Response surface approach to optimize the removal of the critical raw material dysprosium from water through living seaweeds.

Dysprosium (Dy) is a rare earth element with a high economic and strategic value, and simultaneously an emerging contaminant, whose removal from wastewaters is gaining increasing attention. In this work, the Response Surface Methodology (RSM) combined with a Box-Behnken Design (3 factors-3 levels) was used to optimize the key operational conditions that influence the uptake of Dy by two living seaweed, Ulva sp. and Gracilaria sp.. The initial concentration of Dy (10-500 µg/L), water salinity (10-30), and seaweed dosage (0.5-5.5 g/L) were the independent variables, while the removal efficiency (%) and bioaccumulation (q, µg/g) were the response variables. Results highlighted the high capacity of both species to capture Dy. After 168 h, the optimal conditions that led to a maximum of 91 % of Dy removed by Gracilaria sp. were: 500 µg of Dy per L of water, salinity 10, and 5.5 g of seaweed per L. For Ulva sp., a maximum removal percentage of 79 % was achieved in the conditions: any initial concentration of Dy, salinity 20, and seaweed dosage of 3.7 g/L. Independently of the species, the response surfaces showed that the most important variable for the removal is the seaweed dosage, while for bioaccumulation is the initial concentration of Dy. Using RSM, it was possible to obtain the optimal operating conditions for Dy removal from waters, which is a fundamental step toward the application of the proposed technology at large scale.

Can the recycling of europium from contaminated waters be achieved through living macroalgae? Study on accumulation and toxicological impacts under realistic concentrations.

Europium (Eu) strategic importance for the manufacturing industry, high economic value and high supply risk, categorizes it as critical raw material. Due to anthropogenic contamination, Eu levels in ecosystems have been growing, which opens opportunities for innovation: its recovery and recycling from contaminated water as element source - circular economy. In this pioneering study, six widely available living marine macroalgae (Ulva intestinalis, Ulva lactuca, Gracilaria sp., Osmundea pinnatifida, Fucus vesiculosus and Fucus spiralis) were characterized (water content and specific surface area) and evaluated in the pre-concentration and recovery of Eu from contaminated seawater, under different relevant contamination scenarios (10, 152 and 500 µg L-1). U. lactuca and Gracilaria sp. (3 g L-1, fresh weight) proved to be the most effective in removing Eu, reaching up to 85% in 72 h, while the highest Eu enrichment was observed in U. intestinalis biomass, up to 827 µg g-1 (bioconcentration factor of 1800), which is higher than Eu levels in common apatite ores. The effect of Eu exposure on macroalgae growth rate and organism biochemical performance (LPO, SOD, GPx and GSTs) was also evaluated for the first time, to the best of our knowledge. Although no cellular damage was recorded, findings revealed toxicity and defence mechanisms activation, emphasizing the need of further studies on the potential risks associated with the presence of this emerging contaminant in aquatic ecosystems.

Sustainable recovery of neodymium and dysprosium from waters through seaweeds: Influence of operational parameters.

The high demand for greener energy and technological innovation require some crucial elements, such as the rare earths Nd and Dy. Being considered two of the most critical elements (high supply risk), it is vital to recover them from wastes/wastewaters, for later reuse. Here, the influence of operational parameters, such as biosorbent stock density (0.5, 3.0, and 5.5 g L-1), ionic strength (salinity 10 and 30) and contact time (24, 72 and 168 h), in the biosorption/bioaccumulation of Nd and Dy by two living marine macroalgae was evaluated in artificial seawater, seeking the improvement of the process. Results demonstrated that stock density is the most influential parameter, while the ionic strength showed to be a selective parameter, with a major influence only for Dy removal, which can be attributed to the different chemical characteristics observed between light rare earth elements (LREE) and heavy rare earth elements (HREE). For the ranges studied, the greatest removal/recovery for Gracilaria sp. was achieved with a stock density of 3.0 g L-1 at salinity 10, after 72 h for both REEs. For Ulva lactuca optimal conditions were: stock density of 5.5 g L-1 at salinity 10 with a contact time of 72 h for both REEs. Between species, U. lactuca showed to be the most promising, with removal efficiencies up to 98% for Nd and 89% for Dy. Findings substantiate the potential of the proposed process for obtaining Nd and Dy from secondary sources, particularly from low-level contaminated waters.

Bioaccumulation processes for mercury removal from saline waters by green, brown and red living marine macroalgae.

Mercury is a very toxic metal that persists and accumulates in the living organisms present in the aquatic systems and its elimination is an urgent need. Two green (Ulva intestinalis and Ulva lactuca), brown (Fucus spiralis and Fucus vesiculosus), and red (Gracilaria sp. and Osmundea pinnatifida) marine macroalgae were tested for mercury removal from saline waters. The ability of each species was evaluated to the initial mercury concentrations of 50, 200, and 500 µg dm-3 along 72 h. In general, all species exhibited good performances, removing 80.9-99.9% from solutions with 50 µg dm-3, 79.3-98.6% from solutions with 200 µg dm-3, and 69.8-97.7% from solutions containing 500 µg dm-3 of mercury. Among the macroalgae, Ulva intestinalis showed the highest affinity to mercury and it presented an uptake ability up to 1888 µg g-1 of Hg(II) and bioconcentration factors up to 3823, which proved its promising potential on Hg removal.

Nutshells as Efficient Biosorbents to Remove Cadmium, Lead, and Mercury from Contaminated Solutions.

The release of potentially toxic elements into the environment, and their effects on aquatic ecosystems still present a real threat. To avoid such contamination, the use of biological sorbents as an alternative to conventional and expensive water remediation techniques has been proposed. The present study evaluated the potential of 0.5 g L-1 of peanut, hazelnut, pistachio, walnut, and almond shells to remove the requisite concentrations of cadmium (Cd), lead (Pb), and mercury (Hg) from contaminated water. Hazelnut shells were identified as the sorbent with the highest potential and were evaluated in mono- and multi-contaminated mineral water. The influence of sorbent-intrinsic and solution-intrinsic characteristics were assessed. Differences among sorbents were attributed to varying percentages of their main components: cellulose, hemicellulose, and lignin. Matrix complexity increase caused a decrease in Cd removal, presumably due to the diminution in electrostatic interaction, and complexation with anions such as Cl-. When simultaneously present in the solution, contaminants competed, with Pb showing higher affinity to the sorbent than Hg. High efficiencies (>90%) obtained for hazelnut shells for all elements in ultrapure water and for Pb and Hg in mineral water) reveals the high potential of this low-cost and abundant waste for use in the remediation of contaminated waters (circular economy).

Influence of salinity and rare earth elements on simultaneous removal of Cd, Cr, Cu, Hg, Ni and Pb from contaminated waters by living macroalgae.

Potentially toxic elements (PTEs) are of major concern due to their high persistence and toxicity. Recently, rare earth elements (REEs) concentration in aquatic ecosystems has been increasing due to their application in modern technologies. Thus, this work aimed to study, for the first time, the influence of REEs (lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, terbium, dysprosium and yttrium) and of salinity (10 and 30) on the removal of PTEs (Cd, Cr, Cu, Hg, Ni and Pb) from contaminated waters by living macroalgae (Fucus spiralis, Fucus vesiculosus, Gracilaria sp., Osmundea pinnatifida, Ulva intestinalis and Ulva lactuca). Experiments ran for 168 h, with each macroalga exposed to saline water spiked with the six PTEs and with the six PTEs plus nine REEs (all at 1 µmol L-1) at both salinities. Results showed that all species have high affinity with Hg (90-99% of removal), not being affected neither by salinity changes nor by the presence of other PTEs or REEs. Cd showed the lowest affinity to most macroalgae, with residual concentrations in water varying between 50 and 108 µg L-1, while Pb removal always increased with salinity decline (up to 80% at salinity 10). REEs influence was clearer at salinity 30, and mainly for Pb. No substantial changes were observed in Ni and Hg sorption. For the remaining elements, the effect of REEs varied among algae species. Overall, the results highlight the role of marine macroalgae as living biofilters (particularly U. lactuca), capable of lowering the levels of top priority hazardous substances (particularly Hg) and other PTEs in water, even in the presence of the new emerging contaminants - REEs. Differences in removal efficiency between elements and macroalgae are explained by the contaminant chemistry in water and by macroalgae characteristics.

Dual nanofibrillar-based bio-sorbent films composed of nanocellulose and lysozyme nanofibrils for mercury removal from spring waters.

The present study explores the preparation of dual nanofibrillar-based bio-sorbent films composed of cellulose nanofibrils (CNFs) and lysozyme nanofibrils (LNFs) for application in the removal of Hg(II) from aqueous solutions. The free-standing films were fabricated via simple vacuum filtration of water suspensions of CNFs and LNFs and disclose good mechanical and thermal properties. The Hg(II) removal efficiency was evaluated by atomic fluorescence spectroscopy in ultra-pure and natural spring waters contaminated with environmental realistic levels of mercury (50 µg L-1). The removal efficiency is pH-dependent reaching a maximum of 99 % after 24 h at a pH value close to the isoelectric point of the protein. Under the experimental conditions, the sorption kinetics are well described by the pseudo-second-order and Elovich models, suggesting a chemisorption mechanism. These results demonstrate the ability of the dual nanofibrillar-based films to remove Hg(II) from water samples reaching a residual concentration lower than the guideline value for water intended for human consumption (1 µg L-1). Therefore, the CNFs/LNFs bio-sorbents might be a solution to treat low-concentrated mercury-contaminated waters.

Influence of toxic elements on the simultaneous uptake of rare earth elements from contaminated waters by estuarine macroalgae.

The present study tested whether the presence of potentially toxic elements (PTEs) (Cd, Cr, Cu, Pb, Hg and Ni), commonly found in wastewaters, interferes with the ability of macroalgae (Ulva intestinalis, Ulva lactuca, Fucus spiralis, Fucus vesiculosus, Gracilaria sp. and Osmundea pinnatifida) to remove rare earth elements (REEs) (La, Ce, Pr, Nd, Eu, Gd, Tb, Dy and Y), which are key elements for most high technologies (e.g. electronics, aerospace, renewable energy). Results proved the high capacity of living macroalgae to remove REEs from multielement solutions, with the following sequence of bioconcentration factors being observed: U. intestinalis (2790) > Gracilaria sp. (2119) > O. pinnatifida (1742) > U. lactuca (1548) > F. vesiculosus (944) > F. spiralis (841). Competition among REEs to sorption sites on the six macroalgae was minor due to the chemical similarities between the elements. However, Ce and Y were the less removed while Gd, La and Eu the most removed among REEs. Ionic strength was an important factor in the sorption process, with salinity affecting differently the six macroalgae. Surprisingly, the presence of potential toxic elements in solution enhanced the removal of REEs. The most plausible explanation is the preferentially complexation of those elements by carbonates over REEs, which facilitates the binding of REEs cations onto the surface of macroalgae.

Negligible effect of potentially toxic elements and rare earth elements on mercury removal from contaminated waters by green, brown and red living marine macroalgae.

Mercury (Hg) removal by six different living marine macroalgae, namely, Ulva intestinalis, Ulva lactuca, Fucus spiralis, Fucus vesiculosus, Gracilaria sp., and Osmundea pinnatifida was investigated in mono and multi-contamination scenarios. All macroalgae were tested under the same experimental conditions, evaluating the competition effects with all elements at the same initial molar concentration of 1 µmol dm-3. The presence of the main potentially toxic elements (Cd, Cr, Cu, Ni, and Pb) and rare earth elements (La, Ce, Pr, Nd, Eu, Gd, Tb, and Y) has not affected the removal of Hg. Characterizations of the macroalgae by FTIR before and after the biosorption/bioaccumulation assays suggest that Hg was mainly linked to sulfur-functional groups, while the removal of other elements was related with other functional groups. The mechanisms involved point to biosorption of Hg on the macroalgae surface followed by possible incorporation of this metal into the macroalgae by metabolically active processes. Globally, the green macroalgae (Ulva intestinalis, Ulva lactuca) showed the best performances for Hg, potential toxic elements and rare earth elements removal from synthetic seawater spiked with 1 µmol dm-3 of each element, at room temperature and pH 8.5.

A green method based on living macroalgae for the removal of rare-earth elements from contaminated waters.

Low recycling rates of rare earth elements (REEs) are a consequence of inefficient, expensive and/or contaminating methods currently available for their extraction from solid wastes or from liquid wastes such as acid mine drainage or industrial wastewaters. The search for sustainable recovery alternatives was the motivation for this study. For the first time, the capabilities of 6 living macroalgae (Ulva lactuca, Ulva intestinalis, Fucus spiralis, Fucus vesiculosus, Osmundea pinnatifida and Gracilaria sp.) to remove REEs (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy) from laboratory-prepared seawater spiked with REE solutions were evaluated. The assays lasted 72 h with REEs concentrations ranging from 10 to 500 µg L-1. The link between REEs uptake and algal metabolism, surface morphology and chemistry were addressed. Kinetics varied among the species, although most of the removal occurred in the first 24 h, with no equilibrium being reached. Lack of mortality reveal that the algae maintained their metabolism in the presence of the REEs. Green alga U. lactuca stood out as the only capable of efficiently removing at least 60% of all elements, reaching removals up to 90% in some cases. The high bioconcentration factors, derived from mass balance analysis (c.a. 2500) support that the REEs enriched algal biomass (up to 1295 µg g-1) may constitute an effective and environmentally friendly alternative source of REEs to conventional extraction from ores.

Valuation of banana peels as an effective biosorbent for mercury removal under low environmental concentrations.

The use of banana peels as biosorbent for mercury sorption from different aqueous solutions was investigated in this work. The impact of the operating conditions, such as biosorbent dosage, contact time and ionic strength was evaluated for realistic initial Hg(II) concentrations of 50 µg dm-3. Biosorbent dosage and contact time showed more influence on Hg(II) removal than ionic strength, and their increase led to improve Hg(II) uptake achieving final concentrations with drinking water quality. The kinetic behaviour of the sorption process was assessed through the reaction-based models of pseudo-first order, pseudo-second order and Elovich, being the last two more appropriated to describe the process. The equilibrium study showed that Freundlich isotherm provided the best fit to the experimental results (R2 = 0.991), which may suggest a multilayer mechanism at biosorbent surface, and the sorption capacity of banana peels obtained from Langmuir isotherm was 0.75 mg g-1. The ability of banana peels to sorb Hg(II) was also examined under real waters, like seawater and a wastewater, which confirmed the feasibility of the biosorbent. Additionally, a counter-current two-stages unit has been proposed for the application of banana peels as biosorbent in water treatments for mercury removal.

Experimental Measurement and Modeling of Hg(II) Removal from Aqueous Solutions Using Eucalyptus globulus Bark: Effect of pH, Salinity and Biosorbent Dosage.

Different experimental conditions were tested in order to optimize the Hg(II) removal by Eucalyptus globulus bark. Response surface methodology was applied to extract information about the significance of the factors and to obtain a model describing the sorption. The results were generated through the design of experiments by applying the methodology of a three-factor and three-level Box-Behnken design. The factors tested were pH (4.0, 6.5, and 9.0), salinity (0, 15, and 30), and biosorbent dosage (0.2, 0.5, and 0.8 g dm-3) to evaluate the Hg(II) removal using realistic conditions, such as contaminated natural waters with an initial Hg(II) concentration of 50 µg dm-3. The optimum response provided by the model was 81% of the metal removal under the optimal operating conditions: a pH value of 6.0, no salinity, and a biosorbent dosage of 0.55 g dm-3. Concerning the kinetic, the pseudo-second-order equation fitted better to the experimental results with R 2 between 0.973 and 0.996. This work highlights the promising valorization of this biomass, which is an industrial byproduct and makes available information about the influence of the variables for Hg(II) removal in water treatment processes.