Polypropylene non-woven supported calcium alginate hydrogel filtration membrane for efficient separation of dye/salt at low salt concentration

Calcium alginate hydrogel is an eco-friendly material, but its wide application as a self-supporting filtration membrane is severely limited by the weak mechanical properties, which makes it difficult for the large scale preparation and the fixation of the membrane in filtration equipment. In this work, a fiber-reinforced calcium alginate membrane (CaAlg-PP) was prepared by coating calcium alginate (CaAlg) hydrogel on the polypropylene (PP) non-woven fabric treated with ethanol/water (v:v = 1:1) solution. The CaAlg-PP filtration membrane was characterized and used for dye/salt separation under a series of operating conditions. The membrane exhibited the co-operativity of the porous support layer and the CaAlg hydrogel in the compositing process, and also exhibited good pressure resistance, pollution resistance and low anionic dye adsorption efficiency. The optimized CaAlg-PP membrane had a high permeance (e.g. 20.3 L·m−2·h−1 for methyl blue at 0.1 MPa) and high dye rejection (e.g. methyl blue 99.5%), while low salt rejection (e.g. NaCl 7.5%), and the selectivity of methyl blue/NaCl was up to 185. The CaAlg-PP membranes made with simple processes and low-cost materials may provide new strategies for environmentally-friendly and economical low salts-containing wastewater treatment and dye recycling.