Long-term sorption of lincomycin to biochars: The intertwined roles of pore diffusion and dissolved organic carbon

Sequestration of anthropogenic antibiotics by biochars from waters may be a promising strategy to minimize environmental and human health risks of antibiotic resistance. This study investigated the long-term sequestration of lincomycin by 17 slow-pyrolysis biochars using batch sorption experiments during 365 days. Sorption kinetics were well fitted to the Weber-Morris intraparticle diffusion model for all tested biochars with the intraparticle diffusion rate constant (k_id) of 25.3-166 μg g^-1 day^-0.5 and intercept constant (C_id) of 39.0-339 μg g^-1, suggesting that the sorption kinetics were controlled by fast initial sorption and slow pore diffusion. The quasi-equilibrium sorption isotherms became more nonlinear with increasing equilibration time at 1, 7, 30, and 365 days, likely due to increasing abundance of heterogeneous sorption sites in biochars over time. Intriguingly, low-temperature (300 °C) and high-temperature (600 °C) biochars had faster sorption kinetics than intermediate-temperature (400-500 °C) biochars at the long term, which was attributed to greater specific surface area and pore volume of high-temperature biochars and the substantial and continuous release of dissolved organic carbon (DOC) from low-temperature biochars, respectively. DOC release enhanced lincomycin sorption by decreasing biochar particle size and/or increasing the accessibility of sorption sites and pores initially blocked by DOC. Additionally, a large fraction (>75%) of sorbed lincomycin in biochars after a 240-day equilibration could not be extracted by the acetonitrile/methanol extractant. The strong sorption and low extraction recovery demonstrated the great potential of biochars as soil amendments for long-term sequestration of antibiotics in-situ.

Impact of media coating on simultaneous manganese removal and remineralization of soft water via calcite contactor

The aim of this study was to investigate the negative impact of a newly-formed manganese (Mn)-layer on calcite dissolution in the long-term operation of a calcite contactor. Simultaneous removal of Mn and remineralization of soft water in an up-flow calcite contactor was conducted and led to a progressive loading of Mn into the calcite matrix. The calcite contactor demonstrated high Mn removal; however, the hardness release decreased from 32 to 20 mg CaCO₃ L^-1 after 600 h of operation on a high Mn concentration (5 mg L^-1) feed. For an elevated Mn concentration (i.e. 5 mg Mn L^-1) in the feed water, the coated layer was mainly composed of Mn which inhibits the mass transfer from the calcite core to the liquid phase. The superficial layer was identified as 5.2% Mn oxides (MnOx) by X-ray photoelectron spectroscopy (XPS). Therefore, it is postulated that Mn removal starts with an ion exchange sorption reaction between soluble Mn²⁺ from aqueous phase and Ca²⁺ from the CaCO₃ matrix which is followed by a slow recrystallization of MnCO₃ into MnO₂. On the other hand, when the Mn content in the feed water was lower (i.e. 0.5 mg Mn L^-1), a considerably lower amount of MnOx was detected on the coated media. For all the examined conditions, the formation of this coating improved Mn removal due to the autocatalytic nature of the adsorption/oxidation of dissolved manganese by MnOx. A mechanistic model based on calcite dissolution and the progressive formation of a MnO₂ layer was implemented in PHREEQC software to predict the reduction in hardness release expected in long-term operation. The model was calibrated with experimental data and resulted in realistic breakthrough curves. In order to accurately predict the pH of the effluent stream, a slow-rate recrystallization of MnCO₃ into MnO₂ was implemented (compared to the fast precipitation of MnO₂ or the absence of MnO₂ formation).

Sorption of Nb(V) on pyrolusite (β-MnO2): Effect of pH, humic acid, ionic strength, equilibration time and temperature

The sorption of Nb(V) on pyrolusite has been studied and the effect of pH, ionic strength, humic acid, temperature and equilibration time were also investigated in a series of batch equilibrium experiments. The sorption was found to be affected by solution pH, ionic strength and humic acid. The sorption was high in neutral/near neutral pH (~96 %) but lower sorption was observed both in acidic (~55 %) and basic (~85 %) media. Sorption was decreased in acidic pH with increase of ionic strength and reverse effect was seen in basic pH although the effect is less prominent. Presence of humic acid causes enhancement of sorption in acidic pH whereas sorption declined in basic pH. The sorption process is endothermic in acid medium and exothermic in basic medium. In acid medium the sorption is entropy driven process. Kinetics of the sorption study was found to follow pseudo first order in acidic pH whereas pseudo second order in basic pH.

Sorption of non-ionic organic compounds by polystyrene in water

Polystyrene (PS) is a plastic material that is well known for its use in many different applications, e.g. as shock sensitive packaging. With its prevalence across society, PS contributes significantly to the overall plastic load in aqueous systems. Sorption of organic compounds by the plastics, especially micrometer-sized particles, in the environment has become a concern in the past years. The aim of this study was to improve the understanding of sorption properties of PS, one of the major plastic pollutants in the aqueous environment. Batch experiments with PS film (29 μm thickness) were performed for 4 days using a diverse set of 24 sorbates to account for varying molecular properties like polarity or molecular volume. Isotherms were evaluated using different sorption models to elucidate the sorption process of PS. Sorption to PS film was non-linear and absorption into the bulk material was the dominant sorption mode. A clear discrimination between the specific and non-specific interactions in the aqueous environment could be shown. The non-linear sorption to PS was shown to be controlled by the molar volume but also by the polarizability/dipolarity parameter (S) of the ppLFER model. The latter is influenced by the aromatic π-π-interactions of PS with the sorbate. Similar to other plastics like polyethylene, sorption to PS is driven by hydrophobic interactions but phase descriptors of pristine PS were significantly different than descriptors for other environmental relevant plastics.

Carbon nanotube-grafted chitosan and its adsorption capacity for phenol in aqueous solution

Chitosan was covalently grafted onto the surface of multi-walled carbon nanotubes to create a novel chitosan/multi-walled carbon nanotube. The structure of the new material was characterized using Fourier transform-infrared spectroscopy, cross polarization magic angle spinning ¹³C nuclear magnetic resonance, thermogravimetric analysis, XRD ray diffraction analysis, differential scanning calorimetry and scanning electron microscopy. The phenol adsorption capacity was determined and the Langmuir and Freundlich models were used to describe the adsorption isotherms. The adsorption capacity of the novel chitosan/multi-walled carbon nanotube material for phenol (86.96 mg/g) was improved compared to the original chitosan (61.69 mg/g). The kinetic studies showed rapid adsorption, exhibiting Lagergren second-order kinetics. Therefore, this study provides a reference for preparing functional materials from biological substrates that are able to remove toxic pollutants from an aqueous environment.

Adsorption of heavy metal ions (Cu2+, Ni2+, Co2+ and Fe2+) from aqueous solutions by natural zeolite

The process of remove copper, nickel, cobalt and iron ions by natural zeolite of the Yagodninsky deposits, Kamchatka region, from water resources within a concentration range of 0.5-3.5 mg-eq/L has been experimentally investigated. The specified concentrations range was chosen according the contents of heavy metals in the waste water of the mining enterprise of Kamchatka region The values of maximum sorption capacity have been determined. On the basis of studies using X-ray powder diffraction (XRD) it has been established by the Rietveld method of calculation that the zeolite tuff of the Yagodninsky deposit consists of clinoptilolite-Na (23.0 %), clinoptilolite-Ca (52.1 %) and modernite (12.9 %). It has been established that exchange cations are sodium, calcium, potassium and magnesium. The Gibbs free energy has been calculated which is equal for copper ΔG = -25.6 kJ/mol, iron - ΔG = -23.7 kJ/mol, nickel - ΔG = -21.5 kJ/mol and cobalt - ΔG = -20.0 kJ/mol. The obtained results show that natural zeolite can be used as an effective sorbent for extracting of ions Cu²⁺, Ni²⁺, Co²⁺ and Fe²⁺ from polluted waters. On the basis of the analysis of the parameters of the mordenite crystal lattice a decrease in sizes in the direction of the a- and b-axes and, consequently, of the elementary cell volume of the treated zeolite is observed as compared with the initial zeolite in the Cu > Ni > Co > Fe row. New knowledge about the sorption properties of the Yagodninsky deposit zeolites can be interesting for the industrial areas of South-Eastern Asia such as China, Japan, Korea, etc.

Column and batch sorption investigations of nickel(II) on extractant-impregnated resin

Macroporous resin-supported reagents have been identified as potential adsorbents for removal of toxic pollutants. This article presents an experimental designed to evaluate the sorption and desorption of nickel(II) with the help of column and batch procedure using simple extractant-impregnated resin (EIR). Isonitroso-4-methyl-2-pentanone (IMP) as an extractant was impregnated on a solid support like Amberlite XAD-4 to prepare the EIR sorbent. Column experimental conditions such as pH, sample flow rate and volume, eluting solution, and interfering ions were studied to optimize the nickel(II) sorption and recovery from aqueous media. The column results suggest that the quantitative nickel(II) sorption was observed at pH 5-6, and the quantitative recovery (≥ 95%) was achieved by using 1.0 M HNO₃. The high concentrations of cations and anions (except EDTA) present in the spiked binary and multi-element mixture solution show no interferences in both quantitative sorption and recovery of nickel(II), whereas the batch experiments were performed to evaluate nickel(II) sorption behavior using the linearized and non-linearized kinetic and isotherm models. By error function analysis, the Freundlich isotherm and the pseudo-first-order kinetic model were found to describe best the experimental data obtained over the studied concentration range and sorption time, respectively. The maximum sorption capacity of nickel(II) onto the EIR sorbent was found to be ~ 81 mg/g. The mean free energy (E = 10.1 kJ/mol) determined using Dubinin-Radushkevich isotherm suggests chemical nature of nickel(II) sorption on EIR. The novelty of the EIR adsorbent lies in its potential for separation and recovery of nickel(II) at trace level in water samples of different origin.

1,4-Dioxane cosolvency impacts on trichloroethene dissolution and sorption

Solvent stabilizer 1,4-dioxane, an emerging recalcitrant groundwater contaminant, was commonly added to chlorinated solvents such as trichloroethene (TCE), and the impact of co-disposal on contaminant transport processes remains uncertain. A series of batch equilibrium experiments was conducted with variations of 1,4-dioxane and TCE composition to evaluate aqueous dissolution of the two components and their sorption to aquifer sediments. The solubility of TCE increased with increasing amounts of 1,4-dioxane, indicating that 1,4-dioxane acts as a cosolvent causing solubility enhancement of co-contaminants. The solubilization results compared favorably with predictions using the log-linear cosolvency model. Equilibrium sorption coefficients (K_d and K_f) were also measured for different 1,4-dioxane and TCE compositions, and the findings indicate that both contaminants adsorb to aquifer sediments and TCE K_d values increased with increasing organic matter content. However, the K_d for TCE decreased with increases in 1,4-dioxane concentration, which was attributed to cosolvency impacts on TCE solubility. These findings further advance our understanding of the mass-transfer processes controlling groundwater plumes containing 1,4-dioxane, and also have implications for the remediation of 1,4-dioxane contamination.

Effects of particle size and solution chemistry on Triclosan sorption on polystyrene microplastic

PS microplastic particle (<5 mm) is an emerging contaminant of concern in aquatic and sediment systems with reported negative impacts on environmental and human health. TCS is a broad-spectrum antimicrobial which can affect ecosystems and result in long-term human health risks. The interaction between TCS and PS microplastic, partly determines the behavior and dispersion of TCS in the environment. In this study, the sorption kinetics and isotherms for TCS and PS microplastic were investigated. The influences of temperature, pH, ionic strength and coexisting heavy metals were assessed in batch experiments. The pseudo-second-order model (PSOM) was found to effectively describe the sorption kinetics of TCS on PS. TCS sorption on PS was found to be higher within the pH range of 3.0-6.0, while a decrease occurred at pH > 6.0. This result indicates that TCS⁰ was the major species contributing to the sorption process through hydrophobic interaction. Temperature did not affect the sorption of TCS on polystyrene, with sorption K_d values of 0.15, 0.16, 0.18 and 0.17 L/g at 288, 298, 308 and 318 K, respectively. Furthermore, the sorption amount of TCS showed no obvious variation with NaCl concentrations varying between 0.001 and 0.1 M. Finally, the coexistence of Cu(II)/Zn(II) had no significant influence on TCS sorption on PS, as Cu(II)/Zn(II) and TCS had different mechanisms of sorption on PS.

Sorption of polyhalogenated carbazoles (PHCs) to microplastics

The sorption of 5 Polyhalogenated carbazoles (PHCs) [3,6-dibromocarbazole (3,6-BCZ), 3,6-dichlorocarbazole (3,6-CCZ), 3,6-diiodocarbazole (3,6-ICZ), 2,7-dibromocarbazole (2,7-BCZ) and 3-bromocarbazole (3-BCZ)] on to three microplastics [polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)] in a simulated seawater system are studied. Sorption isotherms demonstrated that PVC had the maximum sorption capacity, which can be attributed to polar-polar interaction. The sorption kinetics model showed that the sorption process was controlled by both intraparticle and film diffusion. The sorption of PHCs to microplastics was significantly influenced by temperature, the sorption capacity first increased gradually and then decreased with the increasing temperature. Increasing the salinity decreased the sorption of PHCs onto PP, PE, PVC microplastics. Our results indicated that all three kinds of microplastics can serve as carriers for PHCs in the aquatic environment, which put marine ecosystems at higher risks.

Interpenetrated polymer networks of poly(β-cyclodextrin) and polyvinylpyrrolidone with synergistic and selective sorption capacities

Interpenetrating polymer network (IPN) hydrogels were synthesised using β-cyclodextrin (β-CD) and N-vynil-2-pyrrolidone (NVP) crosslinked with epichlorohydrin and divinylbenzene, respectively, and prepared by four different procedures: simultaneous, sequential, hybrid and a novel one named hybrid-sequential. The IPNs prepared have been characterised by infrared spectroscopy and thermal analysis. The equilibrium swelling in water and the sorption of model substances into the IPNs have also been studied. The model sorbates (1-naphthol, 2-acetylnaphthalene and tannic acid) were selected according to the affinities towards each one of the two constituent polymers. Our studies reveal that these IPNs can be applied for the sorption of substances that can interact with the network by two mechanisms, i.e. inclusion within cyclodextrin cavities and/or via specific interactions with the functional groups present. Besides, due to the complementary character of their constituent polymers, these networks could also serve to retain two substances of different nature such as cetirizine and pseudoephedrine.

Methylmercury sorption onto engineered materials

Four commercially available sorbents (BioChar (BC), ThiolSAMMS^® (TS), SediMite (SM), and Organoclay™ PM-199 (OC-199)) were tested for their ability to sorb methylmercury (MeHg) and MeHg complexed with dissolved organic matter (DOM). Testing sorption behavior with DOM is more representative of the environmental conditions and mercury speciation expected during in-situ remediation efforts. Isotherms were fit using a robust, iterative re-weighting scheme. This fitting approach improves upon the traditionally used indirect sorption method by removing the dependence between aqueous and solid phase concentrations in isotherm fitting. Developed isotherms show that without DOM, BC, TS, and SM adsorbed similar amounts of MeHg while OC-199 sorbed substantially less MeHg. Below an equilibrium concentration of 5.6 ng L^-1 BC was the best performing sorbent, between 5.6 and 20.9 ng L^-1 SM sorbed the most MeHg, and above an equilibrium concentration of 20.9 ng L^-1 TS outperformed the other sorbents. BC and OC-199 showed indication of MeHg sorption saturation over the tested concentration range of 3.5-680 ng L^-1. With DOM, SM outperformed the other sorbents at equilibrium concentrations less than 0.98 ng L^-1 and TS was the superior MeHg:DOM sorbent at higher concentrations. MeHg:DOM sorption was controlled by DOM-sorbent interactions. DOM decreased MeHg sorption onto BC and SM whereas TS exhibited similar sorption with and without DOM. OC-199 had slightly higher MeHg uptake with DOM. East Fork Poplar Creek (EFPC), an industrially Hg contaminated site, was used as a case study example to build a relationship between aqueous and fish MeHg concentrations and subsequently compare the cost of sorbent materials required to meet regulatory objectives. For this case study, SM provided the most cost-effective sorbent option for in-situ remediation efforts to reduce aqueous MeHg concentrations.

Kinetics of neptunium sorption and desorption in the presence of aluminum (hydr)oxide minerals: Evidence for multi-step desorption at low pH

Kinetics analyses of sorption and desorption provide important insight into reaction mechanisms occurring at the mineral-water interface. They are also needed to determine when equilibrium is achieved, identify intermediate chemical species, and inform models describing neptunium mobility. Neptunium sorption to and desorption from four different aluminum (hydr)oxides - bayerite (α-Al(OH)₃), gibbsite (γ-Al(OH)₃), corundum (α-Al₂O₃), and γ-alumina (γ-Al₂O₃) - were investigated as a function of mineral concentration (5 - 170 m² L^-1), neptunium concentration (10^-9 - 10^-7 M), and pH (5.5 - 10.5). Neptunium sorption was characterized by a two-step reaction with an initial fast sorption step occurring within minutes followed by a slower equilibrium process, which was attributed to initial sorption of neptunium to a small number of strong sorption sites followed by sorption of neptunium to a larger number of weak sorption sites. The kinetics data were modeled using the linear and non-linear forms of the pseudo-first and pseudo-second order rate equations and the goodness of fit parameters were compared. Non-linear pseudo-second order rate constants described neptunium sorption to aluminum (hydr)oxides most accurately and were used to determine the reaction orders with respect to mineral concentration and [H⁺]. Neptunium desorption experiments demonstrated that the desorption mechanism changed as a function of pH and that the forward and reverse reactions were not equivalent. At pH ≥ 7.5, desorption reached steady-state within an hour and was accurately described by the non-linear pseudo-second order rate equations. A desorption plateau was observed at pH 5.5 that could not be described by either pseudo-first or -second order kinetics, suggesting the possibility of a multi-step desorption reaction. The comparatively slow desorption kinetics observed here suggests that sorbed neptunium could be slowly released back into the aqueous phase and act as a continuous source of contamination to the environment.

Partitioning of chemical contaminants to microplastics: Sorption mechanisms, environmental distribution and effects on toxicity and bioaccumulation

There is an increasing awareness of the threats posed by the worldwide presence of microplastics (MPs) in the environment. Due to their high persistence, MPs will accumulate in the environment and their quantities tend to increase with time. MPs end up in environments where often also chemical contaminants are present. Since the early 2000s, the number of studies on the sorption of chemicals to plastic particles has exponentially increased. The objective of this study was to critically review the literature to identify the most important factors affecting the sorption of chemical contaminants to MPs. These factors include the physicochemical properties of both the MPs and the chemical contaminants as well as environmental characteristics. A limited number of studies on soil together with an increased notion of the importance of this compartment as a final sink for MPs was observed. Therefore, we assessed the distribution of model chemicals (two PCBs and phenanthrene) in the soil compartment in the presence of MPs using a mass balance model. The results showed a high variation among chemicals and microplastic types. Overall, a higher partitioning to MPs of chemical contaminants in soil is expected in comparison to aquatic environments. As sorption to a large extent determines bioavailability, the effects of combined exposure to chemicals and MPs on the toxicity and bioaccumulation in biota are discussed. Finally, some considerations regarding sorption and toxicity studies using MPs are given.

Leaching behavior of pharmaceuticals and their metabolites in the soil environment

Pharmaceuticals constitute a significant group of emerging pollutants (EPs). The use of pharmaceuticals in animal breeding causes them to reach the soil environment in excrement and fertilizers. Depending on their chemical properties, pharmaceuticals can be sorbed to the soil or be washed out with rainfall and eventually be entered into groundwater. This paper evaluates the mobility of tramadol (TRA) and carbamazepine (CBZ), and two transformation products, O-desmethyltramadol (O-DMTRA) and 10,11-dihydro-10-hydroxycarbamazepine (10-OH-CBZ) in soils. Both pharmaceuticals are applied in human and animal treatment, which makes them enter the environment in native and metabolized form in high doses. Experiments were carried out in accordance with the OECD 106 procedure (batch tests) and DIN 19528:2009-01 procedure (percolation column test). The adsorption coefficients (K_d) for TRA, CBZ, O-DMTRA and 10-OH-CBZ were, respectively, 1.41 ± 0.10, 1.87 ± 0.06, 0.90 ± 0.03 and 0.37 ± 0.07 for sandy soil RS04, and 18.09 ± 0.78, 2.56 ± 0.05, 10.89 ± 0.17 and 0.56 ± 0.38  L kg^-1 for loamy soil RS06. The percolation column test was carried out for sandy soil RS04. The results obtained for TRA and O-DMTRA under static conditions indicated a high mobility of these compounds in soil, whereas the column leaching experiment showed that these compounds bind strongly to soil particles. A correlation between static and dynamic tests was observed in the case of CBZ and 10-OH-CBZ. These compounds will probably be characterized by a high or moderate mobility in soil.

Effect of black carbon on sorption and desorption of phosphorus onto sediments

The sorption behavior of phosphorus onto sediment was investigated with the addition of BC derived from incomplete biomass combustion (PC). The sorption kinetic curves of phosphorus onto PC and sediment could be described by a two-compartment first order equation, and the sorption isotherms fit the Freundlich model well. With increasing amounts of PC added, the sorption capacity increased while the HI did not change much. The distribution of phosphorus forms showed that CaP (ACa-P plus DAP) constituted the highest fraction in the sediment samples. Throughout the sorption process, CaP and OP changed very little, but the Ex-P and FeP increased obviously, and the presence of PC made this increase more significantly. The high specific area and the presence of iron and aluminum, as well as the modification of the sediments surface properties, make the addition of PC be favorable for the sorption of phosphorus onto sediments.

Batch sorption experiments of cesium and strontium on crushed rock and biotite for the estimation of distribution coefficients on intact crystalline rock

The distribution coefficient (K_d) of radionuclides on bedrock is one of the key parameters used in the safety analysis of spent nuclear fuel repositories. Typically, distribution coefficients have been determined using crushed rock. However, recent studies have shown that crushing of the rock increases considerably the distribution coefficient compared with the values of intact rock. This study aimed to test if batch sorption experiments using different grain sizes (i.e. mean diameter of grains) can be used to evaluate the K_d of strontium (Sr) and cesium (Cs) on intact crystalline rock, which would decrease the needed experimental time compared with transport experiments. Here we report the results of the batch sorption experiments with crushed rocks and compare the results with those from a recent study performed using electromigration experiments with intact drill core samples (Puukko et al., 2018). The batch sorption experiments were done for rock samples from Olkiluoto, Finland, as a function of grain size and of Cs and Sr concentration. Furthermore, the specific surface areas of the same rock samples with different grain sizes were determined. It was shown that Cs distribution coefficients correlate with specific surface areas of the studied rocks and biotite, the correlation coefficient being 0.95. The Cs distribution coefficient was highest for biotite at about 0.1 m³/kg at 10⁻⁴ M cesium concentration and increased systematically to about 1 m³/kg at 10⁻⁸ M. Distribution coefficients for rocks were up to about two orders of magnitude lower, being lowest with the rock with the lowest biotite content (3.3%). The distribution coefficient of Sr varied from 0.04 m³/kg to 0.007 m³/kg and behaved in a different manner: it remained constant in two out of three studied rocks in the concentration range of 10⁻⁸-10⁻⁴ M and only in the case of one rock a decreasing trend was seen at the higher concentration range. It was also shown that batch sorption experiments overestimate the distribution coefficient in respect to intact rock. The decrease of the distribution coefficient as a function of grain size can be estimated using a power law function. It was also shown that estimation of distribution coefficients of Cs and Sr for intact rock by extrapolation of distribution coefficients determined for different grain sizes is not possible without increasing grain size, but in that case diffusion into the grains would also affect the results. A new method was developed for estimating the fraction of the inner surface area of the total surface area of crushed grains. For the mean grain sizes of 0.25 mm and 0.75 mm the fraction of the inner surface was found to be 35–70% and 60–90%, respectively. The inner specific surface area was highest with biotite at 1.2 m²/g and lowest with the rock with lowest biotite content (3.3%) at 0.07 m²/g. The surface area analysis revealed that crushing creates and/or allows access to additional inner surface area that is not measured in intact rock. Furthermore, it was demonstrated that sorption of Cs on crushed rock was dominated by mica minerals in multiple concentrations while the effect of mica minerals on the K_d of Sr was not as straightforward.

Effects of dissolved humic acid on fluoroquinolones sorption and retention to kaolinite

Fluoroquinolones (FQs) are widely used in human and veterinary medicaments, and as such are ubiquitous environmental contaminants. Dissolved organic matter (DOM) is widely distributed in natural water and sediment and dissolved humic acid (DHA) is a major component of DOM. The coexistence of DHA might influence the sorption, migration and transformation of FQs, thus determining their environmental fate. In this study, the interaction of DHA and ofloxacin (OFL)/flumequine (FLU) was evaluated using dialysis-bag assays. The sorption of OFL and FLU to kaolinite in the presence of DHA under different pH conditions was investigated. The results revealed that the binding affinities of FQs to DHA were weakened with increasing pH from 4.0 to 10.0 due to the increased negative charge of DHA and subsequent electrostatic repulsion. Sorption experiments indicated that co-precipitation was an important mechanism for OFL/FLU removal from the aqueous phase under acidic conditions. At pH 7.0, the affinity of OFL-DHA/FLU-DHA to kaolinite was weaker than that of OFL/FLU thus suppressed its sorption. At pH 9.5, the affinity of OFL-DHA to kaolinite was stronger than that of OFL and consequently promoted its sorption, but there was no observed effect of DHA on FLU sorption. During desorption, DHA could bind to OFL/FLU and promote its desorption from kaolinite at neutral pH. In binary solute systems of OFL and FLU, OFL was a more effective competitor for the sorption sites of kaolinite than FLU.

Removal and simultaneous reduction of Cr(VI) by organo-Fe(III) composites produced during coprecipitation and coagulation processes

Composites formed during the coprecipitation and/or coagulation of ubiquitous dissolved organic matter (DOM) and Fe in natural and waste water systems might be potential scavengers for Cr(VI) in terms of sorption and reduction. Our objective here was to determine sorption and simultaneous reduction of Cr(VI) on organo-Fe(III) composites (OFC) in relation coprecipitated pH and C/(C + Fe) ratios. Results showed the greatest Cr sorption of 51.8 mg g^-1 on the OFC sample that was precipitated at pH 3 and contained the C/(C + Fe) molar ratio of 0.71. Wherein the Cr(VI) removal subsequent to the coprecipitation was dominated by the sorption on Fe hydroxides. Although amounts of total sorbed Cr decreased with increasing C/(C + Fe) molar ratio, the reverse trend on Cr(VI) reducibility compensated the Cr(VI) removal capability of OFC samples. With C/(C + Fe) molar ratios ≥ 0.89, the increasing amounts of coprecipitated organic matter that homogeneously distributed with Fe domains on OFC surfaces could trigger a significantly pronounced Cr reduction. Collectively, our results suggested an alternative method for Cr(VI) remediation by manipulating C/Fe ratios in suspensions. After the sorption of most Cr(VI) on Fe hydroxides, increasing C/Fe ratio in systems could further improve the Cr(VI) removal efficiency by the reduction of remaining Cr(VI) to Cr(III).

Editorial of the VSI "Antibiotics and heavy metals in the environment: Facing the challenge"

The Virtual Special Issue (VSI) "Antibiotics and Heavy Metals in the Environment: Facing the Challenge" received more than 100 submissions from research teams around the world. Finally, more than 50 papers were accepted and published. These very interesting research papers allow going ahead in the knowledge of different aspects which determine the fate of antibiotics and heavy metals in the environmental. The success of the VSI, as well as reports from scientific databases, indicate that this field of research is clearly growing, which is expected to continue, especially considering emerging pollutants as a whole.

An experimental approach for determining thermodynamic surface complexation descriptors of weak-acid oxyanions onto metal (hydr)oxides: Case study of arsenic and titanium dioxide

The extensive literature review suggests that there are two main reasons for contradictory thermodynamic parameter values obtained via sorption experiments: (1) many of the studies are conducted under unrealistic conditions where the sorbate/sorbent ratios are so high that physisorption is artificially induced; or (2) many of the studies incorrectly calculate the equilibrium constants. The goal of this study is to demonstrate a methodology that describes how to properly determine and verify theoretically predicted thermodynamic descriptors. The study employs arsenate and titanium dioxide as a model sorbate-sorbent pair, which is equilibrated under realistic conditions for a period of 3 days at two different pH conditions (~6.5 and ~8.5) and three different temperatures (7 °C, 25 °C and 35 °C) in 10 mM NaHCO₃. At pH ≈ 8.55, ΔG^o values were -83.38 ± 1.62 kJ/mol, -88.13 ± 0.66 kJ/mol, and -90.78 ± 0.61 kJ/mol for sorption performed at 7 °C, 25 °C and 35 °C, respectively. Decreasing the pH to about 6.65 resulted in slightly less negative values of ΔG^o to -73.38 ± 1.58 kJ/mol, -77.14 ± 1.52 kJ/mol, and -78.75 ± 1.53 kJ/mol for sorption conducted at the same respective temperature conditions. These values overlap with the ΔG^o ranges reported for sorption of arsenate on metal oxides. Change in enthalpy values of ΔH^o = -19.04 kJ/mol at pH ≈ 6.65 and ΔH^o =-9.35 kJ/mol at pH ≈ 8.55 were observed. Based on reports, which suggest that at lower pH more bidentate ligands are being formed, these values are expected. The change in entropy values ranged from ΔS^o = 0.19 kJ/mol K at pH ≈ 6.55 to ΔS^o = 0.26 kJ/mol K at pH ≈ 8.55, which suggests lower level of disorder among the created complexes at lower pH and it is in line with the rationale that bidentate complexes are better organized on the surface of the sorbent and less susceptible with desorption. These findings clearly demonstrate that experimentally obtained ΔG⁰ and other thermodynamic values and trends could be obtained to reflect and confirm model predictions when the existing sorption theory is properly translated into experimental practice. The sorbate-sorbent bond in chemisorption has covalent character, characterized with short bond length and higher bond energy, which makes it less reversible when compared to physisorption, and therefore highly significant from a sorbent remediation-performance practical point of view and long-term waste sorbents disposal. While thermodynamic parameter modeling represents a good first step in determining the suitability of an initial design, experimental techniques potentially have the ability to provide far more superior description of the thermodynamic sorbent/sorbate interactions under realistic conditions.

Modeling of micropollutant removal in full-scale membrane bioreactors: calibration and operations to limit the emissions

Micropollutants are a major concern for aquatic organisms and human health. Membrane bioreactors (MBRs) are an efficient wastewater treatment and water reuse solution, but their micropollutant removal performances are still not fully determined. Modeling micropollutant behavior in MBRs could help better understand and optimize the removal process. Here we provide detailed explanation on a model of micropollutant removal in MBRs that predicts biodegradation and sorption rates. Parameters were calibrated following an iterative two-step procedure developed in this work and using data from two full-scale plants. The calibrated set of parameters was then used (i) to determine the influence of MBR operating conditions such as the duration of aerobic time and the sludge concentration in bioreactor, on micropollutant removal, and (ii) to better understand micropollutant behavior and removal performances in MBRs in response to sudden changes in operating conditions (rain event, F:M ratio). These predictive simulations showed that increasing sludge concentration in bioreactor can decrease effluent concentrations of most of the micropollutants studied by up to 15%, and increasing the duration of aerobic time decreases effluent concentrations of few organic micropollutants tested by up to 15%. Rain events and F:M ratio can increase effluent concentrations of six out of nine micropollutants tested by more than 15%.

Novel remediation of per- and polyfluoroalkyl substances (PFASs) from contaminated groundwater using Cannabis Sativa L. (hemp) protein powder

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a group of environmentally persistent, man-made chemicals used in many industrial products and everyday consumer items. Of the plant proteins trialled, those of hemp (Cannabis sativa L.) were found to be far superior for PFAS removal than the next best protein, soy. The use of hemp plant proteins as a possible pump-and-treat solution to PFAS remediation from groundwater has been successfully demonstrated with very good removals (>98%) of the main contaminants of PFOS and PFHxS in approximately 1 h of contact time, with salinity enhancing removal of short chain PFAS. Changes to the secondary structure of hemp proteins was found using FTIR spectroscopy analysis and calculated based on the integrated areas of the amide I component bands. The amount of β-turns increased from ∼9.3% (control) to 44.1% (undiluted groundwater); with a decrease in random coils (25.6-8.6%); α-helix (19.3-8.6%) and β-sheets (38.8-23.1%). These changes indicate that hemp proteins partially unfold during the reaction with PFAS with other FTIR evidence suggesting sorption at hydrophobic sites of the protein as well as with the side chains of the amino acids aspartic and glutamic acid. The absence of these side chains in soy protein, as evidenced from FTIR and amino acid analysis, being part of the reason why soy removed less (approx. half) of the Σ(PFHxS + PFOS) load when compared to hemp. The findings reported here will lead to new, environmentally friendly methods for PFAS remediation.

Sorption of sulfamethazine onto different types of microplastics: A combined experimental and molecular dynamics simulation study

Microplastics are becoming a global concern due to their potential to accumulate pollutants in aquatic environments. In this paper, sulfamethazine (SMT) sorption onto six types of microplastics, including polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) was investigated by experimental and molecular dynamics simulation methods. The experimental results indicated that SMX sorption reached equilibrium within 16 h. The kinetics of SMT sorption by PA, PVC, PE, and PP could be fitted by pseudo first-order model, while SMT sorption by PA and PET could be described by pseudo second-order model. The partition coefficient K_d values were 38.7, 23.5, 21.0, 22.6, 18.6 and 15.1 L·kg^-1 for PA, PE, PS, PET, PVC and PP, respectively. SMT sorption onto microplastics decreased when pH and salinity increased. The molecular dynamics simulation results indicated that the main mechanisms involved in sorption are electrostatic and Van der Waals interaction.

Sorption of sulfamethoxazole onto six types of microplastics

Microplastics and sulfamethoxazole (SMX) are ubiquitous in aquatic environment. In this study, we investigated the sorption of SMX onto six types of microplastics (polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC) and polypropylene (PP)). The sorption rate and mass transfer steps of SMX was studied by using the phenomenological kinetics models. The effect of pH and salinity on SMX sorption was examined. The results showed that the sorption of SMX onto microplastics reached equilibrium within 16 h. The external mass transfer was the slowest sorption step. The linear and Freundlich isotherms fitted well the sorption equilibrium data. PA had the highest sorption capacity (2.36 mg g^-1 at SMX concentrations of 12 mg L^-1), with high distribution coefficient (K_d) value (284 L kg^-1). The K_d values of PE, PS, PET, PVC, and PP ranged from 22.2 to 30.9 L kg^-1. The sorption capacity of SMX decreased with increase of pH and salinity in the solution.