Efficiency and mechanisms of antimony removal from wastewater using mixed cultures of iron-oxidizing bacteria and sulfate-reducing bacteria based on scrap iron

Microbial community response to hydrocarbon exposure in iron oxide mats: an environmental study

Hydrocarbon pollution is a widespread issue in both groundwater and surface-water systems; however, research on remediation at the interface of these two systems is limited. This interface is the oxic-anoxic boundary, where hydrocarbon pollutant from contaminated groundwaters flows into surface waters and iron mats are formed by microaerophilic iron-oxidizing bacteria. Iron mats are highly chemically adsorptive and host a diverse community of microbes. To elucidate the effect of hydrocarbon exposure on iron mat geochemistry and microbial community structure and function, we sampled iron mats both upstream and downstream from a leaking underground storage tank. Hydrocarbon-exposed iron mats had significantly higher concentrations of oxidized iron and significantly lower dissolved organic carbon and total dissolved phosphate than unexposed iron mats. A strong negative correlation between dissolved phosphate and benzene was observed in the hydrocarbon-exposed iron mats and water samples. There were positive correlations between iron and other hydrocarbons with benzene in the hydrocarbon-exposed iron mats, which was unique from water samples. The hydrocarbon-exposed iron mats represented two types, flocculent and seep, which had significantly different concentrations of iron, hydrocarbons, and phosphate, indicating that iron mat is also an important context in studies of freshwater mats. Using constrained ordination, we found the best predictors for community structure to be dissolved oxygen, pH, and benzene. Alpha diversity and evenness were significantly lower in hydrocarbon-exposed iron mats than unexposed mats. Using 16S rDNA amplicon sequences, we found evidence of three putative nitrate-reducing iron-oxidizing taxa in microaerophile-dominated iron mats (Azospira, Paracoccus, and Thermomonas). 16S rDNA amplicons also indicated the presence of taxa that are associated with hydrocarbon degradation. Benzene remediation-associated genes were found using metagenomic analysis both in exposed and unexposed iron mats. Furthermore, the results indicated that season (summer vs. spring) exacerbates the negative effect of hydrocarbon exposure on community diversity and evenness and led to the increased abundance of numerous OTUs. This study represents the first of its kind to attempt to understand how contaminant exposure, specifically hydrocarbons, influences the geochemistry and microbial community of freshwater iron mats and further develops our understanding of hydrocarbon remediation at the land-water interface.

Facilitating effects of the synergy with zero-valent iron and peroxysulfate on the sludge anaerobic fermentation system: Combined biological enzyme, microbial community and fermentation mechanism assessment

This study evaluated a synergetic waste activated sludge treatment strategy with environmentally friendly zero-valent iron nanoparticles (Fe0) and peroxysulfate. To verify the feasibility of the synergistic treatment, Fe0, peroxysulfate, and the mixture of peroxysulfate and Fe0 (synergy treatment) were added to different sludge fermentation systems. The study demonstrated that the synergy treatment fermentation system displayed remarkable hydrolysis performance with 435.50 mg COD/L of protein and 197.67 mg COD/L of polysaccharide, which increased 1.13-2.85 times (protein) and 1.12-1.49 times (polysaccharide) for other three fermentation system. Additionally, the synergy treatment fermentation system (754.52 mg COD/L) exhibited a well acidification performance which was 1.35-41.73 times for other systems (18.08-557.27 mg COD/L). The synergy treatment fermentation system had a facilitating effect on the activity of protease, dehydrogenase, and alkaline phosphatase, which guaranteed the transformation of organic matter. Results also indicated that Comamonas, Soehngenia, Pseudomonas, and Fusibacter were enriched in synergy treatment, which was beneficial to produce SCFAs. The activation of Fe0 on peroxysulfate promoting electron transfer, improving the active groups, and increasing the enrichment of functional microorganisms showed the advanced nature of synergy treatment. These results proved the feasibility of synergy treatment with Fe0 and peroxysulfate to enhance waste activated sludge anaerobic fermentation.

Use of Microbial Consortia in Bioremediation of Metalloid Polluted Environments

Metalloids are released into the environment due to the erosion of the rocks or anthropogenic activities, causing problems for human health in different world regions. Meanwhile, microorganisms with different mechanisms to tolerate and detoxify metalloid contaminants have an essential role in reducing risks. In this review, we first define metalloids and bioremediation methods and examine the ecology and biodiversity of microorganisms in areas contaminated with these metalloids. Then we studied the genes and proteins involved in the tolerance, transport, uptake, and reduction of these metalloids. Most of these studies focused on a single metalloid and co-contamination of multiple pollutants were poorly discussed in the literature. Furthermore, microbial communication within consortia was rarely explored. Finally, we summarized the microbial relationships between microorganisms in consortia and biofilms to remove one or more contaminants. Therefore, this review article contains valuable information about microbial consortia and their mechanisms in the bioremediation of metalloids.

Recent Advances in Biotechnologies for the Treatment of Environmental Pollutants Based on Reactive Sulfur Species

The definition of reactive sulfur species (RSS) is inspired by the reactivity and variable chemical valence of sulfur. Sulfur is an essential element for life and is a part of global geochemical cycles. Wastewater treatment bioreactors can be divided into two major categories: sulfur reduction and sulfur oxidation. We review the origins of the definition of RSS and related biotechnological processes in environmental management. Sulfate reduction, sulfide oxidation, and sulfur-based redox reactions are key to driving the coupled global carbon, nitrogen, and sulfur co-cycles. This shows the coupling of the sulfur cycle with the carbon and nitrogen cycles and provides insights into the global material-chemical cycle. We also review the biological classification and RSS metabolic mechanisms of functional microorganisms involved in the biological processes, such as sulfate-reducing and sulfur-oxidizing bacteria. Developments in molecular biology and genomic technologies have allowed us to obtain detailed information on these bacteria. The importance of RSS in environmental technologies requires further consideration.

Adsorption Characteristics of Iron on Different Layered Loess Soils

In view of the problem of Fe³⁺ pollution in an iron sulfur mine, different layers of loess soil in the Bijie area were used for adsorption to alleviate the mine wastewater pollution by natural treatment. The effects of the initial concentration of Fe³⁺, adsorption time and pH value on the adsorption performance of top, core and subsoil layers of loess soils were studied by the oscillatory equilibrium method, and the adsorption mechanism of these three soils was analyzed through a kinetic adsorption experiment and infrared spectroscopy. The results showed that the adsorption capacity of Fe³⁺ was improved by increasing the initial concentration and reaction time, but the adsorption rate of the adsorption capacity of Fe³⁺ was reduced. The adsorption rate of Fe³⁺ in the subsoil layer was faster than that in the other two layers. The higher the pH, the higher the adsorption capacity. After the pH was higher than 3.06, it had little effect on the adsorption capacity, but the adsorption rate increased. The first-order kinetic equation, second-order kinetic equation and Elovich equation were suitable for iron adsorption kinetics of three soils. The fitting correlation coefficient of the second-order kinetic equation was close to one, indicating the main role of chemical adsorption. The adsorption rate constant of the subsoil layer was about two times and three times that of the core soil layer and the topsoil layer. The Langmuir model can better fit the isothermal adsorption process. The results of infrared spectroscopy of soil showed that the content of soil organic matter played an important role in the adsorption capacity of Fe³⁺. The subsoil layer had a higher concentration of organic matter and more abundant functional groups, so the adsorption capacity of Fe³⁺ was the highest. The results could provide a theoretical basis for the removal of iron in acid mine wastewater.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Influence of different iron sources on Sb(III) removal from water by active iron-oxidizing bacteria and its mechanism

Iron-oxidizing bacteria played an important role in the treatment of Sb-containing wastewater. In this study, effect of different iron sources on Sb(III) removal ability by isolated iron-oxidizing bacteria (named as IOB-L) was conducted systemically in batch experiment. Moreover, ferrous lactate and zero-valent iron were chosen as iron sources for IOB-L. The results showed that after inoculation of 2% volume of IOB-L, Sb(III) concentration in water decreased from initial 18 mg/L to 4.1 mg/L at optimal pH of 7.0. There was no reaction between Sb(III) and ferrous lactate, whereas corrosion product of iron can adsorb a certain amount of Sb. When active IOB-L cultivated in ferrous lactate, a better removal rate of Sb(III) can be reached with a longer stagnate phase for bacteria. However, Sb(III) removal ability of IOB-L using zero-valent iron as iron source was lower. SEM-EDS, FTIR, and XPS analysis further indicated that ferrous lactate was oxidized by IOB-L and precipitated as biogenic iron oxides which had strong adsorption ability towards Sb(III), whereas zero-valent iron was not a good iron source.

Antimony reduction by a non-conventional sulfate reducer with simultaneous bioenergy production in microbial fuel cells

Environmental toxicity of antimony (Sb) is significantly increased through the widespread industrial application. The extended release of Sb above the regulatory level became a risk to humans habituated in the ecosystem. Conventional methods to remediate Sb demand high energy or resource input, which further leads to secondary pollution. The bio-electrochemical system offers a promising bioremediation strategy to remove or reduce toxic heavy metals. Thus, this research explores the possibilities of simultaneous metal sulfide (MeS) precipitation and electricity production using a full biological Microbial fuel cell (MFC). A non-conventional sulfate-reducing bacteria (SRB) Citrobacter freundii SR10 was used for this investigation, where the MFC was operated for lactate utilization in the bio-anode and Sb reduction at the bio-cathode. This study observed 81% of coulombic efficiency (bio-anode) and 97% of sulfate reduction with 99.3% Sb (V) reduction (bio-cathode), and it was concluded that the MeS precipitation entirely depends on sulfide concentration via SR10 sulfate reduction. The MFC-SR10 offers a maximum power density of 1652.9 ± 32.1 mW/m^3, and their performance was depicted using cyclic voltammetry and electrochemical impedance spectroscopy. The Sb reduction was evaluated through fluorescence spectroscopy, and the Sb (V) MeS precipitation was confirmed as stibnite (Sb₂S₃) by Raman spectroscopy and X-ray photoelectron spectroscopy. Furthermore, the matured anodic and cathodic biofilm formation was confirmed by Scanning electron microscopy with Energy-dispersive X-ray spectroscopy. Thus the MFC with SRB bio-cathode can be used as an alternative to simultaneously remove sulfate and Sb from the wastewater with electricity production.

Effective treatment of aquaculture wastewater with mussel/microalgae/bacteria complex ecosystem: a pilot study

The discharge of aquaculture wastewater increased significantly in China. Especially, high content of nitrogen and phosphorus in wastewater could destroy the receiving water environment. To reduce the pollution of aquaculture wastewater, farmed triangle sail mussel (Hyriopsis cumingii) was proposed to be cultivated in the river. This was the first time that bacteria (Bacillus subtilis and Bacillus licheniformis) and microalgae (Chlorella vulgaris) were also used and complemented ecosystem functions. The pollutants in wastewater were assimilated by Chlorella vulgaris biomass, which was then removed through continuous filter-feeding of Hyriopsis cumingii. While, Bacillus subtilis and Bacillus licheniformis enhanced the digestive enzyme activities of mussel. It demonstrated that approximately 4 mussels/m³ was the optimal breeding density. Under such condition, orthogonal experiment indicated that the dose of Bacillus subtilis, Bacillus licheniformis, and Chlorella vulgaris should be 0.5, 1, and 2 mL respectively. Compared with mussel, mussel/microalgae, mussel/bacteria system, treatment ability of the mussel/microalgae/bacteria system in batch experiment was better, and 94.67% of NH₃-N, 92.89% of TP and 77.78% of COD were reduced after reaction for 6 days. Finally, 90 thousand mussels per hectare of water were cultivated in Kulv river in China, and the field experiment showed that water quality was significantly improved. After about 35 days of operation, NH₃-N, TN, TP and COD concentration were maintained around 0.3, 0.8, 0.3, and 30 mg/L respectively. Therefore, the mussel/microalgae /bacteria system in this study showed a sustainable and efficient characteristic of aquaculture wastewater bioremediation.

Removal of Antimony in Wastewater by Antimony Tolerant Sulfate-Reducing Bacteria Isolated from Municipal Sludge

Antimony (Sb), a global and priority controlled pollutant, causes severe environmental issues. Bioremediation by microbial communities containing sulfate-reducing bacteria (SRB) is considered to be among the safest, economical, and environmentally friendly methods to remove Sb from wastewater. However, the roles of SRB species in these communities remain uncertain, and pure cultures of bacteria that may be highly efficient have not yet been developed for Sb removal. In this study, an Sb tolerant community was enriched from municipal sludge, and molecular ecological analysis showed that Escherichia (40%) and Desulfovibrio (15%) were the dominant bacteria. Further isolation and identification showed that the enriched SRB strains were closely related to Cupidesulfovibrio oxamicus, based on the molecular analyses of 16S rRNA and dsrB genes. Among them, a strain named SRB49 exhibited the highest activity in removal of Sb(V). SRB49 was able to remove 95% of Sb(V) at a concentration of 100 mg/L within 48 h under optimum conditions: a temperature of 37–40 °C, an initial pH value of 8, 4 mM of sulfate, and an initial redox potential of 145–229 mV. SEM-EDX analysis showed that SRB49 did not adsorb Sb(V) but reduced and precipitated Sb(V) via the formation of Sb₂S₃. The results demonstrated the potential roles that pure cultures of SRB species may play in Sb removal and the use of Sb-tolerant SRB strains for Sb remediation.

Synthesis of nano-silica and biogenic iron (oxyhydr)oxides composites mediated by iron oxidizing bacteria to remove antimonite and antimonate from aqueous solution: Performance and mechanisms

Removal of antimony from wastewater is essential because of its potential harm to the environment and human health. Nano-silica and biogenic iron (oxyhydr)oxides composites (BS-Fe) were prepared by iron oxidizing bacteria (IOB) mediation and the batch adsorption experiments were applied to investigate antimonite (Sb(III)) and antimonate (Sb(V)) removal behaviors. By contrast, the synthetic BS-Fe calcined at 400 ℃ (BS-Fe-400) exhibited a large specific surface area (157.353 m²/g). The maximum adsorption capacities of BS-Fe-400 were 102.10 and 337.31 mg/g for Sb(III) and Sb(V), respectively, and experimental data fit well to the Langmuir isotherm and Temkin models, and followed the pseudo-second order kinetic model. Additionally, increasing pH promoted Sb(III) adsorption, while inhibited the adsorption of Sb(V), indicating that electrostatic attraction made a contribution to Sb(V) adsorption. Moreover, different co-existing ions showed different effects on adsorption. Characterization techniques of FTIR and XPS indicated that the main functional groups involved in the adsorption were -OH, C-O, CO, C-C, etc. and Sb(III) and Sb(V) may bind to iron (oxyhydr)oxides via the formation of inner-sphere complexes. The present work revealed that the synthetic BS-Fe-400 by nano-silica and biogenic iron (oxyhydr)oxides held great application potential in antimony removal from wastewater.

Storage strategy for shale gas flowback water based on non-bactericide microorganism control

Shale gas is a promising unconventional natural gas in the world, however the produced flowback water have severe challenges to surrounding water resource. Conventional reuse technology uses bactericide to control corrosive microorganism, which might bring uncontrolled drug resistance and other secondary pollution. In this study, storage strategy of flowback water was designed as a pre-control stage to decline corrosive microorganism. Dissolved oxygen and temperature were chosen as two key parameters based on microbial physiological and biochemical characteristics. Results showed that under the cross effect of temperature and dissolved oxygen, 15 °C and anaerobic condition had the optimal microorganism control effectiveness. Microorganism amount and live/dead cell ratio decreased by 63.7% and 68.74% respectively compared raw water. COD removal efficiency reduced to only 20%, indicating that the microorganism activity was extremely inhibited. However, microorganism in flowback water was more sensitive to dissolved oxygen compared to temperature. Redundancy analysis confirmed that dissolved oxygen contribution was as high as 91.5% while temperature was not significant (p > 0.05), the contribution rate was only 8.5%. Thermococcus, Archaeoglobus, Thermovirga, Thermotoga and Moorella were the dominated thermophilic, anaerobic and sulfate reduction or metal corrosion microorganism in flowback water, so all these identified microorganisms were control targets. Importantly, all the target microorganisms detected in flowback water were declined after different storage strategies. This study provides an effective storage strategy for flowback water to inhibit the microbial amount and activity without biocides addition, which could help promote the green exploitation of shale gas.

Strength and Durability Properties of Antimony Tailing Coarse Aggregate (ATCA) Concrete

Antimony (Sb) is a trace element applied widely in modern industry. A large number of tailing solid wastes are left and accumulated in the mining area after purifying the precious antimony from the antimony ores, causing serious pollution to the environment. The major aim of this study is to investigate the feasibility of utilizing antimony tailing coarse aggregate (ATCA) as a complete substitute for natural coarse aggregate (NCA) in high-strength concrete. Concrete specimens with 25%, 50%, 75%, and 100% ATCA replacing the NCA in conventional concrete were prepared for evaluating the performance of ATCA concrete. The investigators find that ATCA concrete has good workability, and the mechanical properties and long-term behavior (shrinkage and creep) of ATCA concrete with all replacement levels are superior to those of NCA concrete. The durability indices of ATCA concrete, such as the frost-resistant, chloride permeability, and resistance to carbonation, are better than those of NCA concrete. While the alkali activity and cracking sensitivity behavior of ATCA concrete seem to be decreased, nevertheless, the difference is not significant and can be neglected. The researchers demonstrate that all of the control indices of ATCA concrete meet the requirements of the current industry standards of China. Overall, ATCA can be used in concrete to minimize environmental problems and natural resources depletion.

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.

Iron Flocs and the Three Domains: Microbial Interactions in Freshwater Iron Mats

Freshwater iron mats are dynamic geochemical environments with broad ecological diversity, primarily formed by the iron-oxidizing bacteria. The community features functional groups involved in biogeochemical cycles for iron, sulfur, carbon, and nitrogen. Despite this complexity, iron mat communities provide an excellent model system for exploring microbial ecological interactions and ecological theories in situ Syntrophies and competition between the functional groups in iron mats, how they connect cycles, and the maintenance of these communities by taxons outside bacteria (the eukaryota, archaea, and viruses) have been largely unstudied. Here, we review what is currently known about freshwater iron mat communities, the taxa that reside there, and the interactions between these organisms, and we propose ways in which future studies may uncover exciting new discoveries. For example, the archaea in these mats may play a greater role than previously thought as they are diverse and widespread in iron mats based on 16S rRNA genes and include methanogenic taxa. Studies with a holistic view of the iron mat community members focusing on their diverse interactions will expand our understanding of community functions, such as those involved in pollution removal. To begin addressing questions regarding the fundamental interactions and to identify the conditions in which they occur, more laboratory culturing techniques and coculture studies, more network and keystone species analyses, and the expansion of studies to more freshwater iron mat systems are necessary. Increasingly accessible bioinformatic, geochemical, and culturing tools now open avenues to address the questions that we pose herein.