Abstract
A novel method for one-step preparation of antifouling ultrafiltration membranes via a non-solvent induced phase separation (NIPS) technique is proposed. It involves using aqueous 0.05–0.3 wt.% solutions of cationic polyelectrolyte based on a copolymer of acrylamide and 2-acryloxyethyltrimethylammonium chloride (Praestol 859) as a coagulant in NIPS. A systematic study of the effect of the cationic polyelectrolyte addition to the coagulant on the structure, performance and antifouling stability of polysulfone membranes was carried out. The methods for membrane characterization involved scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle and zeta-potential measurements and evaluation of the permeability, rejection and antifouling performance in human serum albumin solution and surface water ultrafiltration. It was revealed that in the presence of cationic polyelectrolyte in the coagulation bath, its concentration has a major influence on the rate of “solvent–non-solvent” exchange and thus also on the rate of phase separation which significantly affects membrane structure. The immobilization of cationic polyelectrolyte macromolecules into the selective layer was confirmed by FTIR spectroscopy. It was revealed that polyelectrolyte macromolecules predominately immobilize on the surface of the selective layer and not on the bottom layer. Membrane modification was found to improve the hydrophilicity of the selective layer, to increase surface roughness and to change zeta-potential which yields the substantial improvement of membrane antifouling stability toward natural organic matter and human serum albumin.
Highlights
Pressure-driven membrane separation processes, in particular ultrafiltration, are widely used for water treatment and purification, wastewater reclamation as well as the separation of liquid media in biotechnology, chemical, pharmaceutical, food and other industries
Distilled water and aqueous solutions of commercial flocculant which is utilized for water treatment (Praestol 859, Ashland Inc., Covington, KY, USA) based on polyacrylamide were used as a coagulation bath upon membrane preparation via non-solvent induced phase separation (NIPS)
The idea of the study was that the addition of polyelectrolyte to the coagulation bath upon membrane formation via NIPS will yield the immobilization of the polyelectrolyte macromolecules into the membrane selective layer (Figure 2)
Summary
Pressure-driven membrane separation processes, in particular ultrafiltration, are widely used for water treatment and purification, wastewater reclamation as well as the separation of liquid media in biotechnology, chemical, pharmaceutical, food and other industries. Membrane fouling reduces the efficiency of the separation process and significantly increases the cost of separation The costs for cleaning consisting of costs for water, cleaning chemicals and wastewater are together with electricity by far the most dominating operation expenditures (OPEX) of membrane plants [4]. The main methods to prevent fouling before its occurrence are pre-treatment of the feed streams, chemical modification to improve the anti-fouling properties of a membrane, and optimization of the operational conditions [5] Polymers 2020, 12, 1017 of one or a combination for the following reasons; i.e., decrease of the flux through the membrane due to the formation of a gel-like diffusion barrier layer, biodegradation of the membrane-forming polymer and materials of the membrane module, the formation of concentrated populations of pathogenic microorganisms on the membrane surface, increasing energy consumption, the need for frequent chemical cleaning, reducing the usage time of the membrane and contamination of the filtrate [1,2,3,4].
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