Electrostatic Bridging Research Articles

Phosphate sorption mechanisms in biochar: Insights from depth profiling of porous structure across pH and pyrolysis conditions

This study examines phosphate (P(V)) sorption mechanisms in Miscanthus biochar, focusing on the effects of concentration, pH, and pyrolysis temperature. Biochars produced at 400 °C (B400) and 700 °C (B700) were analyzed using Freundlich isotherm and depth profiling X-ray photoelectron spectroscopy (DP-XPS). Four sorption mechanisms were identified: physisorption and C-P(V) complexes for both biochars, electrostatic bridging complex (EBC) in B400, and O-P(V) complexes in B700. B400 had higher sorption capacity but relied on weaker EBC, making it more prone to leaching, though it also provides greater P(V) availability for uptake. In contrast, B700 exhibited stronger inner-sphere, resulting in more stable retention. DP-XPS revealed internal enrichment of P(V) and changes in functional groups by pH. These findings indicate that pyrolysis and environmental conditions significantly influence P(V) retention characteristics, and that biochar can be tailored to balance P(V) availability and stability, thereby contributing to improved soil fertility and reduced leaching.

Fusion Dynamics and Size-Dependence of Droplet Microstructure in ssDNA-Mediated Protein Phase Separation.

Biomolecular condensation involving proteins and nucleic acids has been recognized to play crucial roles in genome organization and transcriptional regulation. However, the biophysical mechanisms underlying the droplet fusion dynamics and microstructure evolution during the early stage of liquid-liquid phase separation (LLPS) remain elusive. In this work, we study the phase separation of linker histone H1, which is among the most abundant chromatin proteins, in the presence of single-stranded DNA (ssDNA) capable of forming a G-quadruplex by using molecular simulations and experimental characterization. We found that droplet fusion is a rather stochastic and kinetically controlled process. Productive fusion events are triggered by the formation of ssDNA-mediated electrostatic bridges within the droplet contacting zone. The droplet microstructure is size-dependent and evolves driven by maximizing the number of electrostatic contacts. We also showed that the folding of ssDNA to the G-quadruplex promotes LLPS by increasing the multivalency and strength of protein-DNA interactions. These findings provide deep mechanistic insights into the growth dynamics of biomolecular droplets and highlight the key role of kinetic control during the early stage of ssDNA-protein condensation.

Enhanced interlayer interaction in sulfonated CONs membrane by amino-rich CONs enabling ultrafast proton transport

Covalent organic framework nanosheets (CONs) with porous crystalline features and ultrathin thickness are ideal candidates as membrane building blocks to form well-defined transfer nanochannels. The formidable challenge behind self-supporting CONs membrane lies in weak non-covalent interlayer interactions and thus loose stacking, insufficient strength and structure stabilities. Herein, we propose the fabrication of interlayer force-strengthened freestanding CONs membrane through the electrostatic attraction bridge effect of positively-charged amino-rich CONs (CON–NH2) to negatively-charged sulfonated CONs (CON–SO3H). Ultrathin and large lateral sized CON–SO3H and CON–NH2 are synthesized, followed by restacking to prepare freestanding CONs membrane with CON–SO3H as the membrane bulk. Benefiting from effective interlayer interconnection due to strong electrostatic interaction, the obtained CON–SO3H/CON–NH2 membrane displays features of ultrahigh integrity, dense stacking, eminent water/acid/base/organic solvents stabilities and mechanical strength (109 MPa). The shortened –SO3H distance contributes to construct site-continuous transfer pathways, and the deprotonated –SO3H and protonated –NH2 form acid–base pairs to decrease interfacial resistance, which impart membrane superior proton conductivity of 486 mS cm−1 (80 °C, 100% RH). This interlayer force enhancement strategy offers a promising perspective on achieving densely-stacked CONs membrane with ultrahigh mechanical property and conduction performance for fuel cell application.

Ammonium persulfate oxidized nanofibrillated cellulose as a sustainable wet-end paper reinforcement additive

Nanocellulose fibers (NFCs) with specific characteristics were synthesized using the economically attractive ammonium persulfate (APS) mediated oxidation process to evaluate their potential as wet end additives in paper. The surface charge and morphology of as-synthesized NFC were tailored and characterized, and the barrier and strength properties of NFC-reinforced papers were thoroughly examined as a function of NFC contents and characteristics. The addition of two different cationic polyelectrolytes promoted electrostatic bridging between pulp fibers and maintained NFC retention above 93% regardless of the NFC nature. Results demonstrate that the presence of NFC with lower surface charge yields papers with denser fibrous network, reduced air permeability, and higher specific tensile strength. Higher surface charge NFC, on the other hand, increased floc formation and decreased NFC retention likely due to reduced dispersion and NFC agglomeration with the dual component retention system. Significantly, APS-oxidized NFC may be generally applicable as a competitive alternative to expensive and/or environmentally taxing chemicals typically employed in the manufacturing of a variety of papers and boards.

Plant-based delivery systems for controlled release of hydrophilic and hydrophobic active ingredients: Pea protein-alginate bigel beads

Oral delivery systems for nutrients and nutraceuticals are required for personalized nutrition applications. In some applications, these delivery systems need to encapsulate both hydrophilic and hydrophobic bioactive agents. In this study, bigel beads (2 mm) were prepared using pea protein (PP) and sodium alginate (SA) to form the hydrogel phase, and glyceryl monostearate and soybean oil to form the oleogel phase. The hydrogel phase was crosslinked by using Ca2+ ions to form electrostatic bridges between the alginate molecules. The bigel beads had an oil-in-water type structure consisting of an oleogel dispersed phase within a hydrogel continuous phase. These beads were used to encapsulate and control the release of model hydrophobic (curcumin) and hydrophilic (epigallocatechin gallate) nutraceuticals. The textural and microstructural characteristics of the bigel beads were evaluated by dynamic shear rheology, textural profile analysis, cryo-electron microscopy, and fluorescence confocal microscopy. As the concentration of SA increasing from 0.2 to 1.0%, the hardness of bigel beads increased from 306.75 g to 792.40 g. In vitro digestion experiments showed that most of the nutraceuticals were released in the small intestine, rather than the stomach. Nutraceutical release could be controlled by manipulating bead composition, with the extent of nutraceutical release decreasing with increasing alginate concentration. The bigel beads developed in this study could be used as easy-to-swallow carriers for the controlled release of hydrophilic and hydrophobic bioactive ingredients. These kinds of products may be especially useful for people with dysphagia.

Rheological and dielectric behavior of sodium carboxymethyl cellulose (NaCMC)/Ca2+ and esterified NaCMC/Ca2+ hydrogels: Correlating microstructure and dynamics with properties

Polyelectrolyte-based conductive hydrogels are being extensively explored for applications in energy storage and as electrode materials for batteries. We synthesized ionically crosslinked sodium carboxymethyl cellulose (NaCMC), esterified NaCMC, and Ca2+ doped esterified NaCMC hydrogels. This work aims to understand the effect of Ca2+ ions on the NaCMC and esterified NaCMC. FTIR, SEM, Rheology and EIS studies were performed to understand the structure and dynamics of hydrogels. Results confirmed that Ca2+ ions have an important role in determining the rheological and dielectric response of hydrogels. Power law behavior was observed in their rheological response with exponent (n) of 0.81 for G′ and 0.76 for G″ of ionically crosslinked NaCMC, 5.38 for G′ and 4.70 for G″ of esterified NaCMC, whereas, negative exponents −1.44 for G′ and −1.10 for G″ of Ca2+ ion doped esterified NaCMC. Ionically crosslinked NaCMC hydrogels have relaxation times (τ) in the range of 8.9 × 10−5 s–2.8 × 10−5 s may be due to the formation of temporary dipoles by electrostatic bridge formations with dc conductivity of (0.1 S/cm–5 S/cm), whereas, esterified NaCMC showed relaxation times (10−3 s–8.9 × 10−5 s) with increasing ester crosslinks and dc conductivity of (0.05 S/cm–0.8 S/cm). Interestingly, Ca2+ ion doped esterified hydrogels showed multiple dielectric relaxations on Ca2+ ion addition with different relaxation times may be due to change in ionic environment. The understanding obtained from this work may be useful for designing tuneable hydrogels with optimum electrical and mechanical properties.

Alpha-synuclein phosphorylation induces amyloid conversion via enhanced electrostatic bridging: Insights from molecular modeling of the full-length protein

Fibril formation from alpha-synuclein is a key point in Parkinson's disease, multiple system atrophy, and other synucleinopathies. The mechanism of the amyloid-like conversion followed by the formation of pre-fibrillar soluble oligomers and fibrils is not completely clear; furthermore, it is unclear how the Parkinson's disease-related point mutations located in the pre-NAC region enhance fibrillation. In the present paper, atomistic replica exchange molecular dynamics simulations of the full-length alpha-synuclein and its two mutants, A53T and E46K, elucidated amyloid conversion intermediates. Both mutants demonstrated an enhanced tendency for the conversion but in different manners; the main intermediate conformations populated in the WT alpha-synuclein conformational ensemble disappeared due to mutations, indicating a different conversion pathway. Analysis of the preferable beta-hairpin positions and intermediate conformations seems to reflect a tendency to form a particular amyloid fibril polymorph. A strong elevation of amyloid transformation level was shown also for Ser129-phosphorylated alpha-synuclein. Altered intermediate conformations, the most preferable beta-hairpin positions in the NAC region, and prevalent salt bridges propose the formation of so-called polymorph 2 or even a novel type of fibrils. A better understanding of the detailed mechanism of the amyloid conversion sheds light on the effect of Lewy body-related phosphorylation and might help in the development of new therapeutics for synucleinopathies.

Chitosan-β-cyclodextrin composite flocculants dual-drive for efficient microalgae harvesting: Structural evidences, dehydration process, E-DLVO model behavior and biomass utilization

Flocculation is one of the promising methods for harvesting microalgae. In this study, a series of grafted cationic chitosan-cyclodextrin composite flocculants (CTS/β-CDs) with different structural properties were prepared from chitosan and cyclodextrin. The results showed that the harvesting efficiency of CTS/β-CD-1 for C. vulgaris reached 99.91%. The chain type of polymeric flocculants with moderate graft chain lengths (L = 10–20) and tighter branched chain density distribution (D = 1.0–1.8) was favorable for C. vulgaris harvesting. The addition of CTS/β-CDs caused the discrete C. vulgaris cells to be flocculated and aggregated, and the reorganization of particles resulted in larger particles after flocculation, improving the dewatering performance of microalgae flocs. CTS/β-CDs had no significant inhibitory effect on the extraction of lipids, proteins and carbohydrates, and did not affect the extraction and quality of fatty acid methyl esters, and the re-cultivation experiments of the harvested water showed that chitosan-based flocculant was able to effectively reduce the cost of microalgae harvesting. Electrostatic interactions and bridging were the main harvesting mechanisms between CTS/β-CD-1 and C vulgaris. E-DLVO modeling suggested that flocculation is mainly a result of electrostatic and acid-base interactions when the distance between particles is small. At higher pH, the harvesting efficiency of CTS/β-CD-1 with C. vulgaris decreased. The study contributes to a better understanding of the structure–activity relationship between the structural characteristics of flocculants and the harvesting performance.

Study on flocculation performance and mechanism of cationic polyacrylamide on montmorillonite: Insights from experiments and molecular simulations

To achieve efficient flocculation of fine montmorillonite particles, molecular simulation and flocculation test were investigated to explore the influence of cationic monomer on the performance of cationic polyacrylamide (CPAM) flocculating montmorillonite particles. Three cationic monomers including methylacryloxyethyl trimethyl ammonium chloride (DMC), acrylamide propyl trimethyl ammonium chloride (ATMAC), and methylacrylamide propyl trimethyl ammonium chloride (MAPTAC) were copolymerized with acrylamide (AM) to produce CPAM copolymers. The simulation results suggested the electrostatic interaction was the primary internal propelling force for the stable adsorption of three distinct CPAM copolymers on the montmorillonite/water interface, followed by hydrogen bonding. Flocculation test indicated that CPAM has better flocculation effect on fine montmorillonite particles only when it has strong electrostatic adsorption and bridging capacity. This research establishes a theoretical foundation for the structural design of new flocculants for fine clay minerals.

Construction of chitosan modified cationic lipid droplet emulsions for high-value microalgae harvesting

To reduce the risk of microalgae biomass and environmental contamination, a natural cationic lipid droplet emulsion has been constructed for harvesting microalgae. Using three different microalgae strains (Chlorella vulgaris, Scenedesmus quadricauda and Spirulina platensis), the present work studied the influence of lipid droplet dosage, chitosan concentration, pH on harvesting efficiency, and then the flotation behavior was analyzed by zeta potentials, floc size distribution, algal organic matter component, attenuated total reflectance Fourier transform infrared spectrometer and microscopic observation. The XDLVO theory was used to explain the attachment behavior during the flotation process. The experimental results showed that the maximum harvesting efficiency for two green microalgae strains was over 95% at pH 7, while the optimal dosage and ratio of lipid droplet and chitosan were depended on the microalgae species. The maximum harvesting efficiency for Spirulina platensis was less than 70% since the high salinity of growth medium weakened the bridging and netting ability of chitosan. The mechanism of capturing microalgae by the ballasting agents was mainly physical electrostatic attraction, bridging and netting. In addition, the changes of microalgae components before and after harvesting were less than 5%, indicating this method would not affect the downstream application of microalgae biomass.

Molecular mechanisms of pyrophosphate-mediated selective adsorption of Ni(II) by polyamine-grafted chitosan–wood flour composite from alkaline plating wastewater: EXAFS investigation and theoretical calculations

The efficient removal of complexed heavy metals (HMs) from alkaline electroless plating wastewater is still challenging. A polyamine-grafted chitosan–wood flour-based composite (ACS-AWF) was optimally synthesized. Its adsorption behavior toward Ni(II) in simulated pyrophosphate (PP, the main complextant)–Ni plating wastewater and underlying mechanisms were examined. PP considerably promoted Ni(II) adsorption by up to 108.1%, and the enhancement tolerated excess PP or other substances. Ni(II) adsorption by ACS-AWF was 1.38–∼10 times that of several commercial HM-favored resins in the same complexed system. According to the liquid solute species tracking, solid chemical characterizations (eg. synchrotron radiation X-ray adsorption spectroscopy), and theoretical calculations, it was found that Ni(II), primarily as NiP2O72−, could be captured by charge-assistant coordination with the surface polyamine. Then, the coadsorption of PP altered the interface properties via both electrostatic shielding and bridging effect, enhancing Ni(II)–amine coordination efficiency. A dinuclear multilayer coordination structure [-amine–Ni–PP–Ni–amine-] was proposed as the dominant Ni(II) binding mode in the presence of PP. Ni(II) and PP could be sequentially desorbed from ACS-AWF using gradient elution with ＞95.5% Ni(II) purity. ACS-AWF was then stably reused in five cycles (capacity loss ＜10%). These results may guide adsorbent design and application in HM purification and recycling from complexed wastewater.

Hydroxyl radical induced Cr flocculation via redox reaction: The extending application of heterogeneous advanced oxidation processes on Cr removal

Flocculation is a traditional and effective method to remove Cr from wastewater, but the addition of flocculants inevitably leads to secondary pollution. In this study, Cr flocculation was induced using hydroxyl radical (•OH) (•OH flocculation) generated in an electro-Fenton-like system, achieving total Cr removal of 98.68% at initial pH = 8 within 40 min. The obtained Cr flocs showed significantly higher Cr content, lower sludge yield, and good settling properties compared to alkali precipitation and polyaluminum chloride flocculation. •OH flocculation behaved like a typical flocculant, introducing electrostatic neutralization and bridging. The mechanism proposed that •OH could overcome the steric hindrance of Cr(H2O)63+ and combine with it as an additional ligand. Then Cr(III) was proved to undergo multi-step oxidation to form Cr(IV) and Cr(V). After these oxidation reactions, •OH flocculation took precedence over Cr(VI) generation. As a result, Cr(VI) didn’t accumulate in solution until •OH flocculation was completed. This work provided a clean and eco-friendly strategy for Cr flocculation instead of flocculants and extended the application of advanced oxidation processes (AOPs), which is expected to enrich existing strategies of AOPs towards Cr removal.

Development of emulsion-based edible inks for 3D printing applications: Pickering emulsion gels

Emulsions gels can be used as edible inks for 3D food printing applications because of their tunable composition and viscoelastic properties. Oil-in-water emulsion gels can be created by crosslinking the oil droplets using chemical or physical approaches. For food applications, chemical crosslinking agents are undesirable because they have safety concerns. In this study, Pickering emulsions gels (PEGs) were therefore fabricated by physically crosslinking anionic protein nanoparticle-coated oil droplets with cationic chitosan. Chitosan formed electrostatic bridges between neighboring oil droplets, as well as a network structure in the surrounding aqueous phase. The viscoelastic properties of PEGs could be tuned by adjusting the droplets and chitosan concentrations. These soft materials exhibited physicochemical attributes that made them highly suitable as edible inks for 3D printing applications, including the ability to maintain specific shapes, to form smooth surfaces, and to give a high print fidelity. Moreover, the tribological behavior of these PEGs was similar to that of oil in the mixed and hydrodynamic regimes, indicating that they exhibited good lubrication properties. Overall, this study has demonstrated the suitability of PEGs to be used as edible inks for creating novel food materials by additive manufacturing.

Revealing the behavior of perfluorooctane sulfonic acid in an aerobic granular sludge system: Fate and impact

The biogeochemistry (i.e., migration and transformation) and impacts of perfluorooctane sulfonic acid (PFOS) in an aerobic granular sludge (AGS) system have been studied. The results suggested that PFOS removal rates under 0.1, 0.5 and 5.0 mg/L PFOS treatment were 89.23 ± 0.92 %, 71.92 ± 1.45 % and 48.15 ± 1.90 %, respectively, which was mainly attributed to the adsorption mechanism involving electrostatic, hydrophobic and ionic bridging interactions. Meanwhile, the adsorbed PFOS deteriorated sludge flocculation. Compared with the control, 0.1 mg/L PFOS treatment increased the concentration of effluent suspended solids (ESS) from 70 ± 5 to 238 ± 15 mg/L. Interestingly, the denitrification performance of the AGS improved (i.e., total nitrogen (TN) average removal rate increased from 87.05 ± 0.21 % to 96.56 ± 0.05 %), which was contrary to the outcomes for activated sludge. Further analysis showed that PFOS reduced the percentage of norank_f_norank_o_Ardenticatenales, norank_f_Sphingomonadaceae and Candidatus_Competibacter maintaining the particle stability, which led to the decrease in AGS flocculation. In addition, the relative abundance of nitrite-oxidizing bacteria Nitrospira decreased under PFOS exposure, while the total abundance of denitrifying bacteria (mainly Dechloromonas) increased. This might enhance the short-cut nitrification and denitrification capacity of the AGS system and promote the removal of TN. However, PFOS had no obvious impact on the settleability of AGS and the transformation of chemical oxygen demand (COD) and soluble phosphorus (SOP). Our findings will provide theoretical insights and practical support for risk control in the process of treating fluoride-containing wastewater.

Ultraductile Cementitious Structural Health Monitoring Coating: Waterborne Polymer Biomimetic Muscle and Polyhedral Oligomeric Silsesquioxane‐Assisted C‐S‐H Dispersion

AbstractCement‐based sensors (CBSs) have demonstrated potential in structural health monitoring (SHM) despite rare applications due to their poor flexibility and sensing accuracy/protection with robustness. Herein, a promising strategy is reported to design a waterborne epoxy resin (WEP)‐modified cement‐based composite coating sensorcapable of simultaneous stable SHM and durable protection. The interpenetrating network (IPN) formed by WEP within cement paste is bionic to the toughness and crack resistance of biological muscle tissue and balances the ion permeation performance and polarization of hydration products. The polymerization‐redispersion progress and mechanism of calcium silicate hydrate (C‐S‐H) gel modified with [3‐(2‐aminoethylamino)‐propyl]trimethoxysilane silsesquioxane (C‐POSS) are characterized and revealed. The results show that the muscle‐like IPN increases the cement‐based coatings’ maximum deflection angle to 30° and improves the monitoring accuracy of compressive, tensile, and fatigue microchanges of concrete structures to more than 95%. The POSS···Ca2+···C‐S‐H interaction in C‐POSS partially transferred the intra‐adhesive hydrogen bonds surrounding the nanoconducer into electrostatic bridging ones to maintain an excellent electromechanical conductive dispersion.

Self-Organization Dynamics of Collagen-like Peptides Crosslinking Is Driven by Rose-Bengal-Mediated Electrostatic Bridges.

The present work focuses on the computational study of the structural micro-organization of hydrogels based on collagen-like peptides (CLPs) in complex with Rose Bengal (RB). In previous studies, these hydrogels computationally and experimentally demonstrated that when RB was activated by green light, it could generate forms of stable crosslinked structures capable of regenerating biological tissues such as the skin and cornea. Here, we focus on the structural and atomic interactions of two collagen-like peptides (collagen-like peptide I (CLPI), and collagen-like peptide II, (CLPII)) in the presence and absence of RB, highlighting the acquired three-dimensional organization and going deep into the stabilization effect caused by the dye. Our results suggest that the dye could generate a ternary ground-state complex between collagen-like peptide fibers, specifically with positively charged amino acids (Lys in CLPI and Arg in CLPII), thus stabilizing ordered three-dimensional structures. The discoveries generated in this study provide the structural and atomic bases for the subsequent rational development of new synthetic peptides with improved characteristics for applications in the regeneration of biological tissues during photochemical tissue bonding therapies.

Elastic property of sickle and normal hemoglobin protein: Molecular dynamics

This work focuses on identifying the conformational stability and binding components in sickle and normal hemoglobin to explore the elastic properties and realize the stiffness by using molecular dynamics simulation. Our investigation shows that a larger force is required to separate the beta chain of normal hemoglobin in comparison to the sickle hemoglobin by using steered molecular dynamic. In sickle hemoglobin protein (HbS), the hydrogen bond binding force of the beta chain is 7073.74–12 646.80 pN for pulling velocities of 0.000 20–0.000 40 nm/ps with the spring constant of 800 kcal mol−1 nm−2. Similarly, in normal hemoglobin protein, the hydrogen bond binding force in the beta chain ranges from 12 005.00 to 17 753.70 pN for the same values of pulling velocities and spring constant. This indicates that the normal hemoglobin is stiffer than sickle hemoglobin. We have also analyzed the solvent accessible surface area (SASA) of both proteins, and our investigation shows that the SASA of normal hemoglobin is much less than that of sickle hemoglobin because of the sickled structure of HbS. We have also studied the van der Waals (vdW), electrostatic, hydrophobic, and salt bridge interactions in both kinds of hemoglobin. The sum of vdW, electrostatics, and hydrophobic interactions in HbS is higher, whereas salt bridge interactions are found lower in sickle normal hemoglobin proteins than in normal hemoglobin protein.

Flocculation inspired combination of layered double hydroxides and fulvic acid to form a novel composite adsorbent for the simultaneous adsorption of anionic dye and heavy metals

Currently, simultaneous removal of anionic and cationic pollutants from combined pollution wastewater is a challenging subject. Here, a novel composite adsorbent which can simultaneously adsorb anionic azo dye and heavy metal cations was developed by flocculation inspired assembly of Mg2Al layered double hydroxides (LDH) and fulvic acid (FA). The results show that the negatively charged macromolecule FA is firmly intertwined with the positively charged LDH through electrostatic attraction and adsorption bridging. This composite adsorbent (Mg2Al LDH-FA) can effectively capture anionic Orange II by anion exchange adsorption derived from LDH component with the maximum adsorption capacity of 604 mg/g. Mg2Al LDH-FA also exhibits good adsorption performance for heavy metals due to the complexation with FA and surface precipitation on LDH. The adsorption isotherms of heavy metals coincided with Langmuir model or Freundlich model, and the adsorption capacities for Pb2+, Cu2+, Ni2+, Cd2+ could reach up to 661.5 mg/g, 116.3 mg/g, 117.3 mg/g, 235.2 mg/g respectively. Particularly, Mg2Al LDH-FA can simultaneously uptake Orange II and heavy metals from the stimulated combined pollution wastewater, moreover it shows higher adsorption capacity for each pollutant than that in the single pollutant case as the result of the synergistic adsorption effect between LDH and FA.

Sorption of microcystin-RR onto surface soils: Characteristics and influencing factors

Microcystins are frequently detected in cyanobacterial bloom-impacted sites; however, their mobility potential in soils is poorly understood. This study aimed to elucidate the sorption behaviors of microcystin-RR (MC-RR) in heterogeneous soils and evaluate critical affecting factors. MC-RR sorption followed the pseudo-second-order kinetics and Freundlich model. All isotherms (n = 0.83–1.03) had no or minor deviations from linearity. The linear distribution coefficients (Kd) varied from 2.64 to 15.2 across soils, depending mainly on OM and CEC. Stepwise regression analysis indicated that the Kd was predictable by the fitting formula of: Kd = 2.56 + 0.15OM + 0.28CEC (R2 = 0.45). The sorption was an endothermic physisorption process, involving electrostatic forces, cation exchange and bridging, H-bonding, ligand exchange, and van der Waals forces. The sorption of MC-RR (dominantly behaved as electroneutral zwitterions) at pH > 5 was insensitive to pH change, while more MC-RR (anionic species) was adsorbed at lower pH and in the presence of Ca2+. The study provides insights into the sorption of MC-RR across a range of soil properties and water chemistry for the first time, which is of importance for a better understanding of the mobility potential of microcystins in the terrestrial systems.

Effects of extracellular organic matter on chitosan coagulation-microfiltration harvesting of Microcystis flos-aquae

Extracellular organic matter (EOM) is considered an important cause of membrane fouling when harvesting Microcystis cells using filtration technology. Coagulation pre-treatment has increasingly been applied as an effective method to alleviate membrane fouling. However, the effects and mechanisms of EOM on coagulation-microfiltration of Microcystis cells remain unclear. This study investigated the coagulation-microfiltration performance of EOM-free and EOM-containing Microcystis flos-aquae and explored the effect mechanisms of EOM from the perspective of floc characteristics and deposited algal cake structure. The results showed that the presence of EOM decreased the average flux from 4256.4 L/(m2·h) to 3378.4 L/(m2·h) at the optimal chitosan dosage of 15.11 mg/g. Electrostatic adsorption and/or bridging between carboxyl and amino/hydroxyl groups in EOM and chitosan resulted in a loose floc structure and high compressibility of the cake layer, thus reducing the filtration performance. In addition, interception of EOM in the cake layer contributed to membrane fouling during coagulation-microfiltration. These results revealed the mechanism by which EOM hinders coagulation-filtration performance, which would be helpful for the development of efficient coagulation-filtration-based microalgal harvesting techniques.