Sorption of copper and phosphate to diverse biogenic iron (oxyhydr)oxide deposits

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.

Potassium jarosite seeding of soils decreases lead and arsenic bioaccessibility: A path toward concomitant remediation

Soils are common sources of metal(loid) contaminant exposure globally. Lead (Pb) and arsenic (As) are of paramount concern due to detrimental neurological and carcinogenic health effects, respectively. Pb and/or As contaminated soils require remediation, typically leading to excavation, a costly and environmentally damaging practice of removing soil to a central location (e.g., hazardous landfill) that may not be a viable option in low-income countries. Chemical remediation techniques may allow for in situ conversion of soil contaminants to phases that are not easily mobilized upon ingestion; however, effective chemical remediation options are limited. Here, we have successfully tested a soil remediation technology using potted soils that relies on converting soil Pb and As into jarosite-group minerals, such as plumbojarosite (PLJ) and beudantite, possessing exceptionally low bioaccessibility [i.e., solubility at gastric pH conditions (pH 1.5 to 3)]. Across all experiments conducted, all new treatment methods successfully promoted PLJ and/or beudantite conversion, resulting in a proportional decrease in Pb and As bioaccessibility. Increasing temperature resulted in increased conversion to jarosite-group minerals, but addition of potassium (K) jarosite was most critical to Pb and As bioaccessibility decreases. Our methods of K-jarosite treatment yielded <10% Pb and As bioaccessibility compared to unamended soil values of approximately 70% and 60%, respectively. The proposed treatment is a rare dual remediation option that effectively treats soil Pb and As such that potential exposure is considerably reduced. Research presented here lays the foundation for ongoing field application.

The role of dissolved pyrogenic carbon from biochar in the sorption of As(V) in biogenic iron (oxyhydr)oxides

Water contamination by arsenic (As) affects millions of people around the world, making techniques to immobilize or remove this contaminant a pressing societal need. Biochar and iron (oxyhydr)oxides [in particular, biogenic iron (oxyhydr)oxides (BIOS)] offer the possibility of stabilizing As in remediation systems. However, little is known about the potential antagonism in As sorption generated by the dissolved organic carbon (DOC) from biochar, or whether DOC affects how As(V) interacts with BIOS. For this reason, our objectives were to evaluate the i) As(V) sorption potential in BIOS when there is presence of DOC from pyrolyzed biochars at different temperatures; and ii) identify whether the presence of DOC alters the surface complexes formed by As(V) sorbed in the BIOS. We conducted As(V) sorption experiments with BIOS at circumneutral pH conditions and in the presence of DOC from sugarcane (Saccharum officinarum) straw biochar at pyrolyzed 350 (BC350) and 750 °C (BC750). The As(V) content was quantified by inductively coupled plasma mass spectrometry, and the BIOS structure and As(V) sorption mechanisms were investigated by X-ray absorption spectroscopy. In addition, the organic moieties comprising the DOC from biochars were investigated by attenuated total reflectance Fourier transform infrared spectroscopy. The addition of DOC did not change the biomineral structure or As(V) oxidation state. The presence of DOC, however, reduced by 25 % the sorption of As(V), with BC350 being responsible for the greatest reduction in As(V) sorption capacity. Structural modeling revealed As(V) predominantly formed binuclear bidentate surface complexes on BIOS. The presence of DOC did not change the binding mechanism of As(V) in BIOS, suggesting that the reduction of As(V) sorption to BIOS was due to site blocking. Our results bring insights into the fate of As(V) in surface waters and provide a basis for understanding the competitive sorption of As(V) in environments with biochar application.

Phosphorous removal and recovery from urban wastewater: Current practices and new directions

Phosphate rocks are an irreplaceable resource to produce fertilizers, but their availability will not be enough to meet the increasing demands of agriculture for food production. At the same time, the accumulation of phosphorous discharged by municipal wastewater treatment plants (WWTPs) is one of the main causes of eutrophication. In a perspective of circular economy, WWTPs play a key role in phosphorous management. Indeed, phosphorus removal and recovery from WWTPs can both reduce the occurrence of eutrophication and contribute to meeting the demand for phosphorus-based fertilizers. Phosphorous removal and recovery are interconnected phases in WWTP with the former generally involved in the mainstream treatment, while the latter on the side streams. Indeed, by reducing phosphorus concentration in the WWTP side streams, a further improvement of the overall phosphorus removal from the WWTP influent can be obtained. Many studies and patents have been recently focused on treatments and processes aimed at the removal and recovery of phosphorous from wastewater and sewage sludge. Notably, new advances on biological and material sciences are constantly put at the service of conventional or unconventional wastewater treatments to increase the phosphorous removal efficiency and/or reduce the treatment costs. Similarly, many studies have been devoted to the development of processes aimed at the recovery of phosphorus from wastewaters and sludge to produce fertilizers, and a wide range of recovery percentages is reported as a function of the different technologies applied (from 10-25% up to 70-90% of the phosphorous in the WWTP influent). In view of forthcoming and inevitable regulations on phosphorous removal and recovery from WWTP streams, this review summarizes the main recent advances in this field to provide the scientific and technical community with an updated and useful tool for choosing the best strategy to adopt during the design or upgrading of WWTPs.

Mechanisms of orthophosphate removal from water by lanthanum carbonate and other lanthanum-containing materials

Removing phosphorus (P) from water and wastewater is essential for preventing eutrophication and protecting environmental quality. Lanthanum [La(III)]-containing materials can effectively and selectively remove orthophosphate (PO₄) from aqueous systems, but there remains a need to better understand the underlying mechanism of PO₄ removal. Our objectives were to 1) identify the mechanism of PO₄ removal by La-containing materials and 2) evaluate the ability of a new material, La₂(CO₃)_3(s), to remove PO₄ from different aqueous matrices, including municipal wastewater. We determined the dominant mechanism of PO₄ removal by comparing geochemical simulations with equilibrium data from batch experiments and analyzing reaction products by X-ray diffraction and scanning transmission electron microscopy with energy dispersive spectroscopy. Geochemical simulations of aqueous systems containing PO₄ and La-containing materials predicted that PO₄ removal occurs via precipitation of poorly soluble LaPO_4(s). Results from batch experiments agreed with those obtained from geochemical simulations, and mineralogical characterization of the reaction products were consistent with PO₄ removal occurring primarily by precipitation of LaPO_4(s). Between pH 1.5 and 12.9, La₂(CO₃)_3(s) selectively removed PO₄ over other anions from different aqueous matrices, including treated wastewater. However, the rate of PO₄ removal decreased with increasing solution pH. In comparison to other solids, such as La(OH)_3(s), La₂(CO₃)_3(s) exhibits a relatively low solubility, particularly under slightly acidic conditions. Consequently, release of La³⁺ into the environment can be minimized when La₂(CO₃)_3(s) is deployed for PO₄ sequestration.

Mineral characterization and composition of Fe-rich flocs from wetlands of Iceland: Implications for Fe, C and trace element export

In freshwater wetlands, redox interfaces characterized by circumneutral pH, steep gradients in O₂, and a continual supply of Fe(II) form ecological niches favorable to microaerophilic iron(II) oxidizing bacteria (FeOB) and the formation of flocs; associations of (a)biotic mineral phases, microorganisms, and (microbially-derived) organic matter. On the volcanic island of Iceland, wetlands are replenished with Fe-rich surface-, ground- and springwater. Combined with extensive drainage of lowland wetlands, which forms artificial redox gradients, accumulations of bright orange (a)biotically-derived Fe-rich flocs are common features of Icelandic wetlands. These loosely consolidated flocs are easily mobilized, and, considering the proximity of Iceland's lowland wetlands to the coast, are likely to contribute to the suspended sediment load transported to coastal waters. To date, however, little is known regarding (Fe) mineral and elemental composition of the flocs. In this study, flocs from wetlands (n = 16) across Iceland were analyzed using X-ray diffraction and spectroscopic techniques (X-ray absorption and ⁵⁷Fe Mössbauer) combined with chemical extractions and (electron) microscopy to comprehensively characterize floc mineral, elemental, and structural composition. All flocs were rich in Fe (229-414 mg/g), and floc Fe minerals comprised primarily ferrihydrite and nano-crystalline lepidocrocite, with a single floc sample containing nano-crystalline goethite. Floc mineralogy also included Fe in clay minerals and appreciable poorly-crystalline aluminosilicates, most likely allophane and/or imogolite. Microscopy images revealed that floc (bio)organics largely comprised mineral encrusted microbially-derived components (i.e. sheaths, stalks, and EPS) indicative of common FeOB Leptothrix spp. and Gallionella spp. Trace element contents in the flocs were in the low μg/g range, however nearly all trace elements were extracted with hydroxylamine hydrochloride. This finding suggests that the (a)biotic reductive dissolution of floc Fe minerals, plausibly driven by exposure to the varied geochemical conditions of coastal waters following floc mobilization, could lead to the release of associated trace elements. Thus, the flocs should be considered vectors for transport of Fe, organic carbon, and trace elements from Icelandic wetlands to coastal waters.

Advantages and limits to copper phytoextraction in vineyards

Copper (Cu) contamination of soils may alter the functioning and sustainability of vineyard ecosystems. Cultivating Cu-extracting plants in vineyard inter-rows, or phytoextraction, is one possible way currently under consideration in agroecology to reduce Cu contamination of vineyard topsoils. This option is rarely used, mainly because Cu phytoextraction yields are too low to significantly reduce contamination due to the relatively "low" phytoavailability of Cu in the soil (compared to other trace metals) and its preferential accumulation in the roots of most extracting plants. This article describes the main practices and associated constraints that could theoretically be used to maximize Cu phytoextraction at field scale, including the use of Cu-accumulating plants grown (i) with acidifying plants (e.g., leguminous plants), and/or (ii) in the presence of acidifying fertilizers (ammonium, elemental sulfur), or (iii) with soluble "biochelators" added to the soil such as natural humic substances or metabolites produced by rhizospheric bacteria such as siderophores, in the inter-rows. This discussion article also provides an overview of the possible ways to exploit Cu-enriched biomass, notably through ecocatalysis or biofortification of animal feed.

The Structure of Natural Biogenic Iron (Oxyhydr)oxides Formed in Circumneutral pH Environments

Biogenic iron (Fe) (oxyhydr)oxides (BIOS) partially control the cycling of organic matter, nutrients, and pollutants in soils and water via sorption and redox reactions. Although recent studies have shown that the structure of BIOS resembles that of two-line ferrihydrite (2LFh), we lack detailed knowledge of the BIOS local coordination environment and structure required to understand the drivers of BIOS reactivity in redox active environments. Therefore, we used a combination of microscopy, scattering, and spectroscopic methods to elucidate the structure of BIOS sampled from a groundwater seep in North Carolina and compare them to 2LFh. We also simulated the effects of wet-dry cycles by varying sample preparation (e.g., freezing, flash freezing with freeze drying, freezing with freeze drying and oven drying). In general, the results show that both the long- and short-range ordering in BIOS are structurally distinct and notably more disordered than 2LFh. Our structure analysis, which utilized Fe K-edge X-ray absorption spectroscopy, Mössbauer spectroscopy, X-ray diffraction, and pair distribution function analyses, showed that the BIOS samples were more poorly ordered than 2LFh and intimately mixed with organic matter. Furthermore, pair distribution function analyses resulted in coherent scattering domains for the BIOS samples ranging from 12-18 Å, smaller than those of 2LFh (21-27 Å), consistent with reduced ordering. Additionally, Fe L-edge XAS indicated that the local coordination environment of 2LFh samples consisted of minor amounts of tetrahedral Fe(III), whereas BIOS were dominated by octahedral Fe(III), consistent with depletion of the sites due to small domain size and incorporation of impurities (e.g., organic C, Al, Si, P). Within sample sets, the frozen freeze dried and oven dried sample preparation increased the crystallinity of the 2LFh samples when compared to the frozen treatment, whereas the BIOS samples remained more poorly crystalline under all sample preparations. This research shows that BIOS formed in circumneutral pH waters are poorly ordered and more environmentally stable than 2LFh.

Uranium and neptunium retention mechanisms in Gallionella ferruginea/ferrihydrite systems for remediation purposes

The ubiquitous β-Proteobacterium Gallionella ferruginea is known as stalk-forming, microaerophilic iron(II) oxidizer, which rapidly produces iron oxyhydroxide precipitates. Uranium and neptunium sorption on the resulting intermixes of G. ferruginea cells, stalks, extracellular exudates, and precipitated iron oxyhydroxides (BIOS) was compared to sorption to abiotically formed iron oxides and oxyhydroxides. The results show a high sorption capacity of BIOS towards radionuclides at circumneutral pH values with an apparent bulk distribution coefficient (Kd) of 1.23 × 104 L kg-1 for uranium and 3.07 × 105 L kg-1 for neptunium. The spectroscopic approach by X-ray absorption spectroscopy (XAS) and ATR FT-IR spectroscopy, which was applied on BIOS samples, showed the formation of inner-sphere complexes. The structural data obtained at the uranium LIII-edge and the neptunium LIII-edge indicate the formation of bidentate edge-sharing surface complexes, which are known as the main sorption species on abiotic ferrihydrite. Since the rate of iron precipitation in G. ferruginea-dominated systems is 60 times faster than in abiotic systems, more ferrihydrite will be available for immobilization processes of heavy metals and radionuclides in contaminated environments and even in the far-field of high-level nuclear waste repositories.

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.

Emerging lanthanum (III)-containing materials for phosphate removal from water: A review towards future developments

The last two decades have seen a rise in the development of lanthanum (III)-containing materials (LM) for controlling phosphate in the aquatic environment. >70 papers have been published on this topic in the peer-reviewed literature, but mechanisms of phosphate removal by LM as well as potential environmental impacts of LM remain unclear. In this review, we summarize peer-reviewed scientific articles on the development and use of 80 different types of LM in terms of prospective benefits, potential ecological impacts, and research needs. We find that the main benefits of LM for phosphate removal are their ability to strongly bind phosphate under diverse environmental conditions (e.g., over a wide pH range, in the presence of diverse aqueous constituents). The maximum phosphate uptake capacity of LM correlates primarily with the La content of LM, whereas reaction kinetics are influenced by LM formulation and ambient environmental conditions (e.g., pH, presence of co-existing ions, ligands, organic matter). Increased La solubilization can occur under some environmental conditions, including at moderately acidic pH values (i.e., < 4.5-5.6), highly saline conditions, and in the presence of organic matter. At the same time, dissolved La will likely undergo hydrolysis, bind to organic matter, and combine with phosphate to precipitate rhabdophane (LaPO₄·H₂O), all of which reduce the bioavailability of La in aquatic environments. Overall, LM use presents a low risk of adverse effects in water with pH > 7 and moderate-to-high bicarbonate alkalinity, although caution should be applied when considering LM use in aquatic systems with acidic pH values and low bicarbonate alkalinity. Moving forward, we recommend additional research dedicated to understanding La release from LM under diverse environmental conditions as well as long-term exposures on ecological organisms, particularly primary producers and benthic organisms. Further, site-specific monitoring could be useful for evaluating potential impacts of LM on both biotic and abiotic systems post-application.

Copper uptake, essentiality, toxicity, detoxification and risk assessment in soil-plant environment

Copper (Cu) is an essential metal for human, animals and plants, although it is also potentially toxic above supra-optimal levels. In plants, Cu is an essential cofactor of numerous metalloproteins and is involved in several biochemical and physiological processes. However, excess of Cu induces oxidative stress inside plants via enhanced production of reactive oxygen species (ROS). Owing to its dual nature (essential and a potential toxicity), this metal involves a complex network of uptake, sequestration and transport, essentiality, toxicity and detoxification inside the plants. Therefore, it is vital to monitor the biogeo-physiochemical behavior of Cu in soil-plant-human systems keeping in view its possible essential and toxic roles. This review critically highlights the latest understanding of (i) Cu adsorption/desorption in soil (ii) accumulation in plants, (iii) phytotoxicity, (iv) tolerance mechanisms inside plants and (v) health risk assessment. The Cu-mediated oxidative stress and resulting up-regulation of several enzymatic and non-enzymatic antioxidants have been deliberated at molecular and cellular levels. Moreover, the role of various transporter proteins in Cu uptake and its proper transportation to target metalloproteins is critically discussed. The review also delineates Cu build-up in plant food and accompanying health disorders. Finally, this review proposes some future perspectives regarding Cu biochemistry inside plants. The review, to a large extent, presents a complete picture of the biogeo-physiochemical behavior of Cu in soil-plant-human systems supported with up-to-date 10 tables and 5 figures. It can be of great interest for post-graduate level students, scientists, industrialists, policymakers and regulatory authorities.

Influence of coexisting calcium and magnesium ions on phosphate adsorption onto hydrous iron oxide

Removal of phosphorus (P) from municipal wastewater is of vital importance to the control of eutrophication in receiving freshwater bodies. Typical cations such as Ca²⁺ and Mg²⁺ generally exist in municipal wastewater, and they may affect the sorption behavior and mechanism of iron oxide-based materials for aqueous phosphate (H_xPO₄^x - 3, x = 0, 1, 2, or 3 depending on solution pH). To better apply iron oxide-containing materials as adsorbents to eliminate H_xPO₄^x - 3 in municipal wastewater, a hydrous ferric oxide (HFEO) was prepared and characterized at first and then the impact of coexisting Ca²⁺ and Mg²⁺ on the uptake of H_xPO₄^x - 3 by HFEO was studied. The results showed that, without coexisting Ca²⁺ and Mg²⁺, the kinetic data for H_xPO₄^x - 3 sorption onto HFEO were better described by the Elovich model (R² = 0.953) than the pseudo-second-order (R² = 0.838) and pseudo-first-order (R² = 0.641) models, and the isotherm data were fitted better with the Dubinin-Radushkevich (R² = 0.966) and Freundlich (R² = 0.953) models than with the Langmuir (R² = 0.924) model. The ligand exchange of the Fe-bound hydroxyl group with H_xPO₄^x - 3 and the generation of Fe-O-P bonding played a key role in the uptake of H_xPO₄^x - 3 by HFEO in the absence of Ca²⁺ and Mg²⁺. Coexisting Ca²⁺ and Mg²⁺ greatly improved the adsorptive removal of H_xPO₄^x - 3 by HFEO, including the adsorption capacity and initial adsorption rate. According to the Langmuir isotherm equation, the predicted maximum H_xPO₄^x - 3 adsorption capacity for HFEO at pH 7 in the presence of 2 mmol/L Ca²⁺ (24.7 mg P/g) or 2 mmol/L Mg²⁺ (18.4 mg P/g) was much larger than that without coexisting Ca²⁺ and Mg²⁺ (10.7 mg P/g). The formation of aqueous CaHPO₄⁰ and MgHPO₄⁰ species firstly and then the adsorption of the formed CaHPO₄⁰ and MgHPO₄⁰ species on the HFEO surface to generate the HPO₄^2--bridged ternary complexes (i.e., Fe(OPO₃H)Ca⁺ and Fe(OPO₃H)Mg⁺) had an important role in the improvement of H_xPO₄^x - 3 adsorption onto HFEO by coexisting Ca²⁺ and Mg²⁺.