Kinetics of FeS-mediated denitrification in sediments from the Camargue (Rhone delta, southern France)

Iron sulphides mediated autotrophic denitrification: An emerging bioprocess for nitrate pollution mitigation and sustainable wastewater treatment

Iron sulphides, mainly in the form of mackinawite (FeS), pyrrhotite (Fe_1-xS, x = 0-0.125) and pyrite (FeS₂), are the most abundant sulphide minerals and can be oxidized under anoxic and circumneutral pH conditions by chemoautotrophic denitrifying bacteria to reduce nitrate to N₂. Iron sulphides mediated autotrophic denitrification (ISAD) represents an important natural attenuation process of nitrate pollution and plays a pivotal role in linking nitrogen, sulphur and iron cycles in a variety of anoxic environments. Recently, it has emerged as a promising bioprocess for nutrient removal from various organic-deficient water and wastewater, due to its specific advantages including high denitrification capacity, simultaneous nitrogen and phosphorus removal, self-buffering properties, and fewer by-products generation (sulphate, waste sludge, N₂O, NH₄⁺, etc.). This paper provides a critical overview of fundamental and engineering aspects of ISAD, including the theoretical knowledge (biochemistry, and microbial diversity), its natural occurrence and engineering applications. Its potential and limitations are elucidated by summarizing the key influencing factors including availability of iron sulphides, low denitrification rates, sulphate emission and leaching heavy metals. This review also put forward two key questions in the mechanism of anoxic iron sulphides oxidation, i.e. dissolution of iron sulphides and direct substrates for denitrifiers. Finally, its prospects for future sustainable wastewater treatment are highlighted. An iron sulphides-based biotechnology towards next-generation wastewater treatment (NEO-GREEN) is proposed, which can potentially harness bioenergy in wastewater, incorporate resources (P and Fe) recovery, achieve simultaneous nutrient and emerging contaminants removal, and minimize waste sludge production.

Controls of H2S, Fe2 +, and Mn2 + on Microbial NO3 --Reducing Processes in Sediments of an Eutrophic Lake

Understanding the biogeochemical controls on the partitioning between nitrogen (N) removal through denitrification and anaerobic ammonium oxidation (anammox), and N recycling via dissimilatory nitrate (NO3 -) reduction to ammonium (DNRA) is crucial for constraining lacustrine N budgets. Besides organic carbon, inorganic compounds may serve as electron donors for NO3 - reduction, yet the significance of lithotrophic NO3 - reduction in the environment is still poorly understood. Conducting incubation experiments with additions of 15N-labeled compounds and reduced inorganic substrates (H2S, Fe2+, Mn2+), we assessed the role of alternative electron donors in regulating the partitioning between the different NO3 --reducing processes in ferruginous surface sediments of Lake Lugano, Switzerland. In sediment slurry incubations without added inorganic substrates, denitrification and DNRA were the dominant NO3 --reducing pathways, with DNRA contributing between 31 and 46% to the total NO3 - reduction. The contribution of anammox was less than 1%. Denitrification rates were stimulated by low to moderate additions of ferrous iron (Fe2+ ≤ 258 μM) but almost completely suppressed at higher levels (≥1300 μM). Conversely, DNRA was stimulated only at higher Fe2+ concentrations. Dissolved sulfide (H2S, i.e., sum of H2S, HS- and S2-) concentrations up to ∼80 μM, strongly stimulated denitrification, but did not affect DNRA significantly. At higher H2S levels (≥125 μM), both processes were inhibited. We were unable to find clear evidence for Mn2+-supported lithotrophic NO3 - reduction. However, at high concentrations (∼500 μM), Mn2+ additions inhibited NO3 - reduction, while it did not affect the balance between the two NO3 - reduction pathways. Our results provide experimental evidence for chemolithotrophic denitrification or DNRA with Fe2+ and H2S in the Lake Lugano sediments, and demonstrate that all tested potential electron donors, despite the beneficial effect at low concentrations of some of them, can inhibit NO3 - reduction at high concentration levels. Our findings thus imply that the concentration of inorganic electron donors in lake sediments can act as an important regulator of both benthic denitrification and DNRA rates, and suggest that they can exert an important control on the relative partitioning between microbial N removal and N retention in lakes.

Glyphosate and nutrients removal from simulated agricultural runoff in a pilot pyrrhotite constructed wetland

Pyrrhotite is often considered as a gangue mineral, and discarded in mine wastes and tailings. Glyphosate and fertilizer, often excessively used in agriculture, flow into water bodies with agriculture runoff, and cause pollution of water bodies. In this study, the pyrrhotite was used as a substrate in a pilot constructed wetland (CW) to remove the glyphosate and nutrients from simulated agriculture runoff. In nearly one year, the pilot pyrrhotite constructed wetland (Pyrr-CW) removed 90.3 ± 6.1% of glyphosate, 88.2 ± 5.1 of total phosphorus (TP) and 60.40 ± 5.60% of total nitrogen (TN) on average, much higher than the control CW. The abundances of sulfur-oxidizing bacteria, such as Sulfurifustis, Sulfuriferula and Thiobacillus, were much higher in the Pyrr-CW than those in the control CW. In the Pyrr-CW goethite was produced by pyrrhotite aerobic oxidation (PAO) and pyrrhotite autotrophic denitrification (PAD) continuously and spontaneously. Higher glyphosate and TP removals were resulted from adsorption on the goethite produced, and higher TN removal was attributed to the PAD. High glyphosate and nutrients removal could keep a long term until the pyrrhotite in the Pyrr-CW was used up. The phosphorus (P) sequestered in the Pyrr-CW existed mainly in organic P, (Fe + Al)P and (Ca + Mg)P, and their order was (Fe + Al)P > organic P > (Ca + Mg)P. No heavy metal ions released from the Pyrr-CW. With higher and lasting removal rate, and lower cost, the Pyrr-CW is a promising technology for simultaneous glyphosate and nutrients removal from agricultural runoff and wastewater.

Nutrient removal through pyrrhotite autotrophic denitrification: Implications for eutrophication control

This study investigated nutrient removal kinetics and main influencing factors of natural pyrrhotite autotrophic denitrification (PAD), and nutrient removal performance and the microbial community in the PAD biofilter (PADB). Results demonstrated that both NO₃^- and PO₄^3- in wastewater were nearly completely removed, and biological N removal and chemical P removal took place simultaneously in the PAD process. NO₃^- removal kinetics of the PAD can be described with half-order kinetics. The PAD was effective across a wide temperature range of 11-34 °C, initial NO₃^--N range of 13-52 mg·L^-1 and PO₄^3--P below 60 mg·L^-1. Both NO₃^- and PO₄^3- decreased gradually with wastewater flowing along the PADB. The PADB operation results show that at 12 h HRT, when the PADB treated wastewater containing 30.95 ± 0.97 mg·L^-1 of NO₃^- and 3.02 ± 0.10 mg·L^-1 of PO₄^3--P, the effluent contained 1.15 ± 2.08 and 0.09 ± 0.11 mg·L^-1 of NO₃^--N and PO₄^3--P on average, respectively. In the PADB the dominant bacteria were Thiobacillus and Sulfurimonas, which used pyrrhotite as the electron donor to reduce NO₃^-. The relative abundance of Thiobacillus at the bottom of the PADB increased from 0.81% to 58.65% and that of Sulfurimonas decreased from 97.22% to 12.30%, with exposure to pyrrhotite. From the bottom to the top of the PADB, the relative abundance of Thiobacillus increased from 58.65% to 86.23% and Sulfurimonas decreased from 12.30% to 0.52%. Technologies based on the PAD are promising ways to control eutrophication.

Anaerobic pyrite oxidation in a naturally occurring pyrite-rich sediment under preload surcharge

Pyrite undergoes oxidation when exposed to aqueous oxygen to produce acidic leachate with high concentrations of H⁺, SO₄^2-, and Fe³⁺. The oxidation mechanism is currently ascribed to contact between the mineral and aqueous oxygen. Consequently, management of acidic leachate from acid sulfate soils and acid mine drainage is focused on the prevention of contact between the sediment and aqueous oxygen through the surface. Intriguing though is the fact that in aquatic sediments, redox processes occur in sequence with the oxidizing agents. Among the common oxidants in aquatic sediments are O₂, [Formula: see text], Mn, and Fe, in the order of efficiency. Consequently, following the depletion of oxygen in pyrite-rich sediment, it would be expected that [Formula: see text], followed by Mn and then Fe, would continue the oxidation process. However, evidence of anaerobic pyrite oxidation in a naturally occurring pyrite-rich sediment is limited. Few studies have investigated the process in aquatic systems but mostly in laboratory experimental set ups. In this study, pyrite oxidation in a naturally occurring pyrite-rich sediment was investigated. A section of the sediment was covered with surface surcharge, in the form of compacted fill. The section of the sediment outside the surcharged area was preserved and used as control experiment. Solid phase soil and porewater samples were subjected to elemental, mineralogical, and microbial analyses. The results show excess accumulation of sulfate and sulfide in the anoxic zones of the original sediment and beneath the surcharge, accompanied by the disappearance of [Formula: see text], Mn, and Fe in the anoxic zones, indicating electron transfers between donors and acceptors, with pyrite as the most likely electron donor. The study outcome poses a significant challenge to the use of surface cover for the management of acidic leachate from pyrite oxidation, particularly, in areas rich in [Formula: see text], MnO^-₂, or Fe.

Differential Sensitivity of Wetland-Derived Nitrogen Cycling Microorganisms to Copper Nanoparticles

Metallic nanoparticles (NPs), the most abundant nanomaterials in consumer and industrial products, are the most probable class to enter the environment. In this study, wetland-derived microcosms were incubated with copper nanoparticles (Cu-NP) and ionic CuCl₂ to investigate acute (10 days) and chronic (100 days) exposure towards nitrogen cycling microorganisms. The microbial ecology of wetlands play a crucial role in balancing nitrogen in pristine environments as well as in areas impacted by high nutrient loads (e.g., at wastewater effluent discharges). Gene abundance and expression changes were monitored using the GeoChip 5.0 high throughput functional gene microarray and metatranscriptomic shotgun sequencing (RNA-seq), respectively. After 10 days, the Cu-NP impacted microbial communities experienced structural shifts within microorganisms associated with dissimilatory nitrogen reduction accompanied by lower nitrate removal as compared to the unexposed controls. By day 100, these differences were largely resolved and nitrate removal was similar to the unexposed control. Furthermore, the Cu-NP exposed microcosms tolerated copper and were more resilient and adaptive than the unexposed controls based on the abundance and expression of other functions, including electron transfer, metal homeostasis, and stress response. These findings suggest sudden influxes of Cu-NPs into wetland systems may impair nitrogen removal initially, but long-term microbial shifts and functional redundancy would promote the net flux of total nitrogen out of the wetlands.

Simultaneous nitrate and phosphate removal from wastewater lacking organic matter through microbial oxidation of pyrrhotite coupled to nitrate reduction

This study investigated the efficiency of a pyrrhotite autotrophic denitrification biofilter (PADB) technology for simultaneous N and P removal from wastewater lacking organic matter. A PADB was constructed with natural pyrrhotite as the biofilter medium and inoculated with autotrophic denitrifies enriched from anaerobic sludge. Over an operating period of 247 days, PADB efficiently removed NO3(-) and PO4(3-) simultaneously from wastewater that lacked organic matter. The hydraulic retention time (HRT), and influent NO3(-) and PO4(3-) concentrations affected the removal of NO3(-) and PO4(3-). A longer HRT led to lower concentrations of NO3(-) and PO4(3-) in the effluent. The PO4(3-) removal was influenced by NO3(-) removed; the more NO3(-) removed, the more PO4(3-) removed. As the synthetic wastewater containing NO3(-)-N of 28 mg L(-1) and PO4(3-)-P of 6 mg L(-1) in the absence of organic matter was treated by PADB at HRT of 24 h, total oxidized nitrogen (TON; NO2(-)-N + NO3(-)-N) and PO4(3-)-P concentrations of effluent were as low as 1.13 and 0.28 mg L(-1), respectively. When treatment of municipal wastewater treatment plant (WWTP) secondary effluent with TON of 21.11 mg L(-1) and PO4(3-)-P of 2.62 mg L(-1) at HRT of 24 h, the effluent TON was 1.89 mg L(-1) and PO4(3-)-P was 0.34 mg L(-1). PO4(3-) was removed through the formation of secondary minerals with Fe and Ca. These secondary minerals contained elevated phosphorus, which presents a potential for P recovery from wastewater.

Genomic and metagenomic analysis of microbes in a soil environment affected by the 2011 Great East Japan Earthquake tsunami

BACKGROUND

The Great East Japan Earthquake of 2011 triggered large tsunami waves, which flooded broad areas of land along the Pacific coast of eastern Japan and changed the soil environment drastically. However, the microbial characteristics of tsunami-affected soil at the genomic level remain largely unknown. In this study, we isolated microbes from a soil sample using general low-nutrient and seawater-based media to investigate microbial characteristics in tsunami-affected soil.

RESULTS

As expected, a greater proportion of strains isolated from the tsunami-affected soil than the unaffected soil grew in the seawater-based medium. Cultivable strains in both the general low-nutrient and seawater-based media were distributed in the genus Arthrobacter. Most importantly, whole-genome sequencing of four of the isolated Arthrobacter strains revealed independent losses of siderophore-synthesis genes from their genomes. Siderophores are low-molecular-weight, iron-chelating compounds that are secreted for iron uptake; thus, the loss of siderophore-synthesis genes indicates that these strains have adapted to environments with high-iron concentrations. Indeed, chemical analysis confirmed the investigated soil samples to be rich in iron, and culture experiments confirmed weak cultivability of some of these strains in iron-limited media. Furthermore, metagenomic analyses demonstrated over-representation of denitrification-related genes in the tsunami-affected soil sample, as well as the presence of pathogenic and marine-living genera and genes related to salt-tolerance.

CONCLUSIONS

Collectively, the present results would provide an example of microbial characteristics of soil disturbed by the tsunami, which may give an insight into microbial adaptation to drastic environmental changes. Further analyses on microbial ecology after a tsunami are envisioned to develop a deeper understanding of the recovery processes of terrestrial microbial ecosystems.

Antarctic and Arctic populations of the ciliate Euplotes nobilii show common pheromone-mediated cell-cell signaling and cross-mating

Wild-type strains of the protozoan ciliate Euplotes collected from different locations on the coasts of Antarctica, Tierra del Fuego and the Arctic were taxonomically identified as the morpho-species Euplotes nobilii, based on morphometric and phylogenetic analyses. Subsequent studies of their sexual interactions revealed that mating combinations of Antarctic and Arctic strains form stable pairs of conjugant cells. These conjugant pairs were isolated and shown to complete mutual gene exchange and cross-fertilization. The biological significance of this finding was further substantiated by demonstrating that close homology exists among the three-dimensional structures determined by NMR of the water-borne signaling pheromones that are constitutively secreted into the extracellular space by these interbreeding strains, in which these molecules trigger the switch between the growth stage and the sexual stage of the life cycle. The fact that Antarctic and Arctic E. nobilii populations share the same gene pool and belong to the same biological species provides new support to the biogeographic model of global distribution of eukaryotic microorganisms, which had so far been based exclusively on studies of morphological and phylogenetic taxonomy.

Microbial oxidation of pyrite coupled to nitrate reduction in anoxic groundwater sediment

Although many areas in Denmark are intensively agricultured, the discharge of nitrate from groundwater aquifers to surface water is often lower than expected. In this study it is experimentally demonstrated that anoxic nitrate reduction in sandy sediment containing pyrite is a microbially mediated denitrification process with pyrite as the primary electron donor. The process demonstrates a temperature dependency (Q10) of 1.8 and could be completely inhibited by addition of a bactericide (NaN3). Experimentally determined denitrification rates show that more than 50% of the observed nitrate reduction can be ascribed to pyrite oxidation. The apparent zero-order denitrification rate in anoxic pyrite containing sediment at groundwater temperature has been determined to be 2-3 micromol NO3- kg(-1) day(-1). The in situ groundwater chemistry at the boundary between the redoxcline and the anoxic zone reveals that between 65 and 80% of nitrate reduction in the lower part of the redoxcline is due to anoxic oxidation of pyrite by nitrate with resulting release of sulfate. It is concluded that microbes can control groundwater nitrate concentrations by denitrification using primarily pyrite as electron donor at the oxic-anoxic boundary in sandy aquifers thus determining the position and downward progression of the redox boundary between nitrate-containing and nitrate-free groundwater.