Abstract
This study deals with the development of antifouling ultrafiltration membranes based on polysulfone (PSF) for wastewater treatment and the concentration and purification of hemicellulose and lignin in the pulp and paper industry. The efficient simple and reproducible technique of PSF membrane modification to increase antifouling performance by simultaneous addition of triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol (Synperonic F108, Mn =14 × 103 g mol−1) to the casting solution and addition of polyacrylic acid (PAA, Mn = 250 × 103 g mol−1) to the coagulation bath is proposed for the first time. The effect of the PAA concentration in the aqueous solution on the PSF/Synperonic F108 membrane structure, surface characteristics, performance, and antifouling stability was investigated. PAA concentrations were varied from 0.35 to 2.0 wt.%. Membrane composition, structure, and topology were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The addition of PAA into the coagulation bath was revealed to cause the formation of a thicker and denser selective layer with decreasing its pore size and porosity; according to the structural characterization, an interpolymer complex of the two additives was formed on the surface of the PSF membrane. Hydrophilicity of the membrane selective layer surface was shown to increase significantly. The selective layer surface charge was found to become more negative in comparison to the reference membrane. It was shown that PSF/Synperonic F108/PAA membranes are characterized by better antifouling performance in ultrafiltration of humic acid solution and thermomechanical pulp mill (ThMP) process water. Membrane modification with PAA results in higher ThMP process water flux, fouling recovery ratio, and hemicellulose and total lignin rejection compared to the reference PSF/Synperonic F108 membrane. This suggests the possibility of applying the developed membranes for hemicellulose concentration and purification.
Highlights
The pulp and paper industry is one of the most polluting and water consuming industries in the world
It was revealed that the addition of polyacrylic acid (PAA) into the coagulation bath leads to the formation of a denser selective layer with a smaller pore size and lower porosity
The membrane surface was found to become more hydrophilic and negatively charged with an increase in PAA concentration due to the immobilization of PAA macromolecules on the membrane selective layer surface as well as on the pore walls, which is facilitated by the formation of an interpolymer complex with the triblock copolymer Synperionic F108
Summary
The pulp and paper industry is one of the most polluting and water consuming industries in the world. Wastewater in the pulp and paper industry is usually highly loaded with organic and inorganic compounds, such as lignin, cellulose, hemicellulose, phenols, fatty acid, resins, and others [1]. Valuable substances contained in wood (lignin, hemicellulose, water-soluble aromatic compounds, polymers) are released during delignification and dissolve in technological media (thermomechanical pulp mill (ThMP) process water) during the production of thermomechanical cellulose [2,3]. An urgent problem is the insufficient use of cellulose-processing products (lignin and hemicellulose) [2,3,4]. Most of these substances end up in wastewater from the pulp and paper industry, which entails costly wastewater treatment. Galactoglucomannan is the most common polysaccharide contained in hemicelluloses, and ThMP process water can be used for the production of food packaging films, hydrogels, emulsion stabilizers in the production of alcoholic beverages, and as an additive for increasing paper strength [4]
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