Anionic Polyacrylamide Research Articles

Effect of Anionic Polyacrylamide Polymer on Frost Heave Mitigation and Its Implication for Frost-Susceptible Soil.

Seasonally frozen ground regions occupy approximately 55% of the exposed land surface in the Northern Hemisphere, and frost heave is the common global problem in seasonally frozen soil areas. Frost heave induces uneven deformation of ground and damages railways, road paving, and buildings. How to mitigate frost heave is the most important technical issue in this field that has provoked great interest. Here, using freezing experiments, we investigate the effect of anionic polyacrylamide (APAM) polymer on frost susceptible soil. The results demonstrate a so-far undocumented inhibition of frost heave by APAM in freezing soil, namely APAM (tested at concentrations from 0.0 wt% to 0.60 wt%) slows down the frost heave by a factor of up to 2.1 (since 0.60 wt% APAM can decrease frost heave from 8.56 mm to 4.14 mm in comparison to the control experiment). Moreover, it can be observed that the maximum water content near the frozen fringe decreased from 53.4% to 31.4% as the APAM content increased from 0.0 wt% to 0.60 wt%, implying a mitigated ice lens growth. Hydrogen bonding between APAM and soil particles triggers an adsorption mechanism that accumulates soil particles, and thus can potentially inhibit the separation and growth of the ice lens. Moreover, the residue of APAM due to hydrogen bonding-induced adsorption in the pores of granular media may narrow seepage channels (capillary barriers) and provide an unfavourable condition for water migration. The use of APAM can also increase the viscosity of the solution, which causes a greater water migration resistance. This research provides new insights into APAM-influenced frost heave (introducing APAM into the soil can induce bridging adsorption between APAM polymer segments and a particle surface), can enable engineers and researchers to utilise chemical improvement design and to consider suitable actions (e.g., by injecting APAM solution into a frost susceptible soil or using APAM-modified soil to replace the frost susceptible soil) to prevent frost heave from having a negative impact on traffic roads and buildings in cold regions.

Performance of eco-friendly polymers for soil stabilization and their resistance to freeze–thaw action

Soil improvement methods using environmentally friendly additives have gained popularity with increased environmental awareness. In the future, environmentally friendly polymers can be preferred in the stabilization of many geotechnical applications like the base of roads, landfills, and sub-base of foundations. This means the mechanical properties of these eco-friendly polymers should be investigated in detail. For this purpose, changes in the mechanical properties of specimens treated with different polymer types under freeze–thaw action were investigated. Three types of polymers which are xanthan gum, guar gum, and anionic polyacrylamide polymer were used to improve the strength properties of kaolin clay. The specimens were prepared in 3 different anionic polymer contents and 4 different biopolymer content. After 7, 14, and 28-day curing periods specimens were subjected to 5 and 10 cycles of freezing–thawing to observe freeze–thaw action by conducting unconfined compression tests and the control specimens were directly subjected to unconfined compression tests after the curing period. Regarding the outcomes obtained, both synthetic and biological polymer use induced strength gain. Guar gum which is a biological polymer is the most effective that improves the strength by around 8 times than pure clay. This increment ratio varied between 2 and 3.5 times in polyacrylamide polymer, which is a greater strength increase than in previous studies. In addition, curing time has no significant effect on strength gain in anionic polyacrylamide-contained specimens. It was also observed that freezing–thawing caused a drastic reduction in strength by around 5 to 60%, however, the anionic polymer is the most resistant to freeze–thaw considering the strength loss. As a result, eco-friendly polymers are suitable in regions exposed to freeze–thaw action between the seasons.

Influence of organic and inorganic flocculants on sludge treated by electroosmotic vacuum preloading

The application of electrokinetic geosynthetics in electroosmotic vacuum preloading treatment of dredged sludge suffers the problems of severe clogging and uneven reinforcement effects. The effects of organic flocculant anionic polyacrylamide (APAM) and inorganic flocculant ferric chloride (FeCl3) on the electrical conductivity and permeability coefficient of dredged sludge were obtained in tests, and the optimal flocculant dosage was determined accordingly. A series of electroosmotic vacuum preloading model tests were performed by adding organic and inorganic flocculants to dredged sludge. Slight variations of the discharge rate and settlement amount were noticed between the sludge samples mixed with FeCl3 and APAM at the vacuum preloading stage, but after electroosmosis initiation, the discharge rate of the sludge with APAM became higher, as well as the final settlement. The shear strength and uniformity of sludge with APAM after treatment were better than those of sludge with FeCl3. Compared to FeCl3, electroosmotic vacuum preloading with APAM help increase the effective electric potential of sludge and benefit the discharging of heavy metals.

Binding of Anionic Polyacrylamide with Amidase and Laccase under 298, 303, and 308 K: Docking and Molecular Dynamics Simulation Studies Combined with Experiments.

Amidase and laccase play a key role in the degradation process of anionic polyacrylamide (HPAM). However, the largest challenge of HPAM enzymatic degradation is whether the enzyme can bind with a substrate for a period of time. Here, the most suitable complexes, namely, Rh Amidase-HPAM-2 and Bacillus subtilis (B. subtilis) laccase-HPAM-3, were obtained by docking, and they were carried out for molecular dynamics simulation (MDS) under 298, 303, and 308 K. MDS result analysis showed that Rh Amidase-HPAM-2 was the most stable at 298 K mainly due to a salt bridge and a hydrogen bond, and B. subtilis laccase-HPAM-3 was the most stable at 298 K mainly due to two electrostatic and hydrogen bonds. The LYS96 in Rh Amidase-HPAM-2 and LYS135 in B. subtilis laccase-HPAM-3 had been the most important in their binding process. The binding of Rh Amidase-HPAM-2 and B. subtilis laccase-HPAM-3 was optimal at 303 and 298 K, respectively. HPAM was degraded by mixed bacteria, and the optimal conditions were determined to be 308 K, initial pH = 7, and an inoculated dosage of 2 mL. Under these conditions, the degradation ratio reached 39.24%. The effect of parameters on the HPAM degradation ratio followed a decreasing order of temperature > initial pH > inoculated dosage. The HPAM codegradation mechanism was supposed by mixed bacteria according to test data. The mixed bacteria secreted both amidase and laccase, and they interacted jointly with HPAM. These results lay a theoretical foundation to design and modify the enzyme through mutation experiments in the future.

A Web‐like Three‐dimensional Binder for Silicon Anode in Lithium‐ion Batteries

Si anode is of paramount importance for advanced energy‐dense lithium‐ion batteries (LIBs). However, the large volume change as well as stress generates during its lithiation‐delithiation process poses a great challenge to the long‐term cycling and hindering its application. Herein this work, a composite binder is prepared with a soft component, guar gum (GG), and a rigid linear polymer, anionic polyacrylamide (APAM). Rich hydroxy, carboxyl, and amide groups on the polymer chains not only enable intermolecular crosslinking to form a web‐like binder, A2G1, but also realize strong chemical binding as well as physical encapsulating to Si particles. The resultant electrode shows limited thickness change of merely 9% on lithiation and almost recovers its original thickness on delithiation. It demonstrates high reversible capacity of 2104.3 mAh g−1 after 100 cycles at a current density of 1800 mA g−1, and in constant capacity (1000 mAh g−1) test, it also shows a long life of 392 cycles. Therefore, this soft‐hard combining web‐like binder illustrates its great potential in the future applications.

Characteristics of waste mud treated by construction waste-slag based flocculation-solidification combined method

Nowadays, the flocculation-solidification combined method (FSCM) is considered suitable for mud treatment and recycling. However, the traditional FSCM uses ordinary Portland cement (OPC) as the main solidifying material, which pollutes the ecological environment. Currently, the evaluation mechanism of solidification efficiency is not accurate, the treatment of mud with different water content is not detailed enough, and the assessment of carbon emission is unclear. Accordingly, this paper introduces solid waste such as construction waste powder (concrete and brick mix recycled fine aggregate) and slag powder for solidification based on the traditional FSCM. Within the study context, the alkali activation effects of quicklime, NaOH, and NaSiO3 are compared to develop a new solidification agent. Besides, the flocculation time and peak settling rate are measured experimentally, and anionic polyacrylamide(APAM) is added separately to compare low-water-content mud (LW-MS) (ω < 70 %) and high-water-content mud (HW-MS) (70 %≤ω ≤ 300 %). The intrinsic flocculation-solidification mechanism is analyzed and demonstrated through microscopic testing.Finally, the feasibility of construction waste-slag based flocculation-solidification combined method (CWS-FSCM) is verified through field test. In terms of solidification effectiveness, carbon emissions and economy, CWS-FSCM performs better than the traditional FSCM.

Effect of Agitation on the Dissolution of APAM with Different Molecular Weights and the Equivalent Diameter of Coal Slime Settling Floc with Different Particle Sizes

There are still many problems in the stirring dissolution of flocculants: The law of stirring dissolution of flocculants with different molecular weights is not clear, the microstructure of settling floc with different particle sizes of coal slime is still to be explored, and how to apply the law of flocculant dissolution to industrialization? To solve these problems, firstly, mechanical stirring dissolution tests are carried out on anionic polyacrylamide (APAM) with different molecular weights to explore the stirring dissolution law of APAM with 3–25 million molecular weights. Results indicated that the optimal stirring speed of APAM with 3–6 million molecular weight is 800 r/min. The optimal stirring speed of 8–16 million molecular weight APAM is 600 r/min. The optimal stirring speed of 18–25 million molecular weight APAM is 800 r/min. The stirring power formula for APAM dissolution is improved by fitting the experimental data of 3–25 million molecular weight APAM stirring dissolution. Secondly, through APAM performance test, it is verified that the solubility of powdered APAM is the best under optimal solution. Thirdly, through the image measurement and analysis test of settling floc of coal slime, the change law of equivalent diameter of settling floc of different particle sizes of coal slime under the optimal dissolution parameters are explored. Results showed that when the mixing speed is 600 r/min, the equivalent diameter of −0.5 mm slime settling floc is the largest. When the mixing speed is 200 r/min or 400 r/min, the equivalent diameters of 0.5–0.25 mm, 0.25–0.125 mm, 0.125–0.075 mm, 0.075–0.045 mm and −0.045 mm slime settling floc are the largest. The equivalent diameter is positively correlated with the size of slime, and the equivalent diameter of −0.045 mm slime settling floc is the largest. The size of slime is the dominant factor in the change of fractal dimension. The fractal dimension of −0.5 mm slime settling floc is the largest, and the fractal dimension is little affected by mixing speed. Finally, the relationship between the important dissolution parameters of the APAM stirring dissolution test is numerically fitted. In view of the different geometrical parameters of the stirring barrel, a method of deducing the dissolution and stirring time of industrial flocculants is proposed.

New opportunities in the paper and nonwovens industries with foam-assisted web forming and chemical application

Foam-assisted web forming and chemical application technologies have great potential to improve manufacturing efficiency and product quality in the paper and nonwovens industries. In this study, the benefits of foam forming and foam-assisted application of chemicals were demonstrated in a pilot machine trial. Uniform high-bulk webs of unrefined bleached softwood kraft pulp (BSKP) and viscose fibers were manufactured by foam forming. It was shown that foam formed low-grammage and high-bulk viscose fiber webs can be strengthened by foam-assisted application of latex onto the wet web. Correspondingly, foam-assisted application of carboxymethyl cellulose (CMC) and anionic polyacrylamide (A-PAM) improved the strength of the foam formed low-grammage and high-bulk BSKP web. Overall, the pilot machine results indicated that material cost savings could be achieved and a high-performance product could be manufactured with foam-based technologies.

Accumulation of toxic Pb(II) ions by the iron-containing minerals in the presence of ionic polyacrylamide soil conditioner

The aim of this research was to determine the adsorption–desorption, surface, electrokinetic, and stability properties of aqueous suspensions of iron-containing minerals in the presence of anionic polyacrylamide (AN PAM) and lead(II) ions. Three minerals found in the soil environment, akaganeite, goethite, and magnetite, were synthesized based on the precipitation method. The interaction mechanism of heavy metal ions with polymer flocculant, which are adsorbed on the soil mineral particles, was proposed. It was shown that the best affinity to the AN PAM or/and Pb(II), adsorbed both from single and mixed solution, shows akageneite (characterized by the highly developed specific surface area). Polymer-metal complexes formed in the mixed adsorbate systems are rather stable, evidence of which is reduced desorption and consequently limited bioavailability of toxic lead ions for organisms and plants in soil environment.

Evaluation of the efficiency in the use of anionic polyacrylamide, organosilane and sulfonate for the stabilization of roads with traffic low volume in the Peruvian highlands above 2000 m.s.n.m [Evaluación de la eficiencia en la utilización de poliacrilamida aniónica, organosilano y un sulfonatado para la estabilización de carreteras de bajo volumen de tránsito en la sierra peruana sobre los 2000

The objective of the research was to evaluate the efficiency in the use of anionic polyacrylamide, organosilane and a sulfonate for the certainty of low volume traffic roads in the Peruvian highlands above 2000 m.s.n.m. Tests were carried out with the selected materials; Subgrade, Quarry 1 and Quarry 2, with the stabilizers, which obtained CBR values ​​above 40% minimum for paved roads. The best expression option in terms of its mechanical physical behavior was used using an anionic polyacrylamide dosage of 1kg/m3.

Investigation of the anionic polyacrylamide as a potential adsorbent of crystal violet dye from aqueous solution: Equilibrium, kinetic, thermodynamic, DFT, MC and MD approaches

Hydrogels have been of great interest for the removal of hazardous chemicals and dyes from aqueous media. This study deals with the application of anionic polyacrylamide hydrogels in the removal of cationic dye, crystal violet, from aqueous solutions. Batch adsorption studies presented that the maximum adsorption capacity of dye was found to be 378 mg/g at the initial concentration of 300 mg/L, pH = 5, T = 298 K and 0.039 g of the adsorbent. By analyzing the adsorption mechanism of dye, the kinetic data of dye adsorption fit well with the pseudo-second-order model. The adsorption capability at different equilibrium concentrations follows the Langmuir model, indicating the favorability and feasibility of dye adsorption. The thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic. Density functional theory (DFT), molecular dynamic (MD), and Monte-Carlo simulation studies were applied to support the experimental study.

A biomimetic closed-loop recyclable, long-term durable, extreme-condition resistant, flame-retardant nanocoating synthesized by reversible flocculation assembly.

Flame-retardant coatings have attracted increasing attention in mitigating the fire threat of flammable polymer materials. Their durable application inevitably provides high resistance to various complex environments, however, discarded stable materials will turn into another man-made waste disaster. The paradigm shift toward a sustainable future is to combine durability and recyclability of coatings. Herein, we demonstrate a biomimetic coating that reversibly captures active flame-retardant nanomaterials by flocculation assembly using anionic polyacrylamide covering the polyurethane foam surface. Strong hydrogen bonding and microstructural interlocking provide the coating with high durability under complex harsh conditions (underwater, chemical exposure, hydrothermal aging, long-term external extrusion, etc.). Meanwhile, the disassembly/reorganization of the coating can be easily repeated in response to pH stimulation with a recycling rate of 97%. The experiments and theoretical calculations reveal the mechanism of the reversible flocculation assembly. This biomimetic strategy of responsive flocculation assembly opens the way for functional coatings with integrated durability and recyclability.

Study on permeability performance of cemented tailings backfill based on fractal characteristics of pore structure

The permeability of the backfill has a significant impact on the leaching and transport ability of pollutants to groundwater through the backfill area, and the way of pollutants enter the backfill mainly depends on the pore structure inside the backfill. Therefore, permeability is also a reflection of pore structure characteristics. The test used mine tailings as aggregate, Portland cement (PC 32.5) as cementing material, and added different additives (lime, fly ash, and anionic polyacrylamide (APAM)) to make backfill samples with a mass concentration of 74% and a cement-sand ratio of 1:4 and 1:6, respectively. Four groups of backfill samples with curing ages of 3d, 7d, and 28d were tested by nuclear magnetic resonance (NMR) and centrifugal testing machines, and the T2 spectrum distribution characteristics of the samples before and after centrifugation were obtained. According to the test results and fractal theory, it is found that the four groups of backfill have double fractal characteristics. With the increase of curing age or cement-sand ratio, the fractal dimension of small aperture distribution (Dmin) of backfill pore structure generally increases, while the fractal dimension of large aperture distribution (Dmax) and permeability gradually decrease. Dmax represents the number of large pores and has a high correlation with porosity, indicating that it has a great influence on porosity. The high degree of correlation between permeability and Dmin indicates that the formation of water passage in backfill is related to fine pores. Meanwhile, the permeability prediction results using the correlation between the fractal bound water saturation model and the Coates model show that the measured and predicted values of the bound water saturation, and the predicted permeability values and the calculated values of the Coates model all fit well, which verifies the feasibility of this method.

Flow behavior of impounded fly ash slurries using flow test

Coal ash is one of the largest industrial waste products generated in the United States. Since 1967, several failures in ash impoundments have been reported, releasing millions of gallons of impounded fly ash slurry and resulting in loss of life and mass environmental destruction. Several studies have been carried out to understand the flow behavior of fly ash slurries. However, several questions remain unanswered regarding the flow behavior of fly ash slurries after containment loss. In this study, a new flow test, a miniature version of a cylindrical slump test, was developed to investigate flow behavior of six different fly ash slurries. The flow behavior of these slurries was evaluated based on the yield stress derived from the flow test results. The results showed that some fly ash slurries flowed at higher solids content (>60 %), while others flowed at lower solids content (<50 %) and stopped flowing at higher solid content. Furthermore, some slurries did not flow at all. It was found that the chemical compositions of fly ash, the state of hydration (hydrated or non-hydrated), original solids content when received, and initial solids content of fly ash slurries at the start of the flow test played a major role in the flow behavior of fly ash slurries. The interactions between these factors were complex, and it was difficult to identify the effect of a single factor. Most of the fly ash slurries showed shear flow, and some slurries at high solids content showed elongational flow. The fly ash slurries with shear flow had larger flow areas after containment loss. The addition of an anionic polyacrylamide significantly increased the yield stress by 2.8 – 3.5 times and decreased the flow of fly ash slurries.

The efficacy of linear anionic polyacrylamide solutions in enhancing chill accumulation in peach trees in Southern Australia

The efficacy of linear anionic polyacrylamide solutions in enhancing chill accumulation in peach trees in Southern Australia

Enhancement of biosludge dewatering using proteins through dual conditioning

AbstractIn pulp and paper mills, effective biosludge dewatering is essential in wastewater treatment to reduce the large volume of biosludge that needs to be treated and disposed. The dewatering process normally requires the use of polymers from petroleum‐based sources. This study explores the potential of using cationic proteins such as protamine for biosludge dewatering through dual conditioning with a small amount of a synthetic anionic polymer such as anionic polyacrylamide (APAM). The results show that dual conditioning provides substantial synergistic enhancements in dewatering. The maximum cake solids content of biosludge achieved by adding protamine (7.5%) alone was 12%. By dual conditioning with a small amount of APAM (0.1%), not only the cake solids content was increased to 16%, but also the amount of protamine addition was substantially lowered to 2%. These results, coupled with the change in zeta potential of the particles in the biosludge samples, suggest that the cationic protamine reduced the negative charge of the particles, allowing smaller particles to agglomerate and providing a positively charged framework for the subsequent addition of the negatively charged APAM. After adding APAM, substantial floc‐bridging occurred, allowing smaller flocs to aggregate into larger flocs. These synergistic effects can lower the wastewater treatment cost by reducing the amount of synthetic polymer and by applying low‐value proteins from natural sources.

Effect of cellulose fiber graft copolymerization with glycidyl methacrylate on the papermaking process retention and drainage aid performance

Abstract Improving the retention and drainage aid performance of high speed papermaking processes is an important and challenging issue. In this study, fiber modification was used to improve the papermaking retention and drainage aid performance. The graft copolymerization of glycidyl methacrylate (GMA) with cellulose fibers was initiated using Fe2+-thiourea dioxide(TDO)-H2O2 in a mild aqueous medium; the synthesized polyglycidyl methacrylate grafted cellulose (CPGMA) was used to replace softwood bleached kraft pulp(SBKP) and hardwood bleached kraft pulp(HBKP), to study their retention and drainage aid behavior in the cationic polyacrylamide (CPAM)/colloidal SiO2/ anionic polyacrylamide (APAM) system. Graft copolymerization significantly enhanced the fiber hydrophobicity. Additionally, the papermaking process drainage aid performance and retention rate of the filler increased significantly with an increase in the CPGMA substitution rate. A small amount of CPGMA (0.5 %) significantly improved the dewatering ability and some improved the retention performance of the wet end of papermaking. SBKP-polyglycidyl methacrylate grafted cellulose (S-CPGMA) exhibited better retention and drainage aid performance than HBKP-polyglycidyl methacrylate grafted cellulose (H-CPGMA). Thus, introducing Fe2+-thiourea dioxide(TDO)-H2O2 initiated graft copolymerized S-CPGMA (in mild aqueous media) into pulp could improve the retention and drainage aid performance of the wet part of paper production.

Effect of saturation adsorption of paper strength additives on the performance of paper

AbstractThe use of paper dry strength additives is one of the methods for producing packaging boards with a lower grammage while maintaining mechanical properties. In the present work, papers were formed using dissolving grade kraft fibres, kraft fibres and carboxymethylated cellulose (CMC) modified kraft fibres (C-kraft fibres), with either cationic starch (CS), anionic polyacrylamide (APAM) or anionic polyelectrolyte complexes (PECs). Fibres and sheets were characterized to evaluate how the saturation adsorption of the different strength additives influences the properties of the treated fibres and the final handsheets. The tensile index of papers made from C-kraft fibres was the highest due to the highest adsorption capacity of strength additives. Moreover, the strength additives increased the tensile index by 33–84 %, while z-directional tensile strength was increased dramatically by 46–139 %. Bending stiffness was improved by 2.6–25 %, and the combination of CS and APAM or PECs resulted in a significant improvement in bending stiffness compared to the addition of CS alone. Importantly, the strength improvement did not sacrifice the density significantly. In summary, the knowledge gained from the current study expands the understanding of strength additives and their relationship with fibres of different surface charge and the overall paper properties.

Determining the performance of lignin-based flocculants in improving biosludge dewaterability

In the wastewater treatment plant of pulp and paper mills, biosludge dewatering is needed to reduce the sludge handling and disposal costs. It is usually facilitated by means of the addition of synthetic polymers. There is increasing interest in replacing synthetic polymers with biopolymers derived from low value by-products or industrial residuals to improve the environmental footprint of dewatering. In this study, lignin-based flocculants (LBF) were tested for their ability to improve the biosludge dewaterability based on Capillary Suction Time (CST) and dry cake solids achieved with a Crown Press. The results demonstrate that LBFs alone can significantly enhance dewatering with a decrease in CSTs from 72.7 ± 5.1 s (unconditioned biosludge) to 23.3 ± 0.4 s and an increase in dry cake solids after pressing from 7.1 ± 0.5% to 13.9 ± 1.3% with a relatively high dosage of 7.5% w/w. However, with dual conditioning a LBF and 0.1% w/w anionic polyacrylamide (APAM), the required dosage of LBF was reduced to 3% w/w to achieve a dry cake solids content of 13.8 ± 0.4%, the same as that achieved with Zetag8165, a commercial synthetic polymer. LBF addition lowered the particle surface charge, allowing the particles to agglomerate and enhancing for the biosludge dewaterability. The application of LBFs for sludge dewatering offers novel considerable promise for providing more sustainable approaches by optimizing the use of lignin from different extraction processes, applying various types of lignin modifications in combination with anionic polymers, and exploring different methods of disposal or utilization of the dewatered sludge.

Concentration effects of calcium ion on polyacrylamide fouling of ion-exchange membrane in electrodialysis treatment of flue gas desulfurization wastewater

Residual anion polyacrylamide (APAM) and fluctuating calcium ion (Ca2+) in flue gas desulfurization wastewater after pretreatment could result in ion-exchange membrane fouling during electrodialysis process. Concentration effects of Ca2+ on APAM fouling were systematically investigated and the mechanisms were illustrated. Results of desalination performance indicated that Ca2+ alleviated APAM fouling and the mitigating effect increased firstly and then declined, obtaining the mildest fouling phenomenon in the presence of 1.0 mM Ca2+. Zeta potential and particle radius of APAM in the feed solutions increased as Ca2+ changed the charge balance of APAM molecules and complexed with them. Morphology and chemical structure analysis concluded that APAM molecules were adsorbed on the membrane surface and the fouled layer changed with increasing Ca2+ concentration, from dense layer to reticular structure and then to sophisticated multilayer structure. Calculation of interfacial free energy based on Extended Derjaguin-Landau-Verwey-Overbeek theory confirmed that electrostatic interaction dominated the membrane fouling process. Concentration effects of Ca2+ were more remarkable on membrane-APAM attraction and APAM-APAM repulsion at 0.0–1.0 and 1.0–10.0 mM, respectively. The results contribute to establishing comprehensive understanding of the concentration effects of Ca2+ on polymer fouling of membranes and provide new insights into cleaning process optimization.