Search Results (59)

The composition and diversity of the sensitive benthic Charophyta were examined in 13 lakes and 1 pond located in the Kaçkar Mountains National Park during the summer and autumn months of 2020. While a total of 78 taxa were identified, Cosmarium became the main genus of the flora with 33 species. In the flora, the filamentous members of the Charophyta (12 species) were also noteworthy. Intraspecies variability is very high, with a Subspecies/Species index of 1.11, which reflects the sensitivity of the identified charophyte flora as an indicator of conservation efficiency. The physico-chemical analysis results and bioindicator species indicate that the investigated waters are fresh, with low salinity and a circumneutral or slightly alkaline pH, and are not organically polluted. Comparative statistics and RDA divide the studied lakes into two clusters (northern and southern in the park territory) and reveal the complex factors related to salinity and oxygen saturation as regulators of species abundance in communities. Full article

The substantial volumes of tailings produced during ore beneficiation present significant challenges for sustainable management due to potential public health hazards, particularly from metal leaching. The risk associated with tailings varies greatly depending on their mineralogical composition and climatic conditions. If tailings are classified as a non-hazardous by-product, they may serve as secondary raw materials, offering a sustainable alternative to the reliance on non-renewable primary resources. In this study, the recycling feasibility of tailings from an active copper mine was assessed through mineralogical characterization, environmental tests (e.g., static, kinetic, and leaching tests), and geochemical modeling. This multi-faceted approach aimed to predict the geochemical behavior and reactivity of tailings under varying conditions. Results from the static tests indicated that the tailings were non-acid generating. Weathering cell tests revealed circumneutral pH conditions (6.5–7.8), low sulfide oxidation rates, and low instantaneous metal concentrations (<1 mg/L), except for copper (0.6–3.5 mg/L) and iron (0.4–1.4 mg/L). These conditions are attributed to the low abundance of sulfide minerals, such as pyrite, chalcopyrite, bornite, covellite (<0.1 wt.%), and chalcocite (0.2 wt.%), which are effectively encapsulated within gangue minerals. Additionally, the presence of neutralizing minerals, specifically dolomite (27.4 wt.%) and calcite (2.4 wt.%), further stabilizes pH and promotes metal sequestration in secondary mineral forms. The Toxicity Characteristic Leaching Procedure (TCLP) test confirmed low leachability, classifying the tailings as non-hazardous. Full article

Boron-doped diamond electrodes (BDDEs) offer a highly efficient pathway to mineralize recalcitrant compounds due to their reduced energy requirements, fewer chemical inputs, and mechanical stability. In this work, the electrochemical degradation of paraquat (PQ) and diquat (DQ) was studied using an undivided cell (Condiacell^®-type) at circumneutral pH, and under galvanostatic control. The roles of applied current density, volumetric flow rate, and herbicide concentration were systematically studied through a central composite design (CCD) using a closed-flow reaction setup. Under the best operating conditions (i.e., for PQ: 1.6 mA/cm², 80 mL/min, and 70 mL/min, and 70 mg/L; and for DQ: 1.5 mA/cm², 80 mL/min, and 73 mg/L), a spectrophotometric analysis evidenced that the herbicides were satisfactorily removed (ca. 100%) while mineralization degrees were above 90%. Furthermore, the produced effluents yielded significant increases in seed germination and root length, which suggest a reduction in toxicity. Energy consumptions of 0.13 and 0.18 kWh/g of TOC are reported with the electrochemical cells for the PQ and DQ treatments, respectively. The PQ and DQ treatments by electrooxidation are estimated to emit nearly 2.7 and 38.9 kg CO₂/m³ of water treated, with a cost around USD 250/m³. Carbon emissions could be greatly decreased for PQ (0.28 kg CO₂/m³) and DQ (0.40 kg CO₂/m³) if electricity were generated from renewable resources. Although this study suggests that the use of BDDE can be considered as a green alternative for agrochemical removal due to lower carbon emissions, the environmental profile of the process is determined by the degree of renewability of the electrical grid of each country or region. Full article

Biotic ligand models (BLMs) predict the toxicity of metals in aquatic environments by accounting for metal interactions with cell surface receptors (biotic ligands) in organisms, including water chemistry (metal speciation) and competing cations. Metal binding constants (log K_MBL values), which indicate the affinity of metals for cell surface receptors, are fundamental to BLMs, but have only been reported for a few commonly investigated metals and freshwater species. This review evaluated literature toxicity and uptake data for seven key metals (cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), uranium (U), and zinc (Zn)) and four key competing cations (protons (H), calcium (Ca), magnesium (Mg), and sodium (Na)), to derive average metal binding constants for freshwater organisms/taxa. These constants will improve current BLMs for Cd, Cu, Ni, Pb, and Zn, and aid in developing new BLMs for Co and U. The derived metal binding constants accurately predicted metal toxicity for a wide range of freshwater organisms (75–88% of data were within a factor of two and 88–98% of data were within a factor of three of the ideal 1:1 agreement line), when considering metal speciation, competing cations and the fraction of cell receptors ((f_C)_M^50%) occupied by the metal at the median (50%) effect concentration (EC₅₀). For many organisms, toxicity occurs when 50% of cell surface receptors are occupied by the metal, though this threshold can vary. Some organisms exhibit toxicity with less than 50% receptor occupancy, while others with protective mechanisms show reduced toxicity, even with similar log K_MBL values. For Cu, U, and Pb, the toxic effect of the metal hydroxide (as MOH⁺) must be considered in addition to the free metal ion (M²⁺), as these metals hydrolyse in circumneutral freshwaters (pH 5.5 to 8.5), contributing to toxicity. Full article

Given the limited understanding of species diversity and ecological preferences of diatoms of the genus Navicula in spring ecosystems, herein we present and describe as species new to science, Navicula aquaesuavis Lange-Bert., Levkov, Cid-Rodríguez, A.A.Saber and Cantonati sp. nov. This species was collected from a mountain spring located above the tree line at 1613 m a.s.l. in the Northern Apennines. The Fontana del Vescovo (Bishop’s spring), which is the locus classicus of the new species, has a low conductivity (60–70 µS cm⁻¹), temperature of ca. 5 °C, circumneutral pH (7.3–7.5), relatively low nitrate (ca. 1 mg L⁻¹), and also suffered from a discharge reduction from 1 to 0.1 L s⁻¹ from 2011 to 2023. The putative new species was confirmed by a second finding in Northern Macedonia, and we thoroughly document this second population as well. We seized the opportunity to describe this new Navicula and review the global literature on the diatom genus Navicula in spring ecosystems. Using the results of this review and our own databases on springs and wells in central Europe and Egypt, we discuss the main Navicula species and their environmental preferences in spring habitats. Full article

The altitude of the habitat is one of the important regulators of species survival. Kaçkar Mountains National Park is located in the Eastern Black Sea region of Turkey. This is the first study on the benthic diatom flora of the high mountain lakes in Kaçkar Mountains National Park, which is situated between 2782 and 3075 m a.s.l. A total of 84 diatom species were identified from benthic communities of 15 habitats in summer (19 July, 28 August) and autumn (10 September) months of 2020. The genus Pinnularia (thirteen species) formed the basis of the taxonomic list, followed by Eunotia (five species), Navicula (five species), and Frustulia (four species) genera, respectively. The waters in all the studied lakes were fresh, low-saline, with low-alkaline or circumneutral pH and organically uncontaminated, as evidenced by prevailed bioindicator groups. Statistical methods and comparative floristic results confirm the role of the lake altitude for the diatom species distribution. The species richness of the studied lakes was higher in lakes with lower altitudes. The statistical approach also revealed the potential for an increase in the number of species in high mountain lakes if the study of the diatom flora of the Kachkar Mountains National Park is continued and the species composition of the lakes is replenished. Further studies will be needed to continue exploring this pattern. To protect studied high mountain lakes, their ecological conditions must be constantly monitored in the Kaçkar Mountains National Park. Full article

A fungus, Acremonium strictum KR21-2, produces biogenic manganese oxides (BMOs) that can oxidize exogenous Mn²⁺ ions to form different BMO phases. When other guest ions are present during the BMO formation, it can strongly affect the mineralogical characteristics of the resultant BMO phase. The impact of coexisting Ni²⁺ ions on the mineralogy of BMO phases formed through enzymatic Mn(II) oxidation and its sequestration ability is not yet fully understood. To better understand it, repeated sequestration experiments were conducted using BMOs in Ni²⁺/Mn²⁺ binary, single Ni², and single Mn²⁺ solution systems with a pH range of 6.0 to 7.5. It was observed that simultaneous sequestration of Ni²⁺ and Mn²⁺ was efficient, with irreversible Ni²⁺ incorporation at pH values above 7.0. The resultant BMO phases showed that Ni²⁺-bearing Mn oxides resembling feitknechitite (β-MnOOH) were developed through enzymatic Mn(II) oxidation. At pH values below 6.5, the turbostratic birnessite structure was maintained even in Ni²⁺/Mn²⁺ binary solutions, and subsequently, the Ni²⁺ sequestration efficiency was low. The pseudo-first-order rate constants of enzymatically inactivated BMOs for Mn²⁺ sequestration were two orders of magnitude lower than those of active BMOs, indicating the crucial role of the enzymes in precipitating Ni²⁺-bearing Mn oxide phases. These findings provide new insights into the mechanism of Ni²⁺ interaction with Mn oxide through microbial activity under circumneutral pH conditions. Full article

Wastewater generated in table olive manufacturing processes (WWTOMP) is a seasonal waste difficult to manage due to the high salinity content. The treatment of WWTOMP has been accomplished by including a precoagulation stage with aluminum sulfate, oxidation using the peroxymonosulfate/Fe(III) system, and a final aerobic biological stage. The optimum conditions of precoagulation led to a chemical oxygen demand removal rate of roughly 30–35% without the need for pH adjustment. The peroxymonosulfate(PMS)/Fe(III) system was thereafter applied to the effluent after coagulation. The addition of PMS lowered the initial pH to acidic conditions (pH = 1.5–2.0). Under these operating conditions, the initial PMS concentration and the initial Fe(III) dose showed optimum values. An excess of the oxidant and/or the catalyst partially inhibited the process efficiency, and pH exerted a significant influence. COD removal was substantially increased as the pH of the solution was moved toward circumneutral values in the interval 5–4. Moreover, at pH values of 5 and 7, PMS was capable of reducing COD without the need for Fe(III) presence. The direct oxidation of organics by PMS or the generation of chloride-based oxidants (Cl₂ or HClO) is suggested to occur in parallel to the radical attack from PMS decomposition. An attempt to biologically reduce the final COD to discharge limits failed, mainly due to the high salinity content; however, the 1:2 dilution led to the reduction in COD from 6 to 2 g L⁻¹. Acclimated sludges or saline content reduction should be first considered. Full article

The significant neutralization of waste streams required after the acidic bio-oxidation of sulfidic gold ores could be avoided by performing a novel treatment at circumneutral pH with an in situ neutralization. For the first time, the white-rot fungus Phanerochaete chrysosporium was incubated in a modified culture medium containing corn steep, an industrial waste product, to support microbial activity and, subsequently, the oxidation of a sulfidic ore at an initial circumneutral pH environment. In this investigation, the concentration of the native culture medium ingredients was first evaluated with response surface methodology to attain maximum sulfide oxidation. The statistical analysis proposed a modified culture medium composed of 12.86 g/L glucose, 2.20 g/L malt extract, 1.67 g/L yeast extract, and 0.49 g/L MgSO₄·7H₂O to reach a maximum of 28.7% sulfide oxidation after 14 d-bio-oxidation. pH-controlled batch cultures showed that an increase in initial pH in the range of 5.8 to 7.0 reduced the microbial activity, affecting sulfide oxidation. In addition, the modified culture medium at which yeast extract was substituted with 1.67 g/L corn steep produced comparable microbial activity and sulfide oxidation after 14 d, attaining 21.6% at 5% w/v with a maximum 39 U/L lignin peroxidase and 116 U/L manganese peroxidase. A 40.6% sulfide oxidation and 43.8% gold recovery were obtained after 42 d three-cycle replenishing bio-oxidation and 24 h cyanidation, respectively. Overall, corn steep waste showed the potential to substitute more expensive culture medium ingredients, supporting microbial activity and oxidation of sulfidic gold ores at an initial circumneutral pH and contributing to circularity of waste management. Full article

Over the last half-century, microbial communities of the Kamchatka hot springs have been largely studied using molecular, radioisotopic, and cultural approaches. Generally, these results were obtained for mixed samples of water with sediments, for only hydrothermal water, or for only sediment samples. Simultaneous comparative analysis of the microbial communities of water and sediments was performed for only one Kamchatka hot spring with circumneutral pH. Here, the microbial communities of both sediments and water (separately) of hot spring #4229 (the Uzon Caldera, Kamchatka) with a temperature of 50–56 °C and pH of 3.2 were analyzed by 16S rRNA gene V4 fragment amplicon sequencing. It was revealed that the microbial community of sediments was represented by uncultured phylogenetically deep-branching lineages of archaea, such as ARK-15 within Thermoplasmatota and ‘Ca. Marsarchaeales’ from the Thermoproteota phyla. Metagenome analysis showed that these archaea most probably carried out the degradation of organic matter. The microbial community of the hot water is represented by thermoacidophilic, (micro)aerobic, chemolithoautotrophic, hydrogen- and sulfur-oxidizing bacteria of the genera Hydrogenobaculum (phylum Aquificota) and Acidithiobacillus (phylum Pseudomonadota). Radioisotopic tracing and DNA-stable-isotope probing techniques proved their role as primary producers in the hot spring. The experiment revealed significant differences in the composition and functions of the microbial communities of sediments and water through the example of a typical acidic hot spring in Kamchatka. Full article

Neutral mine drainage (NMD) at Force Crag mine in north-west England has a circumneutral pH and high levels of Zn contamination. A long-term geochemical and hydrological dataset from this site was analysed using a novel molar mass balance approach, which demonstrated that the water chemistry is dominated by species released by the oxidation of sulphides: sphalerite (Zn, Cd, Ni), galena (Pb, mostly removed by adsorption to ferrihydrite) and pyrite (Fe, mostly precipitates as ferrihydrite). The calculations show that the sphalerite:galena:pyrite oxidation ratio is ~1:2:1, but the mine water chemistry is dominated by Zn due to the removal of Pb and Fe by adsorption/precipitation. The acidity released by pyrite oxidation is neutralised by the dissolution of calcite and, to a lesser extent, chlorite. The presence of pyrite is responsible both for the release of acidity and the removal of some contaminant metals by adsorption on ferrihydrite. The concentrations of sulphate, Zn, Cd and Ni in the mine water decrease with increasing flow due to dilution; modest increases in metal flux with flow probably reflect increased oxidation due to greater amounts of oxygenated water flowing through the mine. In contrast, Al, Pb and Cu concentrations are positively correlated with flow due to the flushing of these metals adsorbed to ferrihydrite particles. The influence of temperature is relatively subtle; metal fluxes are a balance between abiotic oxidation (which increases at higher temperatures and flows) and bacterially mediated oxidation (which is depressed at high flow rates when temperatures decrease below 10 °C). These conclusions apply to NMD mine water throughout the UK and elsewhere in the world, including mines hosted in both limestone and silicate rocks. The molar mass balance approach, together with synchronous flow and geochemistry data, provides crucial information for effective mine-water-treatment system design by elucidating the critical roles of flow rate and temperature in determining contaminant concentrations and loads. Full article

Global warming, eutrophication, fisheries overexploitation, species invasions, and habitat loss are the major threats to freshwater biodiversity. The aim of this study was to determine the species richness and diversity of fish in 535 Polish lakes of different morphometry (area of more than 50 ha and a maximum depth ranging from 0.4 to 108.5 m) and trophic status (from oligotrophy to hypereutrophy). A total of 39 fish species were found in the studied lakes, among which eight species were alien invasive. The Shannon diversity index varied between 0 and 2.04.The most common and frequent species were Rutilus rutilus (99.8% frequency) and Perca fluviatilis (99.6% frequency). Ten fish species, including five alien ones, were characterized by a very low frequency (<1%). The number of fish species in single lakes ranged from 1 to 19. In most of the studied lakes, 11 and 12 species (104 and 108 lakes, respectively) were caught. The richest taxonomic composition (19 species) was recorded in the meso-eutrophic lake with an area of 80 ha and a maximum depth of 34.4 m, slightly poorer (18 species) in the hypereutrophic lake with an area of 168 ha and a maximum depth of 2.7 m. The poorest taxonomic composition (one species) was found in a lake with low conductivity and circumneutral pH. Statistical analysis showed that the number of fish species decreased with increasing eutrophication conditions of the studied lakes, while it increased with an increasing area and the maximum depth of these lakes. Full article

Fluorinated Fe₃O₄ microspheres with 7.1 ± 1.4 wt% of fluoride (F-Fe₃O₄-1) were prepared via glycothermal synthesis. Fluorination significantly enhanced the activity of F-Fe₃O₄-1 in catalytic wet peroxide oxidation of anionic dyes (including orange G (OG) and congo red) at pH ~7. However, the promotional effect of fluorination became less obvious for amphoteric rhodamine B and was not observed for cationic methylene blue. After reacting with H₂O₂ (40 mM) for 2 h at pH 6.5 and 40 °C, the decolorization rates of OG (0.1 mM) and the pseudo-first-order rate constant were 96.8% and 0.0284 min⁻¹ over F-Fe₃O₄-1 versus 17.6% and 0.0011 min⁻¹ over unmodified Fe₃O₄. The effects of reaction parameters (initial H₂O₂ concentration and pH value and reaction temperature) on OG decolorization with H₂O₂ over F-Fe₃O₄-1 were investigated. The reusability of F-Fe₃O₄-1 was demonstrated by OG decolorization in eight consecutive runs. Fluorination increased the isoelectric point of F-Fe₃O₄-1 to 8.7 and facilitated the adsorption and degradation of anionic dyes on the surface of F-Fe₃O₄-1 at pH ~7. Scavenging tests and EPR spectra supported that hydroxyl radicals were the main reactive species for the OG decolorization over F-Fe₃O₄-1. Full article

This work aimed to demonstrate Cu₂O/Al₂O₃ as a catalyst of the photo-Fenton process in the UV and visible spectra. Cu₂O nanoparticles were synthesized by laser ablation in liquid and supported on Al₂O₃. The catalytic activity of the resulting solid was assessed in the mineralization of bisphenol A (BPA). The studied variables were type of Al₂O₃$\left(\alpha \mathrm{and} \gamma \right)$, Cu content (0.5 and 1%), and H₂O₂ concentration (1, 5, and 10 times the stoichiometric amount). The response variables were BPA concentration and total organic carbon (TOC) removal percentage. The presence of Cu₂O nanoparticles (11 nm) with an irregular sphere-like shape was confirmed by transmission electron microscopy (TEM) and their dispersion over the catalytic surface was verified by energy-dispersed spectroscopy (EDS). These particles improve ·OH radical production, and thus a 100% removal of BPA is achieved along with ca. 91% mineralization in 60 min. The BPA oxidation rate is increased one order of magnitude compared to photolysis and doubles that for H₂O₂ + UV. An increase of 40% in the initial oxidation rate of BPA was observed when switching from α-Al₂O₃ to γ-Al₂O₃. 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, acetaldehyde, and acetic acid are the BPA oxidation by-products identified using LC/MS and based on this a reaction pathway was proposed. Finally, it was also concluded that the synthesized catalyst exhibits catalytic activity not only in the UV spectrum but also in the visible one under circumneutral pH. Therefore, Cu₂O/Al₂O₃ can be recommended to conduct a solar photo-Fenton reaction that can degrade other types of molecules. Full article

Biogenic Mn oxides (BMOs) have become captivating with regard to elemental sequestration, especially at circumneutral pH conditions. The interaction of BMOs with oxyanions, such as vanadate (V), molybdate (VI), and tungstate (VI), remains uncertain. This study examined the sequestration of V(V), Mo(VI), and W(VI) (up to ~1 mM) by BMOs formed by the Mn(II)-oxidizing fungus, Acremonium strictum KR21-2. When A. strictum KR21-2 was incubated in liquid cultures containing either Mo(VI) or W(VI) with soluble Mn²⁺, the oxyanions were sequestered in parallel with enzymatic Mn(II) oxidation with the maximum capacities of 8.8 mol% and 28.8 mol% (relative to solid Mn), respectively. More than 200 μM V(V) showed an inhibitory effect on growth and Mn(II) oxidizing ability. Sequestration experiments using preformed primary BMOs that maintained the enzymatic Mn(II) oxidizing activity, with and without exogenous Mn²⁺, demonstrated the ongoing BMO deposition in the presence of absorbent oxyanions provided a higher sequestration capacity than the preformed BMOs. X-ray diffraction displayed a larger decline of the peak arising from (001) basal reflection of turbostratic birnessite with increasing sequestration capacity. The results presented herein increase our understanding of the role of ongoing BMO formation in sequestration processes for oxyanion species at circumneutral pH conditions. Full article