Current reverse osmosis and nanofiltration membranes, which are often extremely delicate and thin, generally do not tolerate waters with suspended solids or high loadings of organics. Pretreatment is nearly always employed to reduce these contaminants which can foul or even abrade membranes. Current pretreatment approaches rely on decades-old technology, are expensive or chemically intensive, and can constitute a majority of the system footprint. They are also difficult to adapt for different treatment systems and typically struggle to entirely prevent fouling.
NAWI’s 5.22 project, “Printed Polyelectrolyte Complex (APEC) Membranes for Ultra-high Permeance Nanofiltration,” aims to create the first nanofiltration (NF) membranes for universal pretreatment. These NF membranes would streamline the pretreatment process to be more efficient across different types of treatment systems or water sources while simultaneously saving costs, energy, and treating more water with better output quality.
This project achieve this using a newly developed additive manufacturing process. This process, known as electrospray, which uses high voltage to induce fine, nano-scale sprays to deposit thin and defect-free layers of polymer electrolyte and produce multi-layered membranes with better control. This technique, called “electrospray additive manufacturing,” can form exceptionally thin (~10s of nanometers per layer or less) and defect-free films from any solution-processable polymer.
Electrospray is suited for forming amphiphilic polyelectrolyte complexes (APECs), which bring the positively and negatively charged polymers together to form a material that is both hydrophilic and hydrophobic. These specific properties of APECs create a stronger, adjustable material that better prevents fouling. By using numerous yet exceedingly thin bilayers, the goal of the research is to prevent membrane defects and make pretreatment more efficient, while creating NF membranes with the potential for 5-10 times higher permeance than commercial NF membranes made today.