Mineral Scaling on Reverse Osmosis Membranes: Role of Mass, Orientation, and Crystallinity on Permeability

Organic Fouling on Zwitterionic Amphiphilic Copolymers: Implications in Biofouling

Zwitterionic amphiphilic copolymers (ZACs) have shown promise in resisting the attachment of oil emulsions, proteins, and organic biomolecules, suggesting their potential to prevent microbial adhesion as well. However, there is a lack of comprehensive studies exploring the role of ZACs in regulating cell deposition and subsequent biofilm formation on surfaces. Here, we fabricated ZAC coatings including poly(trifluoroethyl methacrylate-random-sulfobetaine methacrylate) (PTFEMA-r-SBMA or PT:SBMA), poly(trifluoroethyl methacrylate-random-2-methacryloyloxyethyl phosphorylcholine) (PTFEMA-r-MPC or PT:MPC), poly(methyl methacrylate-random-sulfobetaine methacrylate) (PMMA-r-SBMA or PM:SBMA), and poly(methyl methacrylate-random-2-methacryloyloxyethyl phosphorylcholine) (PMMA-r-MPC or PM:MPC). These coatings were assessed for their resistance to conditioning with organic molecules, attachment of Gram-positive, Bacillus subtilis TR11 (B. subtilis), and Gram-negative, Escherichia coli K12 (E. coli), bacteria, and subsequent biofilm formation. Surface characterizations highlighted the role of organic molecule conditioning from the media in altering the ZAC-coated surface properties, subsequently influencing bacterial deposition and biofilm growth. Cell deposition results revealed that all ZAC coatings displayed higher resistance to B. subtilis attachment compared to E. coli, indicating that bacterial adhesion to the surfaces depends on the type of bacteria. Among the tested ZAC coatings, PT: SBMA demonstrated the highest potential for resisting adhesion by both types of bacterial cells as well as exhibiting lower surface energy and lower roughness after organic medium conditioning. These findings contribute to enhancing our fundamental understanding of how zwitterionic materials control biofouling.

Impact of residual aluminum on nanofiltration gypsum scaling: Mitigation roles played by different species

Residual aluminum (Al) is a growing pollutant in nanofiltration (NF) membrane-based drinking water treatment. To investigate the impact of distinct Al species fouling layers on gypsum scaling during NF, gypsum scaling tests were conducted on bare and three Al-conditioned (AlCl3-, Al13, and Al30-) membranes. The morphology of gypsum, the role of Al species on Ca2+ adsorption during gypsum scaling, and the interactions between gypsum crystals and Al-conditioned membranes were investigated. Results indicated that Al-conditioned membranes had lower flux decline than the bare membrane, with the order of AlCl3- Collapse

Key Words

• Brackish water
• Gypsum scaling
• Interface interaction
• Nanofiltration
• Residual aluminum

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MESH Headings

• Calcium Sulfate/chemistry
• Aluminum/chemistry
• Water Purification/methods
• Filtration/methods
• Adsorption
• Membranes, Artificial
• Water Pollutants, Chemical
• Calcium/chemistry
• Crystallization

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Affiliation(s)

Jinjin Jia State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Daliang Xu State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Jiaxuan Yang State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Dachao Lin School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou, 510006, PR China
Longfeng Hu State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Wenxing Jin State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Jinlong Wang State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Weijia Gong School of Engineering, Northeast Agricultural University, 600 Changjiang Street, Xiangfang District, Harbin, 150030, PR China
Guibai Li State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China
Heng Liang State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin, 150090, PR China.

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Influence of zwitterionic amphiphilic copolymers on heterogeneous gypsum formation: A promising approach for scaling resistance

This study aims to investigate the influence of zwitterionic amphiphilic copolymers (ZACs) in the nucleation and growth of heterogeneous CaSO4 at the zwitterion-water interface, which is crucial for the prevention of mineral scaling and consequent downtime or suboptimal performance in industries like membrane desalination, heat exchangers, and pipeline transportation. In situ grazing incidence small angle X-ray Scattering (GISAXS), and quartz crystal microbalance with dissipation (QCM-D) techniques were used to analyze the evolution of CaSO4 particles on two new ZAC coatings: poly-(trifluoroethyl methacrylate-random-sulfobetaine methacrylate) (PTFEMA-r-SBMA, or PT:SBMA) and poly(trifluoroethyl methacrylate-random-2-methacryloyloxyethyl phosphorylcholine) (PTFEMA-r-MPC, or PT:MPC). The results showed that PT:MPC coatings promoted nucleation but inhibited crystal growth, resulting in slower overall reaction kinetics on PT:MPC coatings compared to PT:SBMA coatings. Interfacial interactions involving the substrates, sulfate minerals, and ions were examined, revealing that calcium ion adsorption, primarily governed by electrostatic attraction, played a crucial role in the nucleation and growth processes on both ZAC coatings. The crystal characterization revealed a phase transition from bassanite to gypsum on both ZAC coatings, suggesting that these zwitterionic materials can influence the mineral phase of heterogeneously formed CaSO4 crystals. These findings enhance our understanding of the fundamental mechanisms underlying heterogeneous CaSO4 scaling in the presence of zwitterionic materials.

A Tale of Two Foulants: The Coupling of Organic Fouling and Mineral Scaling in Membrane Desalination

Membrane desalination that enables the harvesting of purified water from unconventional sources such as seawater, brackish groundwater, and wastewater has become indispensable to ensure sustainable freshwater supply in the context of a changing climate. However, the efficiency of membrane desalination is greatly constrained by organic fouling and mineral scaling. Although extensive studies have focused on understanding membrane fouling or scaling separately, organic foulants commonly coexist with inorganic scalants in the feedwaters of membrane desalination. Compared to individual fouling or scaling, combined fouling and scaling often exhibits different behaviors and is governed by foulant-scalant interactions, resembling more complex but practical scenarios than using feedwaters containing only organic foulants or inorganic scalants. In this critical review, we first summarize the performance of membrane desalination under combined fouling and scaling, involving mineral scales formed via both crystallization and polymerization. We then provide the state-of-the-art knowledge and characterization techniques pertaining to the molecular interactions between organic foulants and inorganic scalants, which alter the kinetics and thermodynamics of mineral nucleation as well as the deposition of mineral scales onto membrane surfaces. We further review the current efforts of mitigating combined fouling and scaling via membrane materials development and pretreatment. Finally, we provide prospects for future research needs that guide the design of more effective control strategies for combined fouling and scaling to improve the efficiency and resilience of membrane desalination for the treatment of feedwaters with complex compositions.

Sulfate mineral scaling: From fundamental mechanisms to control strategies

Sulfate scaling, as insoluble inorganic sulfate deposits, can cause serious operational problems in various industries, such as blockage of membrane pores and subsurface media and impairment of equipment functionality. There is limited article to bridge sulfate formation mechanisms with field scaling control practice. This article reviews the molecular-level interfacial reactions and thermodynamic basis controlling homogeneous and heterogeneous sulfate mineral nucleation and growth through classical and non-classical pathways. Common sulfate scaling control strategies were also reviewed, including pretreatment, chemical inhibition and surface modification. Furthermore, efforts were made to link the fundamental theories with industrial scale control practices. Effects of common inhibitors on different steps of sulfate formation pathways (i.e., ion pair and cluster formation, nucleation, and growth) were thoroughly discussed. Surface modifications to industrial facilities and membrane units were clarified as controlling either the deposition of homogeneous precipitates or the heterogeneous nucleation. Future research directions in terms of optimizing sulfate chemical inhibitor design and improving surface modifications are also discussed. This article aims to keep the readers abreast of the latest development in mechanistic understanding and control strategies of sulfate scale formation and to bridge knowledge developed in interfacial chemistry with engineering practice.

Distinct impacts of natural organic matter and colloidal particles on gypsum crystallization

Gypsum scaling via crystallization is a major obstacle limiting the applications of membrane-based technologies and heat exchangers in engineered systems. Herein, we perform the first comparative investigation on the impacts of natural organic matter (Suwannee River humic acid, SRHA) and colloidal particles on the gypsum crystallization process in terms of induction time and crystal morphology. Results show that the presence of SRHA significantly increases the induction time of gypsum crystallization. Specifically, at a solution saturation index of 4.92, the induction time increases 6.5-fold in the presence of 6 mg/L SRHA, compared to the case without SRHA. SRHA also alters the morphology of the formed calcium sulfate crystals, resulting in a polygon-like shape, differing from the characteristic needle-like shape of gypsum in the absence of additives. These changes in crystal morphology are attributed to the adsorption of SRHA on the gypsum crystal surface, blocking the active sites for gypsum growth. In contrast, in the presence of colloidal particles, the observed induction time of gypsum crystallization either decreases or increases, depending on the competitive interplay between the enhancement effect in the nucleation step and the inhibition effect in the subsequent crystal growth step. Furthermore, the formed gypsum crystals in the presence of colloidal particles exhibit a needle-like morphology similar to the crystals formed in the absence of any additives. Our study provides fundamental understanding of gypsum crystallization in feedwaters containing natural organic matter and colloidal particles, highlighting the importance of feedwater composition in gypsum scaling.