On the use of magnetic nano and microparticles for lake restoration

Combined amendment and capping of sediment with ferrihydrite and magnetite to control internal phosphorus release

This study developed novel active capping systems with recycling convenience using ferrihydrite (Fh) combined with magnetite (Mag), and investigated the effectiveness and mechanism for the restriction of endogenous phosphorus movement from sediment into overlying water (OW) by the combined use of Fh and Mag. The Fh/Mag combined amendment effectively hindered endogenous phosphorus release from sediment to OW in dissolved oxygen (DO)-deficit environment, and the immobilization of diffusion gradient in thin film-labile phosphorus (LP_DGT) and mobile phosphorus in the sediment played a key role in the control of endogenous phosphorus liberation by the Fh/Mag combined amendment. Combined capping sediment with Fh and Mag effectively hindered endogenous phosphorus release from sediment to OW in anoxic environment, and the inactivation of LP_DGT in the upper sediment played a key part in the control of sediment phosphorus release by the Fh/Mag mixture capping. The stability of phosphorus immobilized by the Fh/Mag combined covering layer was related to its construction way, and the majority (around 90%) of P immobilized to the Fh/Mag mixture covering layer had low risk of release in common pH (5-9) and DO-deficit environments. The Fh/Mag mixture amendment or capping did not increase the risk of sediment iron release, and it also did not produce a large impact on the diversity and richness of bacterial community in the sediment. The combined utilization of Fh and Mag as a composite amendment or capping material to prevent the internal phosphorus from being moved to OW can make full use of their respective advantages. The Fh/Mag mixture capping wrapped by permeable fabric has high potential to reduce the risk of endogenous phosphorus from sediment into OW due to its advantages of high internal phosphorus release suppression efficiency, environmental friendliness, application convenience and sustainability.

Population dynamics hide phenotypic changes driven by subtle chemical exposures: implications for risk assessments

Ecological risk assessment of chemicals focuses on the response of different taxa in isolation not taking ecological and evolutionary interplay in communities into account. Its consideration would, however, allow for an improved assessment by testing for implications within and across trophic levels and changes in the phenotypic and genotypic diversity within populations. We present a simple experimental system that can be used to evaluate the ecological and evolutionary responses to chemical exposure at microbial community levels. We exposed a microbial model system of the ciliate Tetrahymena thermophila (predator) and the bacterium Pseudomonas fluorescens (prey) to iron released from Magnetic Particles (MP-Fe_dis), which are Phosphorus (P) adsorbents used in lake restoration. Our results show that while the responses of predator single population size differed across concentrations of MP-Fe_dis and the responses of prey from communities differed also across concentration of MP-Fe_dis, the community responses (species ratio) were similar for the different MP-Fe_dis concentrations. Looking further at an evolutionary change in the bacterial preys' defence, we found that MP-Fe_dis drove different patterns and dynamics of defence evolution. Overall, our study shows how similar community dynamics mask changes at evolutionary levels that would be overlooked in the design of current risk assessment protocols where evolutionary approaches are not considered.

The effectiveness and adsorption mechanism of iron-carbon nanotube composites for removing phosphate from aqueous environments

This study successfully employed iron-carbon nanotubes (Fe-CNT) to recover phosphate (P) from water. We examined the effects of various iron concentrations denoted by Fe-CNT-1 and Fe-CNT-2 on P removal and compared them with pristine carbon nanotubes (CNTs). The adsorption capacity of Fe-CNTs was much better than pristine CNTs. According to the high adsorption capacity, Fe-CNT-2 sample was very effective for P recovery and exhibits ∼7 times higher P removal efficiency than that of pristine CNTs. The characterization of the as-obtained adsorbent (Fe-CNT-2) and pristine CNTs were performed using X-ray diffraction, Brunauer-Emmett-Teller method, Field emission scanning electron microscope coupled with energy-dispersive spectroscopy detector (FESEM-EDS), X-ray photoelectron spectroscopy and Transmission electron microscopy. Results demonstrated that iron oxide nanoparticles were successfully deposited on the surface of CNT. The adsorption kinetics and isotherm studies for P removal showed pseudo-second-order rate constants (R² > 0.99) and the Langmuir isotherm (R² > 0.99) respectively, thus revealing that the nature of adsorption was chemisorption. The estimated Langmuir adsorption capacity of Fe-CNT-2 was 36.5 mgP/g or 112 mg PO₄/g at an equilibrium time of 3 h. The ionic strength provided by SO₄^2-, NO₃^-, and Cl^- demonstrated no considerable influence on phosphate adsorption. Moreover, the P adsorbed Fe-CNT-2 was efficiently recovered with different concentrations of desorbing reagents, such as NaOH and NaCO₃^2-. Moreover, the findings of X-ray photoelectron spectroscopy (XPS) analysis demonstrated that OH group played a major role in the P removal by Fe-CNT-2. The findings of this study demonstrate that Fe-CNT-2 had a great deal of application as an effective and stable adsorbent for the P recovery from aquatic environments.

Enhanced remediation of lead (II) and cadmium (II) ions from aqueous media using porous magnetic nanocomposites - A comprehensive review on applications and mechanism

Lead and Cadmium, identified as toxic heavy metals, cause significant imbalance in the eco-system due to their tendency to bioaccumulate. Remediation of heavy metals by conventional adsorptive materials suffer demerits related to low efficiency or removal. Among the variety of adsorbent materials used in the adsorption process, metal oxides- and graphene oxide magnetic nanocomposites have gained a considerable attention. The use of nanomaterials may help to reduce this contamination, but after use, they are difficult to remove from water. An added magnetic property to nanomaterials facilitates their retrieval after use. The magnetic properties of these hybrid magnetic nanocomposites, coupled with unique characteristics of organic and inorganic elements, have found extensive application in water treatment technology. Detailed discussion on functionalisation of magnetic nanocomposites and the enhanced performance are presented. Magnetic graphene oxide-covalently functionalized-tryptophan was reported to have the highest adsorption capacity of 766.1 mg/g for remediation of lead (II) ions and graphene oxide exhibited the highest adsorption capacity of 530 mg/g for Cd (II) ions. The adsorption mechanisms for heavy metal ions on the surface of novel adsorbents, particularly lead and cadmium, using magnetic nanocomposites have been explained with reference to the isotherm models studied. The future scope of research in this area of research is proposed.

A novel Ca/Mn-modified biochar recycles P from solution: mechanisms and phosphate efficiency

The excessive use of phosphate leads to severe environmental issues, such as a shortage of phosphorus resources and water eutrophication. In this study, a novel Ca-Mn-impregnated biochar (CMBC) composite was synthesized by co-pyrolysis at 600 °C for P recovery from solution. The efficiency of P-sorbed CMBC as a fertilizer was assessed via pot experiments. Kinetic experiments exhibited a higher phosphate sorption efficiency for the CM₁BC and CM₂BC composites. Pot experiments revealed that P-sorbed CMBC treatment significantly improved plant growth and yield. Compared with those of the control, the dry weight, fresh weight, and P content of rape leaf (root) P₅₀-CMBC_1.0% treatment increased by 108.6% (350%), 88.7% (396%), and 132.8% (109.3%), respectively. This may be due to the porous surface structures that develop during the treatment and Ca-P precipitation on P-sorbed biochar partly dissolved in the slightly acidic soil (pH: 6.25). The maximum P adsorption values fitted by the Langmuir isotherm model were up to 9.15, 3.19, 15.58, and 20.84 mg g^-1 for CBC, MBC, CM₁BC, and CM₂BC, respectively. The mechanism of phosphate recovery mainly includes electrostatic attraction, surface precipitation, and the formation of inner-sphere complexes with hydroxyl groups that were assessed using BET, zeta potential, SEM-EDS, FTIR, and XPS analyses. These mechanisms suggest that phosphate may be desorbed from the P-laden sorbent, which was consistent with the results of the pot experiments and desorption experiments in aqueous media. These results imply that P-sorbed modified biochar has the potential to be a promising P fertilizer in soil.

Magnetic Adsorbents for Wastewater Treatment: Advancements in Their Synthesis Methods

The remediation of water streams, polluted by various substances, is important for realizing a sustainable future. Magnetic adsorbents are promising materials for wastewater treatment. Although numerous techniques have been developed for the preparation of magnetic adsorbents, with effective adsorption performance, reviews that focus on the synthesis methods of magnetic adsorbents for wastewater treatment and their material structures have not been reported. In this review, advancements in the synthesis methods of magnetic adsorbents for the removal of substances from water streams has been comprehensively summarized and discussed. Generally, the synthesis methods are categorized into five groups, as follows: direct use of magnetic particles as adsorbents, attachment of pre-prepared adsorbents and pre-prepared magnetic particles, synthesis of magnetic particles on pre-prepared adsorbents, synthesis of adsorbents on preprepared magnetic particles, and co-synthesis of adsorbents and magnetic particles. The main improvements in the advanced methods involved making the conventional synthesis a less energy intensive, more efficient, and simpler process, while maintaining or increasing the adsorption performance. The key challenges, such as the enhancement of the adsorption performance of materials and the design of sophisticated material structures, are discussed as well.

Magnetic particles as new adsorbents for the reduction of phosphate inputs from a wastewater treatment plant to a Mediterranean Ramsar wetland (Southern Spain)

This study assessed the convenience of using magnetic particles (MPs) to reduce phosphorus (P) concentration in treated wastewater. The working hypothesis is that MP addition increases P removal in artificial wastewater treatment ponds. Water samples were collected at the inlet and outlet of a semi-natural pond receiving secondary municipal effluent that is discharged in a Ramsar site (Fuente de Piedra, Málaga, Spain). Then, laboratory batch experiments were run to (i) assess the effect of adding MPs on the chemical composition of treated wastewater, (ii) identify the number of adsorption cycles (by reusing MPs) which are able to trap a high percentage of P (>50%) and (iii) select the optimum ratio between MP mass and initial dissolved inorganic P (DIP) concentration. The results show the suitability of using MPs to remove P in treated wastewater due to both their high equilibrium adsorption capacity (q) and P removal efficiency. Lastly, considering its practical and economical relevance, based on the advantages (P removal efficiency) and disadvantages (economic price), the optimum dose of MPs (0.16 g MP mg^-1 P) to achieve a high P removal efficiency (>50%) was identified.

Assessing the viability of recovered phosphorus from eutrophicated aquatic ecosystems as a liquid fertilizer

One of the most important worldwide environmental challenges is the alteration of the biogeochemical cycle of phosphorus (P). P is globally exported from terrestrial to aquatic ecosystems, causing the eutrophication of the receiving waters. In this context, magnetic microparticles (MPs) have been recently proposed for trapping P in natural eutrophicated ecosystems, as well as in treated wastewaters. The main advantage of using MPs is that both P and MPs can be recovered from the treated water. Thus, the working hypothesis of the present study is that P can be desorbed from P-loaded MPs and recovered P can be later used as a fertilizer. To test this hypothesis, the best working conditions for desorbing P from P-loaded MPs were identified; then, an experiment with different plant nutrient solutions (neutralized solutions containing recovered P and an unfertilized control) was carried out with three different plant species: Ocimum basilicum L., Cucumis sativus L. and Cucumis melo L. Finally, germination, height, root and shoot biomass and P concentration in root and shoot were compared among treatments. Our results show that the best conditions for P desorption from P-loaded MPs occurred when using 0.1 M NH₄OH and using H₃PO₄ for neutralizing pH. The greenhouse fertirrigation pot experiment showed that the neutralized solution containing desorbed P from P-loaded MPs can be used as a liquid fertilizer, since its combination with macro and microelements significantly increased plant height, growth rate, shoot and root biomass and shoot and root P concentration. As a result, MPs can be proposed to be used for counteracting the widespread and coupled problems of the exhaustion of the P reserves and the eutrophication of aquatic ecosystems.

Assessing the toxic effects of magnetic particles used for lake restoration on phytoplankton: A community-based approach

Inactivation by adding different phosphorus (P) adsorbents is one of the most frequently used methods for combating inland water eutrophication. The aim of this work was to assess the toxic effects of novel P adsorbents (magnetic particles, MPs) on the phytoplankton community. An outdoor microcosm experiment, containing lake water and surface sediment from a hypertrophic Mediterranean lake, was carried out following a factorial design (n = 5) with three different treatments: control (C), where no MPs were added; Treatment-Water (T-W) and Treatment-Sediment (T-S). In T-W and T-S treatments, MPs were added on the surface water layer and on the sediment, respectively, to obtain a final concentration of 1.4 g MP L^-1. This concentration was based on both the sedimentary mobile P concentration of the study site and the maximum P adsorption capacity of the MPs, obtained from the literature. After 24 h of contact time, the MPs were removed using a magnetic rake. Physicochemical measurements and biological samples were taken after 24 h of exposure to the MPs and at different time points after such exposure (day 2, 7, 21, 35 and 70). Changes in phytoplankton community such as abundance (biovolume and Chla), species composition and taxonomic groups were assessed, as well as changes in the Shannon-Wiener diversity index. Additionally, the eutrophic metric Algae Group Index (AGI), one of the metrics proposed in the Water Framework Directive, was also calculated. Our results indicate that there is no strong evidence to infer that MPs caused an effect on the phytoplankton community, since no significant differences (GLM test; p > 0.05) were found between controls and treatments in any of the studied variables (phytoplankton taxonomic groups, AGI, Chla concentration, biovolume, diversity and community responses). Accordingly, MPs did not cause any toxic effects on the phytoplankton community of the lake, encouraging the use of MPs in a future whole-lake restoration strategy. However, if the final goal of the restoration plan is to combat nuisance cyanobacteria blooms, higher initial MPs doses or repeated MPs applications are required to achieve a reduction in P concentrations below biological thresholds in order to prevent algal blooms.

Magnetorheology: a review

Magnetic Soft Matter is a rapidly evolving discipline with fundamental and practical interest. This is due to the fact that its physical properties can be easily controlled through external magnetic fields. In this review paper, we revisit the most recent progress in the field (since 2010) emphasizing the rheological properties of these fascinating materials. New formulations and flow kinematics are discussed. Also, new members are integrated into the long-lived magnetorheology family and suggestions are provided for future development.

Assessing short-term effects of magnetite ferrite nanoparticles on Daphnia magna

Magnetic nanoparticles (MNPs) are used in a wide range of sectors ranging from electronics to biomedicine, as well as in eutrophicated lake restoration due to their high P, N, and heavy metal adsorption capacity. This study assessed the effects of MNPs on mortality and morphometric changes of D. magna. According to the SEM, the synthesised MNPs were found to have spherical nanoparticles, be uniformly distributed, and have a homolithic size distribution of 50-110 nm. The EDX spectra confirmed the elemental structure and purities of these MNPs. A total of 396 neonates were used for short-term bioassays (96 h) through the MNPs in the laboratory (16:8 photoperiod). Experiments were applied in triplicate for each concentration of CuFe2O4, CoFe2O4, and NiFe2O4 MNPs and their respective control groups. Mortality and morphological measurements of each individual were recorded every 24 h. In the probit analysis, the 96-h LC50 (p < 0.05) for CuFe2O4, CoFe2O4, and NiFe2O4 MNPs was calculated to be 1.455 mg L-1, 39.834 mg L-1, and 21.730 mg L-1, respectively. CuFe2O4 MNPs were found to be more toxic than the other two MNPs. The concentrations of CuFe2O4, CoFe2O4, and NiFe2O4 MNPs drastically affected life span and morphologic growth of D. magna as a result of a short time exposure. The results of this study are useful for assessing what risks they pose to freshwater ecosystems.

Mechanisms that control the adsorption-desorption behavior of phosphate on magnetite nanoparticles: the role of particle size and surface chemistry characteristics

Eutrophication caused by excessive phosphate discharge into surface water has raised wide concern, and the efficient removal of phosphates from wastewater using sorption methods is very important. In our study, magnetite particles with two different sizes and different surface characteristics were chosen as the sorbents to examine their adsorption and desorption behavior toward phosphate. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption methods were used to characterize the morphological and surface chemical properties of the two differently sized magnetite particles. Adsorption kinetics and isotherm models (including the pseudo-first-order, Freundlich, Langmuir and Temkin models) were used to fit the experimental data, and to help with the mechanistic discussions. It was found that the nanometer-sized magnetite (nFe3O4) has a much higher surface area, larger pore volume, higher amounts of surface functional groups, and a lower point of zero charge (pHPZC) value than the micrometer-sized magnetite (Fe3O4). The adsorption kinetics show that reaching adsorption equilibrium in the case of nFe3O4 is much slower, and the particle size or surface characteristics of the magnetite may become the main factor determining the adsorption rate of the phosphate to magnetite in the rapid or slow adsorption step, respectively. nFe3O4 shows much stronger adsorption of phosphate compared to Fe3O4, which may be attributed to the larger surface area of the magnetite with a smaller particle size. In addition, the amount of functional groups and the surface electrical properties may also affect the adsorption of phosphate to magnetite by influencing the formation of the outer-sphere and/or inner-sphere complexes. The adsorption/desorption of phosphate to/from the magnetite decreases/increases with increasing pH, and the extent of change is more marked for nFe3O4. Increasing the ionic strength of the solution increases the adsorption of phosphate to the two differently sized magnetite particles, whereas the presence of humic acid only increases the adsorption of phosphate to Fe3O4. These trends may be caused by the different extents of change of the surface properties or the dispersion state of the two differently sized magnetite particles under different solution chemistry conditions. The results imply that when the synthesis of magnetite-based materials for phosphate sorption is performed, both the particle size and surface properties should be considered in order to realize the efficient and economical removal of phosphate from wastewater.

Ecotoxicity screening of novel phosphorus adsorbents used for lake restoration

Short-term standardized laboratory tests were carried out for evaluating acute and chronic toxicological effects of novel phosphorus (P) adsorbents on Raphidocelis subcapitata (algal growth rate inhibition) and on Daphnia magna (immobilization, with direct and indirect exposure to adsorbents, and uptake-depuration tests). Four P adsorbents were tested: two magnetic (HQ and Fe₃O₄) and two non magnetic (CFH-12^® and Phoslock^®). For the case of the algal growth inhibition test, the EC₅₀ was 1.5 and 0.42 g L^-1 for HQ and CFH-12^®, respectively, and no inhibition patterns were observed neither for Fe₃O₄ nor for Phoslock^®. When organisms were exposed to a direct contact, in the D. magna immobilization test, no statistically significant differences were found in the EC₅₀ values among the four studied adsorbents. The huge difference between direct and indirect contact experiments suggests that toxicity is mainly physically mediated. The uptake-depuration test evidenced a much faster uptake and depuration rates for Phoslock^®, which was precisely the adsorbent with the highest particle size. In a realistic worst-case scenario using data from Honda lake (Almería, Spain), where lake restoration is carried out by a adding a single large dose to bind surplus P in the lake, the predicted environmental concentrations for all adsorbents were lower than EC₅₀ for all adsorbents and they were found to exceed a provisional limit value for ecotoxicity after a short-term exposure. All in all, since neither accumulation nor longer term effects of P adsorbents in the pelagic phase is expected, this risk may however, on a case-to-case basis, be acceptable.

Do magnetic phosphorus adsorbents used for lake restoration impact on zooplankton community?

Magnetic microparticles (MPs) have been recently proposed as innovative and promising dissolved inorganic phosphorus (DIP) adsorbents. However, before using them in a whole-lake restoration project, it is essential to assess their toxicological effects (direct and indirect) on aquatic biota. In the present study we hypothesized that zooplankton community is affected by MPs used for lake restoration. To test our hypothesis we designed a microcosms experiment (n = 15) containing lake water and surface sediment from a hypertrophic lake. Temporal changes (70 days) on physico-chemical conditions and on zooplankton structure (rotifers, copepods and branchiopods) were monitored under different scenarios. In particular, three different treatments were considered: no addition of MPs (control) and MPs addition (1.4 g MPs L^-1) on the surface water layer (T-W) and on the sediment (T-S). After 24 h of contact time, MPs were removed with a magnetic rake. A total of 15 zooplankton species (12 rotifers, 1 branchiopod and 2 copepods) were recorded and a high abundance of zooplankton was registered during the experiment for all treatments. No significant differences (RM-ANOVA test; p > 0.05) in total abundance, species richness and species diversity among treatments were found. The absence of any effect of MPs on zooplankton can be explained because MPs did not significantly alter any of its physico-chemical (e.g. temperature, pH, O₂) or biological (e.g. food quantity and quality) drivers. These results confirm the suitability of MPs as a promising tool for removing DIP in eutrophic aquatic ecosystems.

Determining major factors controlling phosphorus removal by promising adsorbents used for lake restoration: A linear mixed model approach

Phosphorus (P) removal from lake/drainage waters by novel adsorbents may be affected by competitive substances naturally present in the aqueous media. Up to date, the effect of interfering substances has been studied basically on simple matrices (single-factor effects) or by applying basic statistical approaches when using natural lake water. In this study, we determined major factors controlling P removal efficiency in 20 aquatic ecosystems in the southeast Spain by using linear mixed models (LMMs). Two non-magnetic -CFH-12^® and Phoslock^®- and two magnetic materials -hydrous lanthanum oxide loaded silica-coated magnetite (Fe-Si-La) and commercial zero-valent iron particles (FeHQ)- were tested to remove P at two adsorbent dosages. Results showed that the type of adsorbent, the adsorbent dosage and color of water (indicative of humic substances) are major factors controlling P removal efficiency. Differences in physico-chemical properties (i.e. surface charge or specific surface), composition and structure explain differences in maximum P adsorption capacity and performance of the adsorbents when competitive ions are present. The highest P removal efficiency, independently on whether the adsorbent dosage was low or high, were 85-100% for Phoslock and CFH-12^®, 70-100% for Fe-Si-La and 0-15% for FeHQ. The low dosage of FeHQ, compared to previous studies, explained its low P removal efficiency. Although non-magnetic materials were the most efficient, magnetic adsorbents (especially Fe-Si-La) could be proposed for P removal as they can be recovered along with P and be reused, potentially making them more profitable in a long-term period.

Evaluation of dried amorphous ferric hydroxide CFH-12® as agent for binding bioavailable phosphorus in lake sediments

Metal hydroxides formed from aluminum (Al) and iron (Fe) salts can be used as phosphorus (P) adsorbents in lake restoration, but the application entails problems in low-alkaline lakes due to acid producing hydrolysis and potential formation of toxic metal ions. Therefore, we tested the potential of applying CFH-12® (Kemira) - a dried, amorphous Fe-oxide with no pH effect - in lake restoration. Since Fe³⁺ may become reduced in lake sediments and release both Fe²⁺ and any associated P we also evaluated the redox sensitivity of CFH-12® in comparison with freshly formed Fe(OH)₃. CFH-12® was added to undisturbed sediment cores from three Danish lakes relative to the size of their mobile P pool (molar Fe:P_Mobile dose ratio of ~10:1), and P and Fe fluxes across the sediment-water interface were compared with those from untreated cores and cores treated with freshly formed Fe(OH)₃. Under anoxic conditions, we found that CFH-12® significantly reduced the P efflux from the sediments (by 43% in Lake Sønderby, 70% in Lake Hampen and 60% in Lake Hostrup) while the Fe²⁺ efflux remained unchanged relative to the untreated cores. Cores treated with freshly formed Fe(OH)₃ retained more P, but released significantly more Fe²⁺, indicating continued Fe³⁺ reduction. Finally, experiments with pure phases showed that CFH-12® adsorbed less P than freshly formed Fe(OH)₃ in the short term, but was capable of adsorbing up to 70% of P adsorbed by Fe(OH)₃ over 3months. With product costs only 30% higher than Al salts we find that CFH-12® has potential for use in restoration of low-alkaline lakes.

Removal of phosphate from water by amine-functionalized copper ferrite chelated with La(III)

Eutrophication has become a worldwide environmental problem and removing phosphorus from water/wastewater before discharge is essential. The purpose of our present study was to develop an efficient material in terms of both phosphate adsorption capacity and magnetic separability. To this end, we first compared the performances of four spinel ferrites, including magnesium, zinc, nickel and copper ferrites. Then we developed a copper ferrite-based novel magnetic adsorbent, by synthesizing 1,6-hexamethylenediamine-functionalized copper ferrite(CuFe₂O₄) via a single solvothermal synthesis process followed by LaCl₃ treatment. The materials were characterized with X-ray diffraction, transmission electron microscope, vibrating sample magnetometer, Fourier transform infrared spectra and N₂ adsorption-desorption. The maximum adsorption capacity of our material, calculated from the Langmuir adsorption isotherm model, attained 32.59mg/g with a saturation magnetization of 31.32emu/g. Data of adsorption kinetics were fitted well to the psuedo-second-order model. Effects of solution pH and coexisting anions (Cl^-, NO₃^-, SO₄^2-) on phosphate adsorption were also investigated, showing that our material had good selectivity for phosphate. But OH^- competed efficiently with phosphate for adsorption sites. Furthermore, increasing both NaOH concentration and temperature resulted in an enhancement of desorption efficiency. Thus NaOH solution could be used to desorb phosphate adsorbed on the material for reuse, by adopting a high NaOH concentration and/or a high temperature.

Laboratory and pilot-scale field experiments for application of iron oxide nanoparticle-loaded chitosan composites to phosphate removal from natural water

The aim of this study was to apply iron oxide nanoparticle-chitosan (ION-chitosan) composites to phosphate removal from natural water collected from the Seoho Stream in Suwon, Republic of Korea. Laboratory batch experiments showed that phosphate removal by the ION-chitosan composites was not sensitive to pH changes between pH values of 5.0 and 9.0. During six cycles of adsorption-desorption, the composites could be successfully regenerated with 5 mM NaOH solution and reused for phosphate removal. Laboratory fixed-bed column experiments (column height = 10 and 20 cm, inner diameter = 2.5 cm, flow rate = 8.18 and 16.36 mL/min) demonstrated that the composites could be successfully applied for phosphate removal under dynamic flow conditions. A pilot-scale field experiment was performed in a pilot plant, which was mainly composed of chemical reactor/dissolved air flotation and an adsorption tower, built nearby the Seoho Stream. The natural water was pumped from the Seoho Stream into the pilot plant, passed through the chemical reactor/dissolved air flotation process, and then introduced into the adsorption tower (height = 100 cm, inner diameter = 45 cm, flow rate = 7.05 ± 0.18 L/min) for phosphate removal via the composites (composite volume = 80 L, composite weight = 85.74 kg). During monitoring of the adsorption tower (33 days), the influent total phosphorus (T-P) concentration was in the range of 0.020-0.046 mgP/L, whereas the effluent T-P concentration was in the range of 0.010-0.028 mgP/L. The percent removal of T-P in the adsorption tower was 52.3% with a phosphate removal capacity of 0.059 mgP/g.

Going deeper into phosphorus adsorbents for lake restoration: Combined effects of magnetic particles, intraspecific competition and habitat heterogeneity pressure on Daphnia magna

Aquatic population responses to chemical exposure may be exacerbated by intraspecific competition pressures, being also shaped by habitat heterogeneity. Magnetic particles (MPs) have been recently proposed as promising phosphorus (P) adsorbents for lake restoration. This study focuses on assessing the effects of MPs on the abundance of the crustacean Daphnia magna under different levels of both intraspecific competition pressure and habitat heterogeneity. The experimental design consisted of two experiments (in homogeneous and heterogeneous habitats) done in glass jars with four concentrations of MPs: controls of 0g MPsL^-1, and treatments of 1, 1.5 and 2g MPsL^-1. In addition, competition treatments were established by using different population densities, and hence, no competition (C), low (L) and high (H) competition pressures were simulated. The experiments lasted for 7 days, with a 4-day pre-exposure period, in which competition was all allowed to take place, and a 3-day post-exposure period. Twenty-four hours after adding MPs, the MPs were removed by applying a magnetic separation technique. The results showed that competition pressures occurred and significantly reduced population abundances during the pre-exposure period. During the post-exposure period, the combined effects of competition and MPs were detected in both homogeneous (Ho-) and heterogeneous (He-) habitat experiments, showing a significantly drastic reduction in abundances. In fact, the lethal concentration for 50% of the population (LC_{50 -}24h) was 0 and 0.16g MPsL^-1 in the Ho- and He-experiments respectively, indicating that the addition and especially the removal of MPs cause extreme mortality. These results indicated that even though competition plays a role in shaping populations, its influence was down-weighted by the stronger pressures of MPs. In addition, as no significant differences between homogeneous and heterogeneous habitats were found, we may state that the refuge offered was not protective enough to avoid the effects of MPs. In conclusion, the removal of the MPs causes drastic effects on D. magna abundances despite the concentration of MPs, competition or habitat structure. Finally, considering the validated high efficiency of MPs for P removal, and in the context of a future whole-lake application, it is essential to restrict the use of MPs to the moments when D. magna is absent in the study site. Further research on the effects of MP removal on other organisms is required before implementing the addition of MPs as a restoration tool.

Assessment of toxic effects of magnetic particles used for lake restoration on Chlorella sp. and on Brachionus calyciflorus

Laboratory tests, by following standardized Organization for Economic Co-operation and Development (OECD) protocols, were run for evaluating the acute effects of iron magnetic microparticles (MPs), recently proposed for lake restoration, on Chlorella sp. (algal growth) and on the rotifer B. calyciflorus (mortality). In addition, the MPs potential indirect effects on rotifer egg bank were assessed by performing hatching rate test with B. calyciflorus cysts in contact with dissolved iron (Tot-Fe_dis). In the algal growth test, no inhibition occurred at the two lowest MPs concentrations (0.01 and 0.05 g l^-1) which would correspond, considering the adsorption efficiency ratio (Phosphorus: MPs), to P concentrations lower than 0.94 mg P l^-1, much higher than typical concentrations found in natural waters. For higher MPs dose (EC₅₀ for Chlorella sp. was 0.15 g l^-1), no nutrient limitations but high turbidity and Tot-Fe_dis values cause negative effects on algal growth. For the case of B. calyciflorus, LC₅₀ was 1.63 g MPs l^-1 (corresponding to 30.7 mg P l^-1). When analyzing Tot-Fe_dis effect, the hatching rate of B. calyciflorus cysts was 100% for all treatments. To sum up our results for B. calyciflorus acute and chronic toxicity tests, it is extremely unlikely the mortality of adult organisms in contact with MPs as well as an affectation of the rotifer egg bank. In conclusion, it is expected that MPs addition in a real whole-lake application cause minor lethal and sublethal effects on both Chlorella sp. and B. calyciflorus.

A promising application of chitosan quaternary ammonium salt to removal of Microcystis aeruginosa cells from drinking water

This work was aimed toward studying the new application of chitosan quaternary ammonium salt (HTCC), a water-soluble chitosan derivative, on removal of Microcystis aeruginosa (M. aeruginosa) cells during HTCC coagulation and floc storage. Results showed that all cells were removed without damage under optimum coagulation conditions: HTCC dosage 1.5mg/L, rapid mixing for 0.5min at 5.04g and slow mixing for 30min at 0.20g. The high removal efficiency was due to the large size and compact structure of flocs formed by HTCC, which readily settled. During floc storage, HTCC could induce production of reactive oxygen species (ROS), which would accelerate M. aeruginosa cell lysis. But the flocs, into which the cells aggregated, could protect cells from cellular oxidative damage caused by ROS, thus keeping the cells intact for a longer time.

Synthesis and characterization of magnetic chitosan microspheres as low-density and low-biotoxicity adsorbents for lake restoration

We propose a novel magnetic adsorbent for optimal Phosphorus (P) removal from the upper sediment layers. For this aim, magnetic chitosan microparticles were prepared using a reverse-phase suspension cross-linking technique. The resulting particles and suspensions were characterized using scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, magnetometry, thermogravimetric analysis, electrophoretic mobility and turbidity measurements. The hybrids are multicore particles consisting of well dispersed magnetite nanoparticles (approx. 10% w/w) homogeneously distributed within the biopolymer matrix. These microparticles can be easily separated from the water column and sediment using magnetic field gradients. Their P adsorption capacity is evaluated in batch conditions resulting in a maximum P adsorption capacity of M_L = 4.84 mg g^-1 at pH = 7. We demonstrate that these particles are excellent candidates to remove P from water column and also P mobile from the upper sediment layers due to two main reasons: they sediment slower and present lower potential toxicity (due to a their larger size) than conventional iron/iron oxide microparticles previously proposed for lake restoration.

A microcosm experiment to determine the consequences of magnetic microparticles application on water quality and sediment phosphorus pools

This study used microcosms to evaluate the effects of adding iron (Fe) magnetic microparticles (MPs) on water quality, focusing on P concentrations in the water column and sediment. Two treatments were considered for a constant 85:1 MP:P_Mobile molar ratio: T-W, applying MPs on the surface water layer; and T-S, applying MPs on the sediment. MP addition reduced P concentrations in lake water and sediment, with both treatments producing a mean reduction of 68±6% in dissolved inorganic P concentration (DIP) over a 70-day oxic period and reductions of 80±8% (T-W) and 80±4% (T-S) over a 5-day anoxic period. MPs also decreased reactive silicate (Si) concentrations by around 50% in both periods, but dissolved organic carbon (DOC) was reduced by only 15% at 24h after MP addition. Despite the marked decrease in DIP concentration due to MP addition, there was no reduction in chlorophyll a (Chla), because post-treatment total P concentrations (>200μgL^-1vs. >700μgL^-1 before treatments) remained higher than required for changes in the biological community (0.05-0.1mgL^-1). With T-S treatment, there was a reduction of 15% in P bound to Al oxides, clay minerals, and humic substances (P_→NaOH) and of 12% in labile organic P (Org-P_Labile) versus controls. P bound to humic substances (P_{→NaOH, Humic}) was reduced by 11-22% in both treatments. Finally, T-W rather than T-S treatments are recommended for future whole-lake applications to achieve more effective P removal from water and sediment and a higher percentage MP recovery.

Acute and chronic effects of magnetic microparticles potentially used in lake restoration on Daphnia magna and Chironomus sp

Magnetic microparticles (MPs) have been recently proposed as a new and promising tool for restoring eutrophicated waters. In this study, we analyzed the acute (immobilization) and chronic effects of iron (Fe) MPs on Daphnia magna and on the benthic macroinvertebrate Chironomus sp. In the chronic toxicity tests the offspring production (male and female) in D. magna and the mortality of larvae and pupae, and adult emergence in Chironomus sp. experiments were used as the endpoints. The concentration of MPs that caused 50% of immobilized individuals (EC₅₀) in the acute toxicity test was much higher in D. magna (0.913g MPs l^-1) than in Chironomus sp. (0.445g MPs l^-1). The results of chronic toxicity tests in D. magna showed that in presence of dissolved Fe (dFe), parthenogenetic reproduction was significantly affected, while no significant effect on mortality of larvae and pupae and on adult emergence was detected in Chironomus sp. test. Taking into account both that long-term exposure is not likely to occur and the regular dose of MPs potentially used in a restoration plan, we conclude that MPs is a riskless (no toxic effect on planktonic and benthic organisms) and efficient (high P adsorption capacity) tool for lake restoration.

Mesocarbon Microbead Carbon-Supported Magnesium Hydroxide Nanoparticles: Turning Spent Li-ion Battery Anode into a Highly Efficient Phosphate Adsorbent for Wastewater Treatment

Phosphorus in water eutrophication has become a serious problem threatening the environment. However, the development of efficient adsorbents for phosphate removal from water is lagging. In this work, we recovered the waste material, graphitized carbon, from spent lithium ion batteries and modified it with nanostructured Mg(OH)2 on the surface to treat excess phosphate. This phosphate adsorbent shows one of the highest phosphate adsorption capacities to date, 588.4 mg/g (1 order of magnitude higher than previously reported carbon-based adsorbents), and exhibits decent stability. A heterogeneous multilayer adsorption mechanism was proposed on the basis of multiple adsorption results. This highly efficient adsorbent from spent Li-ion batteries displays great potential to be utilized in industry, and the mechanism study paved a way for further design of the adsorbent for phosphate adsorption.

Magnetic microparticles as a new tool for lake restoration: A microcosm experiment for evaluating the impact on phosphorus fluxes and sedimentary phosphorus pools

In the last decades, magnetic particles (MPs) as adsorbents have gained special attention due to their high adsorption capacity and the possibility of recovering them by applying a magnetic separation gradient. For the first time MPs have been tested as P adsorbents in a microcosm experiment in a context of lake restoration. MPs were added to sediment cores from a hypertrophic lake, at Fe:PMobile molar ratio of 285:1 and 560:1 under both, oxic and anoxic conditions. We have found that, under anoxic conditions (anoxic), MPs are able to reduce P release rate from the sediment to the overlying water and to reduce sedimentary PMobile concentration (a 22-25% reduction within 0-4 cm depth compared to controls). Under oxic conditions, the addition of MPs do not affect P fluxes across the sediment and water interface since the lake sediment is naturally rich in iron oxides. However a measured reduction in sedimentary PMobile concentration (12-16% reduction in 0-10 cm depth) contributes to a potential reduction in long-term P efflux.

Effect of chitosan quaternary ammonium salt on the growth and microcystins release of Microcystis aeruginosa

This present study was the first time to research the application potential of HTCC inM. aeruginosacontrol. To balance the inhibition efficiency ofM. aeruginosaand the release of MCs, 1.2 mg L⁻¹was chosen as appropriate dose.

Removal of phosphate from aqueous solution by SiO2–biochar nanocomposites prepared by pyrolysis of vermiculite treated algal biomass

The present work describes the fabrication of SiO₂–biochar nanocomposites by pyrolysis of vermiculite treated algal biomass.

Preparation of magnetic calcium silicate hydrate for the efficient removal of uranium from aqueous systems

Preparation of a magnetic adsorbent for uranium with rapidly and effectively adsorption characteristics via sonochemical and in situ growth method.

The influence of pH on manganese removal by magnetic microparticles in solution

An extensive experimental work is reported that aims to assess the efficiency in manganese (Mn) removal from aqueous solution by carbonyl iron microparticles using magnetic separation techniques. A set of batch experiments are performed to explore the effect of pH, adsorbent concentration, surface coating and contact time for achieving the highest Mn removal efficiency. Mn removal efficiency is extremely high (>98%) for pH values larger than 9 as a result of the chemisorption of Mn oxides onto magnetic microparticles. In contrast, Mn removal efficiency for pH < 9 was significantly reduced as Mn remains as a soluble cation. In this manuscript we demonstrate that the efficiency clearly increases when increasing the adsorbent concentration and when using MnOx(s) coated magnetic particles instead of bare particles. Desorption rates from Mn-loaded magnetic particles at different pHs were always lower than 15%. Furthermore, Mn removal efficiency remained at a very high value (>95%) when reused particles were employed in the adsorption process.

Magnetic nanoparticles: essential factors for sustainable environmental applications

In recent years, there has been an increasing use of engineered magnetic nanoparticles for remediation and water treatments, leading to elevated public concerns. To this end, it is necessary to enhance the understanding of how these magnetic nanoparticles react with contaminants and interact with the surrounding environment during applications. This review aims to provide a holistic overview of current knowledge of magnetic nanoparticles in environmental applications, emphasizing studies of zero-valent iron (nZVI), magnetite (Fe3O4) and maghemite (γ-Fe2O3) nanoparticles. Contaminant removal mechanisms by magnetic nanoparticles are presented, along with factors affecting the ability of contaminant desorption. Factors influencing the recovery of magnetic nanoparticles are outlined, describing the challenges of magnetic particle collection. The aggregation of magnetic nanoparticles is described, and methods for enhancing stability are summarized. Moreover, the toxicological effects owing to magnetic nanoparticles are discussed. It is possible that magnetic nanoparticles can be applied sustainably after detailed consideration of these discussed factors.

Chemical interferences when using high gradient magnetic separation for phosphate removal: consequences for lake restoration

A promising method for lake restoration is the treatment of lake inlets through the specific adsorption of phosphate (P) on strongly magnetizable particles (Fe) and their subsequent removal using in-flow high gradient magnetic separation (HGMS) techniques. In this work, we report an extensive investigation on the chemical interferences affecting P removal efficiencies in natural waters from 20 Mediterranean ponds and reservoirs. A set of three treatments were considered based on different Fe particles/P concentration ratios. High P removal efficiencies (>80%) were found in freshwater lakes (conductivities<600 μ S cm(-1)). However, a significant reduction in P removal was observed for extremely high mineralized waters. Correlation analysis showed that major cations (Mg(2+), Na(+) and K(+)) and anions (SO(4)(2-) and Cl(-)) played an essential role in P removal efficiency. Comparison between different treatments have shown that when increasing P and Fe concentrations at the same rate or when increasing Fe concentrations for a fixed P concentration, there exist systematic reductions in the slope of the regression lines relating P removal efficiency and the concentration of different chemical variables. These results evidence a general reduction in the chemical competition between P and other ions for adsorption sites on Fe particles. Additional analyses also revealed a reduction in water color, dissolved organic carbon (DOC) and reactive silicate (Si) concentrations with the addition of Fe microparticles.

Setting up High Gradient Magnetic Separation for combating eutrophication of inland waters

To find new approaches to devise technologies for handling with eutrophication of inland waters is a global challenge. Separation of the P from water under conditions of continuous flow is proposed as an alternative and effective method. This work is based on using highly magnetic particles as the seeding adsorbent material and their later removal from solution by High Gradient Magnetic Separation (HGMS). Contrast to other methods based on batch conditions, large volumes of water can be easily handled by HGMS because of decreasing retention times. This study identifies the best working conditions for removing P from solution by investigating the effects of a set of four different experimental variables: sonication time, flow rate (as it determines the retention time of particles in the magnetic field), magnetic field strength and the iron (Fe) particles/P concentration ratio. Additionally, the change of P removal efficiency with time (build up effect) and the possibility of reusing magnetic particles were also studied. Our results evidenced that while flow rate does not significantly affect P removal efficiency in the range 0.08-0.36 mL s(-1), sonication time, magnetic field strength and the Fe particles/P concentration ratio are the main factors controlling magnetic separation process.

The pH-dependent surface charging and points of zero charge: V. Update

The points of zero charge (PZC) and isoelectric points (IEP) from the recent literature are discussed. This study is an update of the previous compilation [M. Kosmulski, Surface Charging and Points of Zero Charge, CRC, Boca Raton, FL, 2009] and of its previous update [J. Colloid Interface Sci. 337 (2009) 439]. In several recent publications, the terms PZC/IEP have been used outside their usual meaning. Only the PZC/IEP obtained according to the methods recommended by the present author are reported in this paper, and the other results are ignored. PZC/IEP of albite, sepiolite, and sericite, which have not been studied before, became available over the past 2 years.