Chinese Journal of Chemical Engineering, Vol.28, No.11, 2881-2889, 2020
Ultrafiltration recovery of alginate: Membrane fouling mitigation by multivalent metal ions and properties of recycled materials
Recovery of alginate extracted from aerobic granular sludge (AGS) has given rise to a novel research direction. However, these extracted alginate solutions have a water content of nearly 100%. Alternately, ultrafiltration (UF) is generally used for concentration of polymers. Furthermore, the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials. In this study, membrane fouling mitigation by multivalent metal ions, both individually and in combination, and properties of recycled materials were investigated for UF recovery of sodium alginate (SA). The filtration resistance showed a significantly negative correlation with the concentration of metal ions, arranged in the order of Mg2+ < Ca2+ < Fe3+ < Al3+ (filtration resistance mitigation), and the moisture content of recycled filter cake showed a marked decrease. For Ca2+, Mg2+, Fe3+, and Ca2+ + Fe3+, the filtration resistances were almost the same when the total charge concentration was less than 5 mmol.L-1. However, when the total charge concentration was greater than 5 mmol.L-1, membrane fouling mitigation increased significantly in the presence of Ca2+ or Fe3+ and remained constant for Mg2+ with the increase of total charge concentration. The filtration resistance mitigation was arranged in the order of Fe3+ > Fe3+ + Ca2+ > Ca2+ > Mg2+. Three mechanisms were proposed in the presence of Fe2+, such as the decrease of SA concentration, change in pH, and production of hydroxide iron colloids from hydrolysis. The properties of recycled materials (filter cake) were investigated via optical microscope observation, dynamic light scattering, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The results provide further insight into UF recoveries of alginate extracted from AGS. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.