Molecular insights into membrane fouling caused by polysaccharides with different structures in polyaluminum chloride coagulation-ultrafiltration process

Membrane fouling characteristics and mechanisms in coagulation-ultrafiltration process for treating microplastic-containing water

Microplastics (MPs) are recognized as a significant challenge to water treatment processes due to their ability to adsorb or accumulate alginate foulants, impacting the coagulation-ultrafiltration (CUF) process. In this study, the mechanisms of membrane fouling caused by MPs under varying dosages of polymeric aluminum chloride (PAC) coagulant in the CUF process were investigated. It was revealed that MPs contribute to membrane fouling, which initially intensifies and then alleviates as coagulant concentration increases, with a turning point at 0.05 mM PAC dosage. The most significant alleviation of membrane fouling was observed at 0.2 mM PAC dosage. An in-depth analysis of interfacial interaction energy changes during filtration was conducted using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, demonstrating how MPs alter the interaction forces between foulants and the membrane surface, leading to either the exacerbation or mitigation of fouling. Additionally, it was shown that at optimal coagulant concentrations, the presence of MPs promotes the formation of a loose and porous cake layer, disrupting the original structure and creating a more open block structure, thereby alleviating membrane fouling. These findings provide valuable insights for optimizing the CUF process in microplastic-containing water treatment, presenting a novel approach to enhancing efficiency and reducing membrane fouling.

Enhanced sludge dewatering using a novel synergistic iron/peroxymonosulfate-polyacrylamide method

In the sludge dewatering process, a formidable challenge arises due to the robust interactions between extracellular polymeric substances (EPS) and bound water. This study introduces a novel, synergistic conditioning method that combines iron (Fe2+)/peroxymonosulfate (PMS) and polyacrylamide (PAM) to significantly enhance sludge dewatering efficiency. The application of the Fe2+/PMS-PAM conditioning method led to a substantial reduction in specific filtration resistance (SFR) by 82.75% and capillary suction time (CST) by 80.44%, marking a considerable improvement in dewatering performance. Comprehensive analyses revealed that pre-oxidation with Fe2+/PMS in the Fe2+/PMS-PAM process effectively degraded EPS, facilitating the release of bound water. Subsequently, PAM enhanced the flocculation of fine sludge particles resulting from the advanced oxidation processes (AOPs). Furthermore, analysis based on the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory demonstrated shifts in interaction energies, highlighting the breakdown of energy barriers within the sludge and a transition in surface characteristics from hydrophilic (3.79 mJ m-2) to hydrophobic (-61.86 mJ m-2). This shift promoted the spontaneous aggregation of sludge particles. The innovative use of the Flory-Huggins theory provided insights into the sludge filtration mechanism from a chemical potential perspective, linking these changes to SFR. The introduction of Fe2+/PMS-PAM conditioning disrupted the uniformity of the EPS-formed gel layer, significantly reducing the chemical potential difference between the permeate and the water in the gel layer, leading to a lower SFR and enhanced dewatering performance. This thermodynamic approach significantly enhances our understanding of sludge dewatering and conditioning. These findings represent a paradigm shift, offering innovative strategies for sludge treatment and expanding our comprehension of dewatering and conditioning techniques.

Bioactive interpenetrating hybrids of poly(hydroxyethyl methacrylate-co-glycidyl methacrylate): Effect of polysaccharide types on structural peculiarities and multifunctionality

Crosslinked poly(hydroxyethyl methacrylate-co-glycidyl methacrylate) hybrids prepared in the same experimental condition by adding various polysaccharides of different chemical types; inulin, Na-alginate, starch and κ-Carrageenan were qualitatively compared. The results are presented to extract relevant physicochemical properties for qualitative comparison of structures within the same synthesis batch. Elastic properties and swelling degree of hybrids can be tightly regulated using different types of polysaccharides and by controlling effective cross-linking density. Addition of κ-Carrageenan to copolymer network increased elastic modulus by 6.2-fold in as-prepared state, but greatest increase in effective cross-link density through swelling was observed in alginate-doped gels. An overshooting effect was observed for alginate-doped hybrids; swelling first to a maximum, followed by a gradual deswelling until equilibrium was reached. Compressive elasticity of hybrids is mainly controlled by type of polysaccharides and cross-linking density but also depends on polymerization temperature. The obtained hybrid gels displayed excellent adsorption performance for methyl orange (MO). The highest adsorption capacity was reached with inulin-doped hybrids. The rate of adsorption was very fast and reached equilibrium with 98.9 % efficiency at about 90 min. This approach to modify the properties of hybrid gels with various types of polysaccharides may find wide use in biomaterials and water purification applications.

Novel thermodynamic mechanisms of co-conditioning with polymeric aluminum chloride and polyacrylamide for improved sludge dewatering: A paradigm shift in the field

This study investigated the combined effects of polymeric aluminum chloride (PAC) and polyacrylamide (PAM) on sludge dewatering, aiming to unveil underlying mechanisms. Co-conditioning with 15 mg g-1 PAC and 1 mg g-1 PAM achieved optimal dewatering, reducing specific filtration resistance (SFR) of co-conditioned sludge to 4.38 × 1012 m-1kg-1, a mere 48.1% of raw sludge's SFR. Compared with the CST of raw sludge (36.45 s), sludge sample can be significantly reduced to 17.7 s. Characterization tests showed enhanced neutralization and agglomeration in co-conditioned sludge. Theoretical calculations revealed elimination of interaction energy barriers between sludge particles post co-conditioning, converting sludge surface from hydrophilic (3.03 mJ m-2) to hydrophobic (-46.20 mJ m-2), facilitating spontaneous agglomeration. Findings explain improved dewatering performance. Based on Flory-Huggins lattice theory, connection between polymer structure and SFR was established. Raw sludge formation triggered significant change in chemical potential, increasing bound water retention capacity and SFR. In contrast, co-conditioned sludge exhibited thinnest gel layer, reducing SFR and significantly improving dewatering. These findings represent a paradigm shift, shedding new light on fundamental thermodynamic mechanisms of sludge dewatering with different chemical conditioning.

Quantification of interfacial interaction related with adhesive membrane fouling by genetic algorithm back propagation (GABP) neural network

Since adhesive membrane fouling is critically determined by the interfacial interaction between a foulant and a rough membrane surface, efficient quantification of the interfacial interaction is critically important for adhesive membrane fouling mitigation. As a current available method, the advanced extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory involves complicated rigorous thermodynamic equations and massive amounts of computation, restricting its application. To solve this problem, artificial intelligence (AI) visualization technology was used to analyze the existing literature, and the genetic algorithm back propagation (GABP) artificial neural network (ANN) was employed to simplify thermodynamic calculation. The results showed that GABP ANN with 5 neurons could obtain reliable prediction performance in seconds, versus several hours or even days time-consuming by the advanced XDLVO theory. Moreover, the regression coefficient (R) of GABP reached 0.9999, and the error between the prediction results and the simulation results was less than 0.01%, indicating feasibility of the GABP ANN technique for quantification of interfacial interaction related with adhesive membrane fouling. This work provided a novel strategy to efficiently optimize the thermodynamic prediction of adhesive membrane fouling, beneficial for better understanding and control of adhesive membrane fouling.

Mitigation of protein fouling by magnesium ions and the related mechanisms in ultrafiltration process

Although protein is an important membrane foulant in the water body that may be significantly affected by the coexisting common cation magnesium (Mg²⁺), the effect of Mg²⁺ on protein fouling is rarely reported. In this context, this study selected bovine serum albumin (BSA) as the model foulant, and investigated its fouling characteristics at different Mg²⁺ concentrations (0-100 mM). Filtration tests showed that the protein fouling can be significantly mitigated by adding Mg²⁺, and the specific filtration resistance (SFR) of pure BSA (3.56 × 10¹⁴ m kg^-1) was at least 5 times that of BSA-Mg²⁺ solutions (0.5-100 mM). In addition, an optimal Mg²⁺ concentration exists, which can achieve the lowest BSA SFR. A series of characterizations indicated that the main contributors to the differences in BSA SFR were the changes in BSA adhesion capacity and the thickness and structure of the foulant layer. Basically, the above results were attributed to the hydration repulsion effect of Mg²⁺, which prevented tight adhesion of foulants to the membrane. Moreover, the lowest BSR SFR at 1 mM Mg²⁺ was achieved not only by the hydration repulsion effect but also by the particle size compression due to the conformational change of BSA molecules. This combined effect led to the lowest foulant retention on the membrane surface and delivered to the lowest SFR. This study conducts a thorough inspection into the specific effect of Mg²⁺ on protein fouling and provides a fresh insight into protein fouling control in the UF process.

Fine-tuning of carbon nanostructures/alginate nanofiltration performance: Towards electrically-conductive and self-cleaning properties

Electrically-conductive membranes became the center of attention owing to their enhanced ion selectivity and self-cleaning properties. Carbon nanostructures (CNS) attain high electrical conductivity, and fast water transport. Herein, we adopt a water-based, simple method to entrap CNS within Alginate network to fabricate self-cleaning nanofiltration membranes. CNS are embedded into membranes to improve the swelling/shrinkage resistivity, and to achieve electrical-conductivity. The CaAlg PEG-formed pores are tuned by organic-inorganic network via silane crosslinking. Flux/rejection profiles of Na₂SO₄ are studied/optimized in reference to fabrication parameters. 90% Na₂SO₄ rejection (7 LMH) is achieved for silane-CaAlg₂₀₀-10% CNS membranes. Membranes exhibit outstanding electrical conductivity (∼2858 S m^-1), which is attractive for fouling control. CaAlg/CNS membranes are tested to treat dye/saline water via two-stage filtration, namely, dye/salt separation and desalination. A successful dye/salt separation is achieved at the first stage with a rejection of 100%-RB and only 3.1% Na₂SO₄, and 54% Na₂SO₄ rejection in the second stage.

Molecular insights into impacts of EDTMPA on membrane fouling caused by transparent exopolymer particles (TEP)

While ethylenediamine tetramethylenephosphonic acid (EDTMPA) has been emerged as a stronger chelating agent than ethylene diamine tetraacetic acid (EDTA) for fouling mitigation, and transparent exopolymer particles (TEP) is a major foulant in membrane-based water treatment process, effects of EDTMPA on TEP fouling and the underlying mechanism have been not yet studied. In this study, Flory-Huggins lattice theory was combined with density functional theory (DFT) technology to explore this subject at molecular level. Filtration experiments showed a unimodal pattern of specific filtration resistance (SFR) of TEP sample with Ca²⁺ concentration in range of 0-3 mM. For the TEP sample with the peak SFR value at 1.5 mM Ca²⁺, continuous addition of EDTMPA (from 0 to 100 mg·L^-1) resulted in a sustained decrease in SFR. Energy dispersive spectroscopy (EDS) mapping characterization showed the continuing decline of calcium content in the TEP layer with increase of EDTMPA addition, indicating that EDTMPA successfully captured Ca²⁺ from alginate‑calcium ligation (TEP), and then disintegrated the TEP structure. DFT simulation showed that Ca²⁺ preferentially coordinated with the terminal carboxyl groups of alginate chains to form a coordination configuration that is conducive to stretch the three-dimensional polymer network. Such a network corresponded to an extremely high SFR according to Flory-Huggins theory. EDTMPA addition caused disintegration of the coordination configuration of Ca²⁺ binding to terminal carboxyl groups, which further resulted in collapse and flocculation of TEP gel network structure, thus leading to a continuous SFR decrease. This work provided deep thermodynamic insights into effects of EDTMPA on TEP-associated fouling at molecular level, facilitating to better understanding and mitigation of membrane fouling.

Molecular-level insights into the mitigation of magnesium-natural organic matter induced ultrafiltration membrane fouling by high-dose calcium based on DFT calculation

While magnesium cation (Mg²⁺) universally coexists with natural organic matter (NOM) in the water environment, influence of Mg²⁺ on NOM fouling in membrane filtration process is still unclear. This work was therefore performed to investigate effects of Mg²⁺ on NOM (sodium alginate (SA) as a model substance) fouling and role of Ca²⁺ in mitigating fouling from Mg²⁺ in the ultrafiltration (UF) water treatment process. Filtration tests showed two interesting fouling phenomena: (1) membrane fouling caused by combination of Mg²⁺ and SA maintained at a high value with the increased Mg²⁺ concentration; (2) the high fouling property of Mg²⁺ can be significantly improved by the prominent addition of calcium cation (Ca²⁺). It was found that changes of foulant morphology played essential roles through thermodynamic mechanisms represented by the Flory-Huggins lattice theory. Density functional theory (DFT) calculation showed that the combination of SA and Mg²⁺ tends to coordinate two terminal carboxyl groups in SA, beneficial to stretching alginate chains and forming a stable gel network at low doses. In addition, intramolecular coordination is difficult to occur between SA and Mg²⁺ due to the high hydration repulsion radius of Mg²⁺. Therefore, a dense and thick gel network remained even under high Mg²⁺concentration. Furthermore, due to the higher binding affinity of Ca²⁺ over Mg²⁺, high doses of Ca²⁺ trigger a transition of the stable SA-Mg²⁺ gel network to other configurations where flocculation and aggregation occur, thereby reducing the specific filtration resistance. The proposed thermodynamic mechanism satisfactorily explained the above interesting fouling behaviors, facilitating to development of new solutions to control membrane fouling.