Development of Chlorine-Resistant and Non-Fouling Reverse-Osmosis Membranes For Water Treatment

The three components in the production of potable water used by the reverse-osmosis water purification units (ROWPU) are pretreatment, membrane elements, and post-treatment. This project addresses only the first two components, which are the areas where improvements are most needed. In the pretreatment of feedwater, suspended, colloidal particles that can foul the membrane are removed by the use of flocculants/coagulants and scale inhibitors. Chlorine is also added to reduce microbial populations that can foul the membrane. Because the addition of chlorine in the feedwater causes membrane breakdown and reduces its useful life, an objective in the project was to develop a chlorine-resistant polymer for the RO-membrane. Another objective was to prepare and evaluate a more effective pretreatment polymer for removing foulants. In this project a novel, pretreatment polymer was designed, prepared, and found to be as effective as a flocculant during comparative evaluations against existing pretreatment polymers. However, there is still room for improvement because the compositions were not optimized. The novel polymer is a cationic polymer bearing crown-ether moieties for complexing with metal ions, which is designed to provide secondary mechanisms for flocculation that might facilitate settling and filtration. A chlorine-resistant polymer for use in preparation of the RO-membrane was designed based upon selected functionalities that are known to have inertness towards chlorine. The novel RO-membrane polymer was difficult to realize, but a practical, synthetic route to the necessary monomer was developed. The monomer is water-soluble, which may indicate that water flux could be high in a membrane based on the targeted polymer that contains that monomer.