Sustainable development entails the revival of biopolymer-based membranes for water treatment with the expectation of addressing concerns relevant to the depletion of fossil-based resources and their negative impacts on the environment. However, it is challenging to tune the biodegradability of biopolymer-based membranes such that the filtration performance would be maintained during the service life while reducing the environmental footprint. This study established a conceptual framework of achieving tunable biodegradability by incorporating chitosan membranes with silver nanoparticles. In particular, the membranes were fabricated on the basis of dissolving chitosan in an aqueous urea/alkali solution, which enabled a green approach for forming various porous substructures via phase inversion. The effects of biodegradation on chitosan membranes were investigated in the context of correlating the filtration performance with the geometrical variations in the polymer network. A series of characterization experiments were implemented to corroborate that the degree of protecting the porous substructures against enzymatic digestion should be a function of the silver loading, whereas the service life would be dependent on the silver-leaching rate. Moreover, it was revealed that optimizing the coagulation conditions could be an effective way to control the silver release during the filtration process.

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Efficient separation of oil droplets from oil/water emulsions is necessary for many energy and food industrial processes and for industrial wastewater treatment. Membrane microfiltration has been explored to address this issue because it is simple to operate and low in cost. However, filtration of oil droplets with a size around or less than 1 μm is still a major challenge. Furthermore, the fabrication process for polymeric membranes often uses hazardous organic solvents and petroleum-derived and nonbiodegradable raw materials, which pose additional environmental health and safety risk. In this study, we examined the use of chitosan-based membranes to efficiently remove oil droplets with an average diameter of ∼1 μm. The membranes were fabricated based on the rapid dissolution of chitosan in an alkaline/urea solvent system at a low temperature, thus avoiding the use of any toxic organic solvent. The chitosan membranes were further modified by dopamine and tannic acid (TA). The as-prepared membrane was characterized in terms of surface morphology, pore size distribution, and mechanical strength. The membrane performance was evaluated on a custom-designed crossflow filtration system. The results showed that the modified chitosan membrane with dopamine and TA had a water flux of 230.9 LMH at 1bar transmembrane pressure and oil droplet rejection of 99%. This water flux represented an increase of more than 10 times when compared with the original chitosan membrane without modification. The study also demonstrated excellent antifouling properties of the modified membrane that could achieve near 100% water flux recovery.

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