteristics of sediment P in the uncontaminated Xizhi River and the severely contaminated Danshui River, South China. P accumulation in sediments contributed to higher DGT-labile P concentrations in contaminated reaches, and the highest labile P concentrations were generally observed in summer season at each site. The significant positive relationships (p < 0.05) between labile Fe and P confirmed the Fe-P coupling release mechanism in uncontaminated sediments. Stronger relationships between labile Mn and P at contaminated sites indicated that Mn oxides played an important role in P remobilization. However, sulfate reduction associated with microbial activities (crucial genera: Desulfobulbus, Desulfomicrobium and Desulforhabdus) was considered to decouple the Fe & Mn-P cycling relationship, promoting P release at contaminated sites. The effluxes of sediment P were much higher in the Danshui River (mean 0.132 mg cm^-2·d^-1) than in the Xizhi River (mean 0.038 mg cm^-2·d^-1). And hot season led to growth in P effluxes that was much greater in contaminated river.

Characterization of an anaerobic marine microbial community exposed to combined fluxes of perchlorate and salinity

The recent recognition of the environmental prevalence of perchlorate and its discovery on Mars, Earth's moon, and in meteorites, in addition to its novel application to controlling oil reservoir sulfidogenesis, has resulted in a renewed interest in this exotic ion and its associated microbiology. However, while plentiful data exists on freshwater perchlorate respiring organisms, information on their halophilic counterparts and microbial communities is scarce. Here, we investigated the temporal evolving structure of perchlorate respiring communities under a range of NaCl concentrations (1, 3, 5, 7, and 10 % wt/vol) using marine sediment amended with acetate and perchlorate. In general, perchlorate consumption rates were inversely proportional to NaCl concentration with the most rapid rate observed at 1 % NaCl. At 10 % NaCl, no perchlorate removal was observed. Transcriptional analysis of the 16S rRNA gene indicated that salinity impacted microbial community structure and the most active members were in families Rhodocyclaceae (1 and 3 % NaCl), Pseudomonadaceae (1 NaCl), Campylobacteraceae (1, 5, and 7 % NaCl), Sedimenticolaceae (3 % NaCl), Desulfuromonadaceae (5 and 7 % NaCl), Pelobacteraceae (5 % NaCl), Helicobacteraceae (5 and 7 % NaCl), and V1B07b93 (7 %). Novel isolates of genera Sedimenticola, Marinobacter, Denitromonas, Azoarcus, and Pseudomonas were obtained and their perchlorate respiring capacity confirmed. Although the obligate anaerobic, sulfur-reducing Desulfuromonadaceae species were dominant at 5 and 7 % NaCl, their enrichment may result from biological sulfur cycling, ensuing from the innate ability of DPRB to oxidize sulfide. Additionally, our results demonstrated enrichment of an archaeon of phylum Parvarchaeota at 5 % NaCl. To date, this phylum has only been described in metagenomic experiments of acid mine drainage and is unexpected in a marine community. These studies identify the intrinsic capacity of marine systems to respire perchlorate and significantly expand the known diversity of organisms capable of this novel metabolism.

Variation of volatile fatty acid oxidation and methane production during the bioaugmentation of anaerobic digestion system: Microbial community analysis revealing the influence of microbial interactions on metabolic pathways

Anaerobic digestion (AD) is widely used on waste treatment for its great capability of organic degradation and energy recovery. Accumulation of volatile fatty acids (VFAs) caused by impact loadings often leads to the acidification and failure of AD systems. Bioaugmentation is a promising way to accelerate VFA degradation but the succession of microbial communities usually caused unpredictable consequences. In this study, we used the sludge previously acclimated with VFAs for the bioaugmentation of an acidified anaerobic digestion system and increased the methane yield by 8.03-9.59 times. To see how the succession of microbial communities affected bioaugmentation, dual-chamber devices separated by membrane filters were used to control the interactions between the acidified and acclimated sludges. The experimental group with separated sludges showed significant advantages of VFA consumption (5.5 times less final VFA residue than the control), while the group with mixed sludge produced more methane (4.0 times higher final methane yield than the control). Microbial community analysis further highlighted the great influences of microbial interaction on the differentiation of metabolic pathways. Acetoclastic methanogens from the acclimated sludge acted as the main contributors to pH neutralization and methane production during the early phase of bioaugmentation, and maintained active in the mixed sludge but degenerated in the separated sludges where interactions between sludge microbiotas were limited. Instead, syntrophic butyrate and acetate oxidation coupled with nitrate and sulfate reduction was enriched in the separated sludges, which lowered the methane conversion rate and would cause the failure of bioaugmentation. Our study revealed the importance of microbial interactions and the functionality of enriched microbes, as well as the potential strategies to optimize the durability and efficiency of bioaugmentation.

Continuous sulfur biotransformation in an anaerobic-anoxic sequential batch reactor involving sulfate reduction and denitrifying sulfide oxidization

The pathways and intermediates of continuous sulfur biotransformation in an anaerobic and anoxic sequential batch reactor (AA-SBR) involving sulfate reduction (SR) and denitrifying sulfide oxidization (DSO) were investigated. In the anoxic phase, DSO occurred in two sequential steps, the oxidation of sulfide (S^2-) to elemental sulfur (S⁰) and the oxidation of S⁰ to sulfate (SO₄^2-). The oxidation rate of S^2- to S⁰ was 3.31 times faster than that of S⁰ to SO₄^2-, resulting in the accumulation of S⁰ as a desired intermediate under S^2--S/NO₃^--N ratio (molar ratio) of 0.9:1. Although, approximately 60% of generated S⁰ suspended in the effluent, about 40% of S⁰ retained in the sludge, which could be further oxidized or reduced in anoxic or anaerobic phase. In anoxic, S⁰ was subsequently oxidized to SO₄^2- under S^2--S/NO₃^--N ratio of 0.5:1. In anaerobic, S⁰ coexist with SO₄^2- (in fresh wastewater) were simultaneously reduced to S^2-, and the reduction rate of SO₄^2- to S^2- was 3.17 times faster than that of S⁰ to S^2-, resulting in a higher production of S⁰ in subsequent anoxic phase. Microbial community analysis indicated that SO₄^2-/S⁰-reducing bacteria (e.g. Desulfomicrobium and Desulfuromonas) and S^2-/S⁰-oxidizing bacteria (e.g. Paracoccus and Thermothrix) co-participated in continuous sulfur biotransformation in the AA-SBR. A conceptual model was established to describe these main processes and key intermediates. The research offers a new insight into the reaction processes optimization for S⁰ recovery and simultaneous removal of SO₄^2- and NO₃^- in an AA-SBR.

Anaerobic Methane-Oxidizing Microbial Community in a Coastal Marine Sediment: Anaerobic Methanotrophy Dominated by ANME-3

The microbial community inhabiting the shallow sulfate-methane transition zone in coastal sediments from marine Lake Grevelingen (The Netherlands) was characterized, and the ability of the microorganisms to carry out anaerobic oxidation of methane coupled to sulfate reduction was assessed in activity tests. In vitro activity tests of the sediment with methane and sulfate demonstrated sulfide production coupled to the simultaneous consumption of sulfate and methane at approximately equimolar ratios over a period of 150 days. The maximum sulfate reduction rate was 5 μmol sulfate per gram dry weight per day during the incubation period. Diverse archaeal and bacterial clades were retrieved from the sediment with the majority of them clustered with Euryarchaeota, Thaumarcheota, Bacteroidetes, and Proteobacteria. The 16S rRNA gene sequence analysis showed that the sediment from marine Lake Grevelingen contained anaerobic methanotrophic Archaea (ANME) and methanogens as archaeal clades with a role in the methane cycling. ANME at the studied site mainly belong to the ANME-3 clade. This study provides one of the few reports for the presence of ANME-3 in a shallow coastal sediment. Sulfate-reducing bacteria from Desulfobulbus clades were found among the sulfate reducers, however, with very low relative abundance. Desulfobulbus has previously been commonly found associated with ANME, whereas in our study, ANME-3 and Desulfobulbus were not observed simultaneously in clusters, suggesting the possibility of independent AOM by ANME-3.

Efficient reduction of antimony by sulfate-reducer enriched bio-cathode with hydrogen production in a microbial electrolysis cell

Bio-cathode Microbial electrolysis cell (MEC) is a promising and eco-friendly technology for concurrent hydrogen production and heavy metal reduction. However, the bioreduction of Antimony (Sb) in a bio-electrochemical system with H₂ production is not explored. In this study, two efficient sulfate-reducing bacterial (SRB) strains were used to investigate the enhanced bioreduction of sulfate and Sb with H₂ production in the MEC. SRB Bio-cathode MEC was developed from the microbial fuel cell (MFC) and operated with an applied voltage of 0.8 V. The performance of the SRB bio-cathode was confirmed by cyclic voltammetry, linear sweep voltammetry and electrochemical impedance spectroscopy. SRB strains of BY7 and SR10 supported the synergy reduction of sulfate and Sb by sulfide metal precipitation reaction. Hydrogen gas was the main product of SRB bio-cathode, with 86.9%, and 83.6% of H₂ is produced by SR10 and BY7, respectively. Sb removal efficiency reached up to 88.2% in BY7 and 96.3% in SR10 with a sulfate reduction rate of 92.3 ± 2.6 and 98.4 ± 1.6 gm^-3d^-1 in BY7 and SR10, respectively. The conversion efficiency of Sb (V) to Sb (III) reached up to 70.1% in BY7 and 89.2% in SR10. It was concluded that the total removal efficiency of Sb relies on the amount of sulfide concentration produced by the sulfate reduction reaction. The hydrogen production rate was increased up to 1.25 ± 0.06 (BY7) and 1.36 ± 0.02 m³ H₂/(m³·d) (SR10) before addition of Sb and produced up to 0.893 ± 0.03 and 0.981 ± 0.02 m³H₂/(m³·d) after addition of Sb. The precipitates were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, which confirmed Sb (V) was reduced to Sb₂S₃.

Sulfate-reduction behavior in waste-leachate transition zones of landfill sites

The sulfate reduction behavior of the waste-leachate transition zone of landfill was investigated at different temperatures and moisture contents. Marked differences in the sulfate reduction behavior were observed in the waste-leachate transition zone. The highest H₂S concentration was observed when the solid-to-liquid ratio was 1:3 at both temperatures. Although more leachate led to higher H₂S concentrations, the solid-to-liquid ratio was likely of subordinate significance compared with temperature. The microbial community was more unstable at 50 °C and more extensive mutualistic interactions among bacteria were observed, resulting in SRB showing a more violent response to changes in the solid-to-liquid ratio. At 25 °C, it's the opposite. A temperature of 25 °C was suitable for most SRB (such as Desulfomicrobium and Desulfobulbus), while some specific SRB that did not contain the functional genes (such as Dethiobacter and Anaerolinea) played a pivotal role in the significant differences in sulfate reduction behavior observed at 50 °C. This study provides a theoretical basis for controlling the release of H₂S from landfill.

Bridging spatially segregated redox zones with a microbial electrochemical snorkel triggers biogeochemical cycles in oil-contaminated River Tyne (UK) sediments

Marine sediments represent an important sink for a number of anthropogenic organic contaminants, including petroleum hydrocarbons following an accidental oil spill. Degradation of these compounds largely depends on the activity of sedimentary microbial communities linked to biogeochemical cycles, in which abundant elements such as iron and sulfur are shuttled between their oxidized and reduced forms. Here we show that introduction of a small electrically conductive graphite rod ("the electrochemical snorkel") into an oil-contaminated River Tyne (UK) sediment, so as to create an electrochemical connection between the anoxic contaminated sediment and the oxygenated overlying water, has a large impact on the rate of metabolic reactions taking place in the bulk sediment. The electrochemical snorkel accelerated sulfate reduction processes driven by organic contaminant oxidation and suppressed competitive methane-producing reactions. The application of a comprehensive suite of chemical, spectroscopic, biomolecular and thermodynamic analyses suggested that the snorkel served as a scavenger of toxic sulfide via a redox interaction with the iron cycle. Taken as a whole, the results of this work highlight a new strategy for controlling biological processes, such as bioremediation, through the manipulation of the electron flows in contaminated sediments.

Nitrate attenuation in low-permeability sediments based on isotopic and microbial analyses

This study investigated nitrate attenuation in low-permeability sediments (LPS) in a multi-layer aquifer by integrating hydrochemical, isotopic and microbiological molecular techniques in a field site. In the meantime, the overlying high-permeability sediment (HPS) was also examined on the nitrate attenuation for the sake of comparison. Additionally, laboratory flow-through experiments were conducted to assess the overall nitrate reduction rate in the two types of sediment. The δ¹⁵N-NO₃^- and δ³⁴S-SO₄^2- values were more enriched by approximately 37‰ and 15‰ in the LPS than the overlying HPS associated with substantial reductions of the NO₃^- and SO₄^2- concentration, indicating the occurrence of strong bio-reductions in nitrate and sulfate. The microbial community diversity analyses showed a higher diversity of the denitrifiers encoding nirS- (Shannon Index SI=6.3) and nrf-type gene (SI=2.7), and the sulfate reduction bacteria (SRB) encoding the dsr gene (SI=6.4) in the LPS than in the HPS. The bacterial community structure was influenced by the groundwater hydrochemistry and the redox conditions. Due to the presence of anoxic groundwater with low levels of nutrients, the LPS featured higher abundances of nitrate reducers belonging to Alphaproteobacteria and SRB belonging to the strictly anaerobic class Clostridia relative to the HPS. Notably, chemolithotrophs were abundant in the LPS and likely coupled the reduction of nitrate with the oxidation of iron. Furthermore, the LPS was demonstrated to attenuate nitrate at a rate two times of the HPS in flow-through experiments, and denitrification accounted for approximately 93% of the nitrate reduction. The high nitrate reduction rate of the LPS was likely attributable to its high functional genes diversity. This study confirmed the occurrence of strong nitrate attenuation in the LPS. The LPS was found to play a significant role in protecting aquifers from anthropogenic contamination.

Dissimilatory reduction of sulfate and zero-valent sulfur at low pH and its significance for bioremediation and metal recovery

Redox transformations of sulfur, involving dissimilatory and assimilatory oxidation and reduction reactions, occurs in water bodies and terrestrial environments worldwide, leading to dynamic cycling of this element throughout the biosphere. In cases where zero-valent (elemental) sulfur, sulfate and other oxidized forms are used as electron acceptor in (primarily) anaerobic microbial metabolisms, the end product is hydrogen sulfide (HS^- or H₂S, dependent on pH). While neutrophilic and alkalophilic sulfidogenic prokaryotes have been known for many decades, acid-tolerant and acidophilic strains and species have been isolated and characterized only in the past twenty or so years, even though evidence for sulfide generation on these environments was previously well documented. This review outlines the background and current status of the biodiversity and metabolisms of sulfate- and sulfur-reducing prokaryotes that are metabolically active in low pH environments, and describes the developing technologies in which they are being used to remediate acidic waste waters (which are often metal-contaminated) and to recover metal resources.

Enhanced biostimulation coupled with a dynamic groundwater recirculation system for Cr(VI) removal from groundwater: A field-scale study

A large gap exists between laboratory findings and successful implementation of bioremediation technologies for the treatment of chromium (Cr)-contaminated sites. This work conducted the enhanced bioremediation of Cr(VI) in situ via the addition of organic carbon (ethanol) coupled with a dynamic groundwater recirculation (DGR)-based system in a field-scale study. The DGR system was applied to successfully (1) remove Cr(VI) from groundwater via enhanced flushing by the recirculation system and (2) deliver the biostimulant to the heterogeneous subsurface environment, including a sand/cobble aquifer and a fractured bedrock aquifer. The results showed that the combined extraction and bioreduction of Cr(VI) were able to reduce Cr(VI) concentrations from 1000 to 2000 mg/L to below the clean-up goal of 0.1 mg/L within the operation period of 52 days. The effectiveness of Cr(VI) bioremediation and the relationship between microbial communities and geochemical parameters were evaluated. Multiple-line of evidence demonstrated that the introduction of ethanol significantly stimulated a variety of bacteria, including those responsible for denitrification, sulfate reduction and reduction of Cr(VI), which contributed to the establishment of reducing conditions in both aquifers. Cr(VI) was removed from groundwater via combined mechanisms of physical removal through the DGR system and the bioreduction of Cr(VI) followed by precipitation. In particular, it was found competitive growth among Cr(VI)-reducing bacteria (such as the enrichment of Geobacter, along with the reduced relative abundance of Acinetobacter and Pseudomonas) was induced by ethanol injection. Furthermore, Cr(VI), total organic carbon, NO₂^-, and SO₄^2- played important roles in shaping the composition of the microbial community and its functions.

Sulfate concentrations affect sulfate reduction pathways and methane consumption in coastal wetlands

Coastal wetlands are an important source of methane emissions, and understanding the mechanisms that control methane emissions from coastal wetlands is of great significance to global warming. Anaerobic oxidation of methane driven by sulfate is an important process to prevent methane emissions from coastal wetlands. The effects of environmental changes on this process and the function of the sulfate-methane transition zone (SMTZ) are poorly understood. In this study, spatiotemporal variations in pore-water geochemistry (concentrations of SO₄^2-, CH₄ and DIC as well as δ¹³C-DIC and δ¹³C-CH₄) in the Beidagang wetland, Tianjin, China, were investigated to unravel factors controlling the role of anaerobic oxidation of methane in coastal wetlands. Results show that the geochemical profile of pore-water is characterized by significant spatial and temporal variability, which may be related to changes in sulfate concentration, temperature and dissolved oxygen. The carbon isotope fractionation factors (ε_C) during methane oxidation range from 8.9‰ to 12.5‰, indicating that the sulfate-driven anaerobic oxidation of methane (S-AOM) dominates the methane oxidation in the Beidagang coastal wetland in both winter and summer, in both high and low salinity wetlands, and in both open water and littoral areas. However, sulfate concentration has a strong influence on the sulfate reduction pathways and methane consumption. The consumption of methane and sulfate by S-AOM is more significant in coastal wetlands with high sulfate concentrations, with S-AOM consuming nearly all of the upward-diffusing methane (96%) and downward-diffusing sulfate (96%). In addition, the dissolved inorganic carbon (DIC) produced in the pore-water mainly comes from methanogenesis, accounting for more than 80% of the total DIC pool, but in the areas with high sulfate concentrations in water column, the contribution of S-AOM to the DIC pool is greater, although only a small fraction of the total DIC pool (9%). The depth and width of the SMTZ show a clear spatial and temporal pattern, with active methanogenesis activity and upward high methane flux shoaling the SMTZ and increasing the risk of high methane emissions from coastal wetlands with low sulfate concentrations. Our findings highlight the importance of sulfate-driven anaerobic oxidation of methane in coastal wetlands and the effect of sulfate concentration on it. It contributes to our understanding of the mechanism of methane production and emissions from the coastal wetland system, particularly in light of the increased demand for coastal wetland restoration under global warming.

Reductive dechlorination of trichloroethene under different sulfate-reducing and electron donor conditions

The effect of sulfate presence on reductive dechlorination of chlorinated ethenes has been a matter of conflict among the limited reports found in literature. This paper aims to clarify the misconceptions regarding the performance of trichloroethene biotransformation under sulfate reducing conditions by evaluating the effect of different sulfate concentrations on reductive dechlorination and to assess the influence of electron donor dose on dechlorination rate. To this end, batch experiments containing different sulfate and butyrate concentrations were conducted using trichloroethene-dechlorinating and sulfate-reducing parent cultures. Results demonstrated that if sufficient time and electron donor is provided, complete dechlorination can be achieved, even at up to 400 mg/L initial sulfate concentration. However, the rate of dichloroethene and vinyl chloride degradation is reduced as sulfide concentration increases. Moreover, the excess electron donor dose induced a slightly slower dechlorination rate. The findings of this paper present an explanatory framework for the dechlorination of TCE under sulfate reducing conditions and can contribute to the state-of-art bioremediation of contaminated sites.

Co-digestion of sulfur-rich vegetable waste with waste activated sludge enhanced phosphorus release and hydrogenotrophic methanogenesis

Anaerobic co-digestion of sulfur-rich vegetable waste (SVW) with waste activated sludge (WAS) and the underlying mechanisms associated with methane production and phosphorus (P) release were investigated. Four types of SVW (Chinese cabbage, cabbage, rapeseed cake, and garlic) were utilized for co-digestion with WAS, and the methane yield increased by 7.3%-35.3%; in the meantime, the P release amount from WAS was enhanced by 9.8%-24.9%. The organic carbon in SVW promoted methane production, while organic sulfur and the formation of FeS facilitated P release. Among the four types of SVW, rapeseed cake was identified as the most suitable co-digestion substrate for enhancing both methane production and P release due to its balanced nutrients and relatively high sulfur content. Syntrophic bacteria working with hydrogenotrophic methanogens, iron-reducing bacteria, sulfate-reducing bacteria, and hydrogenotrophic methanogens were enriched. Metabolic pathways related to sulfate reduction and methanogenesis were facilitated, especially hydrogenotrophic methanogenesis. Enzymes involved in hydrogenotrophic methanogenesis were promoted by 76.05%-407.98% with the addition of Chinese cabbage, cabbage, or rapeseed cake. This study provides an eco-friendly technology for promoting P resource and energy recovery from WAS and an in-depth understanding of the corresponding microbial mechanisms.

Bacterial communities in haloalkaliphilic sulfate-reducing bioreactors under different electron donors revealed by 16S rRNA MiSeq sequencing

Biological technology used to treat flue gas is useful to replace conventional treatment, but there is sulfide inhibition. However, no sulfide toxicity effect was observed in haloalkaliphilic bioreactors. The performance of the ethanol-fed bioreactor was better than that of lactate-, glucose-, and formate-fed bioreactor, respectively. To support this result strongly, Illumina MiSeq paired-end sequencing of 16S rRNA gene was applied to investigate the bacterial communities. A total of 389,971 effective sequences were obtained and all of them were assigned to 10,220 operational taxonomic units (OTUs) at a 97% similarity. Bacterial communities in the glucose-fed bioreactor showed the greatest richness and evenness. The highest relative abundance of sulfate-reducing bacteria (SRB) was found in the ethanol-fed bioreactor, which can explain why the performance of the ethanol-fed bioreactor was the best. Different types of SRB, sulfur-oxidizing bacteria, and sulfur-reducing bacteria were detected, indicating that sulfur may be cycled among these microorganisms. Because high-throughput 16S rRNA gene paired-end sequencing has improved resolution of bacterial community analysis, many rare microorganisms were detected, such as Halanaerobium, Halothiobacillus, Desulfonatronum, Syntrophobacter, and Fusibacter. 16S rRNA gene sequencing of these bacteria would provide more functional and phylogenetic information about the bacterial communities.

Complete genome sequence analysis of Archaeoglobus fulgidus strain 7324 (DSM 8774), a hyperthermophilic archaeal sulfate reducer from a North Sea oil field

Archaeoglobus fulgidus is the type species of genus Archaeoglobus Stetter 1998, a hyperthermophilic sulfate reducing group within the Archaeoglobi class of the euryarchaeota phylum. Members of this genus grow heterotrophically or chemolithoautotrophically with sulfate or thiosulfate as electron acceptors. Except for A. fulgidus strain 7324 and the candidate species “Archaeoglobus lithotrophicus”, which both originate from deep oil-fields, the other members of this genus have been recovered from marine hydrothermal systems. Here we describe the features of the A. fulgidus strain 7324 genome as compared to the A. fulgidus VC16 type strain. The 2.3 Mbp genome sequence of strain 7324 shares about 93.5% sequence identity with that of strain VC16^T but is about 138 Kbp longer, which is mostly due to two large ‘insertions’ carrying one extra cdc6 (cell-cycle control protein 6) gene, extra CRISPR elements and mobile genetic elements, a high-GC ncRNA gene (hgcC) and a large number of hypothetical gene functions. A comparison with four other Archaeoglobus spp. genomes identified 1001 core Archaeoglobus genes and more than 2900 pan-genome orthologous genes.

Influence of iron species on the simultaneous nitrate and sulfate removal in constructed wetlands under low/high COD concentrations

Nitrate and sulfate are crucial factors of eutrophication and black and odorous water in the surface water and thus have raised increasing environmental concerns. Constructed wetlands (CWs) are the last ecological barrier before effluent enters the natural water body. To explore the simultaneous removal of nitrate and sulfate, the CW microcosms of CW-Con (with quartz sand), CW-ZVI (quartz sand and zero-valent iron), CW-Mag (quartz sand and magnetite), CW-ZVI + Mag (quartz sand, ZVI and magnetite) groups were set up under the low (100 mg/L)/high (300 mg/L) chemical oxygen demand (COD) concentration. Under the high COD condition, CW-ZVI group showed the best performance in nitrate (97.1%) and sulfate (96.9%) removal. Under the low COD concentration, the removal content of nitrate and sulfate in CW-ZVI group was better than CW-Mag group. The reason for this result was that zero-valent iron (ZVI) could be the electron donor for nitrate and sulfate reduction. Meanwhile, ZVI promoted chemical denitrification under high COD concentration according to PCA analysis. In addition, the produced sulfides inhibited the relative abundance of denitrifying bacteria, resulting in the lowest nitrate removal rate in CW-Mag group with sufficient electron donors. This study provided an alternative method to enhance simultaneous sulfate and nitrate removal in CWs.

Sulfate reduction behavior in pressure-bearing leachate saturated zone

Attention should be paid to the sulfate reduction behavior in a pressure-bearing leachate saturated zone. In this study, within the relative pressure range of 0-0.6 MPa, the ambient temperature with the highest sulfate reduction rate of 50°C was selected to explore the difference in sulfate reduction behavior in a pressure-bearing leachate saturated zone. The results showed that the sulfate reduction rate might further increase with an increase in pressure; however, owing to the effect of pressure increase, the generated hydrogen sulfide (H₂S) could not be released on time, thereby decreasing its highest concentration by approximately 85%, and the duration extended to about two times that of the atmospheric pressure. Microbial community structure and functional gene abundance analyses showed that the community distribution of sulfate-reducing bacteria was significantly affected by pressure conditions, and there was a negative correlation between disulfide reductase B (dsrB) gene abundance and H₂S release rate. Other sulfate reduction processes that do not require disulfide reductase A (dsrA) and dsrB genes may be the key pathways affecting the sulfate reduction rate in the pressure-bearing leachate saturated zone. This study improves the understanding of sulfate reduction in landfills as well as provides a theoretical basis for the operation and management of landfills.

Combined iron and sulfate reduction biostimulation as a novel approach to enhance BTEX and PAH source-zone biodegradation in biodiesel blend-contaminated groundwater

The use of biodiesel as a transportation fuel and its growing mandatory blending percentage in diesel increase the likelihood of contaminating groundwater with diesel/biodiesel blends. A 100L-field experiment with B20 (20% biodiesel and 80% diesel, v/v) was conducted to assess the potential for the combined biostimulation of iron and sulfate reducing bacteria to enhance BTEX and PAH biodegradation in a diesel/biodiesel blend-contaminated groundwater. A B20 field experiment under monitored natural attenuation (MNA) was used as a baseline control. Ammonium acetate and a low-cost and sustainable product recovered from acid mine drainage treatment were used to stimulate iron and sulfate-reducing conditions. As a result, benzene and naphthalene concentrations (maximum concentrations were 28.1μgL^-1 and 10.0μgL^-1, respectively) remained lower than the MNA experiment (maximum concentrations were 974.7μgL^-1 and 121.3μgL^-1, respectively) over the whole experiment. Geochemical changes were chronologically consistent with the temporal change of the predominance of Geobacter and GOUTA19 which might be the key players responsible for the rapid attenuation of benzene and naphthalene. To the best of our knowledge, this is the first field experiment to demonstrate the potential for the combined iron and sulfate biostimulation to enhance B20 source-zone biodegradation.

Integration of the sulfate reduction and anammox processes for enhancing sustainable nitrogen removal in granular sludge reactors

The Anammox and Sulfate Reduction Ammonium Oxidation processes were compared in two granular sequencing batch reactors operated for 160 days under anammox conditions. It was hypothesized that increasing the concentration of SO₄^2- may positively influence the rate of N removal under anaerobic conditions and it was tested whether SO₄^2- reduction and anammox occur independently or are related to each other. The cooperation of N-S cycles by increasing the concentration of influent SO₄^2- to 952 mg S/L in the second reactor, a higher ammonium utilization rate and sulfate utilization rate was achieved compared to the first reactor, i.e., 2.1-fold and 15-fold, respectively. Nitrosomonas played the dominant role in the N metabolism, while Thauera - in the S metabolism. This study highlights the benefits of linking the N-S cycles as an effective approach for the treatment of NH₄⁺ and SO₄^2- - rich wastewater, including lower substrate removal cost and reduced energy consumption.

Induced bioelectrochemical metabolism for bioremediation of petroleum refinery wastewater: Optimization of applied potential and flow of wastewater

Hybrid based bioelectrochemical system (BES) configured with embedded anode and cathode electrodes in soil was tested for the bioelectrochemical degradation of petroleum refinery wastewater (PRW). Four applied potentials were studied to optimize under batch mode operation, among which 2 V resulted in higher COD degradation (69.2%) and power density (725 mW/m²) during 7 days of operation. Further studies with continuous mode of operation at optimized potential (2 V) showed that hydraulic retention time (HRT) of 19 h achieved the highest COD removal (37%) and highest power density (561 mW/m²). BES function with respect to treatment efficiencies of other pollutants of PRW was also identified with respect to oil and grease (batch mode, 91%; continuous mode, 34%), total dissolved salts (batch mode, 53%; continuous mode, 24%) and sulfates (batch mode, 59%; continuous mode, 42%). Soil microenvironment in association with BES forms complex processes, providing suitable conditions for efficient treatment of PRW.

Insight into the mechanisms of denitrification and sulfate reduction coexistence in cascade reservoirs of the Jialing River: Evidence from a multi-isotope approach

The coexistence of denitrification and bacterial sulfate reduction (BSR) processes is commonly observed in natural water systems. However, its formation mechanism remains unclear at a basin scale due to the difficulty of precise identification of these processes. To address this issue, we investigated the spatial-temporal variations in water chemistry and isotopic compositions (e.g., δ¹³C_DIC, δ¹⁵N_NO3, δ¹⁸O_NO3, δ³⁴S_SO4, and δ¹⁸O_SO4) in cascade reservoirs (artificial dam lakes) of the Jialing River, SW China in 2016. The results showed that the denitrification and BSR processes coexisted in the studied reservoirs, which was supported by the positive correlation between δ¹⁵N_NO3 and δ¹⁸O_NO3 and between δ³⁴S_SO4 and δ¹⁸O_SO4, and by the decreasing concentrations of NO₃^- and SO₄^2-. Moreover, covariation of Δ¹³C_DIC, Δ¹⁵N_NO3, and Δ³⁴S_SO4 indicated the dominance of heterotrophic denitrification (HD) in the reservoir waters along with the occurrence of bacterial sulfide oxidation (BSO). In addition to SO₄^2- and NO₃^-, the coexistence of HD and BSR processes were also controlled by the dissolved organic carbon (DOC) in winter and dissolved oxygen (DO) contents in other seasons. Overall, the cumulative effect of cascade reservoirs caused δ¹⁵N_NO3 and δ³⁴S_SO4 to display an upward trend from upstream to downstream in the Jialing River, while δ¹³C_DIC showed an opposite downward trend, which implying that cascade reservoirs may be in favor of the coexistence of the HD and BSR processes. This study therefore concludes that the multi-isotope approach could be a useful technique to ascertain the coexistence mechanism of HD and BSR processes in reservoir water systems.

Pseudodesulfovibrio alkaliphilus, sp. nov., an alkaliphilic sulfate-reducing bacterium isolated from a terrestrial mud volcano

The diversity of anaerobic microorganisms in terrestrial mud volcanoes is largely unexplored. Here we report the isolation of a novel sulfate-reducing alkaliphilic bacterium (strain F-1^T) from a terrestrial mud volcano located at the Taman peninsula, Russia. Cells of strain F-1^T were Gram-negative motile vibrios with a single polar flagellum; 2.0-4.0 µm in length and 0.5 µm in diameter. The temperature range for growth was 6-37 °C, with an optimum at 24 °C. The pH range for growth was 7.0-10.5, with an optimum at pH 9.5. Strain F-1^T utilized lactate, pyruvate, and molecular hydrogen as electron donors and sulfate, sulfite, thiosulfate, elemental sulfur, fumarate or arsenate as electron acceptors. In the presence of sulfate, the end products of lactate oxidation were acetate, H₂S and CO_2. Lactate and pyruvate could also be fermented. The major product of lactate fermentation was acetate. The main cellular fatty acids were anteiso-C_15:0, C_16:0, C_18:0, and iso-C_17:1ω8. Phylogenetic analysis revealed that strain F-1^T was most closely related to Pseudodesulfovibrio aespoeensis (98.05% similarity). The total size of the genome of the novel isolate was 3.23 Mb and the genomic DNA G + C content was 61.93 mol%. The genome contained all genes essential for dissimilatory sulfate reduction. We propose to assign strain F-1^T to the genus Pseudodesulfovibrio, as a new species, Pseudodesulfovibrio alkaliphilus sp. nov. The type strain is F-1^T (= KCTC 15918^T = VKM B-3405^T).

Process integration for biological sulfate reduction in a carbon monoxide fed packed bed reactor

This study examined immobilized anaerobic biomass for sulfate reduction using carbon monoxide (CO) as the sole carbon source under batch and continuous fed conditions. The immobilized bacteria with beads made of 10% polyvinyl alcohol (PVA) showed best results in terms of sulfate reduction (84 ± 3.52%) and CO utilization (98 ± 1.67%). The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was investigated employing a 1L packed bed bioreactor containing the immobilized biomass. At 48, 24 and 12 h HRT, the sulfate removal was 94.42 ± 0.15%, 89.75 ± 0.47% and 61.08 ± 0.34%, respectively, along with a CO utilization of more than 90%. The analysis of variance (ANOVA) of the results obtained showed that only the initial CO concentration significantly affected the sulfate reduction process. The reactor effluent sulfate concentrations were 27.41 ± 0.44, 59.16 ± 1.08, 315.83 ± 7.33 mg/L for 250, 500 and 1000 mg/L of influent sulfate concentrations respectively, under the optimum operating conditions. The sulfate reduction rates matched well with low inlet sulfate loading rates, indicating stable performance of the bioreactor system. Overall, this study yielded very high sulfate reduction efficiency by the immobilized anaerobic biomass under high CO loading condition using the packed bed reactor system.